You are here:

Roofing/metal roof in cold climate unheated building


I have an unheated shed in a cold northern climate. It has a low slope, 2:12, and was designed structurally to carry a heavy snow load. It's a simple, single ridge, gable roof with no valleys.

I would like to install a metal roof over a plywood deck, but was unsure what layers of material to use  between the roof decking material and the metal roofing. I had a cold weather condensation problem years ago on a similar building in which metal roofing was installed directly over wood purlins.

I have two questions.

1. What would be the best type of metal roofing to use on this low slope roof?
2. What layers of material should I use between the plywood roof deck and the metal roofing panels?

Thank you.

You say this is an unheated building but you have condensation on the inside on a previous structure.

In regards to the type of metal roof it would have to applicable for the low slope and take hydrostatic pressure.

I suggest you install a self-adhesive vapor retarder on the plywood deck and then rigid insulation such as a XPS polystyrene (RoofMate) before you install the metal roof.
The metal roof would be installed over sub-girts that would be installed over the vapor retarder before the insulation is installed.

Check out:
You may find what you need there in regards to metal roof type and methodology of construction.  


All Answers

Answers by Expert:

Ask Experts


D. John Henderson


My 33 years in the building science business has involved air barriers, waterproofing, and flat & steep slope roofing systems.


My roofing encompasses commercial systems (BUR, mod-bit, single-ply) and residential applications (asphalt shingles, cedar shingles, slate and metal. I am cognizant of code stipulations in regards to FM and UL for commercial roofs.

Attended numerous courses offerd by Roof Consultants Institute, Roofing Industry Educational Institute, Factory Mutual Research Corporation, University of Wisconsin, and BURSI. Lectured for RCI and mentored at a local university for a Building Science Certificate.

Past/Present Clients
Government, commercial businesses such as The GAP, hospitals, school boards as a roof designer.

©2017 All rights reserved.