Fitting Wide, Narrow Joists: How To Install Underfloor Insulation

Sometimes you’ll come across extra wide or narrow joists under your floor.  Here’s how to make your insulation fit perfectly using our simple ‘Turn and Tear’ method.

Most commonly, standard joists have 430mm space between them, making our 450mm-sized polyester insulation perfect for a nice snug fit. However, not all houses adhere to this standard sizing. Occasionally, we come across homes that have extra wide or narrow joists across the entire home. Usually, there are just a few rows of odd-width joists towards the edges of the home, because not all homes have the right size for neat rows of standard-sized joists.

How To Fit Standard-Sized Insulation To Wide and Narrow Joists

What do we do if the joists are too wide or too narrow to fit the standard 450mm-sized insulation?

The answer is to ‘Turn and Tear’ your insulation. Our premium GreenStuf Polyester Insulation, the best underfloor insulation for Australian homes, can be torn easily in one direction using your bare hands. This means you can create sections that have the exact width that you need to fit either for wide or narrow joists.

Simply create the torn sections one by one and line them up between the joists, stapling as you go.

Here’s a breakdown of how we ensure the best thermal performance when up against wide or narrow joists:

1. Rotate your insulation 90°
2. Tuck the end into the joist space next to Joist A
3. Measure to the outside edge of Joist B (this gives you a little extra wide for a nice snug fit)
4. Tear the piece
5. Press the new end piece in between the joist and secure by stapling as normal along the inside, bottom edge of the joist
6. Pinch and staple the ends into the floor to ensure there is no room for air movement and rodent access
7. Repeat to fill the whole space

Standard, wide or narrow joists: Here’s how we do it.

In this video, Maurice Beinat demonstrates how we install our polyester insulation using a stapling technique that’s exclusive to polyester.

You can learn more about why we recommend 450mm insulation for standard 430mm joist spacing by clicking here.

Boost your thermal comfort and lower your energy bills FOREVER! Stuff up your floors with the best underfloor insulation in Australia.