Replace traditional shingled roof with metal roof? Experiences?

[toppop52]

When installing it on a house with an existing roof, I've seen where they just nail purlins right on top of the existing shingles. This is a mistake and will lead to issued down the road. The purlins need to be solid and anchored to the rafters. The shingles make this impossible to do and you end up with loos purlins, which means the metal moves and the gaskets on the screws leak fairly quickly.

Not arguing, I'm not a roofer, but why can't they be nailed to the rafters over shingles, there are nails and screws as long as you want and it would seem simple to locate the first rafter and measure from there, checking occasionally on the inside to make sure you're on target. What am I missing?

 

[lilranch2001]

I am curious how the roof penetrations are handled
That would be where I would think a lot of issues are created

 

[Bengineer]

OP, I found this recent blog post where the guy D-I-Ys his metal roof over sheathing very informative. He describes how & what he bought and the install and makes the point that it shouldn't cost much more than shingles. I also found the mfr's product info on the parts & details of install very informative. I have no connection to either. I was just interested in learning the ins & outs of metal roofs for my next house / re-roof. It is clear that there are many more variables than with shingles. The roofing material, coating, solar reflectance, color, profile/shape, over purlins or over sheathing, exposed / hidden fastener install, clips or screw down, roofer experience with the product and so on. It seems like a lot to learn, but also the potential of a much higher performing and longer lasting roof.

HTH

 

[tcreeley]

Not arguing, I'm not a roofer, but why can't they be nailed to the rafters over shingles, there are nails and screws as long as you want and it would seem simple to locate the first rafter and measure from there, checking occasionally on the inside to make sure you're on target. What am I missing?

I screwed down 2x4's running with the rafters over the shingles. I also used a nail gun setting at angles. I ran the 2x4.s for the metal perpendicular to the first set. I wanted a large air pocket that was vented. Snow gets deep on the roof. I used to have large ice dams. I don't get them anymore.

I like metal roofing. Pre-drilling your screw holes is a good idea -otherwise the burr and depression from screwing straight through the metal can do a job on the rubber washer. Over tightening is not good either.

I used washered aluminum roofing nails on my fiberglass roofed wood drying shed. Those nails are backing out a bit from the shrinkage and expansion. Same thing happens on old houses with shingles and roll roofing when the sun gets to it.

 

[toppop52]

I screwed down 2x4's running with the rafters over the shingles. I also used a nail gun setting at angles. I ran the 2x4.s for the metal perpendicular to the first set. I wanted a large air pocket that was vented. Snow gets deep on the roof. I used to have large ice dams. I don't get them anymore.

I like metal roofing. Pre-drilling your screw holes is a good idea -otherwise the burr and depression from screwing straight through the metal can do a job on the rubber washer. Over tightening is not good either.

I used washered aluminum roofing nails on my fiberglass roofed wood drying shed. Those nails are backing out a bit from the shrinkage and expansion. Same thing happens on old houses with shingles and roll roofing when the sun gets to it.

That's what I mean, I don't see why that would be a problem, but as I said, I'm no roofer.

 

[paulharvey]

I screwed down 2x4's running with the rafters over the shingles. I also used a nail gun setting at angles. I ran the 2x4.s for the metal perpendicular to the first set. I wanted a large air pocket that was vented. Snow gets deep on the roof. I used to have large ice dams. I don't get them anymore.

I like metal roofing. Pre-drilling your screw holes is a good idea -otherwise the burr and depression from screwing straight through the metal can do a job on the rubber washer. Over tightening is not good either.

I used washered aluminum roofing nails on my fiberglass roofed wood drying shed. Those nails are backing out a bit from the shrinkage and expansion. Same thing happens on old houses with shingles and roll roofing when the sun gets to it.

I agree with predrilling. I used to do pre engineered metal buildings, and if the screws don't line up it really looks bad.

