Metal Roofing Over Insulated (SIP) Panels

June 21, 2009 | Filed under: Misc, Roofing Answers, Roofing Installation

Q: I have a new structure with 12 1/4″ structural insulated panel roof at a 2:12 pitch. (The low pitch is due to code which requires me to retain the snow load.) There is no attic space to ventilate and the roofing must be applied to the top surface of the insulated (SIP) panels. Even though the roof has an R value of 50 and there is 11 1/4″ of EPS foam between the panels, I have heard war stories from people who suffered moisture damage to the top skin (1/2″ OSB) of the SIP after a few years. Ice dams are a common problem in this climate.

What I know is that I will have to put some Ice and Water barrier to deal with ice dams and I need to have some way to prevent condensation on the inside. These seem like contradictory requirements. How do you suggest I handle this situation? Thanks

A: I think your only safe way is to add a vented airspace on top of the SIPs, followed by decking, underlayment and roofing.

Make certain that the roof you install is approved for that pitch. I would suggest a mechanically seamed standing seam.

2 responses to “Metal Roofing Over Insulated (SIP) Panels”

  1. Larry says:

    Todd, I am a designer & SIP material supplier and I am looking at a large townhouse project. The roof structure is 10.25″ SIPs on a 2/12 pitch and the developers are going with either metal roofing or a torch down system. For the metal roofing it’s a not brainer: we’ll strap it and create an air space but we’ve never done a torch down on SIPs. Can you offer some advice? Thanks. Larry

    • toddmiller says:

      Larry,

      I cannot help you much with the torchdown other than we share the same concern — ventilation.

      Will you have a vapor barrier on the bottom side of the SIPs and make sure the joints between them are properly sealed? If so, then there probably isn’t anything special to do with torch down. Of course you could build a roof over the SIPs and ventilate the resulting chamber.

      As far as metal … you’re aware I assume that many types of metal roofing are not suitable for roof pitches of less than 3:12. You may need to consider a mechanically seamed standing seam.

      I hope this helps.

      Todd

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