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Deck over flat roof garage

bfnj5j8's picture


Existing condition:

I recently purchased a house (raised rancher) with a treated lumber deck (28'LX12'w) over my flat roofed garage attached at one end. There is a 1/12" drain located in the approximate center of the flat roof (asphalt coated) to catch any rain coming through the deck. Also, it catches any falling debree as I live in a wooded area whic eventually clogs everthing. The deck floats on the roof since, for obvious reasons, you would not want to nail the runners down forone thing.


The deck was constructed by laying treated 2X4s directly on the roof and nailing 3/4 treated boards to create the finished surface. During periods of heavy rain, the water backs up on the roof as it cannot find it's way to the drain by virtue of the "grid effect", thus finding it's way into the garage ceiling.


If anyone has a better idea how to fix this please jump in. My solution was to lay out a floating grid in a "star burst" pattern with the all of the grid ends pointing to th ecenter drain. This would allow water to flow to be channeled to the drain via the under lying 2X4s. The drain would be the center, so to speak, with the 2X4s radiating to the edges. However, I would apply a high quality rubber membrane roof before initiating any of the grid work. I would like to extend the roof line over this area, but fear I would lose too much natural light as this end of the house has two 8ft patio doors installed and allow a lot of light.




Severna Park, MD


Anyone have any thoughts on this.    



(post #95745, reply #1 of 2)

center drains are notorious for helping one to experience leaks, but they can work if everything is done right.

You absolutely need to get that deck off there first. The rubber roofing is a good idea as is the radiating spoke layout. better would be to re-pitch the roof to shed water off of it altogether though.

run a search here for EPDM to find other threads on the subject.


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(post #95745, reply #2 of 2)


Thanks for your insight. Improving the pitch is definitely the better idea to shed water her.  I'll investigate the best way to approach this idea.