Should I densepack wall cavities prior to exterior insulation?
House was built in '64. We live in climate zone 5A, though on the edge of 4A (might be 4a in a few years). We opened up one wall during a kitchen reno and found R13 fiberglass. But it's starting to seperate from the kraft paper, and the paper itself is starting to fall apart. We would like to replace all the windows and siding, so figured an external layer of insulation would be a worthy investment. The plan for now is strip back to sheathing, new self adhesive WRB, new windows installed at shearwall, 2-3in eps/roxul based on price, strapping, new siding.
Is it worth densepacking the walls before doing the WRB?
The kraft paper falling apart or separating from the insulation is no great concern, and you could blow in cellulose without causing any problems, but there is an easier and cheaper way. First check out this page on insulating the exterior of walls, and your question is sort of answered in there anyway –
The best way to insulate walls is from the exterior
Since you’re already going to be insulating the exterior, rather than incurring the cost and hassle of insulating the outside AND the inside, I think you’re way better off on all fronts if you just beef up the outside a little more. Here’s why – since your stud cavities already have batts, you’d only pick up a minor amount of additional R value by blowing in dense-packed cellulose insulation, and with that comes an entire new set of costs – cellulose installers have to cut holes, then you have to repair them all.
Whereas, you’re already incurring all the costs of exterior demolition and installing rigid insulation, so if you went an additional inch or two thicker, you would get far greater R value per dollar than doing cellulose as well.
Here you can see a video of how we installed Rockwool panels on the exterior of sheathing, which works, but there are new interesting ways to attach it. this one may interest you, it’s ThermalWall rigid foam insulation panels from Legalett that have rails on the interior of the foam so you can attach them with short screws, then attach the strapping to the same rail with more short screws, so you have no thermal bridging. It also comes in a variety of thickeness. Also Cascadia clips is another exterior insulation fastening system for either rigid foam or Rockwool.
Mike, Thanks for sharing your wealth of knowlege. I really like the look of the ThermalWall but unfortunately can't accomidate anything that thick. We are limited to 4in of total wall thickness. That puts us in the 2in range for insulation.
My wife also prefers the "outie" windows which as you know presents it's own set of challenges. In trying to solve that problem, I found a company making a thing called Thermalbuck. They also have an insulation that works with the Thermalbuck to make a nice system. The insulation is Neopor GPS by BASF, which I can tell is an EPS foam. It seems to offer a slightly better R-value per inch than normal EPS. Have you heard of the Thermalbuck and Thermaltite products? Any thoughts?
Hi Gordon, thanks for the kind words.
We don't dispute the higher R value claims of EPS foam with Graphite, that legit. As for other products - there are lots of new innovations in building materials, and we are very much in favor of any that help break thermal bridging, which these seem to do. Neither of those ones seem like snake oil to us!