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nomechanic 01-31-2010 08:14 AM

Need ideas for low slope, low priced roof
My repair shop is 22x52 with under than a 3/12 slope -- it's a lean-to roof coming off a larger barn. At present, I have old glavanized metal attached to 3" furring strips that are nailed to 6x24' trusses placed 16" OC. (I know...24' single span yellow pine...can't find those anymore). Anyway, the metal roof is shot after 40 yrs -- countless repairs -- and it leaks all the time so I need to replace it with something cheap but that works. Also, with 24' single span, weight is a concern. I assume at 5/24 slope that shingles are out.

Options considered:

1. Tear off galvanized roof -- install OSB, cover with felt and install some type of rolled asphalt or rubber material. Not sure how to do this. Equipment required? Sounds expensive.

2. Tear off glavanized roof -- install new metal roof (the painted 26 gauge stuff) without seams. My only concern here are the vertical seams could leak with such a low slope...

Any ideas would be appreciated.


Grumpy 01-31-2010 01:25 PM

Pictures would help. No offense but sound slike it may be a flimsy structure. Adding additional weight such as OSB may cause the roof to collapse.

First make sure that the entire framing structure can support the weight of the new roof structure. Make sure any rafters/joinsts are not spafed further than 24" apart. Then install a 5/8" CDX plywood or 3/4" if the weight and budget is not a conern. I do not prefer OSB for exterior applications.

Finally a great do it ourself roofing system for this application would be a self adhering modified bitumen roof system. Certainteed makes a great system, Flintastic SA. I have used it regularly, and is the ONLY low slope roofing system I will install directly over a roof substrate without first installing an insulation board. This is because it is a multi ply system (base sheet, optional mid ply, and a granulated cap sheet).

Dont forget the metal edging that is mandatory for a professional installation and a clean look. Without the edge metal, the edge of the plywood can rot after a few years exposed to the elements.

While I would not expect this roof to last 40 years, it seems like your metal roof didn't really last 40 years either and needed to be repalced a long time ago. You'll get 12 years out of a 2 ply and possibly 20 years out of a 3 ply self adhering modified bitumen roof system.

Good luck.

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