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Fire Proof Building

For the past few summers I’ve been somewhat caught off guard by how vulnerable I have felt when dry winds are blowing and smoke fills the sky. I remember very clearly being on the roof, with a mask on, cleaning out the gutters and small piles of leaves. As an industrial hygienist I know about the harms of dust and smoke from wildfires, but when the time came to defend my own home I felt overwhelmed and unprepared. I remember looking around our valley and seeing tightly packed homes in the foreground with golden brown, grassy hills in the background. Trying to clean ash off my solar panels I caught myself thinking, “I wish I could enjoy a fire proof building!”

Can a Building be Fire-Proof?

The short answer is no. At some point a fire is hot enough to melt steel and destroy concrete, and even before concrete is destroyed all contents within a building would be destroyed. So technically I suppose you cannot have a “fire proof” building. When a hundred structures are burning within feet of each other and the wind is howling in your direction, the only way to survive is to evacuate because the fire is too intense for any typically constructed building. However, experts now use the term “fire-hardened,” and everyone does agree that you can significantly reduce the risk of catastrophic fires by following some simple recommendations. Just as I can look at a building and point out weak spots in moisture management and things that are likely to cause long-term water damage or mold growth, a fire expert can similarly evaluate a building for fire risk. This obviously piqued my interest and now I’m happy to share these concepts with you.

Disclaimer: You cannot have a fire proof building. These concepts are borrowed from other sources and in no way should these substitute for having a professional assessment, and from engaging licensed design and construction professionals to harden your building. Lastly, just reading this won’t do anything to reduce your risk! Get out there and make some improvements.

How Do Fires Start and Spread?

In order to understand the why of fire hardening, one must first understand how fires start and spread. Remember the fire pyramid?

Fires need fuel, oxygen and heat. (period)  If you eliminate any of these variables – you will extinguish a fire. Thinking preemptively, if you reduce any of these variables in a given area you reduce the risk of fire occurring. Examples include:

  • Fuel – Including gases (e.g., propane, oxygen, etc.), liquids (e.g., gasoline, alcohol, etc.) and solids (e.g., leaves, trees, fences, decks, wooden siding, etc.) provide fuel for fires. Eliminating or protecting these fuels from fire is the most obvious means of fire hardening.
  • Oxygen – Many fire suppression systems, such as fire extinguishers or helicopters dropping flame retardant foams, operate by removing oxygen from an active fire. Shoveling dirt over a camp fire is an example of suffocating a fire.
  • Heat – Combustion requires an initial heat source. Ignition may start from a chemical reaction, lightening, electrical sparks, cigarette butts or a random ember flying from an unprotected chimney. Cooling materials will slow down a fire, and if you remove enough heat fast enough it will extinguish a fire.

Recent catastrophic fires in California have occurred in a perfect storm. Trees (fuel) have grown too close to power lines and eventually a spark (heat) can start a fire. Dry winds blow the fire across crispy fields and through forests full of dense undergrowth and standing dead trees. Intense fires create their own weather patterns with massive uplifts of wind which lift up and carry embers far ahead of the actual blaze. Those embers ignite smaller fires ahead of the major fire, and by the time the bigger fire meets the smaller fire it’s a raging storm of heat and destruction. In some instances embers from wildfires have started fires up to a mile away from the big fire. Once in an urban setting fires jump rapidly from building to building, and embers fly into buildings and land in cluttered gutters and on dry wooden decks. The hot, dry wind distributes embers but also increases temperatures and desiccates materials so when ignition occurs it’s instant and the fire spreads very quickly.

Any building in the midst of a fire storm is unlikely to survive, but there are many things we can do to reduce the risk of fire in the more common “small fire” incidents of which we are more accustomed. In every major fire – the initial ignition source started small. Taking these steps not only fire-hardens your building, but you’re taking some steps toward reducing risk for your entire community.

Practical Fire Hardening Tips:

Here are tips from Ready For Wildfire to harden your building and make it more fire resistant:

  • Roof
    • The roof is the most vulnerable part of your building. Buildings with wood or shingle roofs are at high risk of being destroyed during a wildfire. Build your roof or re-roof with materials such as composition, metal or tile. Block any spaces between roof decking and covering to prevent embers from catching.

