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What are the options for adding Exterior Roof Insulation?
Marlo Raynolds
Aug. 29, 2020Updated: Sept. 24, 2020
Hello,
The discussions on adding exterior wall insulation to a home have been very helpful. But in searching I have not found much related to adding exterior insulation to the roof. Our home does not have an attic. So wondering what systems have been successful - SIPs?
Thanks.
Choosing the best way to insulate a roof depends on how it is currently built. Let us know from bottom up if you can, and your climate zone as well. SIPs is certainly a possibility, But SIPs usually come with OSB on either side, which may not be necessary. A product that may actually fit your purpose is ThermalWall insulation panels if the circumstances are right. They are foam panels with a metal rail in the center so they could be attached using short screws, which is much more affordable and it breaks the thermal bridge. But it really depends on your current roof assembly, so let us know what you have right now and hopefully we can help point you in a good direction.
The process of dissasembling a metal roof and solar panels then re-installing them is no small affair, so just looking at the labour cost alone, unless you have almost no insulation up there (and if it met R2000 then its not bad at all) I doubt you will ever recoup your investment through energy savings.
Are the scissor trusses filled with cellulose or batt insulation? I assume at this point that under your solar panels and metal roof is sheathing, with likely an air space underneath the sheating at the top of the insulation. If that is the case, laying SIPs or ThermalWall panels on the sheathing won't do anything at all since cold air would be flowing underneath your new insulation. I don't think there is any cheap way to add much insulation to your roof unfortunately as you would need to remove everything and build up to accomodate more insulation in the scissor truss cavity. What kind of insulation is up there and how much? And where is the house? (City or climate zone).
Thanks. We are in Canmore, Alberta (I think zone 7A). Pretty sure it is fibreglass batt in the scissor truss, and it will be well done based on having pulled back a few things here and there for various projects. I guess the other option, if I really wanted to go there would be to add insulation on the inside of the ceiling. But I think you are right, hard to see it pay back. Will focus on the exterior walls.