Recent Details: Superinsulated RetrofitsChainsaw1

This post is for building and insulation ┬ánerds. I’ve been thinking a lot about the superinsulation projects I’ve accomplished over the past decade and what those retrofits cost. Yesterday I got an eMail from Eric Doub of Ecofutures in Boulder Colorado about a superinsulation project his company is doing that Eric calls the Big Wrap. Eric and I will be presenting on superinsulated retrofits at the Affordable Comfort conference in Denver next week on Thursday at 3:30 PM. Eric is wrapping a home using a frame wall and closed-cell spray polyurethane foam. The details he described are interesting and truly unique.

Comparing Modern Methods to Ancient History

Eric Doub retrofit wall ready for spray foam.

Eric Doub retrofit wall ready for spray foam.


I have my own unique solution to the superinsulated retrofit that revolves around high-density polystyrene sheets (2 lbs per cubic feet). Neither Eric nor I can help comparing our solutions to the chainsaw retrofit championed by Harold Orr of Saskatchewan and Bob Corbett of Montana in the early 1980s. That solution depended on wood framing and fiberglass batts. Neither Eric nor myself is confident that our solutions are an advance over the chainsaw retrofit approach. The reason for this self doubt is cost. I did a spreadsheet this week comparing the retrofit wall sections from a cost and thermal-resistance perspective. Here is a short description of the retrofit wall sections compared first listing the wall components from outdoors to indoors. Then I inserted the summary cost comparison referring to these same wall details.

Superinsulation Retrofit Wall Details

Install foam flush to the 3.5-inch window extension fin. The strips are treated half-inch CDX plywood.

Krigger’s approach of exterior stripped EPS.


1.) EIFS stucco exterior, 6 inches of virgin 1.5 lb/cf density EPS foam, open-cell SPF foan in 4″ stud cavity, lath and plaster
2.) Steel siding, 4″ HD EPS foan sheathing, wood siding, 2″ blown cellulose insulation, plank sheathing, 4″ blown fiberglass, lath and plaster.
3.) Steel siding, 2.5″ HD EPS, plywood sheathing, R15 fiberglass batt, 1/2″ PIC foam sheet, 1/2″ drywall.
4.) Steel coil stock, 2.5″ HD EPS foam sheathing, 8″ reinforced concrete, 2.5″ HD EPS, 1/2″ drywall
5.) Wood lap siding, plywood sheathing, 9.5 inch blown fiberglass 2.0 lb/cf density, 1/2″ drywall
6.) Siding, OSB sheathing, 3 R15 fiberglass batts, old siding, old sheathing, old cavity insulation, 1/2″ drywall.
SprInsWallTable