Author Topic: Roof-over question  (Read 1342 times)

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Offline THEN808

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Roof-over question
« on: October 20, 2015, 02:11:48 PM »
Hey ALL! 

Newbie here, just moved from Hawaii to Southern Colorado.

So let me explain...we just bought a property that has an older manufactured home on it.  There are some leaks from the roof and have decided to do a "ROOF-OVER".  Basically we are adding 2x4 trusses over a slightly domed roof and putting up 29g tuff rib metal panels over that.

My questions are, would it better to run it with 2x4 purlins or osb on top and how/what kind of insulation and barrier should we put on top of it? 

I've been trolling through your  forum and am hearing all kinds of problems with condensation so now I'm worried.  Doesn't seem as easy as I would have expected.

Any advice would be greatly appreciated!

MAHALO in advance!

Offline Don_P

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Re: Roof-over question
« Reply #1 on: October 20, 2015, 03:55:23 PM »
I'd use 5/8 osb, it might be worth looking at a slight scissor truss to get the roof down enough to look right. If it does need the insulation I'd look into foam on the existing roof, venting either the gables or soffit and ridge.

Offline akwoodchuck

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  • Homer, AK
Re: Roof-over question
« Reply #2 on: October 20, 2015, 04:29:30 PM »
+1 on the 5/8 OSB or CDX, with 30# felt underlayment....never have to worry about it, or not for a long time at least. I've remodeled many a structure with metal on purlins, in most cases the screws were jacked out...something to do with the expansion/ contraction of the solid wood, I reckon. I also like to go with the #9 screws to start off  (1/4" head)... that way in 20 years when it's time to replace the screws, you just get a bag of 5/16" head (# 14, I think?) and run em right in the old holes, they hold fine. Predrill the panels, you'll be glad you did, and juuussst set those screws snug...if the washer's mashed down or the metal's dimpled, they're too tight. Oh and don't fall down...  8)
"The lyf so short, the craft so long to lerne."


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