Metal roof over old asphalt shingles - tar paper?

Old 06-25-03, 10:29 AM
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Metal roof over old asphalt shingles - tar paper?

We have a two-story addition on our house with a simple peaked asphalt shingle roof - no vents or corners or gutters or anything complex. There is one layer of asphalt shingles on the roof and they're completely shot.

Money is very tight, so to repair the roof I plan on using the materials I already have on hand - corrugated metal sheets, 2x4's, and tar paper.

The plan is to lay tar paper peak-to-edge over top of the shingles, run 2x4's horizontally across, then screw/nail the corrugated metal to the 2x4's, with a top ridge piece from Home Despot to cap it off.

Is this a good plan? Is the tar paper unnecessary/redundant/likely to cause more problems than it's worth? Would it be better to completely strip the old asphalt shingles before putting on the metal roof? If so, how much better? We're in Texas and the forecast is 90-100 degree days for the next five months, so I'll be working on the roof from dawn up until about 9:30 or so (until the heat gets too much), and would of course like to minimize the time spent up there.

Oh, one other option - I do have a quantity of 1/4" plywood sheets, so that could be put down either over the whupped shingles, or over the tar paper, or over the existing plywood if the shingles get removed.

Suggestions/comments welcome!
Old 06-25-03, 08:25 PM
bungalow jeff
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Strip the shingles and replace any damaged sheathing. Don't let a potential $ savings give you a poor quality job that has you spending twice as much in a fraction of the time for the next replacement.
Old 06-26-03, 05:48 AM
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You are correct, and thanks for the sound advice, Jeff. The reason why I'm considering/questioning leaving the old layer of shingles on is because this is a *really* quick'n'dirty fix - the metal roof I plan on slapping on isn't Fabral or other commercial roofing product, it's sheets of corrugated aluminum of the type used on sheds and chicken coops.

Yeah, I know, do it right the first time and I'll be much happier later, but time and money are both serious considerations right now and this corrugated fix is a step better than the blue-plastic-tarps-held-down-with-bricks-and-boards
solution. Luckily, we're in a very rural area and there's no zoning board or neighborhood commission to get excited over the ugliness. I just want to keep the interior dry until the horrible US economy/job situation picks back up and money is available for a real replacement to the roof. Right now, having Mr. Tax Appraiser see a chicken coop roof on the house addition isn't necessarily a bad thing, too.

I figure that leaving the old shingles on will maintain some protection, especially since the few things I've read on do-it-yourself roofing have said it's okay to put a second layer of shingles over a deteriorated first layer (when the "real" job gets done later on).

Is the tar paper going to make a significant difference, or should I go straight to the furring strips and corrugated sheets? Should I skip the furring strips and just screw the corrugated sheets straight to the old shingles, or do that with tar paper laid/glued down first? I'm really a complete novice at this (former city boy now living out in the country) ...

Last edited by Therion; 06-26-03 at 06:33 AM.

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