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Fire-Resistant Details for a New Build

carsonb | Posted in General Questions on

Hello GBA,
here is my rundown of thoughts on fire prevention on a new build in Zone 5b on the west coast.  Some people may have useful advise, or perhaps some of my research will help others.  The home is in a remote region, but still in the middle of a city and has a fire hydrant on the property, so hopefully the likely hood of a wild fire hitting it is pretty low, but here is a rundown of my thoughts to help mitigate risks.

1.  Materials –
i.  siding – It is too late to go back and change all siding now, and honestly I don’t like stucco, but the siding is made up of cedar shingles, clapboard, and there are timberframe elements on the exterior.  I looked into it and I can get a class-A fire rating by using a fire retardant spray over the wood surfaces using a product like this:
ii. rigid foam- polyiso is used behind the siding.  Supposedly polyiso will offer better fire protection than other foam options like EPS.  mineralwool would have been better here, but I’m assuming not worth the cost.  I would assume the house is already gone if it is burning away the polyiso.

2.  Rainscreen worries –
Homeslicker is used behind wood siding and foam as a ventilation gap.  Since there is foam behind it, this is mostly for increasing the longevity of the siding.  The gap is very small, so for fires this should be fine, or at least so says Joe (  According to the specs on Homeslicker, it has a Flame Spread Index of 15, and from what I could find anything in the 0-25 range is considered class A.

3.  Overhangs and soffits –
Overhangs are great from many articles I’ve read.  Helps with solar heating/shading and avoids water damage issues on walls.  But it appears to be be bad for fires.  I currently have no plan for this, other than to rely on the same fire protective coating used for the siding.  Soffit vents and rainscreens will be screened to avoid ember intrusion.

4.  Defensible space –
I am currently arguing with the HOA to change their manual to be able move my firewood storage to be away from the house.  There are several large ponderosas on the property that may pose a danger.  Other than that, at the advise of a local nursery I am planning on removing highly flammable plants from anywhere near the house and he actually recommended planting some plants such as rabbitbrush and aspens that apparently can help prevent fire spread.  (

5.  Sprinklers –
I was going with all native plants and hoping to forgo irrigation almost entirely aside from occasional hose end use, but I’m currently rethinking this to get sprinklers that can cover much of the perimeter.  I briefly considered putting some that may hit the house, but I think it would be better to have some hose end sprinklers on hand I can hit the house with.

6.  Windows –
Apparently windows being blown in from fire is an issue.  I’m not quite sure what to do here.  Tempered glass is expensive.  I’m wondering if having some hardiboard planks to put up over windows before evacuation would be wise.

7.  Interior fire suppression system –
I’m not sure how much this would help for a wild fire.  If it’s needed, I would assume the house is gone.  I do see things like the haven system mentioned that may be cheap to put in, but those seem to be more for small house fires to give more time for the fire department.  Likely not useful for a forest fire.

Hopefully this was useful to someone, thanks for any advise, and stay safe out there.

GBA Prime

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  1. user-6184358 | | #1

    Here is the California Wildland- Urban Interface Code -

    San Diego County has good details on how to follow the codes- especially for building eaves

    1. carsonb | | #5

      wow, that code makes me appreciate all that architects/builders have to go through. I'm not well versed in building code, but I didn't see anything on eave construction under the wildfire section, just on references to vegetation and defensible space. The sections on fire code for enclosing stairwells and material sections for portions of the home seemed pretty daunting - it would seem that wood trim or furniture would be effectively banned in many instances.

  2. dickrussell | | #2

    For forest fire protection, I have wondered about how well it would work to have a roll-down metal mesh. It would have to be tight enough to stop blown embers, strong enough to withstand fire-driven wind when anchored at roof and ground, and light enough so that one rolled up section at a time could be hung at the outer edges of roof overhangs by a pair of people when a fire threat loomed. The sections would be rolled down and anchored to the ground prior to evacuation. Has this been done anywhere? What would be the downsides to such a scheme?

    1. carsonb | | #4

      Dick, there are several commercial products that do what you describe. The downside is they are pretty hideous and seem made more for commercial use. You are basically trimming your windows in metal slides for the shutters. I think having something rigid you could attach before evacuation, assuming you have time, would be a better solution.

  3. GBA Editor
    Kiley Jacques | | #3

    Hi Carson,

    This is such an important question. Contributor Scott Gibson wrote an excellent article about it that you might glean from:
    Building to Survive in Wildfire Country.

    1. carsonb | | #6

      thank Kiley, I hadn't seen that one. I found an Oregon equivalent to the California fire risk locator mentioned:

  4. rockies63 | | #7

    Try Brandguard vents.

    If you're planning a metal roof you should put a fire resistant barrier underneath it. The heat from a wildfire can pass through a metal roof and set the roof decking on fire.

    For windows, install hooks above the windows and have some metal trays made (thick gauge metal with edges bent up 2" to form a tray) to completely cover the windows (and maybe the doors too). Then install 2" Roxul Comfortboard mineral wool panels between the edges and bolt metal rings to one of the edges.

    When a wildfire is reported in your area slip the panel's rings over the hooks and secure at the bottom with a pin. The panels should completely cover the opening.

    1. carsonb | | #8

      I like the hook idea. Sounds like a business opportunity for someonr given wildfires may be ever increasing.

  5. user-6184358 | | #9

    Here is a San Diego County Document it has a link to eave construction pasted here

    With a metal roof in order to get a class A rating it needs the proper underlayment or gypsum board under it.

    1. carsonb | | #10

      Thanks Tim, "Noncombustible or fire-retardant treated wood shake used as an exterior wall covering shall have an underlayment of minimum 1/2-
      inch fire-rated gypsum sheathing that is tightly butted, or taped and mudded, or an underlayment of
      other ignition-resistant material." My builder wants to build a wall that is cedar shingles - homeslicker - osb layer - 2" polyiso - osb layer - framing/insulation - drywall. Would the OSB and the polyiso be considered ignition resitant? What if I sprayed the same fire retarder on the outer OSB layer? Perhaps I'll inquire about using exterior gypsum board, but the original point of the second layer of OSB was for an easy nail base for windows and siding over furring strips.

  6. user-6184358 | | #11

    The fire treatment indicates it works on untreated doug fir. I don't know if OSB will absorb it properly. Plywood may be better. Talk to the mfg to see if it will work on OSB or plywood.
    I think most foam is just solid oil - perhaps the mineral wool would be best as it will not burn.
    Comment #7 interior fire sprinklers - they have been proven to save lives and reduce property damage. The are required in new houses in California. They are there to save the lives of the occupants.

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