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Old 09-24-2013, 01:13 PM   #1
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adding 2nd floor deck over existing roof


Hello all,

I am considering building a small deck on the second floor over part of the first floor. The space is roughly 10.5' x 14'. On two sides is a sturdy block wall which would bear the load of that part of the deck fine. On the other two sides however is an angled part of the roof, so I'm not clear where I should put the ledger board(s) or how to support that part of the deck if I don't use ledger boards. The building was built in 1871 but had a new roof put on in the 60's, and it's one of those odd roofs that comes down almost to the first floor (I think it's called a mansard roof?) The bottom of the roof extends down on two sides of the space the deck would occupy, and is pierced by 2 window openings. This sounds really awkward to explain, hopefully the pictures make it a bit clearer...

view from above


sketch of the space as viewed from the corner of the block wall


so as you can hopefully see from the pictures, there is a small piece of roof over the 1st floor bounded on 2 sides by the lower part of the roof and open on the other 2. I'm not sure how I should support those 2 sides of the deck. any suggestions or advice are welcome!

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Old 09-24-2013, 01:17 PM   #2
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adding 2nd floor deck over existing roof


Pictures would be helpful!
Real photos!

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Old 09-24-2013, 01:23 PM   #3
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adding 2nd floor deck over existing roof


unfortunately I won't be able to oblige until the wife gets home with the good camera until then drawings will have to suffice
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Old 09-24-2013, 04:15 PM   #4
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adding 2nd floor deck over existing roof


as promised, pictures:











hopefully this gives a better idea exactly what is going on!
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Old 09-24-2013, 10:18 PM   #5
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adding 2nd floor deck over existing roof


Hm. That doesn't look very promising. Even if you could safely attach a ledger board to the gambrel roof rafters, and run joists over to the concrete block wall, what sort of access do you have in mind? All you have at the moment is two windows. You're not planning on climbing out there through those, are you? And keep in mind that the depth of the joists plus decking will reduce the size of those openings even further. Let's say you're considering replacing one of those windows with a proper door (no small task, mind you). You have some significant challenges with that ledger board. For one, those rafters were not designed to support half the weight of a deck. Sure, you'd be attaching to them near their base, but still. It all looks very iffy to me. Honestly, if you're very determined to do a deck there, get a structural engineer to see if what you have there will safely support a deck. The only thing I can strongly suggest is that you don't start screwing lumber through the roofing. You're all but certain to end up with roof leaks and a lot of interior water damage...not to mention a potentially very dangerous deck.
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Old 09-24-2013, 10:40 PM   #6
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adding 2nd floor deck over existing roof


yup, these are all thoughts I had. the idea would be to put a small french style door in the window frame - the window opening is about 72" x 31" so it could accommodate almost a full size door. Would it be possible to allow the roof itself to bear the weight?
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Old 09-25-2013, 06:27 AM   #7
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adding 2nd floor deck over existing roof


Quote:
Originally Posted by Execut1ve View Post
yup, these are all thoughts I had. the idea would be to put a small french style door in the window frame - the window opening is about 72" x 31" so it could accommodate almost a full size door. Would it be possible to allow the roof itself to bear the weight?
You'd have to know how the roof was framed. 2x6s 24" OC? No way. 2x8s 16" OC? It just might be strong enough. Bottom line, it's impossible to say from a set of pictures. That's why I recommend getting an engineer involved.
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Old 09-25-2013, 07:15 AM   #8
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adding 2nd floor deck over existing roof


very well said. I also just realized my post was ambiguous. I was trying to convey that the deck would rest on top of the little piece of first floor roof using some clever trusswork, not that the deck would be supported by the overhanging roof from the second floor, but I think you picked up on that :D
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Old 09-25-2013, 07:58 AM   #9
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adding 2nd floor deck over existing roof


It's not a good idea to set any kind of framing, directly on a low-slope roof.
The roof you have looks relatively new.
We would not put a deck over that unless it was a new "EPDM" -
(or equivalent) - or a metal (probably copper) roof.
We'd warranty the EPDM roof 10 yrs. - the copper roof 50yrs. -
(if it's done correctly!)
No matter what the size the rafters are - you don't want to have
any contact/traffic on a roof!
What you're looking at has so many important, details involved -
(flashing/counter flashing/structural etc...) -
As "cortell" suggests -
Engineer!

A "DIY" job?!?
Probably - NO!
Good luck!

(Also, you probably will not get a standard size door in the window
openings that you have)

Last edited by rossfingal; 09-25-2013 at 08:00 AM.
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Old 09-25-2013, 08:02 AM   #10
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adding 2nd floor deck over existing roof


Well, you asked about ledger board placement, which to me implied attaching one side of the deck to the "wall" (gambrel rafters, which are almost wall-like in their pitch). Honestly, if that were possible, that would give you the best design strength. On one side, you have a load bearing masonry wall to support one side of the deck. If you had sufficiently strong bearing on the other side, then you wouldn't be limited by the design strength of the semi-flat roof. However, that's the big unknown. And of course, the clearance issues I mentioned. If you go the route of bearing on the semi-flat roof, make sure you build a floating deck. You do not want to fasten through the roofing material, as that will likely result in water penetration. If not immediately, eventually. As for the floating deck, I would rip deep joists at an angle to give you a platform that is close to level (but not entirely--pitched 1/8" per foot towards the street side). Make sure you consider railings in the design.

Most importantly, think permits. You will likely not be able to build this deck without one. You could try, but all it takes is one concerned neighbor to have the city inspector come by and shut you down. Because the deck would build on top of existing structure, I'd be surprised if the city would let you build this thing without an engineer's stamp.

Anyway, best of luck. Your first concern should be safety. Your second should be water penetration. Whatever you do, don't wing it :-) It's one thing to build a deck in the backyard. It's another to build it on top of a roof. I would without a doubt hire an engineer to design this.

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