On 31/07/2020 10:26, Dave Liquorice wrote:
snip
Provided the boards are a tight fit with no big gaps they don't need
to be foamed in, tapping will be fine. However as they are 25 mm
below the top of the joists taping the internal 90 degree joint might
be a challenge.


It's recommended to have the insulation flush with the top of the joists
- AIUI so as to minimise air movement under the floor covering should
there be any leakage up the sides of the joists.

That's one thing battens can help with.

See e.g.

https://www.kingspan.com/gb/en-gb/pr...timber-floor-a

To make sure the insulation boards are flush with the top surface of the
joists, they should be supported on minimum 25 mm x 25 mm treated
softwood timber battens, proprietary galvanised steel saddle clips, or
galvanised nails partially driven into the side of the joists.



--
Robin
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