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Small Cabin Forum / Cabin Construction / Cabin Roof- Metal or Asphalt?
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# Posted: 24 Jul 2008 14:11

We're having a number of maintainance issues this summer, the roof being #3 of 5 (septic pump failure, floor disaster, mink invasion, and fallen trees [causing roof,gutter damage]). We clean the moss and plant growth from the roof each spring/summer, but this causes loss of sand/weakening of shingles over time. We've been advised to go with a metal roof. One contractor said remove the old shingles, another said install the metal directly over the old shingles creating insulation; cooler in summer, warmer in winter. We're on a tiny peninsula and 2.5 sides of the cabin are in heavily wooded area, 1.5 sides are exposed to a lake, only 10-15 feet away. It would seem this may create a problem with moisture (rotting the 1st layer of roof) by placing a metal one over it. Due to weather, time, $$$, and help availability- We don't have a lot of 'wiggle-room' for error... Again, any positive/negative experience with either?

# Posted: 5 Aug 2008 13:17

You are locked into thinking that there will be moisture under the metal roof. In reality, one hot day & all the moisture will steam away. It will lonly leak 30 to 50 years out when the metal rood starts to fail.

I agree with the one who said to leave the asphalt shingles in place. If you want, you might even install 3/4" purlins (strapping) & install the metal on top of those. Even better, insulate with 3/4" rigid foam insulation between the purlins. It will support the roof better, keep the metal roof very quiet during rain, & add even more insulation for all seasons. The purlins also make it easy to walk on the old roof as you install the (slippery) metal one.

A metal roof, on tar paper, on plywood, is rather noisey in the rain. But once you add insulation, (Inside or out) that noise disipates quite a lot.

A metal roof on purlins & insulation on asphalt shingles on tar paper on plywood will be so much quieter. You simply won't even know it's raining!

Also remember to install screws on TOP of the high points of your metal roof. (Depending on the brand & type) Read the mfg's installation instructions & I'm sure you will enjoy choosing metal.

Good luck!


Central Maine Woods
& Southern NH Cities.

# Posted: 5 Sep 2008 13:48

You absolutly do not install metal roofing by screwing it on the highs. You will kink the profile of the sheet. Look at any metal roofing the is installed with screws. You will not find one screwed on the profile highs.

# Posted: 27 Apr 2009 20:44

I put metal roof on over asphalt shingles, 2 layers, with screws in the flats as described. Works great, is fireproof, important where I am. Best source I found: Lowes Home Center. You custom order it cut to length along with flashing and peak cover and go to it. It's painted so no glaring galvanized look. I have a 40 degree peak so paid an itinerant roofer who didn't mind that do the job. Very affordable. Make sure the screws are plenty long enough. This will strengthen the overall roof, perhaps eliminating the need for end knee braces due to the reinforcement effect on board covered roofs.
Best, Todd F.

# Posted: 1 May 2010 10:15

Anyone with a good resource to see a profile of the layers to a metal roof over 1" lumber. I'm building a timberframe with an open ceiling design. 1 in white pine for the ceiling but not sure what goes on top to prep for the metal roof.

# Posted: 1 May 2010 13:34

There are MANY users in mid-MO of this companies products. Good to do biz with.

NO, I have no affiliation....

sheet metal roofing
# Posted: 27 Jun 2011 15:18

Check into the speculations on the sheet metal roofing panels and you will be able to figure it out. Call your sheet metal roofing supplier. After you do this you should be fine.

# Posted: 27 Jun 2011 16:55

If you're confident that your current roof decking and shingles are in good condition, adding purlins (and rigid insulation if you like) and metal roofing over them is fine. However, if there is even the slightest chance that your roof deck or rafters were damaged by the tree falling and any subsequent leaks, you should strip the roof down to wood and make the necessary repairs before installing the new metal roofing.

If you install a new metal roof, no matter how perfectly done, over an existing shingled roof that is damaged (more than a couple torn or missing shingles) it will fail long before the industry average (20+ years).

# Posted: 27 Jun 2011 18:37

I have seen a bunch of installs around here last few years, every one of them old homes, being fixed up. Every one of them, installed the metal over the shingles. As long as you have a clean flat surface, I don't see why you should have to do a tear off.

# Posted: 11 Aug 2011 01:00

While it is not necessary to tear off the old roof it does reduce the weight of the roof substantially and can increase the ventilation which is critical in a metal roof install. Using concealed fasteners (snap lock, etc) and standing seam is the way to go. The concealed clips allow movement of the panels due to expansion and contraction. Surface screws use rubber(like) washers to seal them but the holes can grow due to panel movement and eventually leak in extreme climates. The standing seam reduces the risk of seam leakage as they are elevated by the depth of the standing seam. They also look much better.....

# Posted: 11 Aug 2011 10:55

The metal I've used over shingles required adding 1x4 or 2x4 purlins over the old material or any warantee was void. I used 1x6's along the edges to be sure I hit solid wood with the gable trim.

Pay attention to the recomended screw spacing of the metal manufcturer before installing purlins. I've seen screw spacing wider than manufacturers requirements, and this in a high wind area (120+ mph not uncommon).

Cat gives good advice.

# Posted: 12 Aug 2011 13:55 - Edited by: toyota_mdt_tech

I had a metal roof put on my cabin. It has felt on the roof sheating, then the metal roof. Its not noisy at all inside, but I have an attic space and ceiling is insulated well. In fact, I cant hear rain at all. I went metal because of less maintanance and to allow snow to slide off. I get up to 3 feet of snow at my cabin in the winter.

I'd leave the shingles on too. Create a better vapor barrier and more insualtion to reflect heat. Like otyehr said, the heat would steam away any moisture underneat anyway. Metal roof has ridges to allow breathing anyway.

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