Tuesday, December 20, 2022

The best time to insulate

Continuing on our series about timing, we thought it would be best to start at the beginning. Insulating your house depends a bit on what you already have.  Our house had 1.5 inches of foil faced fiberglass batt insulation in the exterior walls.  Restated, we had almost no insulation in our house...  The best time to insulate a house like that is, as soon as possible.  I would also say, the best time to insulate your attic is as soon as possible.  Heat rises, and it will rise right out of your house without a properly insulated attic space. 

Let’s say however, that your house is pretty well insulated, meaning that the exterior walls are fully filled and the attic is perfect.  If you plan to replace the siding on your house, this would be a good time to add some continuous exterior insulation.  Think of it like wearing a sweater in the winter (normal insulation), but then you go outside and realize that a big puffy winter coat would really be a great addition.  This is what I’m talking about.  Wrapping your house with a layer of insulation is like putting on a winter jacket.  It helps bridge all of the gaps between the buttons, or in this case, the wall studs.  I’ve put together a fairly standard detail drawing of how this might work.  If you are talking to a contractor about this kind of work, show it to them and tell them you are interested in continuous insulation.  It will add money to your project, but the benefit will be noticeable in the winter when your heating bill goes down.


There are some options here in terms of types of insulation and there is an opportunity to make a better decision. When we talk about insulation "in" the walls, cellulose is, by far, the best. It doesn't have the highest R-value, but it is easy to retrofit an existing home, it's made from recycled paper, and, most importantly, it can dry if it gets wet. (walls are prone to develop moisture either from temperature changes, or the fact that you breathe inside your house... and your breath contains moisture.) Foam insulation is not ideal. It contains lots of harmful chemicals and tends to shrink over time, negating the effort now. That said, there are some very difficult areas to insulate, so this might be the right solution given the circumstance.


Exterior insulation is a little different. There are a couple of options, but usually you want to go with a rigid board type of insulation. Mineral wool, or a wood fiberboard are good alternatives (see below for links) They are good at wicking moisture, and they are good insulators.

There are other ways, and if you are interested, feel free to reach out and we can talk about some other alternatives. They are just a little too complicated to explain here.


Sometimes there are government programs that can help you to pay for a project like insulating your house.  A quick google search will probably help you determine if there is a program near you.  In our case, we live in a town that uses National Grid (local utility), so the Mass Save program helped us.  They paid for 75% of our insulation project, bringing our total out of pocket cost from $7,500 down to $1,200.


Mineral wool: https://www.rockwool.com/north-america/products-and-applications/products/comfortboard-80/


Wood fiber board: https://gutex.de/en/product-range/products/walls/

(this product comes from Germany, so it is likely more expensive due to shipping etc.)


Our own insulation project:

Holes in the exterior where they "blew in" cellulose insulation.

Fiberglass insulation (pink) between the floor joists in the basement.
Spray foam (yellow) sealing the joint between the wood framing and the foundation.





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