Is spray foam a good way to insulate a house from the exterior?
Hi,
I have found this site very helpful - very appreciative to the experts who take the time to share their knowledge.
We need to replace the siding on our house. We will likely replace with a Hardie Board board and batten rain screen. However, the contractor can also remove the sheathing down to the studs and reinsulate first.
He reccomends 2lb closed cell spray foam in between the studs (applied from the outside). I guess this will spray to the back of our interior drywall.
I have no idea if we have an existing vapor barrier behind our drywall but doubt it - this is an older wood framed bungalow.
In addition, i dont expect our interior drywall forms a very great air barrier either - we have the usual holes from outlets etc but we have a lot of windows and other installations - all done seemingly DIY so I have no idea if they are well sealed to the interior drywall.
After research on this site and others, it seems that spray foam is the best way to go, as it will provide a vapor / air barrier in addition to insulation. I don't really like the potential for harmful offgassing, but because we will not remove our interior drywall, I don't really know how we can air seal / vapor seal behind the drywall - this seems neccesary for other types of insulation.
Does anyone have experience with re-insulation from the exterior of the wall (so between the studs but from outside)? Is spray foam reccomended or is there something I am missing?
Any help is grately appreciated!
Simon
Spray foam in this case will provide everything you are looking for – insulation, air barrier and vapor barrier. And you are wise to consider the toxicity of it, spray foam has until recently been among the most harmful types of insulation in terms of greenhouse gas emissions. But there are a couple of companies who have switched to new blowing agents that are much safer, you can find them in this page –
New blowing agents for spray foam insulation don't cause climate change
I would go ahead with spray foam in this case, the only thing I would suggest is that if you are at all chemically sensitive first check to see if you can get a sample of it for a smell test before you install it. From what we have read about it, it that it is less toxic that traditional spray foams, which is great, but once it’s on you can’t remove it if you can’t stand the smell. And it isn’t that it will permeate for ever, but certainly for the first days or weeks after it is completed you may notice it.
And here is our page on the best way to insulate walls from the outside, that may give you some valuable tips as well. And the only other point I think you should keep in mind is that the junction between the wall and the roof. They can be tricky since many of those older bungalows have low roof lines making it tricky to insulate well while still allowing ventilation. This page will tell you how - What causes ice dams and how to fix them. Hope that helps Simon, let us know if you have more questions.