      Vent Detail from Fine Home Building

  • Vents
    • Vents on buildings create openings for flying embers.
    • Cover all vent openings with 1/8-inch metal mesh. Do not use fiberglass or plastic mesh because they can melt and burn.
    • Protect vents in eaves or cornices with baffles to block embers (mesh is not enough).
  • Eaves and Soffits
    • Eaves and soffits should be protected with ignition-resistant* or non-combustible materials.
  • Windows
    • Heat from a wildfire can cause windows to break even before the buildings ignites. This allows burning embers to enter and start fires inside. Single-paned and large windows are particularly vulnerable.
    • Install dual-paned windows with one pane of tempered glass to reduce the chance of breakage in a fire.
    • Consider limiting the size and number of windows that face large areas of vegetation.
  • Walls
    • Wood products, such as boards, panels or shingles, are common siding materials. However, they are combustible and not good choices for fire-prone areas.
    • Build or remodel your walls with ignition resistant* building materials, such as stucco, fiber cement, wall siding, fire retardant, treated wood, or other approved materials.
    • Be sure to extend materials from the foundation to the roof.
  • Decks
    • Surfaces within 10 feet of the building should be built with ignition-resistant*, non-combustible, or other approved materials.
    • Ensure that all combustible items are removed from underneath your deck.
  • Rain Gutters
    • Screen or enclose rain gutters to prevent accumulation of plant debris.
  • Patio Cover
    • Use the same ignition-resistant materials for patio coverings as a roof.
    • Ignition-resistant building materials are those that resist ignition or sustained burning when exposed to embers and small flames from wildfires. Examples of ignition-resistant materials include “non-combustible materials” that don’t burn, exterior grade fire-retardant-treated wood lumber, fire-retardant-treated wood shakes and shingles listed by the State Fire Marshal (SFM) and any material that has been tested in accordance with SFM Standard 12-7A-5.
  • Chimney
    • Cover your chimney and stovepipe outlets with a non-combustible screen. Use metal screen material with openings no smaller than 3/8-inch and no larger than 1/2-inch to prevent embers from escaping and igniting a fire.
  • Garage
    • Have a fire extinguisher and tools such as a shovel, rake, bucket, and hoe available for fire emergencies.
    • Install weather stripping around and under the garage door to prevent embers from blowing in.
    • Store all combustible and flammable liquids away from ignition sources.
  • Fences
    • Consider using ignition-resistant or non-combustible fence materials to protect your building during a wildfire.
  • Driveways and Access Roads
    • Driveways should be built and maintained in accordance with state and local codes to allow fire and emergency vehicles to reach your building. Consider maintaining access roads with a minimum of 10 feet of clearance on either side, allowing for two-way traffic.
    • Ensure that all gates open inward and are wide enough to accommodate emergency equipment.
    • Trim trees and shrubs overhanging the road to allow emergency vehicles to pass.
  • Address
    • Make sure your address is clearly visible from the road.
  • Water Supply
    • Consider having multiple garden hoses that are long enough to reach all areas of your building and other structures on your property. If you have a pool or well, consider getting a pump.
Creating Defensible Space
According to FEMA, one of the most effective means of protecting a building from fire is creating what’s known as “defensible space” around a structure. Reducing combustible materials around a structure has two obvious benefits: a) reduce fuel (and fire intensity) for a fire, and b) create space for emergency crews to quickly access fires and more easily keep fires at bay. Some debate the distance of the actual zones, but everyone agrees on the fundamentals of creating defensible space.
When making defensible space there are generally three zones to prepare:
  • Zone 1
    • Eliminate all combustible materials in Zone 1 (within 30 feet of the home) such as fire-prone vegetation, firewood stacks, combustible patio furniture, umbrellas, and dimensioned lumber decking. Desirable substitutions include irrigated grass, rock gardens, stone patios, metal patio furniture, and noncombustible decking.
    • Before fire season begins, remove combustible litter on roofs and gutters and trim tree branches that overhang the roof and chimney.
  • Zone 2
    • Ensure that Zone 2 includes only individual and well-spaced clumps of trees and shrubs and/or a few islands of vegetation that are surrounded by areas with noncombustible materials.
    • Use hardscape features such as driveways and paved or gravel walkways or patios to create firebreaks throughout the yard.
    • Plant fire-resistant, low-volume vegetation that retains moisture well and needs minimum maintenance such as pruning and removing dead and dying branches.
    • Separate auxiliary structures such as a detached garage, pump house, pergola, and utility shed from the home by at least 50 feet. Increase the distance if the structure is used for the storage of combustible materials.
    • Comply with recommended construction practices related to fire resistance for auxiliary structures.
    • Ensure that patio furniture is either made of noncombustible material such as metal or is at least 30 feet away from the building. Store patio furniture in a location that is protected from ignition by a wildfire.
    • Place woodpiles at least 30 feet from the building and store the wood in a vegetation free zone such as a graveled area.
    • Store fuel tanks away from a structure at the minimum distance that is required by code or greater and place underground or on a noncombustible pad.
  • Zone 3
    • Reduce fuels that are farther than 100 feet from the building by thinning and pruning vegetation horizontally and vertically as discussed above. Thinning and pruning in Zone 3 can be more limited than in Zone 2. The goals in Zone 3 are to improve the health of the wildlands and help slow an approaching wildfire. Zone 3 is also an aesthetic transition between the more heavily modified Zone 2 and the unmodified surroundings.
Do what you can to protect your buildings and those within them, and know that any steps you take to fire proof your building will also help keep the larger community a little bit safer.

Fire Proof Building | Healthy Building Science

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Dust Settling on Outside Patio or Furniture?

I was sitting on my porch in San Francisco watching kids play on the wooden deck and started to wonder, “is the dust on my porch contaminated with lead dust? If so, how best to clean it up?” So I did a little experiment and tested for lead dust before and after three different cleaning scenarios. This quick experiment demonstrated there is good reason behind the EPA’s recommended lead cleaning protocols.

How much lead is too much?

The U.S. government defines leadbased paint (LBP) as, “any paint, surface coating that contains lead equal to or exceeding 1.0 mg/cm2 or 0.5% by weight.”

Lead Paint Testing using XRF Gun

The exterior of my 1890’s earthquake cottage in San Francisco is covered in lead-based paint (LBP.) You

Lead Paint Testing using XRF analyzer

can see my exterior paint has a high lead content as measured by my XRF analyzer with a reading of 15 mg/cm2. (XRF, X-ray fluorescence, is a non-destructive technique used to find how much lead is in paint.) We recently bought a new XRF gun for Healthy Building Science and I love this lead testing gadget! It is a great way to quickly screen for lead paint in a building.

The exterior paint on my home is in pretty good condition (no paint chips!), but I was curious to see if there was a lead dust hazard on the wood of my back deck. If the wood is contaminated with lead, what is the best way to clean it up?

Spoiler alert: Yes, I found high levels of lead dust. The way to clean it up is to HEPA vacuum, wet wipe with detergent, repeat HEPA vacuum and wet wipe. The moral of the story is two-fold: 1st) no dust, then no lead dust hazard; 2nd) if lead dust then follow the EPA’s lead cleaning recommendations, they work.

Summary of EPA Lead Abatement Protocol

Lead Testing Dust Wipes

The EPA recommends a combination of HEPA vacuuming followed by wet wiping with detergent, then repeating.

Does this combination really work? I decided to test this for myself. I took four dust wipe samples from my back deck:

1 control (no action taken)

2 HEPA vacuum only

3 HEPA vacuum and wet wipe

4 HEPA vacuum and wet wipe repeat HEPA vacuum and wet wipe

This demonstrates the importance of a) regular inspections by those familiar with environmental hazards, and b) regular deep cleaning. Just like your car or teeth, you should consider a regularly scheduled maintenance service for your home and office. The combination of inspections, testing and regular maintenance is effective at identifying problems early and minimizing risks.

Lead Dust Cleaning Study Results

The results undeniably prove the technique works! No lead was detected after the final complete round of HEPA vacuum, wet-wipe and repeat HEPA vacuum, wet-wipe.


