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I'm renovating (most of) a small house - in particular, my architect and I are doing our best to insulate it to R=3.8 (the local standard), not counting the inherent heat resistance of the (brick, masonry) walls. We'll use Biofib (based on hemp+cotton+linen) on most of the first floor - counting an air layer and a fireproof panel, we are talking about 18cm, which is not great but also not terrible. It has plenty of virtues besides being good heat insulation - it has good sound insulation properties, works well in summer, regulates moisture, doesn't slowly kill you (if there is a huge fire and the fireproof panel is breached, you are basically in The Name of the Rose, but it certainly doesn't kill you *slowly*), etc. In some places, though, we simply don't have enough 18cm. We may use a vacuum-packed product in the bathroom (not much of a temptation to nail things to the shower wall, is there). However, the shape of the wall in (a) the toilet (b) (more importantly) the large staircase is just too irregular for the installation of vacuum-packed products to be feasible. Phenolic is not an option for indoor insulation where I am (too much fume). We can't seem to get airgel panels in the local market, and airgel blankets cost a fortune. One can't apply more than 8cm of Fixit airgel plaster (a useful product otherwise). So, by exclusion, we arrive at PUR (polyurethane) and its cousin PIR. I am a bit concerned about using PUR and PIR on a staircase - their reputation for emissions in case of fire is not great. (We'd put them behind a fireproof panel, obvs.) The architect says PIR is not as bad as PUR in this regard. However, this study (from 11 years ago) seems to indicate otherwise: http://clok.uclan.ac.uk/1536/1/Stec and Hull_Fire_Toxicity_of_Insulation_Materials_EnergyBuildings_2011.pdf What do people here think? (Worst comes to worst, in case of fire, I can just jump from the first-floor windows, but, if my parents visit and a fire starts then, they might feel differently, at least for a crucial moment or two.)

This is from the approved plans for the floor section in my house, passed in 2007. 85mm polyurethane insulation in the floor is a slight puzzle - it was technically a renovate not a rebuild. From 2007 Building Regs what would the minimum be for that situation? The u-value seems to be about 0.26. I decided to have a little look to respond to a debate on the other thread about how much floor insulation is necessary for ufh to be a practical proposition. I can see from the 75mm screed why my ufh response has a delay in it, but even with that spec I like it. Ferdinand