How to install underfloor insulation between joists?

Ando1

Underfloor insulation is designed to be a friction fit between solid timber floor joists typically 450mm wide, my house has I Joists so only a small part is a friction fit and the remainder is either a 10 mm gap both sides as shown in the attached sketch or if I slide it to one side a 30 mm gap. My question is will the bat installed as per the sketch provide suitable insulation or should I slide the bat to one side and pack the other with a cut piece of bat note in both cases the bat will be supported with straps

MitchellMc

Welcome to the Bunnings Workshop community @Ando1. It's great to have you join us, and many thanks for your question on insulation.

Ideally, you want the insulation to fit snugly between the joists with no gaps. In your situation, it would be best to slide the bat to one side and pack the other side with a cut piece so the full width is filled. Another option is to use wall insulation that comes in 580mm widths and trim it down to 450–460mm for a tight fit.

The main difference between wall and underfloor insulation is that underfloor insulation has a sprayed glass coating on one side to prevent wind from blowing through it. This is especially important when there are no walls under the house, and it can get breezy. Ensuring a snug fit and proper wind protection will give the best thermal performance.

Please let me know if you have any questions.

Mitchell