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September 29, 2014

Roof Deck Drainage

Sweet looking sleepers
A roof deck over living space is always a complicated bit of design.  Here is our scenario.

The underlying structural decking is flat, since it was installed on floor trusses.

Since we want the roof to drain well, we needed to add some slope to the surface.

I carefully cut a lot of sloped 2x framing lumber ("sleepers") to create a sloped structure.

(Yes, I actually took this on - not sure why the framers didn't think it was in their scope...  #GCproblems)

All are nailed and screwed down to the structural floor.

Note that they all slope to one corner of the deck where the drain will be located.

3/4" plywood decking is cut to follow the new sloped surface.
3/4" T&G plywood cut to fit - dry run, prior to insulation

Then the cavities between the sleepers are filled with insulation.

A bead of adhesive is applied, and the decking is screwed down over the insulated sleepers.

Now when the roofers apply their roof membrane, it will drain all to the drain in one corner.

We are using a TPO membrane.

Atop the membrane will eventually be placed a finish surface of concrete pavers.  They are supported by leveling pedestals to make up for the sloped surface beneath them.

Until the roof membrane is installed, this roof deck is a source of worry - it is basically a swimming pool that we've waterproofed with a tarp, and we hope very much the tarp won't leak.  I've had to deploy and remove this tarp a dozen times now as I work on this.
Drainage slope works!  Hopefully the tarp keeps doing so as well.

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