Durable Wood for Porch Decking

What natural wood species might be suitable for a covered porch floor? June 26, 2009

A lumber dealer has recommended soft maple for exterior decking on a historical house to keep the costs down. Any thoughts on the performance of soft maple in an exterior setting? It will be primed and painted.

Forum Responses
(Architectural Woodworking Forum)
From contributor T:
Soft maple for exterior use - guess he's looking to guarantee you'll be back later. Cypress, cedar, or pine would last longer and be more historically accurate. Ipe or cumaru if you want to ensure you’ll never have to replace the material.

From contributor C:
It will rot in very little time. More work, more sales for the lumber dealer - a win-win situation.

From contributor A:
Some of the old timer's still frame decks with doug fir framing. That turns to dust in 15-20 years. As long as your customer is still on speaking terms it might be a good plan for future work. Likewise soft maple is a poor choice for exterior applications.

From contributor G:
If it's sealed well with paint, won't the moisture have a tough time penetrating the wood?

From contributor Z:
Fir or yellow pine will be better and historically accurate. The old flooring most likely was one of them. Soft maple is a short term solution to a long term problem and a waste of time and money.

From Gene Wengert, forum technical advisor:
Paint will certainly help seal the wood from moisture, but it is not a perfect seal. Also, when the paint gets a hole (nail, furniture cracks the finish, etc.), the moisture will get in but then will have a hard time getting out. Also, around the joints, you will get moisture even if painted. Your supplier is so incorrect, that I would be cautious in relying on any information he provides. Heart pine would be excellent. If you are not tied in to using a "correct" species, then treated pine would be ideal. Keep in mind that you might use an incorrect species and be happy, but when you sell the house, it might be viewed negatively to have the incorrect wood.

From the original questioner:
Thanks for all your feedback. I asked the question because I had a feeling it was not a good choice of wood for exterior use. We are now looking at white oak of vertical grain fir.

From Gene Wengert, forum technical advisor:
Quartersawn white oak (same grain as vg fir) that is only heartwood would do fairly good indeed.

From contributor F:
If I may, let's stack questions. I work in a lot of historic districts and I see fir porches and decks that are over a hundred years old, never touched, treated, southern exposure, and covered but still open to the elements and they are still in near perfect condition. I understand the whole heart wood old growth thing. Is this why they have lasted so long? I've done treated work that termites have eaten yet see untreated old fir still there.

From Gene Wengert, forum technical advisor:
For the natural decay resistance of the heartwood of various species, see Table 3-10 at the following link.

Contributor F - when you mention fir, I assume you are talking about douglas-fir and it is used in the PNW, but away from the coast?

Chapter 3, Wood Handbook

From contributor N:
Here in the Chicago area it is all doug fir. We have over 100 Victorians in woodstock and I have never seen anything original other than the fir. My previous home was built 1896 and the porch was doug fir. That is the historically correct material.

From Gene Wengert, forum technical advisor:
Decades ago, southern pine lumber was not sent out of the Southern USA much; it could not compete pricewise. Favorable railroad rates allowed a lot of douglas fir (almost always coastal d-fir from Oregon and Washington), as well as hemlock and ponderosa pine, to come into the Midwest and other regions of the country and be priced very low. North-south rail rates were quite high, so SYP could not compete. There were a lot of Douglas fir plywood plants that sent plywood all over the USA as Southern pine plywood was not common much before 1960 as the adhesive issued was not resolved, in addition to rail shipping costs.

In addition to Douglas-fir, there are also some species that are called true firs, such as balsam fir, subalpine fir and so on. Often time’s fir and hemlock grew together out West, so hem-fir combination was and is common when grading and marketing lumber. In Canada, fir grows with pine and spruce, so there is a marketed grade that mixes the three and is called SPF, which is common throughout the East, Midwest and South today.

Today, it would be unusual to see fir lumber, as fir is mixed with other species (hem-fir and SPF). Likewise, fir plywood would not be seen, but if some plywood is called fir, then it is referring to Douglas-fir and not true fir. (Exceptions for special orders; true fir trees are generally too small to make veneer profitably). Eastern white pine was used throughout the East and Midwest as it was abundant and, if kept away from very damp locations, performed well.

From contributor S:
Aside from the historical aspect, have you considered kiln dried pressure treated tongue and groove porch decking? Pressure treated southern yellow pine is a great material for exterior decking and add to it the kiln dried process and you can paint it and it will hold up for many years. We did a historically accurate exterior siding and trim job for a 1940’s Florida cottage and used the KDAT for all the siding and trim. It only comes in dimensional lumber sizes so you must have it milled into the final product.

From contributor F:
I'm located in Ohio, so I'm a little ways from the coast. We see a lot of fir throughout the Dayton and Cincinnatti area, from framing to exterior decking. I was mainly wondering if new growth fir would be anything near comparable. We see a lot of poplar casings with deteriorated paint in great condition, yet I've replaced these with poplar molded to match, and seen these decay within several years. I've since been wicking the ends in a Jasco copper product with great results. My only conclusion is that the tighter the growth rings, the less susceptible to rot, insects and moisture. Thanks for the input.

From Gene Wengert, forum technical advisor:
The tightness of the rings is not a good indicator of old growth. That is, some second growth grows slowly too. Treating the ends by dipping is a very good idea. Sometimes the entire piece is dip treated. Yellow poplar has little natural decay resistance. I do wonder if the fir you are getting is douglas-fir, as the transportation costs would be really high. I suspect that it might be one of the true firs from Canada.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
Moisture will slowly diffuse through any painted surface. I am now using douglas fir lumber that has been coated with marine epoxy glue just like a boat is built, and then painted. It does take much longer to do but the job is excellent. See, for example, West System epoxy. It can be used as a glue or barrier or be combined with fiberglass.