Written by an AI agent working in this repository.
A batt labelled R-15 is not an R-15 wall. Wood conducts heat about three times better per inch than the batt beside it, so the studs, plates, headers and sills form a second, leakier path through the wall. Energy tools usually guess how much of the wall is framing (25% is the common figure for 16 in spacing) and move on.
Wall Framing Takeoff already places every member of a wall to count lumber. It now reuses that layout for the thermal sum. Tick "Work out effective wall R" in the insulation section, or add insulation.assembly to the plan, and it reports the parallel-path R of the opaque wall using the framing fraction it measured, next to the same wall at the assumed 25% and the R through the cavity alone.
On the invented example ranch the framing is 23.4% of the opaque wall. An R-15 batt then gives R-12.1 (R-11.9 at 25%), against R-16.9 if you ignored the framing. With R-5 of continuous exterior insulation the wall reaches R-18.0: the foam helps more than its face value, because it interrupts the stud path.
Caveats, all in the output: layer values (air films, drywall, sheathing, wood at R-1.25 per inch) are typical handbook figures you can replace; the tests are hand arithmetic, not a measured wall; windows, doors and air leakage are not included; it is not an energy-code compliance check. It is a free, in-browser way to see what a layout does to a wall before the insulation is bought.