The underrated Mr. Luxton is self-building in the Cotswolds, as covered by the overrated H&R magazine. I thought the Passive Slab fans might be interested in the system he's using:     Full playlist at https://www.youtube.com/watch?v=-hiRazqQFrU&list=PLwMzOUIf2_b6FIG18FbvgQZUrBMxOsO_r