New Roof

September 17, 2007 11:03 AM

What new material would you use to replace an old cedar shingle roof?

The pitch is moderate to slight (about 4/12), winter snow load is average, fire hazard is extreme, so I will be looking for a new material. Metal, perhaps. It must be strong enough to walk on occasionally, and resistant to raccoons, squirrels, and woodpeckers that want to nest in my attic. Anyone have experience installing a sheet metal roof on top of existing shingles, or is this not a good idea? What materials have worked well for you?

posted by weapons-grade pandemonium to home & garden (13 comments total)

My roof is steeper than yours. I installed a steel roof over existing shingles. I ran 1x4 strapping on 24 inch centers over top of the old shingles, and then screwed the steel to the strapping.

It worked quite well.
posted by davey_darling at 11:09 AM on September 17, 2007

Metal is an excellent choice and is straight forward to install. 4:12 pitch is well within the limit for a standing seam panel, you can go as low as 2:12. You'd have to strap your shingles to install the sheets but it can be done. Best practise though is to install the metal roofing over the roof sheathing as that provides the best impact resistance. With the exception of a green roof metal is the most resistant to damage from being walked on.
posted by Mitheral at 11:16 AM on September 17, 2007

Solar shingles!
posted by delmoi at 11:20 AM on September 17, 2007

Although I have no experience installing a metal roof, I do know that tin roofs are strong enough to bear the weight of a grown man (Dad helped knock down and rebuild a barn with a tin roof when it fell down during an ice-storm - even damaged, the tin held up to being walked upon).

I wouldn't install tin roofing over old cedar shingles mainly because the surface isn't flat and properly prepped to take the new roof. If I were doing it, I'd pull off the old shingles to expose the plywood underneath, replace the tyvek and/or plywood if necessary, and then proceed to install the tin as per the instructions. Rona has lovely little how-to-s on installing roofs.
posted by LN at 11:23 AM on September 17, 2007

Mitheral & davey_darling: The strapping is for smoothness, strength, or attatchability? The strapping under my shingles is 1" x 5" with 7.5" centers, so the gaps are only about 2.5". Extremely strong.
posted by weapons-grade pandemonium at 11:26 AM on September 17, 2007

Personally, I'd remove the shingles before installing the new roof. Note also that some localities have homeowner rules that prohibit metal roofing for obscure aesthetic reasons. Check into that if you can.

On the snow load, note that snow tends to sluice right off a standing-seam roof (well, actually it builds up to a point and THEN slides off en masse). This may not be desirable; there are widgets available to prevent that, which you may want to investigate.
posted by aramaic at 11:27 AM on September 17, 2007

Years ago, my father worked for these guys. I'm fuzzy on the details, but iirc, the product supposed to replace cedar shakes/shingles and is made of various recycled cements and paper and such and is supposed to be fire proof or fire resistant or something.
posted by jjb at 12:11 PM on September 17, 2007

The strapping is for smoothness and attachability (mainly attachability)

Running the strapping gives you places that are guaranteed to hold a screw, every time. If you drive a screw through the panel into nothing (i.e. gap in sheathing, rotten part of sheathing), you are left with a hole in your brand new roof. Not a very nice thing to happen.

The strappen can also be shimmed in order to smooth out any sagging that the roof may have.

When I strapped mine I also ran 16 inch pieces of 3/4 ply along the valleys - this helped to ensure that the valley flashing had a good solid base.
posted by davey_darling at 12:14 PM on September 17, 2007

Metal, standing-seam roofs are great. Definitely remove the cedar shingles first, though, as they do not afford an adequately secure base for the metal panels.

OTOH, the product jjb links too would be a great replacement for the cedar. That way, you could retain the rustic look.
posted by Thorzdad at 12:51 PM on September 17, 2007

Metal, standing-seam roofs are great.

and really expensive. they are constructed from strips of sheet metal with specialized 'crimping' tools and require a fair amount of forethought to install, hence the cost.

metal roofs are either 'standing seam' or screw on. I wouldn't recommend nailing on a metal roof over a residence.

the strapping is to make sure the screws hold. but also, with screw on panels they are sealed by neoprene tape along the edges so it is advisable to have the panels be flat and not flex up so as to break the seal of the tape.

best practce would dictate removing the shingles...
posted by geos at 4:11 PM on September 17, 2007

geos writes "and really expensive. they are constructed from strips of sheet metal with specialized 'crimping' tools and require a fair amount of forethought to install, hence the cost. "

Even standing seam is screwed on. There are residential products that just snap together, no special tools required. I prefer standing seam because the panels are narrower and therefor easier to manage and the screws are protected from the weather so they don't need maintenance. Surface screwed products need the screws inspected and possibly replaced every few years after an initial 15 years. The standing seam is about 15% more expensive but it is also generally guaranteed for 50+ years instead of 35. But it's worth it for the DIYer just because the panels are 1/3rd the width and the screw locations are prepunched.
posted by Mitheral at 4:52 PM on September 17, 2007

Great info. Thanks, everyone.
posted by weapons-grade pandemonium at 8:47 AM on September 18, 2007

If you're looking for something eco friendly or "green" you might want to consider synthetic shakes, tile, or slate. There are some manufacturers that use recycled HDPE - plastic from water bottles, beer cups, etc - and recycled rubber from tires that are very realistic looking, light weight, long lasting (50 years or better), and recyclable at the end of their service life. They aren't cheap but you won't have to replace them as often as wood shake or asphalt shingles which also reduces the burden on landfills.
posted by ProSpec at 9:46 AM on July 27, 2008