Why siding can be a fire hazard (and why it sometimes doesn’t matter).

Photo by Eric Ardito on Unsplash

In our last article, we touched on roofing and why the material of your roof really can be integral to keeping your home safe. Now, let’s cover what’s protecting the rest of your home: siding. For those of you who are unfamiliar, siding is basically the outside material of your home that you visibly see. Siding comes in a lot of different varieties and qualities. And whether or not you need to replace it? Well, it depends.

For any home, risk is relative. The wildfire danger someone faces in Eastern Oregon might not be the same as the wildfire risk someone faces in Northern California. Your risk is relative to where you are, and what you feel comfortable with taking chances on.

Siding is something in defensible space that can be seen as a ‘nice to have’ all the way to ‘TOTALLY must have’ depending on where you live. The reasoning behind it can be a bit complicated, and that’s because fires can start in 3 different ways: embers, heat, and direct flame exposure.

Some siding can be more resilient to embers hitting it, and then bouncing off because it’s a vertical plane. It’s less of a concern than roofs because it doesn’t land flat and stay on the material all the time, so it has less time to ignite.

If you have gravel surrounding your house, and embers come and bounce off the siding and fall down: they’re going to burn out and you won’t need to be concerned. However, if your house is surrounded by highly flammable Rosemary and an ember falls into a bush and it catches fire, and then spreads that fire to your vinyl siding, you have an issue.

If you live in a medium risk wildfire area with lots of empty defensible space around, you might not feel the need to upgrade your siding. If you live in a high-risk wildfire area with trees all around that you don’t have the stomach to remove, upgrading your siding might be the best bet to keeping your home longer.

So, what qualifies good or bad siding? It’s the same as roofs: your safest bets for siding are plain and simple: non-ignitable materials. These are metal, stucco, concrete, synthetic, masonry, stone, etc. Your worst bets are plastics like vinyl, untreated wood, straight OSB or particleboard, and more.

Similar to roofs, you have options for what you can do to protect your siding.

First and foremost, making sure that nothing flammable around it will catch fire, and then expose your siding to direct flame contact.

You can also use flame retardant, and maybe only replace siding in the areas that you feel are especially vulnerable. Maybe you don’t have enough to replace ALL of your siding, but you can replace half the siding closest to the bottom with metal or stone.

For example, I, Amanda (the article author and programming person at Faura), live in an aluminum tiny house in rural Washington with medium fire risk. I also have aluminum studding, Rockwool insulation (which is fireproof) everywhere in my home, and the belly pan of my tiny house is sheet metal.

There’s some treated wood that acts as trim around my house, but for the most part because my house is mostly un-burndownable, I feel comfortable taking the risks of having highly flammable plant species closer to my home. That being said, I know because I’m rural I’m farther away from fire stations, and could be left to my own devices in a wildfire. So, if a fire gets close, I would still put flame retardant on my wooden trim and move my house to be further away from trees.

When a bunch of bad practices align, it creates very rare circumstances that leads to very terrible disasters. This is known as the ‘Swiss Cheese’ safety model.

The Tenerife Airport disaster is a great example of this. There was a terrorist attack earlier in the day of the accident that diverted everyone to a smaller airport, there was crew fatigue and stress (as well as annoyed passengers), equipment that wasn’t up to the task of keeping air traffic control informed as a thick fog rolled in, and it resulted in the worst aviation disaster in history.

A bunch of terrible coincidences line up, and then something takes advantage of it. That’s how wildfire sees your home.

How much fuel is there? What can I burn? How can I get from wherever I am to consuming that? Wildfire doesn’t care. It just takes advantage of whatever is around it.

That’s why the goal of preparing your home from wildfire is to reduce the likelihood of fire even getting close to your home, and to especially reduce the likelihood of the fire actually igniting your home. Let’s for a second imagine an A-frame cabin with a metal roof and cedar shake siding in the woods during a wildfire.

For imagination sake, the theoretical house is as follows:

• The cabin is far away from trees, but has a bunch of leaves and other forest debris around it.

• The cabin owner stacked wood under the deck, and didn’t rack up the leaves collecting in the backyard.

• The cabin is an A-frame, meaning the roof is a huge part of the overall surface area of the building. The roof is metal and Class A rated.

• The siding is cedar shake from the top to the bottom.

So, now imagine that we’re a wildfire. We would travel through the leaves surrounding the house, because branches from trees on fire fell to the ground and ignited the forest floor around it. We don’t ignite the roof, but we get close to the siding. We catch the cedar shake siding on fire, and it spreads up. Uh oh!

Notice how the cabin owner took SOME defensible space measures that did keep the property safe for a little bit longer. But, he forgot some crucial things that lead the fire close enough to the house. He’s gonna have a hard time explaining that one to his cabin Airbnb guests.

He could have:

• Replaced the bottom half of his siding with metal

• Removed leaves around the property

• Added dirt around the home in a wide enough circle to create a firebreak

• Used flame retardant on his siding so it didn’t ignite

Taking steps back, defensible space is really about that. It’s not about taking all of the steps (unless you have the money to do so, in which case you should if you can), but taking the most effective steps and navigating what you can in an attempt to keep it safe. It depends on the person, home, space, and budget. There’s also not always a ‘right‘ answer, or there’s multiple easier steps you can take.

That’s really what defensible space is about: learning about your risk, your points of concern, and figuring out what tradeoffs you want to make, and what your budget is within your risk tolerance.

P.S: If you are jealous of my (hopefully) unburndownable tiny house and would like to see how your own house stacks up, take the assessment that me and my cofounder made to help homeowners see their wildfire risk at assessment.faura.us. It’s free, it’s easy, and it will tell you what you need to fix and how to do it.