Steel Roof Underlay

[kylemac]

Hey Guys

Looking for some more opinions on my build, was just reviewing my roof drawings and my original plan was to just strap my 4/12 trusses with 1x4 and apply the steel roof, done this on a few barns sheds and porches but none of these spaces had an insulated space below them. The more and more ive been thinking about it and reading up on it, it seems like I should still be sheeting the roof and tar paper/ waterproofing, in my case I would probably do 7/16 OSB and tar paper and then strap 1x4 on top of this, due to condensation from the bottom side of the steel roof building up and then dripping or falling down onto your insulated space, obviously eventually causing mold etc. Am I right on this or do some people just strap and apply it? I feel for the extra cost of the OSB and tar paper it doesn't seem like much to save me a big headache in the long run

 

[TractorJeff]

Right or wrong, the 3 roofs I have done have the Tin laid right on the tar paper. One has an insulated room below it and the other two are cold storage.

 

[PugetDude]

Condensation is the issue. several ways to deal with it. OSB/Tarpaper is probably the best option for a DIYer, another is to order the sheets with a FILC coating on the backside.

 

[kylemac]

Right or wrong, the 3 roofs I have done have the Tin laid right on the tar paper. One has an insulated room below it and the other two are cold storage.

Thanks jeff,

what I was getting at was saying if you don't have any sheeting or tarpaper and just steel roofing on strapping it could cause an issue, in which you have sheeting and tar paper so I believe you did it the right way!

 

[kylemac]

Now that im on the subject I guess now I really don't have to strap the roof since I will be applying OSB and waterproofing? I will be also doing vinyl siding over my wall sheathing and am now wondering if that is not necessary as well?

 

[PugetDude]

OSB will eliminate the need for strapping, as long as it is rated for your truss centers.

 

[Bretny]

There was a thread on here a bit ago where the underlayment was spray foamed and ripping away from the trusses. So make sure you use a strong material built for this or OSB. Tar paper is not something I would bother with. If your in the snow belt use ice and water shield on the lower 6ft too.

 

[dcg9381]

I don't think it was so much ripping away from the trusses, but it was falling off whatever moisture barrier or insulation that they sprayed the foam on to...

 

[yeldogt]

What's the manufacturer say/ recommend ....

There are just too many different types .. and the screw down "industrial" are particular/interesting because they need a barrier under them with living space .... because they leak

 

[Falcon67]

If I was doing a metal roof, I would for sure use synthetic underlayment and not "tar paper".

 

[Ben W]

I used taped Zip sheathing and the metal directly overtop.

 

[kylemac]

Thanks guys,

I think with all the talk I will do OSB sheeting and synthetic underlay for the roof, just too make sure I wont have any issues, and sounds like laying the roof right on the sheeting will be the way to go!

 

[PugetDude]

Thanks guys,

I think with all the talk I will do OSB sheeting and synthetic underlay for the roof, just too make sure I wont have any issues, and sounds like laying the roof right on the sheeting will be the way to go!

Use 5/8" (19/32) OSB- the screws can pull out of the thinner stuff in a strong windstorm- many jurisdictions here in the US are now requiring it.
Cost difference is minimal and you will appreciate the stiffer roof when you're up there sheathing it.

 

[Bretny]

Yes OSB is pretty poor for holding power. At the cost of 5/8 OSB you should at least price out 1/2in plywood. I have found local lumber yards are cheaper than big box stores for this sort of thing.