Sample Id Results in microgram per square foot
1 Control 1200 μg/ft²
2 HEPA 96 μg/ft²
3 HEPA vacuum and wet wipe 14μg/ft²
4 HEPA vacuum and wet wipe repeat HEPA vacuum and wet wipe >10 μg/ft² Undetected!
EPA Recommendations for Controlling Lead Hazards

Here is more information from the EPA for protecting people from lead hazards:


  • Wash children’s hands, bottles, pacifiers, and toys often.
  • Make sure children eat nutritious meals high in iron and calcium. Children with good diets absorb less lead.
  • Remove shoes at the door or wipe soil off shoes before entering your house.
  • Run water for 15 to 30 seconds before drinking it, especially if you have not used your water for a few hours. Call your local health department or water supplier to find out about testing your water, or visit epa.gov/lead for EPA’s lead in drinking water information.
  • Cleaning: Vacuum then Wet Dust   – Not a smart idea to dust then vacuum with a non HEPA vacuum because you are then just spreading the lead dust all over the house.
  • Your pediatrician can check for lead with a simple blood test. Children’s blood lead levels tend to increase rapidly from 6 to 12 months of age, and tend to peak at 18 to 24 months of age. A simple blood test can detect lead. Blood lead tests are usually recommended for: Children at ages 1 & 2 and children or other family members who have been exposed to high levels of lead.
  • If you rent, notify your landlord of peeling or chipping paint.
  • Keep painted surfaces clean and free of dust. Clean floors, window frames, window sills, and other surfaces weekly. Use a mop or sponge with warm water and a general all-purpose cleaner. (Remember: never mix ammonia and bleach products together because they can form a dangerous gas.)
  • Carefully clean up paint chips immediately without creating dust.
  • Thoroughly rinse sponges and mop heads often during cleaning of dirty or dusty areas, and again afterward.
  • Wash your hands and your children’s hands often, especially before they eat and before nap time and bedtime.
  • Keep play areas clean. Wash bottles, pacifiers, toys, and stuffed animals regularly.
  • Keep children from chewing window sills or other painted surfaces, or eating soil.
  • When renovating, repairing, or painting, hire only EPA- or state approved Lead-Safe Certified renovation firms.

To learn more about EPA’s requirements for RRP projects visit their Get Lead Safe page, or read The Lead-Safe Certified Guide to Renovate Right.

If you have concerns about lead in or around your building or want lead dust testing, please complete this form and HBS can send you an estimate to provide lead inspecting and lead testing services for the San Francisco Bay Area.

Written and directed by Anne-Lise Breuning.

Lead Dust Testing Outside? | Healthy Building Science

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Is Clean Crawlspace Really That Important?

Crawlspaces are generally not what anyone would consider “clean.” When was the last time you went into a crawlspace? It’s typically a dark, dank environment where critters and odors run scare away even the most brave DIY building owners! Often old construction materials and cardboard boxes are crammed down below, providing harborage and food for mold and all sorts of furry critters. The stack effect dutifully draws air from crawlspaces up through small holes, gaps and cracks in the building and that nasty and wet air makes its way into your home. In 80% of the buildings we inspect we end up suggesting the crawlspace be professionally cleaned and upgraded. While not as sexy as a new roof or new flooring, a clean crawlspace can significantly increase the durability and healthy enjoyment of your building, by eliminating unwanted heat loss, moisture, pests and odors.

It’s possible you’re in the <20% of buildings with a clean crawlspace or basement already, but the odds are stacked against you. If you still have any doubts lift the hatch and take a look and sniff. If you wouldn’t want to spend 30 seconds down there – keep reading and consider having an industrial hygienist come to test the crawlspace.

Safe and Secure Crawlspace Access is Important

Crawlspaces have often been treated with legacy pesticides to prevent termite and rodent infestations. Mold is also a likely inhabitant of crawlspaces and unconditioned basements. If professionals feel compelled wear protective clothing and respirators into your crawlspace to protect themselves from biological and chemical contaminants, do you really want them entering and exiting the crawlspace via the floor of a kitchen pantry or bedroom closet? If access to a crawlspace is so constricted it would add days of labor time for excavation or make bringing in necessary building materials impossible, it often pencils out to have crawlspace access moved or expanded.

Children and pests aren’t often uttered in the same sentence, but a solid and secure access hatch will keep both out of the crawlspace! The above photo illustrates a prefab metal access hatch with hydraulic hinges, air-sealing gaskets, and a padlock. This access hatch will last longer than most of the house, and be a luxury for service professionals who have to periodically enter and inspect the crawl space. Sufficient sizing of the access points is also important, as is not blocking access with mechanical systems such as ductwork or drain pipes.

Air Migrates From Crawlspaces into Living Zones. Carpet acts as air filter.

If access is indoors careful consideration must be made to not to cross-contaminate the building while work is ongoing below. Where carpet is covering an access hatch there are often visual signs of the carpet acting as an air filter for air entering the home via stack effect or other pressurization. Access hatches indoors should be air-sealed, and when significant work is done in the crawlspace the surrounding area within the home should be placed in containment with negative air and air-scrubbers running. When contractors are working significantly more dust is generated than on an average day, and that dust may well contain legacy pesticides, biological contaminants (feces, mites, mold spores, bacteria), heavy metals and hazardous fibers (fiberglass or asbestos).

Crawlspace Upgrade Opportunities

There are always economies of scale to consider with any renovation project. When the project involves tight spaces and specialty contractors dealing with access issues, it’s especially important to take a step back and consider the big picture. The last thing you want is to complete your crawlspace remediation and realize you missed a golden opportunity to accomplish another important objective that would have been easy and affordable during the previous push.

Goals for a crawlspace upgrade usually involve moisture management, improved air quality, pest protection, long-term durability of structural elements, improved thermal comfort and and energy efficiency.