I'm considering using Rib-12 panels when I add two bed rooms to my double wide next year. Shingles have gotten really expensive, and Rib panels can be had for less than $2/Lf for a 3 ft wide panel. I have all the screws from an 8800 sq trailer shop I did years ago (as superintendent; not my own) and that is a major cost saver. My plain is 7/16" OSB, 30# felt, and metal. I don't thick I will use the 1.5" foam under metal as it's just too much money. But back to point: that's roughly $66 per square; (unless my math is bad), you can't get 3 tab 20 year shingles for that price... Now that is 29 gauge metal of coarse; and yes, I would prefer 26 gauge, but on top of OSB instead of purlions I don't see the need (might change mind based on finances when I start).

 

[MAN IN BLACK]

if existing is in decent shape, can a metal roof be installed directly on top of shingled roof ? It would seem (to me) to quiet the metal and also insulate.

I did my house 5 years ago.
Put a strapping @12" centre over old shingle, cut a 4" strip on both side of the ridge to install a full length ridge vent and screwed metal sheets (36" x whole length of slope 18.5') over at every second strapping (24")
Almost not hear the sound of falling rain inside.
Looks real good...no more wind damage.
Big bonus...no mess, nails , shingles to pick up and haul to the dump.
Down side...almost double the price of a shingle roof...but will last 50 years +.....maybe a coat of paint after 20 years or so.
Black:thumbsup:

 

[DeereMann]

Hi, Ihfarm -

We got disgusted with asphalt shingles in 2002 when they started shrinking & curling after only 12 years. Found out there was some defective GAF batches and they wouldn't cover warranty except for token pro-rated payment.

So I did some research & found the new steel roofing. The steel was 2x cost of asphalt, but essentially guaranteed for life. I had some extra money back then, so went for it.

This was a good decision. Still looks fine, and we've weathered several severe hail storms since then where the rest of the neighborhood had to replace their asphalt shingles. Further more, it is fire proof (protects from fast moving pine crown fires if you live in the woods).

I guess the saying you get what you pay for holds true with this. Yes, I would do it again, despite the larger cost (app. $12,000 vs. $6,000).

Hope this helps.

 

[lhfarm]

Thanks for all the great replies. I'm going to research roofers in the area who specialize in metal roofs and get some quotes. Again, I appreciate the advice.

 

[EddieWalker]

Not arguing, I'm not a roofer, but why can't they be nailed to the rafters over shingles, there are nails and screws as long as you want and it would seem simple to locate the first rafter and measure from there, checking occasionally on the inside to make sure you're on target. What am I missing?

When installing the purlins, you want them as solid as possible. They go horizontally across the rafters and need to be attached directly to the rafters. If you attach them to the sheeting, they can work their way loose over time. A metal roof should last fifty years, so there is a lot of time, weather and movement that has to be taken into consideration.

I'm not saying it's impossible to hit a rafter every time, especially once you figure out where they are and measure it out on every purlin. It's just that the odds of a crew doing it every time are pretty slim.

The second problem is that the shingles are uneven and allow for future movement. This is assuming that there is only one layer of shingles on the roof. If there is more then one layer, it's just going to be that much more uneven. Then there is the length of the fastener. Are you using full 3 inch nails or screws? An inch and a half through the purlin, half an inch through the shingle, half an inch through the decking only leaves half an inch of nail going into your rafter. That's not going to hold anything in place for very long. I would want as much going into the rafter as I could get. With impact drivers and 3 inch screws, I know I can get that screw counter sunk half an inch into the wood and have half the screw or more into the rafter.

Last reason to remove the shingles is to inspect the decking. What has been going on up there and is there any damage? Valleys and areas around vents are famous for leaks and damage. How does the decking look? I absolutely hate to cover up a problem and if I'm spending the money for a high quality roof that is going to last the rest of my life, I am going to do everything I can to make sure it's going to last as long as possible.

In my line of work, I've found that the additional time and expense in materials is insignificant to the overall scope of the job. Cutting corners to save time or a buck always ends up costing more in the long run. While I'm not a roofer, I do enough repairs to roofs to see a pattern in why they fail.

Eddie