On Tuesday, 6 December 2016 22:26:03 UTC, Tim Lamb wrote:
Insulation between joists below under floor heating.

Having promised no wall hung radiators I am now stuck with getting the
job done! Ground floor no real problems: grooved insulated sheet to take
the pipes covered with standard chipboard or screed for the new bit.

Upstairs life gets expensive and difficult. All the suppliers call for
insulation below and in contact with the heated floor. In a chalet
bungalow, there is no such thing as a standard floor joist spacing. The
dormer cheeks are double or triple timbered and the intervening space
filled with ladder work on joist hangers. Elsewhere walls have double
supporting timbers.

I have been considering cross battens but this adds a huge cost and the
suggested sizes (30mm x 70mm) are not found off the shelf and
particularly not untreated.

Pre-grooved chipboard is an alternative and cheaper solution. Both
systems call for insulation between the joists and in contact with the
underside of the floor. PIR foam is not cheap, needs careful
cutting/fitting together with supporting battens. Rockwool is cheaper
and easy to cut and fit but... how do you stop it ending up resting on
the ceiling plaster board, light fittings and electrical wiring?

Chicken wire netting? Some sort of cross batten or?? My floor joists are
9" deep and Rockwool 6". Perhaps lengths of plain galvanised fencing
wire stapled between the joists? Any impact on wi-fi transmission?


--
Tim Lamb

Rigid foam bats can be bought far more cheaply as "seconds".
(Minor damage)
Just Google "insulation boards seconds" to find some local toyou.