During a crawlspace inspection our industrial hygienists generally include the following:

  • Identify access and egress issues (can we get in and out without danger of being trapped)
  • Identify any threats to life and safety (rattle snakes, standing water with live electrical wires, etc.)
  • Determine if the space is dry enough to seal and insulate (may require additional site or under-building drainage improvements)
  • Determine air barrier location: crawl space floor or walls and grade (where to install an air-barrier is an important decision left to your licensed design and building professionals)
  • Determine what grade of ground cover you’re going to install (common vapor barrier or advanced radon mitigation material)
  • Survey mechanical, electrical and plumbing for opportunities (if not now, consider low-hanging fruit future proofing before installation of any new insulation or sheet-good products that will cover up access)
  • Determine appropriate insulation for the surfaces considered (enough R-value, easy to install properly, within budget, not harborage or food for pests or mold, non toxic, etc.)
  • Collect measurements and pictures to estimate any suggested improvements
Water Control Strategies Vary Depending on Primary Sources

Strategies for enhancing a basement or crawlspace will vary depending on how much water and moisture are present. If there is an artesian well springing up under the building the moisture control strategy will be very different than if there is minimal soil dampness. Liquid water from rain, stormwater runoff, poorly located downspouts, or leaking plumbing pipes would be considered “bulk water,” and these are the worse offenders.

Compliments of Gavin Healy

In the moderate climate of the San Francisco Bay Area condensation is not often a significant problem unless there is excessive bulk water evaporating in a confined and poorly vented space. Capillary action, or the ability of a material to transport water vertically (think about a towel left hanging over a bathtub) is frequently problematic when concrete or wood are in direct contact with wet soil. Lastly, evaporation of bulk water or soil moisture can create dampness problems sufficient to form condensation and support mold growth. Of all these things controlling bulk, liquid water is the most important function of a well built basement or crawlspace

It is critically important that the primary source of water is addressed in your crawlspace work. This may involve fixing plumbing leaks, installing french drains outside the home, installing submersible pumps under the building, etc. No crawlspace solution is 100% until you have considered and planned for these common moisture sources.

What is Best Insulation for Crawlspace or Basement?

First determine the goals of adding insulation to a crawlspace or basement. The primary purpose of insulation is to improve thermal comfort and reduce energy consumption. In the San Francisco Bay Area we have a very moderate climate zone where floor insulation for existing buildings is often considered optional. However, if you’re about to embark on a crawlspace improvement project this is an opportune time to consider proper insulation materials and installation techniques.

Crawlspace renovations almost always involve removing old insulation (usually poorly installed fiberglass), air-sealing, and reinstalling new insulation. While the primary goal of insulation is to resist temperature transmission, secondary goals should include a) not providing habitat or food for unwanted critters, b) not creating an opportunity for trapped moisture to support microbial growth, and c) not negatively impacting indoor air quality. For these reasons we generally do not recommend large applications of rigid foam products or anything with a paper (mold food) or foil (vapor barrier) backing. Blown-in dense-pack cellulose is a good choice for this climate zone. [Note: There are some applications where rigid or spray foam is the best option available, but these scenarios seem to be the exception and not the rule.]

If you’re building from scratch it’s an excellent opportunity to better insulate and extend the thermal envelope of the building to include the entire crawlspace or basement. When you extend the thermal envelope of the building to include the crawlspace you must now mechanically condition and ventilate the space so there is inevitably an energy cost, but there is also an energy and comfort benefit to air sealing creating less of a temperature difference between “indoors” and under the floor. For retrofits in this climate zone we often do not recommend insulating the crawlspace floor and perimeter foundation walls, and instead insulate the crawlspace ceiling (building floor between or over joists) and allow the space to ventilate naturally.

How To Locate the Air Barrier and Vapor Barrier in a Crawlspace?

This is one of those “it depends” answers. Seriously, where to install an air barrier or vapor barrier in a crawlspace depends on far too many variables to have a simple answer. Building science is an expertise in itself and generally this decision is left to the licensed design and construction professionals on the job. Suffice it to say that installing an air barrier is almost always a good idea as air leakage is one of the biggest energy losses AND ways contaminants enter a building. Infiltration is a very real phenomena. However, installing a vapor barrier is tricky business and if it’s in the wrong location it may very well cause significant damage to the building.

Photo compliments of Gavin Healy.

Crawlspace air barriers are usually sheet good products including sheet-goods that come in a roll, or a 4’x8′ solid sheet like plywood. If you can put your mouth to it and not easy blow through (e.g., drywall, Tyvek, plywood, foam, caulk, etc.) it is probably considered an air barrier (or “air retarder.”) Any of the common sheet products commercially available will do.  The objective is simple: reduce air transfer between the crawlspace and the occupied portions of the home. The how-to is a bit more complicated and may involve sheet goods, expandable foams, caulks, etc. While it’s not rocket science, good air-sealing does take a lot of attention to detail and one must know the right product options for each situation, as well as how to affix each product with a compatible material or fastener without compromising the air barrier.

If there is no insulation between floor joists and crews are already working below the building it’s an opportune time to accomplish other air-sealing tasks. Using foam backer rod, caulk and expanding foam one can air-seal around plumbing, electrical, data and general framing cracks, holes, and gaps. Under kitchens and baths and around chimneys are frequently very leaky, and before new insulation is installed be sure to air seal these areas before they are made inaccessible by new insulation.

Vapor barriers are more complicated. A vapor barrier (or “vapor retarder”) will stop vapor (moisture laden air) movement from one side to the other. Examples of vapor barriers include sheet plastic, most foam products, vinyl flooring or vinyl wall paper, glazed tile, etc.

So why are vapor barriers tricky? Since vapor barriers restrict moisture movement they also inadvertently trap moisture. If the underside of vinyl flooring gets wet due to a plumbing leak or condensation, moisture is then trapped between vinyl and a wooden subfloor. That moisture cannot easily dry to the inside. The slow rate of drying may allow dry rot and microbial growth. In our climate zone vapor barriers are often either accidentally installed without much consideration, or intentionally installed on the crawlspace floor. Some building science experts believe the only good place for a vapor barrier in our climate is directly over the soil beneath a building.

Around the San Francisco Bay Area the most consistently right place to install a vapor barrier is over the soil under a building. It is hard to go wrong with installing plastic over the soil and/or below the slab or rat slab. The material should be thick enough to not be punctured, reinforced so as not to tear, light in color for good visibility and reflectance, and properly rated as a vapor barrier or vapor retarder. Materials rated for radon mitigation are guaranteed to get the job done, but there are plenty of other 3-ply materials available on the market that will work to minimize soil moisture (and gases) from entering the space.

