08/22/2026
No battens. The foam board goes straight onto the steel.
Extruded polystyrene cut to fit the corrugation and glued flat to the wall — no timber frame behind it, no cavity, no air gap.
What that buys you is width. A batten grid plus mineral wool eats 3 to 4 inches off each side. This eats about 2 inches, and in a room that starts at 7'8" wide, four inches of floor space is a real difference you feel every day.
XPS also runs roughly R-5 per inch against about R-3.5 for wool, so you get more performance out of less thickness.
The bit that decides whether it works: every joint gets foamed. Look at the second shot and there's expanding foam down each seam and around the corner post. Miss one and you've made a channel where warm inside air reaches cold steel and condenses — inside the wall, where you'll never see it.
The trade-off is fixings. Nothing to screw a shelf into later without hitting steel.
Built by Cargo House.
Foam board or battens and wool?