Will a tongue and groove deck make the underneath waterproof?

bsacksNovember 5, 2006

I'm replacing an existing ipe deck. I would also like the space under the deck to be a usable patio and therefore want to somehow waterproof the underside of the deck. The guy who came to give a quote on rebuilding it suggested using tongue and groove mahogany, which he says will prevent any water from passing to the underneath area. Is he right? He will pitch the deck slightly so the water drains off the side.

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No. It will still leak water.
T&G has gaps at every strip of wood for expansion and contraction as the wood changes moisture content.
UNless you get teh wood wet and keep it that way it will leak when it dries and the gaps open.

    Bookmark   November 5, 2006 at 9:50AM
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Like brickeye says, T&G decking will not waterproof your deck. If you don't mind the look of metal roofing you can use it underneath the joist after you modify the framing. I've done it on several projects like storage rooms & workshops under decks with good success.


    Bookmark   November 5, 2006 at 10:17AM
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I'm confused, you're saying that the deck will leak when it's dry (gaps will open), but if it's dry, what's there to leak? If this is not a good solution, is there one that will work well and not look ugly?

    Bookmark   November 5, 2006 at 12:50PM
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Yo sacks,,when we install T$G ipe I make sure it drains,leaks, so that it passes water the same as any other decking. No matter how its installed T&G decking will drain wet or dry.If its jamed up so tight it has trouble draining the ipe will buckel up until it can drain easly.X 10 with mahogany.

That guy who came by had no idea what he was talking about,like pitching the deck is going to change anything ! ghesssssss

Al has an way to do it for not much money thats been working for him for a few years. I use a torch down roof under the decking to dry in underneith. John

    Bookmark   November 5, 2006 at 8:22PM
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Thanks John. I'm really doubting this contractor now. I read the post about using a torch down roof. Do you put it between the joists and the deck or do you put it under the joists? If it's between the 2, don't you have a problem with airflow?

    Bookmark   November 6, 2006 at 10:49AM
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Torch Down roof under Deck>>> Frame your project with fall,pitch, say in a 12' span you will only need 1 1/2'' of fall. Plywood over the frame,torch down on the plywood with all needed flashing including under the door. 2x4 acq stringers laying flat in the direction of the flow on 16'' or 2' depending on the decking size,screw the decking to the stringers Not Past The Stringers Into The Roof!!! air flow is fine with 1 1/2'' under the whole thaing.

Fasten the posts to the rim joist,I dap out the posts 1 1/2'' x how ever big the rim is and land them on the decking.

Bang Bang, Done. J

    Bookmark   November 6, 2006 at 12:09PM
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Thanks so much! This is what this forum is all about.

    Bookmark   November 7, 2006 at 7:51AM
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You can also use an underdeck drainage system like Rain Escape or Dry-B-Lo.

    Bookmark   November 7, 2006 at 3:49PM
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I'd be worried about trapped moisture etc with the torch down roof concealed under your t&g not to mention ventilation and water leaking through the nails or fasteners...too many things to go wrong in my opinion.

I actually like the idea of roofing fixed UNDER the joists, you just put a little blocking that tapers so that the roofing material allows water to fall away from the building. I agree t&g will never hold water, and it isn't meant to. It needs to expand and contract, and the main thing is to ensure good ventilation so everything can dry out.

The Rain escape stuff looks interesting, what I like is it acts as a flashing over the joists, if you use the caulking as directed, it should protect them, as the top of the joists is a prime place for rot.

    Bookmark   November 7, 2006 at 5:50PM
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Guys I am a Person that strives for low preasure, in my life and my work.

The under deck drain systems are so pron to so many problems that I wont even go into it. Runing flashing/rubber sheet over the joists with a dip inbetween is so silly its not even funny anymore.

I have installed roof top decks exactly the way I discribed for 10 years now with out a single call back.

    Bookmark   November 7, 2006 at 6:29PM
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uh oh, I've glued and screwed and put the t & g as close as poss. They are 2 x 6 fir from an old horse barn , appx 70-80 yrs old , planed, sanded and stained on all six sides with behr from home depot. I'm going to build a roof over top but it will still be open to some rain - south facing in southern BC, canada ( rain forest ) , am I going to be having problems with expansion and contraction with moisture etc.
I too was hoping that I could have a waterproof deck but need as much headroom as poss below. What are my chances ?

    Bookmark   April 18, 2008 at 3:21AM
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Quick post: I had two large decks on my home waterproofed by Grant Barlow. He did an amazing job. I have a yard equipment room below one deck and a den below the other. Both had water coming into my home because the decks weren't built right originally.

He put a plastic material on my decks. It's perfectly dry now. He has a website about his products. He calls himself "waterproof deck expert" of something like that. I'll look up his web address and put it in this email.

Good luck. Bruno

Here is a link that might be useful: http://www.mywaterproofdeck.com

    Bookmark   November 8, 2008 at 1:06PM
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