As your designers or builder before installing any new barriers in your crawlspace. A fundamental concept in building science is to try and align all barriers (thermal, weather, air, vapor) from slab, to floor, to wall, to roof. This is not always possible, but know that improper placement of any of these layers may cause more harm than good for your building. So proceed with caution.

Photo compliments of Gavin Healy.

Signs You Need A Clean Crawlspace

If there is ever standing or running water under your building you should address the bulk water issue. Musty smells or frequent condensation on windows are other signs you likely need to address moisture in the crawlspace. If there is evidence of critters under the building and repeated efforts to rid them have failed, you must invest some time and money down below. If your feet are cold standing barefoot indoors, yup – time to look under the floor. It’s not a fun job and you cannot see the improvements, but trust me when I tell you that you’ll sleep better at night (or work better during the day) knowing you’ve got a clean crawlspace.

For residential projects in San Francisco, Marin County, and Sonoma County, let Four Season Stewardship help you with the planning and execution of your clean crawlspace!

Special thanks to Bill Hayward and Carl Grimes of Hayward Healthy Home, and Gavin Healy of Balance Point Home Performance for their contributions to my knowledge on this subject, and some photos for this blog. Also gratitude to the PG&E Energy Center for hosting great seminars on high performance crawlspace upgrades.

Clean Crawlspace is Better For You and Your Home | Healthy Building Science

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Air Quality Index (AQI) and You

During the 2018 Paradise Fire smoke wave many in the Bay Area obsessively checked online for air quality information and updates. Here is an overview of a handful of real-time air quality websites I found helpful and how they compare. Keep in mind that climate change plus newer and cheaper monitoring equipment means that air quality information sources can change quickly. Air Quality Index (AQI) sites use a map to show the AQI number for an area. But what does this AQI number mean and why do different sites report different numbers?

Here is a short summary of the sites I used around the San Francisco Bay during the Paradise Fire.

Air Quality Info My top two choices for air quality: EPA airnow.gov and PurpleAir.com.

Runners up included breezometer app and my native iphone weather app.

EPA airnow.gov PurpleAir.com
Pros: most widely used. High quality sensor (~$75,000 each)

Cons: fewer sensors can misrepresent microclimates, refreshes every 2 hours. Site overwhelmed with web traffic during smoke wave.

AQI number tends to be lower

Pros: Near instant readings, Many more sensors to show more detailed levels of air quality. Cons: not as accurate in higher concentrations (~$250 each).

AQI number tends to be higher

EPA Airnow Fire Shows 2.5PM monitors for The Bay Area. Note only one for San Francisco Purple Air Nearly 50 monitors in San Francisco
iphone weather app Breezometer app
Pros: Super easy to access.

Cons: The source of this info has not been disclosed by Apple. I speculate it is based on EPA airnow.gov data. Slower to refresh than purpleair.com

Pros: Breezometer has easy to use app. One great feature is the ability to compare air quality at different saved locations. Shows 2.5PM counts in ug/m3.

Cons: the app stopped working at times during the smoke wave. They developed their own version of AQI, so hard to compare numbers to other sites.

FYI Here are some other sites I used to track the fire and smoke during the Paradise Fire.

Smoke and Fire Info

California Smoke Information Blog

California Wildfires traffic/fire Map

Smoke from Wildfires Map

San Francisco Dept of Emergency www.sf72.org

What is the Air Quality Index?

Here are some of the dirty details behind AQI websites. First off, we need to nail down what is meant by AQI – Air Quality Index.

AQI is a color coded, simplified index for reporting daily air quality. The EPA’s AQI index can help inform questions during smokey/smoggy days – “Should I keep my asthmatic child home from school?” or “Will the soccer game be cancelled” or “Do I need to wear a mask?”

“It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.” source airnow.gov

What is Particulate Pollution – specifically 2.5 PM?

The sky looks hazy, that is particle pollution, a mixture of solid particles and liquid droplets found in the air. Some particles are large enough to be seen with the naked eye and others are so small they are measured using an electron microscope. At Healthy Building Science we count 2.5 PM particulate pollution with our Lighthouse Laser Counter. These particles can be made up of hundreds of different chemicals.

Driving South in our RV searching for cleaner air during the Paradise Fire. On the road, monitoring particulate air pollution with the Lighthouse Particle Counter during Paradise Fire smoke wave.

Fine particles (PM2.5) are very bad for your health – causing 4.2 million premature deaths worldwide per year in 2016…read more from the  World Health Organization. They trigger or worsen chronic disease such as asthma and heart attack. They are considered to be the more harmful than larger particles because they penetrate the lung barrier to enter directly into the blood system.  China recently lowered 2.5PM pollution in urban areas, residents are now expected to live 3.3 years longer! Source

All 2.5 particulate pollution is harmful to human health and the smoke from burning town contains additional harmful pollutants compared to a forest fire. The AQI does not differentiate the type of particulate pollution. The chemical makeup from wood smoke vs smoke from a burning car or hardware store can be significant. Therefore, the smoke from burning buildings in Paradise, CA contained more harmful pollutants, such as, flame retardants, plastics, asbestos, than the smoke from the following forest fire. Weather Underground is recommending Purple Air monitors to track “deadliest type of air pollution” – 2.5PM particles.

If you really want to geek out on the numbers – here is a table comparing the AQI number to 2.5 PM counts. At Healthy Building Science we have a number of gadgets to monitor 24-hr Average 2.5 PM concentration.
Real Time Air Quality Maps

On day 7 of the Paradise Fire, the San Francisco Unified school district cancelled school as the AQI hit 235  – PURPLE Very Unhealthy Level.  BUT Purpleair.com was showing AQI in the 400’s.  

November 15, 2018 airnow.gov November 15, 2018 purpleair.com

So why the difference in AQI numbers at airnow.gov vs purpleair?  The most obvious difference is that the EPA’s AIQ number includes 5 major air pollutants where as purpleair is only monitoring 2.5PM particulate pollution. They both use their own secret sauce to calculate/ average out their AIQ numbers.  I found it best to use AIQ as a way to compare air over time and at different locations and I now resist the urge to narrow down to specific AIQ readings.

