Tiny House Episode 20: Fireproofing with Cement Board

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In this video, I talk about how I retrofitted the areas around the furnace exhaust and the chimney with cement board and steel. One of the big advantages to building a tiny house on a trailer is that since the "house" isn't a permanent structure, building codes don't apply. However, just because you don't have to follow code doesn't mean you should be reckless. I had this image in the back of my mind of all my hard work going up in flames due to some oversight so ensuring I was building safely was important to me.

The two areas of concern, the furnace exhaust and wood stove chimney, probably would have been fine but I decided to be extra cautious and upgrade the exit points anyway. The furnace exhaust, for example, was designed to go through a sheet metal and foam exterior and I had it running through wood and foam. The chimney pipe I used wasn't to code because the stove called for a 4" chimney and in Canada the chimneys rated for wood stoves and fireplaces by code have to be no smaller then 5". I didn't want an oversized chimney because I had read that this could lead to issues getting a proper draft. I suspect the people writing these codes never imagined someone would install a stove quite this small. Regardless, I wanted to have no doubts that these appliances were safe and not simply installed with bare minimum precautions.

Cement board similar to this was used to help fireproof the chimney, furnace exhaust and under the wood stove.

The main combustible material that was in close proximity to the chimney and the furnace exhaust was the sheathing. The insulation was Roxul which, as I previously mentioned, is virtually fire proof. After considering several different materials I ended up settling on cement board for my fireproofing needs. Since I needed a piece for under the hobbit stove anyway, I didn't have to buy extra. I then confirmed that cement board definitely doesn't burn by testing it with a blow torch.

Before and after the cement board and extended steel plate were added to the furnace exhaust.

I remember taking pictures of the modification process but they were lost along the way. Unfortunately, I don't enough enough images to do a step-by-step walk through but the basic procedure was cutting out the wood sheathing and replacing it with cement board. I even went a step further with our wood burning stove by lining the trusses closest to the chimney with cement board as well. Once this was done, I expanded the metal plates and flanges to cover the cement board. The areas around the furnace exhaust and chimney were now fireproof.

The sheathing under the chimney roof flashing was replaced with cement board. If you look closely, you can also see an extra piece of metal over the top of the flange. I installed this so I could cut the shingles back further since they are also flammable.

As I mentioned earlier, these extra precautions probably weren't necessary and are most likely even safer than code. Regardless, I can now sleep easy knowing that even in the event of a chimney fire or furnace malfunction the tiny house won't burn down.

Thanks for reading/watching everyone! Please upvote, follow and resteem to support this work. As always, comments are welcome and I would be more than happy to answer any questions you may have about tiny houses.

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