To avoid hijacking the other thread, thought I would ask this in a new one as there are obviously some knowledgeable builders on here.
Our house has next to no under floor insulation - it is a timber framed house sitting on piles. Built in the mid 80s the 'insulation' is like a foil backed bubble wrap about quarter of an inch thick stuck to the bottom of the chipboard flooring, which means the floor is always cold and it costs us a fortune to heat in the winter.
I want to insulate under the floor but it will be a faff. There are basically two options I am aware of
- Rockwool type insulation. Each bay between floor joists to have a sheet of OSB supported by a batten at each side along the bottom, and the rockwool will be between the ply and the floor making a snug sandwich.
- One or other of the types of rigid foam sheet insulation that can be ordered to size (or cut to size) and fitted solid against the underside of the floor (in fact it would be against the existing foil/bubblewrap insulation).
The first one would be my preference and is how we insulated the extension, but as space is tight under there it will be immensely difficult to fit under at least half of the house as we obviously have to work from underneath.
The second one would probably be easier to fit but I am wary of it, as unless it is a very good fit, the slightest air gap around it would appear to render it completely useless as the cold air just flows around it and gets to the floor anyway. And, due to the bulk of it, shipping it all down here makes it very expensive as freight is by the cubic metre.
Are there any other alternative options around that I should investigate?