You are here:

Roofing/metal roof in cold climate unheated building

Advertisement


Question
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.

Answer
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: www.metalconstruction.org/index.php
You may find what you need there in regards to metal roof type and methodology of construction.  

Roofing

All Answers


Answers by Expert:


Ask Experts

Volunteer


D. John Henderson

Expertise

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

Experience

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.

Education/Credentials
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.

©2016 About.com. All rights reserved.