Replacement of covered porch decking

[MWStout]

My house is ca. 1927, located in Northeast. I would like to replace the tongue and groove decking on my front porch.The porch is fully enclosed on two sides, partially enclosed on the other two sides (with three foot walls) and is covered with a roof. The porch is over the front corner of the basement, so the replacement decking and subfloor must be waterproof. The current decking is painted and peeling (and contains lead paint -- yuck). I am considering T&G mahogany, but my research indicates that this is a poor choice for watertight applications (and with no air circulation beneath). My questions:

1. What T&G decking material might you recommend? If I use mahogany, should it be sealed on all six sides and with what product?

2. What type of barrier should I install between the joists and the decking to make the decking waterproof yet inhibit deterioration of the decking?

3. If I find there is damage to the subfloor or joists (some of the current decking is loose at the edge) should I use plywood for the subfloor.

Any other tips appreciated. I am concerned about doing this work and then having cupping or warped decking or water penetration to the basement.

Thank you.

 

[glennjanie]

Hello MWStout:
You have a tall order there, trying to make a wood floor waterproof. The only way I see it can be done is to repair/replace the subfloor and I prefer the plywood route, I would make it Underlayment grade Tounge&groove OSB. As you install the subfloor, glue it to the joists, glue the end joints and the T&G which will help to waterproof a little. That type of OSB is very tolerant of moisture for a while.
Ultimately the waterproofing has to be on top of the wood flooring, using a heavy duty sealer and several coats of Porch And Floor enamel. If the water is stopped anywhere else it will lay there and soften the wood, causing quick rot.
Glenn

 

[inspectorD]

This is always a tough area to keep dry. My suggestion is to get a really good carpenter, remodeler,roofer over to give you some ideas. Not knowing what else could affect your issues is also limiting response.
There are interlocking decking materials, with drainage for this type of application, but if they freeze, could cause problems.
I would seek some professional help.

 

[MWStout]

Thanks for your tips guys. I opened up the existing decking over the past weekend to see what I have to work with. The joists were in excellent shape, no moisture or rot. I found a New York Herald Tribune newspaper from Dec 5, 1926 in the section nearest the porch steps and it was in decent shape. They had constructed a subfloor between the joists and filled that with what 3 inches of what I assume to be asbestos-type product. The fill served to insulate the floor and absorb moisture ( I guess ). Anyway, the asbestos is being professionally removed this week. Then my plan is to put in a new subfloor (using pressure treated plywood) and then layer with a peel and stick product for roofing that selfs-seals around nails. Or I may use some epdm if I can get a small quantity (porch is only 9 by 12). I will put in 1/4 inch sleepers on the joists and put decking on that. I recognize that this a sub-optimal solution, but it is better than the existing. I think long-term the best solution is to enclose the porch and be done with it.

Thanks for your help.

 

[inspectorD]

Sounds like you have a handle on that job, glad to help.

Let us know how it turns out, folks love to see picturesround here.

I also love finding those treasures, but they tend to take up too much of the job when you have to stop to read the paper.