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Discussion Starter · #1 ·
am submitting a quote to do a four plex with a flat roof. I've never framed one in before and was wondering if anyone had any insight on things that have worked for them as well as maybe some things to be cautious of. Total roof area will be roughly 5500 sq ft. I know that there should be atleast a 2 degree slope just wondering if the best way is to rip a 2x's down from the high point down to nothing or if there is a better way.
 

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am submitting a quote to do a four plex with a flat roof. I've never framed one in before and was wondering if anyone had any insight on things that have worked for them as well as maybe some things to be cautious of. Total roof area will be roughly 5500 sq ft. I know that there should be atleast a 2 degree slope just wondering if the best way is to rip a 2x's down from the high point down to nothing or if there is a better way.
I'm only able to recommend a couple of things with what details you've given(then length of slope/span).
Anyhow, If you can still make it work great by adding a little more slope than the usual scale, (i.e. 3 degrees instead of 2), I believe it helps in reducing future puddling.
We normally try to drop a 1/2" every 2' from highest to nothing.
However, A very long span, I wish we would've sloped it a hair more, due to settling.
I've only done about 30-40 flat roofs, so maybe someone else might be a bit more specific.
 

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Discussion Starter · #5 ·
Thank guys I'll post a picture of what they gave me a little later
 

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Forming and Framing
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We are doing 5 town houses.. flat top c/w mansard facade.
Area is somewhere in the 5k + range.
I joist flat ceiling, 2x6 rippers on top.
As far as i am concerned for the span of 40' (run of 20') ripping 2x6s diagonally is the best route.
Depending on the run, you may need to rip 2x8.. 2x10.. to nothing to achieve the slope.
If the slope is high enough you might want to consider doing a 2x6 rafter over lay.. and every 48" building a knee wall or posting down to the ceiling joists (provided they run perpendicular to the rafters.
I will dig up pics somewhere.
 

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FramingPro has some good ways of going at it. It is our usual method of choice on one or the other he mentioned.
However, it would be nice to know if there are parapet walls and if the ceiling joists run perpendicular with the way the slope needs to go.
Is so, another added approach to FramingPro's recommendation(and possibly cheaper in cost) is to look into Tapered ISO Insulation systems. We've decked the ceiling joists and by-passed the purlins/over-lays/rippers (whatever you happened to call them) and laid the tapered insulation panels(on ply-wood) as directed for slope. (Google has images of them)
I just thought i'd add another idea that might help, if not here...maybe for another job.
 

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We are doing 5 town houses.. flat top c/w mansard facade.
Area is somewhere in the 5k + range.
I joist flat ceiling, 2x6 rippers on top.
As far as i am concerned for the span of 40' (run of 20') ripping 2x6s diagonally is the best route.
Depending on the run, you may need to rip 2x8.. 2x10.. to nothing to achieve the slope.
If the slope is high enough you might want to consider doing a 2x6 rafter over lay.. and every 48" building a knee wall or posting down to the ceiling joists (provided they run perpendicular to the rafters.
I will dig up pics somewhere.
Where your tapers get very thin are you installing blocking underneath for support?
 
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