Inside: Tips for choosing the right wall insulation; comparing spray foam insulation to fibreglass insulation; understanding R-value for exterior and interior walls.
Our basement renovation is almost at the finish line and I’m starting to tally up all the separate projects and decisions that went into making this space a reality. In case you are just hopping in now, our renovation consisted of levelling and insulating a wooden porch floor, and then converting that outdoor room into an interior space.
Obviously, the insulation was crucial in making this space workable. The old garden room used to be so cold in the winter my paint would freeze and so hot in the summer, you couldn’t stand in there for very long at all. Today’s post is an extremely practical one about how to pick the right home and wall insulation.
First things first, let’s get the basics down when it comes to insulation.
By the way, you might want to start at the beginning of this long renovation 🙂 Here’s where I wrote about levelling and insulating the floor, and here’s a post about how we’ve budgeted for this entire home renovation.
Types of Insulation
There are typically two types you’ll be choosing between if you are an average homeowner – fibreglass insulation (which is what we ended up with) and spray foam insulation (which we seriously considered).
The main differences? Spray foam insulation requires a professional to install it and it comes with a higher R-value (more on this in a second). It creates an extremely tight seal between the studs and the exterior wall. 
It is literally sprayed into the wall cavity, 1-inch at a time and layered. Then it hardens in place. The average exterior wall will require approximately 3 inches of spray foam to achieve a good R-value.
Fibreglass insulation is faster to install (ours went in in less than an hour) and it’s easier to work with. You still need to wear a mask and make sure you get as tight a fit between the studs as possible. It also tends to be a little bit less expensive than spray foam.
What should the R-value be for exterior walls?
R-value refers to how insulated a space is against heat transfer and loss. To give context, the old exterior garden room did have insulation – but it was the minimum R-value available, an R11, and it wasn’t installed correctly (large gaps in the insulation and it wasn’t thick enough). 
So in effect, we weren’t even getting the bare minimum insulation in this space. Do I recommend using R11 insulation for exterior walls? Maybe if it’s a garden shed. But not if you plan to use the space and be in it for any extended period of time.
Current codes expect a residential home to have at least R18 and ideally an R24 or higher. We achieved that with our fibreglass insulation between the studs. An important consideration when you’re installing insulation is the ceiling space as well as the floor. 
Our floor used to be a porch. There is about 12-inches of space between it and the bare ground, so we re-insulated the floor to well above code, bringing it to R33. If this were an attic space, you’d also want to consider using a combination of fibreglass and spray foam insulation to tightly seal your ceiling area.
Things to consider when insulating exterior walls
A few things to note – R11 insulation should not be used on exterior walls around windows. It’s almost completely ineffective when used in smaller areas like that. So if you are using it, make sure to increase the thickness or switch to a higher R-value product. 
You’ll also want to pay special attention to sealing cracks around outlets on exterior walls which is where a lot of heat and air transfer can happen. 
