July 15

Underfloor Insulation: Sizing and Joist Width


What is standard joist width, and what size insulation is best?

Our GreenStuf Polyester Underfloor Insulation is slightly wider than the space between standard joists, but don’t be alarmed, we designed it that way.

Here’s why we choose to use 450mm wide insulation when standard joists have 430mm space in between them.

Remember, the performance of underfloor insulation comes down to two things: coverage and loft (thickness and density).

Snug Fit Polyester Insulation on a Standard Floor Joist
The easiest way to explain why it’s so much better to have the insulation a little wider than the space is to take you through how to install insulation the ecoMaster way:

  • First, we press the insulation up in between the joists. The additional width makes the material fit snuggly, making excellent contact with the floor and holding in place while it is stapled in place.
  • Next, we pinch and staple the material to the inside edge of the joist. This causes the insulation to “pillow” slightly, giving you the extra benefit of 120 mm thick insulation even though a standard joist is only 90 mm deep.

Under Your Floor

430mm space Floor Joist

Standard floor joists are installed with 430mm space in between them and 90mm depth. However, if your joists are not 450mm wide (called 450 centres in the trade), you can still install insulation under your floor. See below.

R2.0 and R2.5 Insulation

R2.0 and R2.5 polyester underfloor insulation

Our R2.0 and R2.5 polyester underfloor insulation are 450mm wide and 120mm thick, this means that it can fit snuggly into standard joist spacing. The R2.0 and R2.5 are both 120mm thick, the difference being the density and weight of the material.


Wooden Joist Stuffed with Polyester Insulation

This is a cross-section of our sample floor fitted with polyester underfloor insulation the ecoMaster way.

Are Your Joists Wider than Standard?

If you have variable width joists, you can use the “tear and turn” method to make sure you get the best coverage. Learn how to ‘turn-and-tear’ here.

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Contact ecoMaster To Get The Best Underfloor Insulation

ecoMaster delivers and installs home insulations in Melbourne and Sydney. To learn more about polyster, visit www.underfloorinsulationaustralia.com.au

You may also talk to an ecoMaster staff at 1300 326 627 for orders.

Learn More


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