Northern Sonoma County Air Pollution Control District published a detailed guide and in-depth comparison of airnow vs purple air.

Stepping back from the numbers is all fine and good unless you are a decisionmaker for other people such as elementary school principals at Sonoma County School. They have been instructed:  

  • On days with questionable air quality, superintendents shall check purpleair.com at 5:00 am.
  • If the Air Quality Index (AQI) is listed at 275 or above, districts may cancel classes.

Yes, this public school district is choosing NOT use the EPA airnow.gov and instead use purpleair.  This is a time of great change with climate chaos and affordable, emerging technologies. Great coverage of Sonoma County School’s decision on this wine country parents’ blog. Great overview of government vs private sources of air quality data here nytimes.com

Sonoma County School Air Quality Guidelines. source

I appreciate the Sonoma County Office of Education for taking a stand and publishing this guide and I plan to use it during future smoke waves.  Also, check out my blog on DIY Box Fan Filters.

Let’s wrap up this AQI ramble with the EPA’s Actions People Can Take to Reduce Particle Pollution:

  • Conserve electricity
  • Use dry, seasoned wood for fireplaces and stoves
  • Carpool, use public transportation, bike, or walk when possible
  • Avoid idling of car engines for long periods of time
  • Keep car tires properly inflated
  • Maintain car, boat, and other engines to ensure maximum fuel efficiency
  • Buy an electric car (I added the last one)

Written by Anne-Lise Breuning, Industrial Hygienist and Environmental Inspector for Healthy Building Science

Air Quality Index (AQI) and You! | Healthy Building Science

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How To Avoid Lead Dust During Home Renovations

Containment, Wet Methods, HEPA Vacuum and Prompt Clean-up are the main work practices to follow in order to reduce exposure to lead dust during renovation. Sticking to these main concepts will help avoid the most common pathways of exposing your family to lead dust. Whether or not the paint in your home contains lead, it is always a good idea to follow these safe work practices as paint may also contain other harmful compounds.  A lead paint inspection can be helpful to know if the paint in your home is lead-based paint (LBP is ≥0.5% lead content by weight).

Sticky mat at entrance/exit to work area can cut down on tracking lead dust into home.

Lead Renovation Containment

Lead abatement is best left for the processionals. There are certifications necessary to be hired to provide lead testing, lead surveys and lead abatement. Side note: In the industrial hygiene industry we generally say “abate” when talking about minerals like lead and asbestos, and “remediate” when it’s a living organism like mold or bacteria. We would also advise to hire trained and certified lead professionals, but many homeowners cannot afford to hire lead experts and lead abatement teams.

When doing repairs yourself, contain the work area so that dust does not escape from the into the rest of the home. A common mistake made by well-meaning do-it-yourself homeowners is to leave belongings where they can be exposed to dust. Here are more tips on how to avoid lead dust by setting up a proper containment area:

  • Completely remove all belongings from work area and clear belongings from entrance/passageways to work area. A well-prepared area will be easier to clean.
  • Cover floors and furniture that cannot be moved with heavy-duty plastic and tape, and seal off doors and heating and cooling system vents. Use 6-mil plastic. Do not be tempted to use the thinner sheet plastic as it tears easily. Take extra care to protect carpet or other porous materials as it is extremely difficult to clean after exposure.
  • Keep children, pregnant women, and pets out of the work area at all times.
  • Remove work clothes carefully, turning inside out, to avoid tracking dust outside work area.
  • Use sticky door mats at entrance/exit to work area to trap dust. (These can be found at most large hardware stores).
Wet Methods to Minimize Dust During Construction

The main source of exposure for lead is in dust – so do your best to AVOID CREATING AIRBORNE DUST in the first place.

  • Mist surfaces before scraping and use wet sanding techniques. Continue to mist while working.
  • Use sanders or grinders that have HEPA vacuum attachments which capture the dust as it is generated.
  • Minimize pounding and hammering – pry and pull instead.
  • Mist before drilling and cutting to reduce dust creation. Foam, such as shaving cream, can be used to capture dust when cutting or drilling. (This avoids dangers of using water with electrical tools.)
  • Score paint before separating building components. This will help give you a cleaner break and helps prevent paint from chipping when a paint seal is broken.
HEPA Vacuum and Prompt Lead Dust Clean-up
  • Daily and after work is complete there should be NO VISIBLE paint chips or dust. Debris needs to be bagged as areas are completed and by the end of the day.
  • Clean up thoroughly by using a HEPA vacuum and wet wiping to clean up dust and debris on surfaces.
  • Mop floors with plenty of rinse water before removing plastic from doors, windows, and vents.
  • Use a wash bucket and a rinse bucket using disposable rags and be sure not to double dip the rags. Work horizontal surfaces from top to floor. Work your way out of the room doing about a three-foot section at a time, once with the soap water and once with the rinse bucket. You must dispose of rags each time for a thorough cleaning.
  • Concrete floors are sometimes better to paint after cleaning as surface is porous and lead dust is sometimes hard to remove. Hardwood floors are better to seal since they are porous and retain lead dust.
  • Dust wipe lead clearance testing is required by CDPH after professional lead abatement, consider taking dust samples to make sure work area has been sufficiently cleaned.
More information:

This blog covers some of the basics of protecting your family from lead dust during DIY home repairs and renovations. There are many more government-provided guidelines and recommendations available:

EPA Renovate Right Pamphlet

CDPH Childhood Lead Poisoning Prevention Branch

CDPH Testing your home for lead

Home Renovation: Tips for How To Avoid Lead Dust When Doing Repairs Yourself | Healthy Building Science

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Here in San Francisco and surrounding areas kids are stuck indoors during this smoke wave caused by our wild fires with little or no air filtration. In San Francisco the school buildings are older and are not setup to have building wide air filtration.

Since the last fires, I have been curious about the DIY box fan air purifier made from items that can be found in most hardware stores- box fan, 20-inch x 20-inch x 1-inch MERV 13 filter and some duct tape.

There is a serious need for air filtration in schools and homes. How well will this DIY set-up clean the air?

Some parents of children with breathing issues are deciding to keep their kids home.
The SFUSD current response to the unhealthy air quality is to close windows and stay indoors, no current plans for air filtration due to cost.

