Building a Fire-Safe(r) ADU

By Renée J. Schomp, Director, Napa Sonoma ADU Center

With wildfires more and more prevalent in Napa and Sonoma counties, homeowners are inevitably doing a lot of thinking about what we can do to protect what for many of us is our single greatest investment – our home. And for the folks we serve at the Napa Sonoma ADU Center, our home includes our accessory dwelling unit, as well!

With nearly 800 homes destroyed or damaged, and more than 1,000 commercial and other structures burned (at time of publication) across Napa and Sonoma counties due to the Glass Fire, compounding the hundreds of homes lost in the LNU Complex fire just recently extinguished, the already existing need for housing in our communities has only deepened.

As we begin to rebuild together as a community coming out of these most recent tragedies, our nonprofit is here to support homeowners better understand the ins and outs of accessory dwelling units to help build housing units for family members, teachers, nurses, firefighters, and others in need of homes.

And we want to help you understand the concrete action steps you can take to ensure that you are building — and rebuilding — in a way that will protect your ADU in the long-term.

The good news is, Cal Fire just came out in 2020 with an updated handout with simple guidance for homeowners regarding low-cost ways to both harden your home and create defensible space around your home. The full list is available below.

Because building an ADU oftentimes means that you may be digging trenches and engaging in other types of yard work or even landscaping on your property and near your primary residence, when you’re building an ADU is the perfect opportunity for you to think about not only building it with fire resistant materials but also creating defensible space around your home.

And we have good news — Napa and Sonoma County homeowners have access to some excellent local resources to help you get started! You can reach out to your local fire safe council to learn more and request a customized educational home assessment designed to help you prioritize how to best harden your home and create defensible space around your home for fire safety:

1. Fire Safe Sonoma

2. Napa Communities Firewise Foundation

To learn more about fire safe councils and what they do, check out the state fire safe council and this useful definition of what a fire safe council is, exactly!

To dig a bit deeper into building with fire safe materials and some thinking on the associated costs, check out this recent North Bay Business Journal article, “New California laws build on research into wildfire-resistant construction.”

Low Cost Retrofit List

10 Low Cost Ways to Harden Your Home 

1. When it is time to replace your roof, replace with a fire-resistant Class A roof  material. 

2. Block any spaces between your roof covering and sheathing (bird stops). 3. Install noncombustible corrosion resistant metal gutter covers on gutters to  prevent the accumulation of leaves and debris in the gutter. 

3. Cover your chimney and stovepipe outlets with a noncombustible corrosion  resistant metal mesh screen (spark arrestor), with 3/8-inch to 1/2-inch  openings.** 

4. Cover all vent openings with 1/16-inch to 1/8-inch noncombustible corrosion resistant metal mesh screens.** 

5. Caulk and plug gaps greater than 1/16-inch around exposed rafters and blocking to prevent ember intrusion. 

6. Inspect exterior siding for dry rot, gaps, cracks and warping. Caulk or plug gaps  greater than 1/16-inch in siding and replace any damaged boards, including  those with dry rot. 

7. Install weather stripping to gaps greater than 1/16-inch in garage doors to  prevent ember intrusion. The stripping must be compliant with UL Standard 10C.  9. When it’s time to replace your windows, replace them with multi-paned windows  that have at least one pane of tempered glass. 

8. When it’s time to replace your siding or deck, use compliant noncombustible,  ignition-resistant, or other materials approved by the OSFM. 

5 No Cost Ways to Create Defensible Space and Enhance  the Effects of a Hardened Home 

1. Regularly clean your roof, gutters, decks, and the base of walls to avoid the  accumulation of fallen leaves, needles and other flammable materials (see Defensible Space for more details). 

2. Ensure that all combustible materials are removed from underneath, on top of, or  within five feet of a deck. 

3. Remove vegetation or other combustible materials that are within five feet of  windows and glass doors. 

4. Replace wood mulch products within five feet of all structures with  noncombustible products such as dirt, stone, or gravel.

5. Remove all dead or dying grass, plants, shrubs, trees, branches, leaves, weeds,  and pine needles within 30 feet of all structures or to the property line. 

   *This list was developed as a best practices guide and to assist homeowners to ensure their home is  more ignition-resistant from wildfires. Low cost can be subjective. Some of these items are based on  upgrading to more stringent materials when that feature is up for replacement due to normal maintenance  or lifespan, i.e. roofs.  

   ** Do not use fiberglass or plastic mesh as they can melt or burn. 

List was last updated January 31, 2020