I have put thermo foil under all my carpets, and I am putting it in all my cupboards as well, worth a try, got it from wickes they had an offer last year 3 for 2, hope this helps
Jackie, October 2015
use bubble foil insulation you can get it off e-bay its very cheep and easy to install
jim, October 2013
try www.greenplanetinsulation.co.uk check with them if suitable for your project.
Rolls of insulaton sandwiched between foil thin but effective as used to insulate in houses. But as John says don't obstruct airflow KEEP ALL VENTS CLEAR. You can hold it in position with staples so add a staple gun to cost and fix edges with plastic PVC strip as used to trim around PVC windows/doors You could also cross batten with same plastic strip to help prevent sagging. Plastic no maintenance plywood would need to be marine ply [expensive] and re-coated every possible 2 yrs if not every year.
If the roll insulation is suitable then that and plastic strip results in no maintenance.
I wouldn't use either foam or polystyrene unless its guaranteed FIRE PROOF not just fire retarded as the latter might not conform with insurance cover you may have. Also find out the fire proof level of the rolls from the above website. Failing to get a satifactory reply from the website try search for static/mobile homes manufactures and ask them if they could recomend an underfloor insulation.
Bob, April 2009
Better to use a closed cell foam rather than ply, which won't insulate very well - but do make sure that water can't lie anywhere as it could rot out any wood or metalwork as you'll also restrict airflow.
