water tight decking

[farmerpsv]

Hey all,
been awhile, busy building the house. i am putting a two level wrap around porch on my house. I would like the unroofed upper deck to serve as a roof for the lower, which means it needs to be water tight/proof. have been looking high and low for a 'system'. i want to be able to put a hot tub on the second level, so the decking material needs to have crush resistance (have considered fiberglass tongue and groove.) am thinking i may have to use marine grade plywood and then fiberglass that. i've never used fiberglass before, but can't think of anything that would be fairly permanent and water tight. don't like the under the roof systems, or the idea of putting a sub roof under decking. anyone out there know of a way to do this? is fiberglass hard to do a good job without seams showing, etc.? thanks for any ideas
paul

 

[turnkey4099]

There are systems for that application. For the life of me I can't recall the name of the one my BIL has in British Coluimbia on his wrap around deck. Very hard surface, totallyi water proof (he has a shop and garage under it) and good looking. Perma deck or something of that sort. You should be able to find something similar by checking at a lumber yard. Not the big box stores. Ask where there is some expertise.

Harry K

 

[MarkV]

I’ve never seen fiberglass used, it would seem like it would be a slick surface when wet. The most common method I’ve seen around here would be a rubberized roofing material, used on commercial flat roofs, with floating deck board panels set on top. By floating panels I am thinking of 2x4 framed sections that support 5/4 deck boards and are laid without attachments to the rubberized roofing material. The down side in your application would be the thickness of the system I would think. By the time you frame it with enough strength to hold a hot tub and water, plus the sub-floor and roofing, then the panels, it would be hard to make the proportions look right on a second floor porch.

Hope you will let us know what you come up with.

MarkV

 

[sgt_rjp]

This is one product I've seen to create a water-tight deck:
http://www.xccentdecking.com/drydeck_aluminum.html
It's aluminum but there is also steel(PVC coated).

Another option is to use traditional decking but use a system of panels and gutters below the decking to carry the water off. Here is just one product
http://www.vadeck.com/images/dryspace4.pdf
This, if not a similar product, is available at Home Depot.

None of these products are cheap, but they usually justify their price by saying your really getting two spaces for the price of one.

 

[browns40]

Hi Farmer,

I wouldn't shy away from using fiberglass at all... can be made non-skid very easily with sand/grit on final coat.

Incredibly strong, easy to do--it's what we make commercial fishing vessels & boats out of...

 

[_RaT_]

Hey all,
been awhile, busy building the house. i am putting a two level wrap around porch on my house. I would like the unroofed upper deck to serve as a roof for the lower, which means it needs to be water tight/proof. have been looking high and low for a 'system'. i want to be able to put a hot tub on the second level, so the decking material needs to have crush resistance (have considered fiberglass tongue and groove.) am thinking i may have to use marine grade plywood and then fiberglass that. i've never used fiberglass before, but can't think of anything that would be fairly permanent and water tight. don't like the under the roof systems, or the idea of putting a sub roof under decking. anyone out there know of a way to do this? is fiberglass hard to do a good job without seams showing, etc.? thanks for any ideas
paul

It will be the substrate that has the water proof integrity you desire. A hot tub/spa with 60 plus square feet of surface won't harm many surfaces. The problem you have is finding a substrate that won't leak once the decking is applied. The decking will provide two functions, a desireable look as well as substrate protection from UV, and physical damage. I know bithuthane will seal around nails, screws etc, bit I don't know about long term reliability. Torchdown is a possibility, but you would need a floating deck system. If it was me, I'd be looking at a surface made of tile or concrete over a waterproof membrane, much like a shower pan.

 

[EarPlug]

Here is a couple of places to try

http://www.dry-b-lo.com/
http://www.lockdry.com/
http://www.rainescape.com/
http://www.americandrydeck.com/

Jack

 

[bugstruck]

If it was me, I'd be looking at a surface made of tile or concrete over a waterproof membrane, much like a shower pan.

