Roof Deck Drainage

[QualicoreHomes]

Hello Chiefs, 

I have a designing question which I hope I can throw out on this tread also.  I have been asked to design a deck on a roof or deck in a roof (not sure what the right term is) which I have not done before.  Personally I do not like water on a (almost) flat surface and I'm wondering about which drain system to go with.  Would you recommend a floor drain in the middle of the deck or a deck sloping to the end of the roof with a channel or scupper draining onto the roof?  I have attached a picture of the last scenario?  Some of you must have done a lot of these and I was wondering which would be the best way (or if there is another would love to hear that too) is for designing such a deck.  Thanks in advance!!  

[ShaneK]

Last one I did I put 1/12 roof below deck and put a rubber roof on it. Obviously thought has to be put into load support, roof repairs some day ect........

[Ridge_Runner]

Last one I did I was able to drain it out over the lower, front roof section. I used a membrane roof system sloped to drain (I don't like the scuppers). Used "duck boards" under removable deck flooring panels; make sure you add the recommended double thickness membrane under the bottom of the duck boards (sleepers) to protect the main membrane. If you are building in a cold climate the center drainage system will give you problems. Some have resorted to providing a heat source just to keep the drain lines working when the temp is below freezing. A reminder of one hard fact: the deck area must be kept clean, especially from the buildup of leaves and other debris. No system will drain as designed unless the drainage path is kept clear. With finished space below this type of inset deck it is even more of a problem/headache. There are those who say this type of deck is great if done right and maintained. My question is, "did you ever see one?"

[javatom]

Lose the roof at the perimeter walls and replace with a rail.  This will provide unrestricted flow.

[chief58]

TREX makes a drainage system that might work for you call Trex RainEscape 

[javatom]

The trex system is really only used for a deck with exterior space under it, not interior space.

[chief58]

I understand that wasn't sure what he had underneath and what kind of height there was, even with putting the railings he has to protect the underneath

[ShaneK]

Post the plan so we can we can play in the sandbox too.

[QualicoreHomes]

Thanks for the replies, I'm a little hesitant to post the plan because it is in the preliminary stages and I'm still learning the ropes of this program, kind of like hanging out with the big guys when you're still growing .  

 

6 hours ago, Ridge_Runner said:

Last one I did I was able to drain it out over the lower, front roof section. I used a membrane roof system sloped to drain (I don't like the scuppers). Used "duck boards" under removable deck flooring panels; make sure you add the recommended double thickness membrane under the bottom of the duck boards (sleepers) to protect the main membrane. If you are building in a cold climate the center drainage system will give you problems. Some have resorted to providing a heat source just to keep the drain lines working when the temp is below freezing. A reminder of one hard fact: the deck area must be kept clean, especially from the buildup of leaves and other debris. No system will drain as designed unless the drainage path is kept clear. With finished space below this type of inset deck it is even more of a problem/headache. There are those who say this type of deck is great if done right and maintained. My question is, "did you ever see one?"

 

I agree and am hesitant to draw this.  To make it even worse is that the ceiling of the first floor and floor of the second floor are only 2x10's so not much to work with for sloping when underneath this deck needs to be living space.  The customer has a home that he wants to convert into separate living quarters, one on the main floor and one in the basement and then a bachelor suite on the second floor with this deck attached.  

Thanks for the advise!!

Roof_Deck_Plan.plan

[DRAWZILLA]

Dex-o-tex can slope the decking material to give you 1/8" slope which has ICC approval for less than 1/4"

[WesternDesign]

We use a similar method as Nick

Pocket Deck Details

 

[QualicoreHomes]

Thanks for the tips!, also the video!  He raises an interesting point about the details also; I realize he uses sketchup but he doesn't draw too much detail in his model he says but draws separate individual details or vignettes for this which I don't do but instead I try to get the model cleaned up and more detailed. 

 

[Michael_Gia]

I would bring my deck to come out and over the top of the lower wall and add a railing. 

 

Then you could just drain with a gutter and downspout. 

 

Membrane as if if you were building a flat roof. That way whatever you throw on top is just for decoration - tiles, trex, cedar planking, heck even a Persian rug!

 

Also, often overlooked and a real weak spot is how the waterproofing is done around the patio door. (If you get snow where you are, that is). 

[Ridge_Runner]

28 minutes ago, Michael_Gia said:

 

Also, often overlooked and a real weak spot is how the waterproofing is done around the patio door.

I agree; this is an area that doesn't sometimes get enough detail. Do it right the first time or you will regret it very quickly.

[MoeGia]

I usually raise the patio door in these situations (create a curb). If you use decking and sleepers over the membrane you will have to push the door up.  This gives a little more room for flashing around the door, but it is still a weak spot.  Maintenance will be crucial.

[RL-inc]

Based on the 2x10 ceiling/ floor framing I can see some fairly serious issues headed your way.

The way I would frame this you would need at least 5" or so from the top of the framing member to the top of finished decking as measured at the door threshold.

(See attached pics of a simple covered living area with deck- sorry I don't have and better pics of the actual assembly as described below.)

 

Joists should be slope ripped and covered with pt plywood and TPO membrane- water will run along this surface toward drainage scuppers or gutters.

Slope of the above should be approx. 1/8" per ft.

TPO should be run up the wall surface 12-18" or so.

Then sleepers would be installed over the top of this assembly that finish decking can be fastened to.

These sleepers can be ripped to counter the slope of the plywood surface below.

Glued down to TPO only- no penetrations.

Keep in mind that the ceiling assembly from below is now a roof and must be insulated as such- this may require closed cell foam or similar to achieve the require R-value depending on your area.

[QualicoreHomes]

Thanks for the advise everyone, much appreciated!! I have decided that in order to get this working properly we will have to sink the area under the deck by about 18" so this gives me about 24-30" of room to work with for decking boards, sleepers, slope and ceiling joists etc.  When I have this more completed I will post a cross section of the deal and let you have the final say 

[ShaneK]

This was drawn in version X so it's old. I will share file if it helps.

[QualicoreHomes]

Yes if you would be willing that would be really nice!!  My oldest version on my current computer is X9, I started with X7 but I never had that installed on this computer but I assume I would still be able to if that's needed.  Is that old enough?