Following the instructions from the Mariposa County Health Department, “How to Build an Inexpensive Room Filter”, we made our Box Fan room filter. In 2 separate rooms

Using our Lighthouse 3016-IAQ Laser particle counter, air samples were collected for 2 minutes, with a 2 min delay. This set-up was done in 2 rooms: one with the box fan and one with the HEPA filter.
Box Fan was able to drop PM2.5 particulates down 77%, the HEPA filter dropped the PM10 down 94.46%

See results complete results in chart below:

After testing, I was impressed how well the DIY Box Fan was able to remove particulates from the air. Yes, HEPA will provide more filtration, but if cost is an issue than the DIY Box Fan MERV 13 is a sensible choice. Further testing needs to be done with higher MERV ratings and over longer periods of time.

MERV 13 Box Fan set up at 2 feet from particle counter.

HEPA air purifier (AeraMax 300) set at 2 feet from particle counter.

Lighthouse monitor taking air samples.

HEPA air purifier (AeraMax 300) set at 13 feet from particle counter. This unit was currently in the classroom.

DIY – Box Fan MERV 13 versus HEPA Air Purifier | Healthy Building Science

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I am writing this on November 13, 2018.  For the past week the state of California has been cloaked in thick, noxious smoke from the wildfires burning out of control.  Northern California is mostly affected by the Camp Fire near Chico, CA and Southern California by the Woolsey Fire.  Many people are rightly concerned about the potential health affects of wildfire smoke.

Even wearing a mask and running my indoor HEPA filter on turbo, I am suffering from respiratory distress and lower energy.  It is indeed BAD OUT THERE!

I have seen and heard an avalanche of information on all the social media sites, as well as traditional media.  It can be very confusing to sift through all this information and get to what’s true and helpful.

As an industrial hygienist and an air quality expert, I am going to try to distill the facts from the “fake news” and give you solid recommendations as to how to best protect the health of you and your loved ones.

From the U.S. Environmental Protection Agency site – AirNow.

What is in wildfire smoke?

  • Smoke is a complex mixture of carbon dioxide, water vapor, carbon monoxide, particles, hydrocarbons and other organic chemicals, nitrogen oxides, and trace minerals.
  • Fine particles are the principal pollutant of concern from wildfire smoke for short-term exposures (hours to weeks).

What are some of the health effects of wildfire smoke?

  • Fine particles can be inhaled deeply into the lungs; exposure to the smallest particles can affect the lungs and heart.
  • Fine particles are respiratory irritants, and exposure to high concentrations can cause persistent cough, phlegm, wheezing, and difficulty breathing.
  • Exposure to fine particles can affect healthy people, causing respiratory symptoms and reductions in lung function. Particle pollution may also affect the body’s ability remove foreign materials from the lungs, such as pollen and bacteria.
  • Studies have found that short-term exposure (i.e., days to weeks) to fine particles, a major component of smoke, is linked with aggravation of pre-existing heart and lung disease.

Where Can I Find Info on my local Air Quality?

There are so many websites that can give you some info on local air quality.  Here are the 3 sites I use:

airnow.gov – From the USEPA and local Air Quality Management Districts, this site has current conditions and forecasts.  You can enter your zip code and zoom in.

Purple Air – This site uses the internet of things.  Purple air units are purchased and installed individually by customers on their homes and offices.  The Purple Air units measure air quality at that location and then the unit sends this info to Purple Air, who compiles all of the data and maps it for you.  So you get a pretty good picture as there are thousands of units and thus thousands of data points.  Big Data at its best.

Air Visual –  This site is run by IQAir, who manufactures and sells portable filters and built in systems, including HEPA filters.  I believe they get their info from the same sources as airnow, but the map is good and easy to read.

Honorable Mention – BAAQMD – This is the website for the Bay Area Air Quality Management District.  This is good if you live in the San Francisco Bay Area, but I find the site clunky and its info is also in the Airnow.com site, so I don’t really find this site too useful, but it does have some pertinent information.

For information on health effects and what to do, I refer to the California Department of Public Health Website:

How to Tell if Smoke is Affecting You Smoke can cause:
  • Coughing.
  • Scratchy throat.
  • Irritated sinuses.
  • Shortness of breath.
  • Chest pain.
  • Headaches.
  • Stinging eyes.
  • Runny nose.

If You Have Heart Disease, Lung Disease or a Pre-Existing Respiratory Condition, Smoke Might Make Your Symptoms Worse

People who have heart disease might experience:
  • Inability to breathe normally.
  • Cough with or without mucus.
  • Chest discomfort.
  • Wheezing and shortness of breath.
  • Even healthy people may experience some of these symptoms in smoky conditions.
Protect Yourself Following are ways to protect your health:
  • Pay attention to local air quality reports. Listen and watch for news or health warnings about smoke.
  • If you are advised to stay indoors, keep indoor air as clean as possible. Keep windows and doors closed unless it is extremely hot outside. Run an air conditioner if you have one, but keep the fresh-air intake closed and the filter clean to prevent outdoor smoke from getting inside. If you do not have an air conditioner and it is too warm to stay inside with the windows closed, seek shelter elsewhere.
  • Use a high-efficiency particulate air (HEPA) filter to reduce breathing problems. Room air cleaners, which utilize a HEPA filter, may reduce the number of irritating fine particles in indoor air.

Do not add to indoor pollution. When smoke levels are high, do not use anything that burns, such as candles, fireplaces or gas stoves. Do not vacuum because it stirs up particles already inside your home. Do not smoke because smoking puts even more pollution into the air.


Most dust masks are not effective in reducing smoke exposure during a wildfire because they are not designed to filter very small particles and do not fit well enough to provide an airtight seal around the wearer’s mouth and nose.

  • Surgical masks that trap small particles are designed to filter air coming out of the wearer’s mouth and do not provide a good seal to prevent inhalation of small particles or gases in smoke.
  • Inexpensive paper “comfort” or “dust” masks commonly found at hardware stores are designed to trap large particles and do not provide enough protection for your lungs.
  • Mask use may give the wearer a false sense of security, which might encourage too much physical activity and time spent outdoors. Also, wearing a mask may actually be harmful to some people with heart or lung disease because it can make the lungs work harder to breathe.

