Very first appearing in Fine Homebuilding, issue 250 (April/May 2015), Stephen Bonfiglioli’s “Breaking the Thermal Bridge” highlights a practical technique for attending to among the consistent weaknesses in traditional wood framing: thermal bridging through studs. As interest in higher-performing structure enclosures continues to grow, the easy approach described in this post still uses a beneficial example of how thoughtful detailing can enhance wall efficiency without adding extreme cost or complexity.
You may say I’ve always been ahead of the curve as far as structure performance goes. When I began building in 1977, my homes had 2 × 6 walls and R-19 insulation, while code-built homes had 2 × 4 walls with R-11 insulation. Other contractors, subs, and suppliers stated I was crazy for installing more insulation than the building code required, however I’ve constantly believed that building energy-efficient homes made best sense. In my mission for performance and comfort, I tried just about every high-performance wall assembly there was, all of which seemed excessively complex and pricey. Then one day 12 years back, I asked myself, “What if I fur out the interior wall with strips of stiff foam and strapping?” I reasoned that the foam strips would attend to thermal bridging, include thickness to the wall to accommodate high-density fiberglass batts, and expense less than alternative methods. I have actually been developing my walls this way since.
Foam selection
I assemble lengths of 1-in.-thick high-density expanded polystyrene (EPS) foam and 1 × 3 strapping picked up from my regional lumberyard. While the strapping is easily available, the high-density foam isn’t constantly a stock product, so I buy my foam from Insultech in Bridgewater, Mass. This foam withstands compression more than routine EPS, and it can be found in convenient 1-1/2-in. by 4-ft. pieces. Alternatively, I might cut complete sheets of rigid foam into 1-1/2-in.-wide strips on a tablesaw.
While it may appear to make sense to use extruded polystyrene (XPS) or polyisocyanurate insulating strips, both of which have higher R-values, R-value matters really little in this application. EPS is the least costly type of stiff foam, and with an R-value of R-4 per in., it creates enough of a thermal break to adequately slow heat transfer through the framing.
< img src="https://images.greenbuildingadvisor.com/app/uploads/2026/04/10150425/Screenshot-5522.png"alt=""width ="285"height =" 316 "/ >< img src="https://images.greenbuildingadvisor.com/app/uploads/2026/04/10150448/Screenshot-5523.png "alt =""width =" 285 "height ="378"/ > Speed and strength As soon as we have a brand-new home dried in or a remodel gutted, we can include the foam strips to a whole 3000-sq.- ft. home in a day or less, conserving us substantial money and time when compared to more-complicated wall assemblies. Also, since the foam strips are covered with 1x3s, drywall and trim can be set up with standard fasteners rather of utilizing long nails or screws to find the framing behind the foam. The 1x3s likewise allow the house owners to hang images and shelves more quickly later on.
Do not forget the air barrier
Air-sealing is vital when using fiberglass batts (see “Making Fiberglass Work,” FHB # 246), so we fill any holes or gaps with spray foam before installing the high-density R-30 batts. We take care to fill the stud cavities entirely with very little compression.
Our locality needs vapor retarders on the interior-facing side of exterior walls, so we use MemBrain vapor retarder in mix with air-sealing tape and acoustical sealant to develop a total air barrier that avoids warm interior air from condensing in the wall cavities throughout the winter. MemBrain is a so-called clever vapor retarder with a permeability that increases as humidity rises to promote drying. To ensure drying to the exterior, we complete the assembly with plywood, carefully comprehensive housewrap, and wood siding.
Expense contrast
My wall is much more economical than alternatives such as SIPs or outside foam. Labor and products– consisting of the foam strips, strapping for connecting trim and drywall, and batts of high-density R-30 fiberglass insulation– cost $1.50 per sq. ft. of living area. For contrast, installing 1-1/2-in. or 2-in. stiff insulation over plywood or OSB sheathing and adding blocking or furring for windows, siding, and trim expenses more than $3 per sq. ft. of living space.
Stephen Bonfiglioli is a contractor in Middleboro, Mass. Images by Patrick McCombe. Illustrations by Vince Babak.
This post originally appeared in Fine Homebuilding issue 250, April/May 2015.
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