felt or synthetic underlayment for metal roof

[/pine]

just curious...is the metal going down on sleepers? Or is it laying directly on the underlayment ?

Anytime there is a quick change in temperature metal roofs will cause condensation...just curious how this is addressed?

in FL, where there is high humidity...if a solid decked roof (formerly shingel/tile etc) is being replaced with metal...a water proof base sheet (felt will work but becomes brittle) is applied with (usually) 1x4 pt boards run perpendicular to the metal on top of the base sheet...often there are weep vents cut into the 1x4's...the metal is then pre-drilled for screwing down to the 1x4's.

It is not uncommon on cold mornings that warm up quickly for moisture to be seen running from the weep holes in the bottom edge 1x4s...I can imagine what happens to that moisture if there is no way for it to escape...

 

[JB4310]

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.

I think its one layer now due to the fact that everyone is installing architectural shingles. With the higher profile and added weight of those Timberline type shingles you can't put another layer over them.

Don't know our code now, it always was 2, but only one for architectural.
Maybe it's changed to 1 also so as to eliminate any confusion?

JB.

 

[2manyrocks]

just curious...is the metal going down on sleepers? Or is it laying directly on the underlayment ?

Anytime there is a quick change in temperature metal roofs will cause condensation...just curious how this is addressed?

in FL, where there is high humidity...if a solid decked roof (formerly shingel/tile etc) is being replaced with metal...a water proof base sheet (felt will work but becomes brittle) is applied with (usually) 1x4 pt boards run perpendicular to the metal on top of the base sheet...often there are weep vents cut into the 1x4's...the metal is then pre-drilled for screwing down to the 1x4's.

It is not uncommon on cold mornings that warm up quickly for moisture to be seen running from the weep holes in the bottom edge 1x4s...I can imagine what happens to that moisture if there is no way for it to escape...

I'm trying to decide whether to put it on 1x4 sleepers or directly on the existing roof deck over an underlayment. A friend of mine is suggesting I also use the sleepers because of the condensation issues you mention. I don't think our humidity in Middle TN is quite like FL, but we get humidity.

One roofer is suggesting 30 lb felt. Reading some of the roofer's forums elsewhere, there appear to be mixed opinions on using felt as a proven product versus what happens to synthetic after it's been installed 20 years. There were also some differences of opinion about whether felt seals nail holes better than some of the synthetics.

The primary benefit of synthetics that I can find appear to be that they are much lighter and more durable when left exposed for a while than felt.

Not knowing these other guys on the other websites, I really wanted to hear about the actual experiences of other TBN members to help me figure out what to do.

I appreciate all of you reading through this and trying to help me.