Hi

A couple of questions;

1. Can anybody tell me the name of the solid insulation which is a
solid foam, backed on both sides with foil?

2. I'm about to start building a downstairs WC in the under the stairs
cupboard (has plenty of standing room) of our house, which is
victorian. I want to use this insulation on the inside of an outside
wall as it's very cold under there. I was thinking of say 50mm (2")
studs on the wall, with the solid insulation fitted between, and then
plasterboarded over the top. Seems like a good place to conceal the
copper pipe from the hot water tank almost directly above. Does this
sound sensible, or will I be causing myself damp problems, building
code issues etc?

Regards,
Mark