Many types of masks cannot effectively filter out small smoke particles. They can however, provide some protection from the larger smoke particles that can become airborne when sweeping up soot or ash during cleanup activities. Some types of masks can also filter out up to 95% of small smoke particles. These masks are marked with one of the following: “P95,” “R95” or “N95”, and tend to be more expensive than ordinary dust masks. Other masks with higher ratings (marked “P100,” “R100” or “N100”) can filter out even more particles. If properly fit to the wearer’s face, such masks can provide significant protection against particles in smoke. Without a good seal around the wearer’s mouth and nose, even these masks will not be effective. Also, they do not protect against irritating gases in smoke.

I also found out some interesting info on how long you should use an N95 mask before replacing it.  I think the best advice is – 10 DAYS 

Related topics:

Berkeley Lab – How to protect yourself and your family from wildfire smoke

How to detox after wildfire smoke inhalation

Three years in a row California has had severe wildfire smoke.  This appears to be the new normal, so please be aware and be safe!

WILDFIRE SMOKE!!! | Healthy Building Science

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With the legalization of marijuana, some black-market growers are abandoning their illegal cannabis grow operations. Grow ops, often set up in rented properties, can leave a mess for landlords to clean up. Many of these properties are also put up for sale and then become the responsibility of the homebuyer. Identifying a grow-op is often not that difficult because of the distinctive and lingering odor. However, eliminating that odor and identifying other potentially dangerous issues and modifications is another matter.

Common Grow-Op modifications

Ventilation crudely roughed-in and installed through siding.

Modifications to ventilation, air conditioning, electrical, and water lines are common in indoor cannabis grow operations.

Growing plants indoors creates high humidity that needs to be expelled. Different approaches to this could involve splicing into existing household ductwork. New ductwork could also be “installed” by cutting holes in the building to exhaust to the exterior, or worse, exhausting to somewhere else inside the structure. Exhaust ducted into attic, crawlspace, or wall cavities can lead to mold problems and potentially structural damage.

Holes created in the building envelope for ventilation may not be weather tight which could allow rainwater or pests access.

The high electricity demands of grow-ops may lead to unsafe electrical modifications.  Electrical generators may also be used to meet the demand. In this case, diesel contamination may exist on site.

The use of pesticides and fungicides can also lead to site contamination. Pesticide residues can remain on surfaces. Pesticides could also be spilled or disposed of on site. There may be soil contamination or pesticide-soaked building materials from any spills that occurred. Surface or soil lab sampling may be necessary to determine the extent of the contamination.

Another potential hazard is that the property was also used for the manufacture of other drugs, such as methamphetamines. Contaminants from meth pose a health hazard for those performing the cleanup if they aren’t properly protected.

Outbuilding used for a grow op is fed with a 200-amp service and a vent through the exterior wall that now houses birds.

How to clean up a cannabis grow-op

  • Establish if the site is also contaminated by manufacture of other drugs. Surface sampling may be necessary.
  • Hire a licensed electrician to inspect and repair unsafe electrical modifications.
  • Hire a licensed mechanical contractor to inspect and repair modifications to the household HVAC ducting.
  • Inspect for mold and moisture related damage to the structure. These can occur from excess humidity, from leaks in irrigation lines, or from moisture intrusion through poorly installed ventilation.
  • Test for pesticide residues or other contaminants, such as spilled fuel.
  • Remove all water damaged materials such as subfloor.
  • Remove residues from surfaces that harbor odors. Fatty terpenes are responsible for the odors and they are very sticky and difficult to remove. You’ll need to clean all surfaces with soap. The surfactants in the soap can cut through the terpenes. Porous surfaces will be more difficult, if not impossible, to clean and may need to be discarded.
  • Presence of extensive interior mold may require professional mold remediation.

In Canada where growing plants for personal use indoors is now legal, real estate agents have recognized the risks to property associated with indoor grow-ops. The Ontario Real Estate Association (OREA) has developed a five-point plan for the impacted properties with the goal of to making buildings safe for homeownership and for homebuyers.

Among their recommendations is to inspect illegal grow operations and determine what actions are required to make it safe. OREA also recommend that all licensed home inspectors are required to have training on how to spot the signs of a former marijuana grow-op.

Hole cut through subfloor leads directly to crawlspace.  Discarded wood from the modification dumped there can attract mold and termites. Also, note the rotting subfloor.

Links: Ontario Real Estate Association 5-point plan

Five Point Plan

Cleaning up a Cannabis Grow Operation | Healthy Building Science

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Healthy Building Science by Healthybuilding - 6M ago
5 interesting things about EMF (Electromagnetic Fields):

EMF Testing | Healthy Building Science

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Healthy Building Science by Healthybuilding - 6M ago
6 things people should know about water quality:
  1. Source matters! One of the most important variables in water quality is the source. Does the water come from an open water source like a lake or reservoir? Is it treated and delivered to a site via the municipal or county water service? Or is it a spring or well onsite? Each of these sources come with their own unique pros and cons.
  2. Piping matters! Another important variable is how water is transported within the building. There are different concerns between galvanized, copper and plastic piping. (https://healthybuildingscience.com/2015/10/30/new-construction-piping-plastic-vs-copper/)
  3. “Lead-Free” isn’t “Lead-Free.” What? That’s right. If you really want lead-free solder you have to specify “100% lead-free.” (https://healthybuildingscience.com/2012/12/14/what-is-lead-free-drinking-water/)
  4. People are exposed to more chlorine byproducts via inhaling steam during bathing than drinking water throughout the day. Strange fact that leads many toward whole-house water filtration.
  5. In order to properly specify a water filtration system you need to know the following: source water, volume of water use, intended use of water (e.g., drinking, bathing, irrigation), and water quality parameters such as how hard the water is, heavy metal levels, bacteriological contamination, etc. Without these variables you may not get the right water filtration system.
  6. Healthy Building Science offers water quality testing (https://healthybuildingscience.com/environmental-services/environmental-testing/water-quality/), filter specification and installation, as well as regular water filter replacement services.

Water Testing | Healthy Building Science

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