felt or synthetic underlayment for metal roof

[skipmarcy]

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.





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

In 2006 when I built my house by myself I used 1x4x16' pine lath boards - they were a whole lot easier to install by myself than plywood and cheaper too !!! The foil bubble wrap has been an excellent choice too - mine is reflective foil on both sides and has helped with heating/cooling tremendously and is an excellent moisture barrier. All seams are taped with metal duct tape. You can't necessarily tell in the pics but the bubble wrap sags between the lath (on the roof) and leaves a small air gap between the metal and itself, the only direct contact is at the boards themselves. My framing nailer made quick work of attaching the lath boards to the trusses, the foil bubble was attached with button cap nails by hand - a little slower but worked very well. I built my utility shed with this same construction except it is a gambrel roof.

 

[JB4310]

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.

Ok. thanks, I just looked up how long it could be left exposed, not familiar with it otherwise.

I work on old slate roofs, when they were put on 100+ years ago, of course felt was the only option. you should see what happens to felt after 125 years under slate on the south side. Pure dust if you try and move/touch it, I mean particles no larger than mushroom spores, dust!

Those roofs will leak under certain conditions due to the ancient underlayment, even though we maintain them and there are no missing slates. There's a critical 2" bib overlap in slate roofing that is not enough to always repel water when the wind blows or the snow/ice piles up.

JB.

Winter slate roof inspection, working hard. Yeah right!

 

[JB4310]

In 2006 when I built my house by myself I used 1x4x16' pine lath boards - they were a whole lot easier to install by myself than plywood and cheaper too !!! The foil bubble wrap has been an excellent choice too - mine is reflective foil on both sides and has helped with heating/cooling tremendously and is an excellent moisture barrier. All seams are taped with metal duct tape. You can't necessarily tell in the pics but the bubble wrap sags between the lath (on the roof) and leaves a small air gap between the metal and itself, the only direct contact is at the boards themselves. My framing nailer made quick work of attaching the lath boards to the trusses, the foil bubble was attached with button cap nails by hand - a little slower but worked very well. I built my utility shed with this same construction except it is a gambrel roof.

Your metal roof looks great, many years of maintenance free service I'm sure.

What are the ramps for, loading materials up to roof?

That's not typical roof deck construction these days, but if it worked for you that's good. My 75 year old house has 1x6 - 1x8 tongue and groove boards both on the roof and walls. IMO better than plywood or OSB, i'm sure some will disagree, but I have never felt a 1x board roof soft under my feet like with plywood.

JB

 

[skipmarcy]

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.





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

Yes, the ramps are how I got my trusses set on top of the walls, were just barely tall enough too !! I have no problem walking on my roof, of course I keep my feet over top of the 1x but if sitting for some reason I can plop my butt down anywhere with no problems. My metal is the 29 ga. galvalume.

Your metal roof looks great, many years of maintenance free service I'm sure.

What are the ramps for, loading materials up to roof?

That's not typical roof deck construction these days, but if it worked for you that's good. My 75 year old house has 1x6 - 1x8 tongue and groove boards both on the roof and walls. IMO better than plywood or OSB, i'm sure some will disagree, but I have never felt a 1x board roof soft under my feet like with plywood.

JB

 

[2manyrocks]

I just talked with the metal supplier. They are recommending I put down 15 lb felt or heavier directly on the roof deck and then screw the metal down onto the roof deck (1x pine boards).

They aren't recommending or pushing synthetic underlayment.

I'm trying to think through whether to put down the synthetic underlayment to give myself more time to get the metal on. Everything else on this project has taken 3x as long as anticipated so far.

Does anyone have any good suggestions for how to push the roof tear off so it falls in a trailer to haul off without having to pick it up off the ground? I've seen some chutes installed out of windows to get building materials to fall in a dumpster before. Just curious if there's something moveable you can put up against a house to try to funnel the roof tear off into a trailer as you tear it off.

 

[RoMad]

I put a new metal roof on my house 3 years ago. I bought 26 gauge galvalume and put it on 12' long 1x4's. I bought the lumber from the same place as the roofing. I put the boards on top of the old roofing and screwed them through the roofing and into the trusses. This is pretty much the standard around here. I was very suprized at how little noise it makes when it rains. I was also suprized by how fast rain runs off of it compared to a shingle roof.
I did not put anything other than the boards between the old and new roof.
A few of my neighbors have reroofed with metal and they all used contractors. All of them left the old roofing on.

 

[2manyrocks]

I have two layers of asphalt shingles now. Leaving them on would avoid having to tear them off and haul them away. My metal supplier says I should install felt because it would be bad for the metal to rub against the roof deck. I suspect it would be really bad to have metal rubbing directly against old shingles--so in that case, 1x4 purlins would be needed.

 

[JB4310]

I just talked with the metal supplier. They are recommending I put down 15 lb felt or heavier directly on the roof deck and then screw the metal down onto the roof deck (1x pine boards).

They aren't recommending or pushing synthetic underlayment.

I'm trying to think through whether to put down the synthetic underlayment to give myself more time to get the metal on. Everything else on this project has taken 3x as long as anticipated so far.

Does anyone have any good suggestions for how to push the roof tear off so it falls in a trailer to haul off without having to pick it up off the ground? I've seen some chutes installed out of windows to get building materials to fall in a dumpster before. Just curious if there's something moveable you can put up against a house to try to funnel the roof tear off into a trailer as you tear it off.

How much more $ is the syn underlayment, It's not like new construction where if it leaks a little before the roof is done no big deal. if it leaks into your home, could be costly.

Regarding getting the debris away from the house, I don't do whole reroofs, just repairs, but I see most guys just use a blue tarp hanging down to keep the house clean and crap out of the bushes. there's always some cleaning up after.

I put a new metal roof on my house 3 years ago. I bought 26 gauge galvalume and put it on 12' long 1x4's. I bought the lumber from the same place as the roofing. I put the boards on top of the old roofing and screwed them through the roofing and into the trusses. This is pretty much the standard around here. I was very suprized at how little noise it makes when it rains. I was also suprized by how fast rain runs off of it compared to a shingle roof.
.

What spacing did you use on the 1x4's, and without the metal fully supported can you walk on it without it bending?
Metal is great for keeping roof free of snow as well.

JB.

 

[JB4310]

I have two layers of asphalt shingles now. Leaving them on would avoid having to tear them off and haul them away. My metal supplier says I should install felt because it would be bad for the metal to rub against the roof deck. I suspect it would be really bad to have metal rubbing directly against old shingles--so in that case, 1x4 purlins would be needed.

Or just underlayment over the shingles?

Though that may raise code issues 2 layers is usually max.

JB.

 

[mojoinco]

According to the manual I read in the link, they recommended either 30# felt or the ice guard:

Metal Roofing, Siding and Building Materials Installation Guides - Metal Sales Manufacturing

One thing to consider is local code for layers of roof. I can not have more than one layer (don't know when it changed from 2). And of course, the overall weight (which I speculate is the reason I can only have one layer). We have snow though.