Waterproof Deck Above Livable Space

Cor

I have waterproofed a deck for typical decking using a torch down roof system and then sleepers to attach the deck boards to. Height restrictions make that impossible in this application. Does anyone know if I can lay down plywood, seal it with one of those paint-on poly ethylene type membranes and then PL glue down tongue and groove decking. I've seen it done but I'd like some other opinions.

bob the builder

What kind of decking is it? Pressure treated, fir, composite. I guess I would be concerned that it will expand and contract and your glue won't hold. Also how much height do you have to play with from existing torch down to finished deck height?

Bob

Cor

I'm using tongue and groove cedar that will be painted. My concern is the same as yours. I have no room to build the deck up at all. I just don't know about piercing the membrane with nails. At the same time there is a chance that adhesive won't hold. I guess I should first get specs from paint-on membrane companies and maybe call a rep. What do you think? Thanks for the response.

DecksEtc

Please don't paint that cedar.

Cor

I have to paint it. It's what the homeowner wants. Cedar or redwood painted. My concern is the application.

bob the builder

I guess if glue was a good route to take I would glue down all my decks because it's easier. Still not sure what height restrictions you have. Assuming that the pitch of the roof is good and you were going to use 3/4" plywood. Could you use a 1x4 treated, screw it to decking from underneath with a 1"5/8 deck screw. Then attach rubber membrane strips to bottom of 1x4 in contact with roof. Of course you would have to build in sections and then lay them down. Also I would paint 1x4's for longevity and make sure not to impede the water drainage.

Bob

Cor

By the way, this is the front porch of a San Francisco victorian. The original deck still exits. It has t and g cedar nailed directly to the joists and has just now started to leak although there is no sign of rot. The space below is unfinished basement but obviously I still need to assure it stays dry. The porch has an overhang that offers some protection but bay area weather comes with heavy winds and rains. Maybe I just need to build it the same way. If the floor is maintained it may be fine.

Terry, Nothing is ever left unpainted on a queen anne and people here don't want anything exterior unless it's cedar or redwood. Way more $ than sense!

bob the builder

Opps I misread your post. I thought you already had a torched roof, but you were saying in the past you have done that type of job. Can't suggest what you are saying, but it does remind me of porch I repaired a while back. The contractor attached epoch composite deck board directly to rubber roof with rubber caulk. I wasn't sure exactly how much time expired before I saw it. I can say it looked good except for the 1 board I repaired was warped like you wouldn't believe. I would not suggest doing that, nor would I have done that job, but the customer seemed happy with it.

Bob

Cor

Thanks again Bob. I'm sorry I wasn't more specific - this is my first time on this thing! Anyway, this is an existing deck rebuild. More of a restoration with new spandrels, brackets, corbels, posts...etc. looking for absolute perfection. This problem is killing me because I can't afford to lose more than 3/4 inch of space without creating a lip above the threshold, the pitch is just right, and all the framing is solid and rot free (old growth rough cut redwood). What you suggested is how I've done this in the past but I don't have room for plywood and sleepers. I just though of something. Maybe I could run cleats along the joists 3/4 inch below the top and flush the ply with the tops of the joists. Then I could seal it with a membrane and lay down 1x
sleepers and send the water to a gutter. What do you think? I may have to resort to call my old boss. Humiliating, but he has thirty more years building in the bay area than me! That's last resort.

bob the builder

I don't think screws would be sufficient for cleats, possibly joist hangers, what a pain....

Bob

Cor

I talked to my old boss today and he told me to just build it the same as existing and quit worrying. He said as long as the paint is kept up it will be fine and if a little water gets through to the basement then that's tough s---!
That's easy for a man with a million dollar company to say but I guess that's what I'll do. Thanks again for the advise-nobody else seemed to want to touch this one!

DecksEtc

I understand that you have to do what the customer wants. What I was getting at, and I should have elaborated, is that it would be better to use a good quality solid stain as opposed to paint.

I had a customer this year that insisted on painting a beautiful fence and porch I did in cedar. Despite my recommendations for stain, she still went ahead and painted it. I just hate covering up beautiful cedar with paint or solid stain. To each their own...

Oregon_Rob

If it's flat and you are using nails or screws, it will leak and if allowed to continue, given enough time, rot. As long as the customer knows this, no problems.