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Metal roof assembly

Kim jarrett Published: July 12, 2019, 12:15 p.m.Last updated: July 17, 2019, 12:07 p.m.

Hi,

 I live in  Nova Scotia, Canada - Climate Zone 6 - and am considering installing a through-fastened steel roof (panels 36'wide cut to length). My house has a vaulted ceiling (no attic). The roofing deck consist of 2x6" T&G pine boards running from eaves to ridge and is visible from the interior as my finished ceiling.​

 ​The approach that I am considering using to install the fastened through metal panels on the BACK roof (4/12 pitch), in sequence from start to finish:

  1. strip entire roof down to deck; 

  2. cover 2x6' pine roof deck with either an air barrier or vapor barrier. What is recommended at this stage of the install of the roofing assemby? Air or Vapor barrier?

  3. install two layers of 1 -1/2 inch EPS expanded polystyrene​;

  4. cover with a high temperature roof underlayment​; Air or Vapor underlayment?

  5. installing 1x4" purlins​; then

  6. installing metal panels to purlins, leaving both eaves and ridge opened for air movement.​

Would this be advisable? Any suggestions would be much appreciated.

Regards,

Kim

Responses (3)

K
Kim jarrett July 19, 2019, 9:09 p.m. Reply

Thank you very much for the advice above. It certainly provides options worth exploring.  

What would your thoughts be on replacing the 10 inches of EPS (R4) with EPS Silverboard SB-35 foam insulation (R5)?  Would this be equally effective?  Would it alter your recommendations for how to proceed in a manner that is most in line with my inital approach? For instance, would it still be recommended to apply the 'peel and stick’ air and vapor barrier membrane over the wooden roof deck, then apply the rigid foam panels, followed by the drainage plane membrane?

If using the Silverboard SB-35 foam insulation would be equally effective, would it be better to use 3" sheets rather than 1-1/2" sheets? 

Many thanks in advance, 

Kim

Mike Reynolds July 24, 2019, 8:07 p.m. Reply

Hi Kim,

I would go with raw EPS myself. The foil has a purpose and an application, but it doesn't do you any good in this case. It's intention in foam panels is to act as a vapour barrier, to reflect infrared heat, and in some cases, like with Polyisocyanurate, to contain gases within the foam. None of that is applicable to you, so you'd be paying more for now reason. EPS foam can vary slightly in R value but I don't think you're getting a whole lot more value from Silverboard rather than standard EPS sheets that you could probably get for a little cheaper. 

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