I recently got a request from Isabel who asked if I could do an episode on building a fire resistant house. For those of us who want to make our homes as safe possible, incorporating some fire resistant features is a smart idea. Interestingly, many ordinary, everyday homebuilding materials are either naturally fire resistant or they can become fire resistant with a few tweaks. Although most building materials are not 100% fire proof, many materials that we’ll talk about today will give your house a fighting chance if it’s ever threatened by fire. Homes built with the right materials, the right landscaping layout, and smart detailing have a far better chance of escaping a fire with less damage.
Before we move on, I think it’s particularly important that I remind you of our disclaimer:
The purpose of this podcast/post is simply to educate and inform. It is not a substitute for professional advice. The information that you hear/read is based the only on the opinions, research and experiences of my guests and myself. That information might be incomplete and it’s subject to change, so it may not apply to your project. In addition, building codes and requirements vary from region to region, so always consult a professional about specific recommendations for your home.
Alright, let get right into it. This one’s for you, Isabel. Thanks for the show idea.
Building codes typically require that a home’s walls, floors and roof be fire resistant in accordance with standards set forth by the International Building Code (IBC). Regional building codes may be more stringent, depending on the general threat of fire in your area. Fire resistant homes are designed to contain a fire, keep it from spreading, and give sufficient time to discover a fire, control it and evacuate the home, if necessary.
Fire resistance ratings are expressed in the number of minutes or hours a structure can withstand a fire. According to the Engineered Wood Association, a one-hour rating indicates that a structure or material can contain flames and high temperatures, and support its weight, for at least one hour after the fire begins.
Exterior fires which start outside a home or structure account for 55% of fires in the Western US and 36% of fires in the East.
Only 9% of exterior fires are considered natural disasters, while the vast majority of exterior fires start as arsen or from open flames that might come from things like lighters or matches. Fire resistant construction can buy valuable time for homes, whether or not the source of the fire is natural or man-made.
It seems that we in the United States are behind the Europeans with regards to fire resistant construction. On one forum I read, a European man wrote in and said: We (Europeans) build only fire-resistant houses, from baked bricks or concrete bricks, metal facades, or other materials. The roofs are concrete colored tiles or metal. Nothing that’s easy to burn.
That European went on to say he was amazed at the lack of fire resistance seen in US construction, particularly given that US homes average hundreds of thousands of dollars.
Let's educate ourselves about some things that we can do to make our homes more fire resistant. Now, you probably won’t incorporate every feature on our list, but the greater the risk of a fire damaging your home, the more features you may want to include.
1. Build on Level Ground.
This tip is mainly for those of you who live in areas plagued with wildfires. Wildfires generally moves faster uphill, and slower on level ground. The rate of fire spread could double for every 20-degree increase in slope. And if you’re building on a cliff or ridge, position your house at least 30 feet back from the ridge or cliff and at least 30 feet away from neighboring houses, again, on level ground if possible.
2. Garages and sheds.
Many fires begin in storage sheds and garages where flammable substances such as paint thinners and gasoline are stored. First and foremost, minimize the number of flammable substances you keep on site. For even greater protection, keep the main house detached and at least 30 feet away from garages and sheds so you can minimize spread and damage from any fire that starts outside your home.
Steel-framed windows fitted with single-pane Pyrostop glass will probably give you the greatest amount to fire resistance. Pyrostop glass is rated to withstand fire for up to two hours. Here’s how Pyrostop glass works: A clear layer of heat-absorbing material inside the glass changes into a super hard material during a fire, reducing the risk of the window breaking.
If you don’t want to go to the extreme of buying specialized glass, another option is to choose more energy efficient windows. As a general rule, insulated, multi-paned windows withstand fire better than single paned windows. Triple pane windows hold up longer than double-pane windows which hold up longer than single pane windows in a fire.
The outer window pane will typically break in a blaze, leaving the inner layers intact. Having more than one pane also means that the inner layer of glass heats up more evenly and slowly, helping the inner layer resist cracking and breaking during a fire. Tempered glass, like that used for sliding patio doors, has also been found to withstand heat longer than standard plate glass. And, In general, smaller window panes survive better than larger ones.
Now, what about the window frame? Well, steel offers the best protection, but it’s very expensive and it’s not offered by many window manufacturers. The next best options are wood and aluminum, which are said to perform similarly in a fire. Vinyl is the least fire resistant choice.
Avoid acrylic skylights which can quickly melt during a fire and leave a large hole in the roof. If you live in an area prone to wildfires, you might consider adding non-flammable window shutters to your home, which are similar to hurricane shutters.
Install a roof made of Class A, fire-rated materials such as metal, clay tiles, slate, or cement composite roofing. If you want more economical roofing options, look into recycled rubber roof tiles or fiberglass based asphalt shingles. They both offers excellent fire resistance when installed with fire-code-compliant underlayments. In fact, make sure any roof underlayment you use is fire resistant no matter what type of roofing you choose.
If you have your heart set on wood shakes, or some other combustible roofing materials, you can apply a fire retardant treatment. Those fire retarders won’t last forever, though. They must be reapplied every 5 years or so. Otherwise the wood will not stay fire resistant because the fire resistant chemicals leech out over time.
Finally, choose a sloped roof and not a flat roof. Roofs with a greater pitch are much more fire resistance than flatter roofs. The steeper the roof, the more protection you’ll have. That’s because burning embers can more easily roll off a steep roof before those embers start a fire.
5. Exterior Wall Cladding
For exterior siding, opt for non-flammable materials such as fiber-cement siding, cultured stone, natural stone, brick, or stucco.
