felt or synthetic underlayment for metal roof

[ray66v]

U are correct, however many use the self adhesive ice and water shield as the ultimate underlayment.

I know some are doing the entire roof with ice and water shield. And in some cases it might be a good idea. But, on most of the field of a large roof, where there are no edges, or valleys, it's just extreme overkill.

Not to mention walking on ice and water shield, on a hot day, messes it up

 

[slowzuki]

I put my steel down using 2 details. On the north side, I used steel directly on the closed cell foam with the joints taped. The formed channels were not closed off with foam strips and vent via ridge vent at the top.

On the south side I used strapping to space the steel up above the foam to keep the temperatures lower. Same venting.

No underlay anywhere.

No ice damming has occurred even in years that others have problems. The strapped side is way louder in the rain, allows drumming of the roofing. No leaks or condensation problems.

 

[brandoro]

I found the invoice for material, my underlay is Titanium UDL-30. Good stuff, tough, not slippery, I fastened it with shingle nails. Not many shingle nails, my theory being that the metal roofing would hold it down pretty well for the long term.

 

[2manyrocks]

I think that's the same stuff one contractor included in his bid.

There's a building going up nearby that has the same product installed on it. They've been working on this building since October, and I suspect the contractor installed it as much for his own convenience as anything in putting the metal roof down when he could get to it because there's still a section that has no metal on it.

All the old barns and many of the older houses around here have metal installed on open lath 1x4's. I'm not sure if we're making progress putting metal down over solid decking with underlayment.

 

[JEH412]

All the old barns and many of the older houses around here have metal installed on open lath 1x4's. I'm not sure if we're making progress putting metal down over solid decking with underlayment.

The section on our roof that had slate just had the slate stripped off and the underlayment put down over the open lath. The rest of the roof was already sheeted in, since it had asphalt shingles, but the contractor said there was no need for it on that section.

John

 

[PILOON]

The section on our roof that had slate just had the slate stripped off and the underlayment put down over the open lath. The rest of the roof was already sheeted in, since it had asphalt shingles, but the contractor said there was no need for it on that section.

John

Trust me, I tore off a galvanised metal roof that was laid on plywood without underlayment and the galvanised metal was almost rusted thru and the ply was near finished.
That roof was not quite 10 years old!
That was an unheated porch roof in a cold climate.

 

[JB4310]

I wouldn't think rubber membrane would be needed under metal roof except at valleys and maybe eaves, just a heavy felt.

The whole idea of metal it to prevent ice dams and leaks due to it's minimal amount of joints/seams compared to shingles. Many houses up north just have the metal on the lower 2-3 feet of roof to prevent ice and water back up issues.

I'm a huge advocate of rubber underlayment where it's designed for, as well as single ply epdm rubber roofing. Maybe check with the manufacturers about their specs on underlayment, if they say there's even the slightest advantage to using rubber then for sure do it.

All the old barns and many of the older houses around here have metal installed on open lath 1x4's. I'm not sure if we're making progress putting metal down over solid decking with underlayment.

I agree, maybe not any better, but it's the evolution of construction, no one is gonna install 1x4 boards any more. Plywood is so much faster, so you're forced to go with some type of underlayment to protect the wood and metal from that zero clearance contact as well as prevent water leak if there should be any through/around the metal.

JB

 

[JB4310]

I think that's the same stuff one contractor included in his bid.

There's a building going up nearby that has the same product installed on it. They've been working on this building since October, and I suspect the contractor installed it as much for his own convenience as anything in putting the metal roof down when he could get to it because there's still a section that has no metal on it.

That's pushing it, leaving it uncovered for that long, that company's warrantee would be voided after 180 days being exposed to UV. That's probably longer than most though, so it must be good stuff.

JB.

 

[2manyrocks]

I should have said they started the building in October. The underlayment went on maybe November-early December. Not sure. They've got most of his roof on except for one section that I can see.

His underlayment appears to be staying put. I haven't seen the owner, but next time I see him I'm going to ask if he's had any roof leaks.

There's a difference in the old 1x4's and this splinter wood they sell today, also. I agree that I couldn't see using today's 1x4's for this application.

 

[ray66v]

I wouldn't think rubber membrane would be needed under metal roof except at valleys and maybe eaves, just a heavy felt.

Synthetic underlayment such as Titanium UDL, is synthetic felt. It's not rubber membrane, or any form of ice guard. It's simply a modern version of tar paper. It's about 100x stronger, it's lighter, and wider.