Choosing a Material for Porch Flooring
I am preparing to replace the floor of a client’s covered front porch here in Massachusetts. They want painted tongue-and-groove wood, like their existing floor. I’m told by a local carpenter friend and the local lumberyard that what is typically used around here for this purpose is 1×4 tongue-and-groove clear vertical grain Douglas fir.
I can’t find a lot of information about installing a porch floor out of that material, including in the GBA encyclopedia entry on porches and decks. So, a few questions:
Is there a different/better material I should consider for a painted, tongue-and-groove front porch? (They do not want to use one of the tropical hardwoods.)
Will the Douglas fir be strong enough to support people without bounce and sag, without a plywood subfloor? The existing floor is 5/4 fir, and likely old growth stuff. What I can find is 3/4″ thick, and I’m concerned it won’t be strong enough.
Is today’s Douglas fir, once painted, likely to be rot resistant enough for a covered porch, at least for 10 years or so?
Do I need to treat the wood with borate or something else, or can I just prime it on six sides?
Thanks for any info on this subject.
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Probably not the "greenest" option, but have you considered composite T&G decking? I rebuilt a porch on a Victorian home last year. I too was concerned about the longevity of available wood. Also the homeowner was tired of painting the south facing porch each year. I ended up using a T&G composite from Timbertech/Azek that maintains the vintage porch look.
Douglas-Fir is moderately rot resistant. Painted, and under a covered porch it should be fine for a reasonable period. This is borne out by the fact it's the de facto standard in the region. It's susceptible to insect attack. If you have problems with that in your area, some kind of treatment might be a good idea.
Black Locust would be better, both in terms of rot resistance and resistance to bending, although Douglas-fir is surprisingly stiff for a softwood. Black locust would probably outlast the house in a covered porch application. Availability is very region-dependent, but if you can get it, the price should be reasonable.
Porch floors in MA and other parts of New England were often done with T+G CVG fir. Traditionally, the floor joists would run parallel to the house and the floor boards would slope toward the exterior, and that's still a good approach. Even new fir has a bit of rot resistance but nothing like the old stuff. Providing good roof overhangs, good airflow below the floor and prefinishing all six sides (not just with primer, but with a finish coat to really seal the grain) will extend the life. It still won't last forever but it should last at least 15-20 years and probably more. Just be aware that painted tongues and grooves will take some effort (and a rabbet plane) to assemble. 1x T+G fir will span 16" safely, without much bounce, but of course tighter joist spacing or thicker floor boards would be better. Older porch floors are often framed with ±20" o.c. spacing which is too big a span for 1x material.
One of several downsides of synthetic decking and other materials that last forever is that, well, they last forever. On new porches and decks I use wood of various sorts but not T+G, I just leave small gaps between boards.
Thank you Brad, Trevor and Michael for the excellent information. This forum never disappoints.
I personally like the feel of a porch floor that is less stiff and more compliant and moves just a little underfoot. As long as it's not excessive. It is surprising just how it transforms the feel of a porch to something most people associate with old fashioned porches. It makes you really "feel" as well as see that you're in an outdoor space.
I like the synthetic porch materials. I would never go with one that tries to simulate an unpainted real wood appearance though; they just aren't convincing. I have a light grey porch floor that goes with that old fashioned look even though its synthetic. No T&G, which works much better for outdoor spaces. T&G does not let wind blown rain (or snow) to move through easily and will eventually cause problems outdoors.