Can I use Drywall batts to insulate basement ceiling?

[DanT1981]

Hi all.

I have a cold victorian house with a basement that is generally 10degrees colder than the ground floor, which is therefore made to feel very cold, all the time, as a result.

I have installed 100mm ISO hardboard insulation already, and that has helped somewhat, but there is still a 1.5 / 2 degree temp difference on the wooden floorboard of the ground floor, compared to chest height.

I have 80mm left between the outer side of the ISO and the end of my basement ceiling rafters.

Therefore, my idea was to install some rolls of traditional batt insulation in there to increase my R. Only issue is I can't find any at 80mm.

I can find some drywall cavity slabs (85mm example below):

85mm Knauf Dritherm 37 Glass Mineral Wool Cavity Slab Insulation - 4.3

Knauf DriTherm Cavity Slabs are semi-rigid and rigid glass mineral wool slabs well-known for their water-repellent and non-combustible qualities. Length: 1200mm, Width: 455mm, Thickness: 85mm, Coverage: 4.37m², Slabs: 8.

diybuildingsupplies.co.uk

There is also some 50mm ceiling batt insulation available.

So the questions are:

Can the cavity batts be used in ceilings OK?

And, would using the 50mm traditional batts (therefore leaving a 30mm void between the ISO and batt), be better or worse insulation overall?

Do point out if I am saying anything stupid here. Genuinely need help to avoid making an expensive mistake.
Thanks!

 

[AC Power]

I would certainly try that. I have batt insulation in my basement joists, thus insulating the upstairs thermally and audibly.

However, I would also staple a sheet plastic film (vapor barrier) over the insulation once your done. This helps a LOT. The migrating air in the basement can make its way into areas of your insulated floor joists, especially if you have a slight positive static pressure in the basement respective to the main floor. If you have a forced air furnace, your static is likely sitting around .5" water column when the fan is on (provided your furnace has a fresh/outside air intake).

 

[DanT1981]

Thanks for the tip about the vapour barrier!

 

[AC Power]

Your Welcome.