Naturally fire-retardant brick or stucco walls meet or exceed one-hour fire ratings, depending on their thickness. A layer of gypsum underneath will slow the transference of heat from the siding to your framing.
Fiber-cement siding usually carries a Class A fire rating and can withstand 2 to 4 hours of high heat before your home's structure starts to fail.
Vinyl siding is not as protective, but it will work too, as long as all gaps and crevices beneath the vinyl are sealed. Since vinyl siding typically melts and sloughs off during a fire, any unsealed openings and gaps beneath vinyl will allow fire to get inside the home.
6. Vents and other openings.
Cladding your home in fire-resistant siding won't matter much if burning embers find their way in through cracks, gaps or other openings. So be sure to enclose eaves, soffits, and fascia with complementary fire-retardant trim.
To decrease the chances of burning embers finding their way inside your home through exterior vents, cover openings such as soffit vents, gable vents and dryer vents with 1/8 inch metal wire mesh. Cover chimneys with a 1/4-inch wire mesh, if local code allows. Be careful that the mesh that you choose does not trap fireplace exhaust gases. You can also put metal screening around crawlspaces and beneath decks, to keep fire and embers out.
Decks are where fires often start— sometimes from windblown embers and sometimes from charcoal falling out of a grill. A fire that starts on an attached deck can easily spread to the house.
If you want to use wood decking material, it should be periodically treated with a fire retardart. A maintenance free choice would be a concrete deck which is naturally fire resistant. You could also choose composite decking. Many composites tend not to burn the same way wood does. In many cases, composite decks sort of fall apart and drop to the ground without spreading the fire to the rest of the house.
If your landscape design includes trees that will grow large, space them at least 30 feet apart. Place shrubs at least 20 feet from your house and other structures, like storage sheds and garages. And keep the area under large trees free of smaller trees and shrubs. That way, if a fire does start in a tree or shrub, it can’t spread as easily. You’ll also want to regularly remove dry leaves and branches from your yard and gutters since they can readily catch fire.
Untreated wooden fences act like as kindling to stoke a fire. If you want a wood fence, apply a fire retardant. Alternatively, add a masonry structure that sits between the house and the fence or simply build the fence of masonry or metal.
Choose traditional concrete blocks, insulated concrete forms or Autoclaved Aerated Concrete Blocks. Autoclaved Aerated Concrete Blocks are building blocks made of aluminum and concrete. They are half the weight of traditional concrete blocks, but have higher insulating qualities. For every square inch of block you use, you get an hour of protection from flames.
ICFs walls are walls made of a 4- to 6-inch-thick concrete core sandwiched between foam insulation. ICF walls can withstand flames for up to three hours longer than a wall framed with conventional lumber. Some ICF makers are increasing the fire-resistance of their products even further by adding special flame-retardant chemicals to foam.
A more economical option is to frame with traditional dimensional framing lumber that has be treated with fire retardant chemicals.
Steel garage doors are best for fire resistance. Look for models with a center core made of polyurethane foamed-in-place insulation. This is a heat-resistant material. Some steel doors also have a protective coating on the door's exterior to help to prevent the spread of flames.
Steel entry doors are better protection against fires than wood or fiberglass entry doors. Metal doors keep fire out for longer.
If you really want the beauty of a real wood door, many manufacturers make fire rated wood doors. Fire rated MDF doors are also available.
Proper weather stripping on entry door is recommended no matter what type of door you go with. Weather stripping on the bottom of the door will help prevent smoke from entering the house and, as a bonus, will provide more energy efficiency throughout the year.
12. Insulation and Caulk.
Most types of insulation are fire-rated, but mineral wool, also known as rock wool, is one of the most fire resistant of them all. It’s made of naturally non-combustible fibers and can withstand heat in excess of 1,800 degrees F. Unlike fiberglass insulation, mineral wool does not melt when exposed to such high heat. .
Cellulose insulation is made from recycled paper, so it obviously needs to be treated with fire retardant additives to protect your home from fire. Many cellulose insulation manufacturers add the non-toxic retardant boric acid.
Make sure any insulation that you choose is used around electrical boxes and that all gaps are filled because those uninsulated areas are more vulnerable to the spread of fire.
Another way to eliminate gaps where fire can move through walls and spread into the rest of your home, is by using fire rated caulk. Caulking gaps around pipes, windows and doors can help contain fire. Metacaulk makes a water-based, fire-rated caulk that expands and hardens at about 375 degrees F to seal off voids. Most silicone-based caulks will begin to char and burn at around 300 degrees.
13. Recessed lights. Look for can/recessed lights with special housing that protects against insulation fires. Insulation around hot can lights can cause fires. Special housing units keep insulation away from the hot bulb.
14. Sprinkler systems.
Today’s residential fire sprinkler systems are available in sleek, concealed units that won’t make your home look like a commercial space. And installing sprinklers in your house may even lower your homeowner's insurance.
Systems usually turn on in response to extreme heat in an area. Residential sprinklers can usually extinguish small fires, but for very large flames, the sprinklers may only be able to help contain the flames until the fire department arrives. Prices vary, but on average, good quality concealed sprinkler heads will run you about $60 each, plus you’ll have to pay about $1.50 per square foot for fire resistant CPVC piping.
Those are some features that we can include in our new homes to make them more fire resistant. I think you can see from our list, that it doesn’t necessarily take a lot of specialized products to protect our homes. Consider adding the things that make the most sense for your budget and level of risk.
That’s all I have for you this week. I hope you learned as much as I did.
Thanks for stopping by.