Flat roof suggestions

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Old 08-20-12, 09:28 AM
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Flat roof suggestions

Hi,

I have a one story block building with a flat approximately 18' x 38' roof. The roof is rolled ashphalt roofing with torched seams. It is about 16 years old and it has developed an increasingly large area of ponding. No leaking yet but I know I am just getting lucky. The flat roof has approximately 18" eaves. What suggestions do you have for repair/replacement?

I assume the highest cost best option would be to frame a pitched/gabled roof on top of the existing one? If so, what would minimum pitch be and any other tips?

If going a less expesnive route what could be done?

Thanks for your input.
 
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Old 08-21-12, 07:54 AM
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you are right the best solution to a flat roof is make it not flat. If you do add a pitch to the roof I would make it enough to allow for asphalt shingles which means a 3/12 pitch or greater. if you want to avoid the expense of framing the roof then I would utilize a single-ply roof system such as EPDM (60 mil rubber) because it will eliminate alot of the seams on the roof and seams are likely future leak points. I would assume that the roof has a low slope pitch to a gutter on one side and I would add new tapered insulation to increase this pitch to be 1/4 per foot. In other words over 18 feet (if you pitch in the short direction) the insulation would be 4 1/2" higher on one side than the other. This should help eliminate the chance of future ponding plus additional insulation never hurts (assuming this is conditioned space you are roofing over) good luck.
 
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Old 08-21-12, 10:58 AM
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Thank you. Now some follow up questions if you are willing: If I frame a gable roof I assume I would frame right over the old one rather than tearing it off. There is fiberglass insulation in the 2" x 8" flat roof rafters, but of course there is zero ventilation. Now would be my chance to allow for some venting. Any recommendations? For example -- cut a row of slots (not sure how wide) perpendicular to the flat roof rafters the length of the roof and then vent the gable roof? It is a conditioned space. Block on slab. No gutters. Never have laid a level on it yet or notice which way the inadequate slope is pitching. I am inclined toward your EPDM suggestion as framing will be a ton on $$$. Eliminating ponding is very important to me. Any idea of what a ballpark price would be? Is this doable by a homeowner who is pretty handy?
 
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Old 08-22-12, 07:53 AM
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I will try to go thru the questions one by one
1) I would place the new roof framing on the wall directly adjacent to the existing 2x8s so that you are resting on the bearing wall. This means you are tearing off the existing roof decking and probably pulling the insulation. You might be able to sit on top of the deck but getting the load transfered to the wall will be difficult.
2)ventilation of the flat roof area depending on the depth of the insulation in the rafter space. If it is filled solid then you will not accomplish anything by cutting in slots. In addition you should have ventilation in the overhang.
3)EPDM roof price? no idea for your area but some factors that affect it are: the type of insulation you use (perlite, EPS, XPS, poly-iso, etc.), how many layers of insulation (two layers with the edges staggered will save energy and eliminate thermal breaks) mil thickness of the rubber (45, 60, 90, 115 fleecebacked), additional framing and trim around the perimeter, new gutter and downspouts, etc.
4) DIY project? definitely if you have the time, at least for most of the project. Demolition is obviously something you could do, insulation installation is not hard assuming you are mechanically fastening it with screws and plates. laying out the EPDM is not that hard either. The only thing you may want help with is the flashing since this will be the area where the system typically either succeeds or fails.
 
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