How to build a deck over a flat roof correctly

Old 01-03-06, 10:58 PM
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How to build a deck over a flat roof correctly

Attached is a picture of the plans detailing how my designer envisioned building the wood deck over the flat roof that is our sunroom. I'm at the stage of building this area now and roofing it and the roofer has told me that he would prefer for no sleepers or wood members to lie on the rubber membrane directly. So, I have a couple of questions on how to build this deck.

First, the plans don't really show how the sleepers or joists are attached to the house. Since they are cut to be level (the roof is pitched), they are thinner on the side next to the house and become full width (2x4) on the edge of the deck. So, I question, if I end up with about .5" on that 2x4, how can it possibly be attached to the house?

The posts for the railings are shown to be simply attached to the deck but that doesn't seem too strong to me. My framer was telling me that they are usually placed through the roof sheathing and nailed to the rafters below, but I find this option a little scary since it opens the roof to potential leaks on that post, even if we flash it correctly now.

So basically, I'm confused as how I should tell the framer/roofer to frame or waterproof this area. Anyone ever build one and have experiences how to do it?


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Old 01-04-06, 03:37 AM
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HOw to build a deck over a flat roof correctly

Your roofer is right, and your framer is in "Catch-22".
Since you have the space, raise your deck 5", install a ledger against the house with carriage/lag bolts, install joist hangers. Now on the open end, you will have to be creative, as there will have to be support added, without interfering with the drainage of the roof pitch. I would suggest bolting 4x4, spaced every 8' minimum starting outside the corners to the top outside plate of your room, and installing a band board from your ledger all the around the unit, installing joist hangers, giving a place for the new floor joists to rest. By starting outside the corners, you allow for drainage and you won't interfere with your gutters. The intermediate 4x4's should extend only down to the bottom of your framing band, and should be carriage bolted twice for rigidity. This should give the support you need. Dropping the deck below sill level still allows for water drainage, and keeps it from backing over your door sill.

As always, consult with your local authorities before you do this, as you may violate certain codes in your area.
Old 01-08-06, 06:27 AM
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I've done a dozen or so similar to what your looking at though the finished product may not be what your looking for. For the past 5 or 6 years, we've been using the material used in truck bed liners (Vortex, Rhino, etc). It is sprayed on by one of their companies pro's over Advantech or similar t&g plywood. The difference is that the bed liner is also your finished surface (can be painted to match home or trim). Not near as attractive as mahogany or redwood would be but we've yet to see a failure in our harsh climate. May not apply for your needs or wants but I thought I'd offer it as a possible option.

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