On Fri, 31 Jul 2020 00:20:32 -0700 (PDT), Tricky Dicky wrote:

As part of the kitchen refurbishment I am looking to insulate the floor
which at present is a suspended T&G floor on 100mm joists. I am looking
at fixing 25 X 25 battens to the bottom of the joists and dropping 75mm
foam insulation in between the joists.

The insulation is very light and when cut to be an interference fit
all the battens are for doing is acting as a stop. 20 x 6 lath will
do that and be easier to fix. I'm assuming that the crawl space under
the joists is not big enough to squeeze through to shove errant
sections of insulation back up.

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.

--
Cheers
Dave.