Someone just asked for advice on Facebook, and I figured I should save it here so I don't need to type it again when someone asks later.


We've had just about every kind of insulation in our house. So, more than you asked for, but hopefully useful. Also, if you don't know about it, you should go to and have Eversource pay for 50% of your costs - a great program, we paid $3500 and save ~$1000 a year in fuel, plus the house feels warmer. Air sealing is the most important (one reason spray foams are better; the R value of cellulose and fiberglass goes to something around 1 or 2 if there is air movement)

1. Urea formaldehyde... Just looking at the name should have been enough for people to realize it was a bad idea, but it was the original spray in foam and was quickly banned in some other countries, but lasted here a while. Not counting the short term installation problems of causing cancer, in the long term, it shrinks and getting rid of it is really hard and is really bad for your lungs once it turns into powder.


2. Fiberglass: other than environmental issues, is the good old standby. Rodents don't eat it, and as long as your walls are thick enough and are air sealed, works well.


3. Rock wool: better than fiberglass for environment and easier installation on walls.  More expensive than fiberglass, but worth it to me. We built a jig make it really easy to cut squarely (you cut it with a long bread knife so it fits perfectly, and holds itself in the wall, no stapling needed).  We were using it in an application that didn't need a vapor barrier on the inside of the wall (see XPS exterior foam below).


4. Cellulose, in attics, great way to add to existing insulation, though not a vapor barrier at all. In walls, only good at high pressure/density, otherwise it settles.


5. Closed cell (isocynene and lots of other patented names that are mostly all the same thing). Vapor, moisture, air barrier. Terrible environmental issues for manufacture and installation, but great R value and air sealing, particularly for old buildings that have thin walls. And as far as we know, doesn't shrink, our grandkids will probably complain about that...


6. Open cell foam: not as good as closed cell, rodents eat it, lower r value. Can be poured in a wall, so easier to install in some cases. 


7. EPS foam sheets: good for below ground/ foundation installations. Like all of the foams, bad for the environment.


8. XPS foam sheets, great for outside-the-wall, continuous (unlike everything else, also insulates the studs, which at higher insulation installations, really subtracts from the total R value), bad for the environment, but can be reused from old buildings.


We own an 135 year old Victorian that used to have ~4 air changes an hour (it's hard to imagine all the air that my pellet stove heats leaving the house 15 minutes later...) and we've shrunk it to 1 air change an hour and are doing another round this month. I don't know if we'll ever have to worry about not being leaky enough (like someone said above, which is a real problem for new installations, but really hard to get to in an old house), but that would be a great problem to have (as long as it is handled).

Posted by Jon Daley on October 29, 2020, 10:40 am | Read 2348 times
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