Hi Rat, Now we're talking. Lightweight concrete over a waterproof membrane would work as a base for tile, stone, or pavers. Just have to engineer the support structure adequately. Nobody really has a good, simple product for this application that I've ever seen. The aluminum decking link above would have to be hot in summer. Odd that they don't have a better website too.

Fiberglass would definitely work. I'm at least pretty handy and that stuff kicks my keyster. It's easy for the guys who boatbuild and work with it regular but it's very technique/process oriented. There's an art to simple gelcoat touchup that I haven't mastered, so I'd have to head in another direction when the mat and resin came out.

 

[farmerpsv]

Thanks all for the input,

I have looked at the aluminum, they say it does not get hot. I'm not impressed by the under gutter systems, my main problem with that is all your framwork is exposed to water since it's attached under the framing. The subroof is another I've ruled out because of thickness issues, and seems there should be one surface I can use instead of being redundant.

I'm leaning towards fiberglass, sand would put a nonskid surface mixed with the gel coat...but is very labor intensive, figure it would take about 4 coats to give me 1/8 inch of fiberglass. There's also a vinyl system that you put down as a sheet. will keep looking and let you know what i do.
paul

 

[CurlyDave]

I am looking for a similar waterproof deck for our new house, but I have another requirement -- fireproof also. I want to be able to put a propane BBQ grill on the deck and not have to worry about burning drips of grease.

We are looking at wood support/waterproof membrane/backerboard/slate or tile, although the concept of a real roof under a fireproof deck has a lot of appeal.

Why don't you want extra thickness? I just added more height to the lower floor and can make the deck any thickness I want.

 

[farmerpsv]

Hey CurlyDave,

I already have the ledger in place, it's a 2x10. all of my joists going from the house to the posts will be double 2x10s (8 posts). the joists between the double 2x10s will be 2x8s on 16" centers. because of the placement of the ledger and the size of the joists, i only have so much space left for flooring. i originally was going to do tile, but am concerned about the added weight. i imagine i'd need 1 1/2 " of sub floor for stability...thats what i usually use when i tile. add the weight of the tile and hot tub, seems heavy.

 

[CurlyDave]

Have you had an engineer look at your plans?

I suspect you can keep the existing ledger board, its load carrying capacity will be determined by the way it is fastened to the house studs.

I have never been a big fan of the construction I think you are describing. If I have this right, the 2x8s on 16" centers will be parallel to the house wall. If you put the right beam on top of your posts, you could use 2x10s on 16" centers perpendicular to the house for about the same lumber cost and I think you would have a stronger structure.

Take a look at the span tables here: span tables .

You can design the deck for any load you want.

I would consider putting one extra post directly under the hot tub and I bet you could use tile or stone as a surface.

 

[farmerpsv]

CurlyDave,
the joists are perpendicular to the house. each post will have a double 2x10 joist, then there are single 2x8 joists 16" on center between each double joist. i will cantlever the joists on a double 2x10 beam that will be attached to 6x6 posts. the porch is wrap around, L shaped. the hot tub will sit on the inside corner of the porch, or corner to corner up against the house (to put it another way). i already have the lower deck built and put a post under the diagonal joist that spans 14' from the corner of the house to the corner pier. I put a 4x4 under that near the house for added support. i plan on taking the 1x6 corner trim off the house and replacing it with a double 2x6 corner for added support for the upper diagonal joist, where the hot tub will be. didn't have an engineer, did get it approved by the county engineer (though they don't know about the tub plans!). also, 2x10 ledgers are attached to the house with2- 1/2x5" bolts every 24" (county spec calls for 1 every 23"). I may end up using under deck gutters. when constructing the deck they can be used under the decking on top of the joists, so that would avoid exposing all the framing to weather.
paul

 

[CurlyDave]

I would find a local engineer and show him your plans (tell him about the tub).

This will save you money in the long run. He will size the joists correctly for the loads the deck will see.

You may save enough on materials to cover his fee, or you may have to beef it up a bit, and you will be far ahead to know that before you build.