Underfloor Insulation

If you have a suspended timber floor, Glasswool insulation is an ideal solution for providing thermal and acoustic performance.

Homes lose more energy through the floor and ceilings combined than through external walls. Installing insulation in the underfloor and ceiling will compensate for the walls being missed out. An un-insulated underfloor will lose up to 20 per cent of internal heating or cooling.

To help address the effects of wind-wash, there is a new insulation product available that comes with a wind-wash barrier. Earthwool® insulation roll with a wind-wash barrier has a high thermal performance of R1.7 and a wind-wash barrier to provide protection from air movement under the floor (wind-wash occurs when there is air movement across the face of unfaced products, which draws out heat energy to reduce thermal performance). Furthermore, it is easier to install as it can be directly stapled in place. View our install video for more information.

Installation Instructions
DIY Installation Video

Underfloor insulation installation instructions

These instructions should be read in conjunction with local standards AS 3999 and all applicable local, state and federal building regulations. Before you start installing, please make sure you are familiar with our safety instructions and precautions. Ensure that you use tools and equipment that are suitable for the intended application. This will include suitable safety equipment.

Try and avoid staples made from metal or other conductive materials if possible. Installing underfloor insulation can be hazardous due to the working environment and electrical cables.

Do not start work until the site is safe!

Assess the underfloor condition and structure together with the method of installation you are to use based on the appropriate requirements established in the building code, site assessment and or plans provided. Installation must be completed to the requirements of relevant standard: AS 3999:1992. When insulating any floors, care should be taken to ensure that sub floor ventilation is maintained according to AS/NZS 1860 or heed the recommendations of particleboard/timber flooring suppliers.


  • Sharp Knife for trimming insulation

  • Ladder

  • Suitable clothing (see our safety instructions and precautions)

  • Tape measure


  • The rolls are manufactured at 600mm wide to suit joist spacings of up to 600 centres. The width of the underfloor roll must be a minimum of 50mm greater than the width of the cavity.

  • To calculate the number of packs needed, determine the area (m²) to be insulated by multiplying the length by the width or wall height. The number of m² of insulation material is clearly marked on each pack. Divide the total area to be insulated by the m² in a pack to determine the number of packs required (don’t forget to round up to the nearest whole pack). Allowances should be made for areas that are unable to be insulated.


  • If possible leave the insulation in the packs until you’re in position and ready to install.

  • Before installing the product measure and cut the roll into convenient and manageable lengths.

  • Before installation, gently agitate the insulation by gently shaking or bouncing the product it on its side until it recovers to thickness stated on the label.


  • Before friction fitting each roll ensure you identify any electrical cabling. Extreme care must be taken not to staple through any electrical wiring.

  • Friction fit underfloor roll between the joists with the excess material folded down evenly either side.

  • When abutting insulation ensure there is a close firm fit with no gaps.

  • Where required, use a sharp knife to cut the insulation to fit. It is important that when you cut the insulation that you avoid coming into contact with any electrical services.

  • Secure the insulation in place by stapling down the turndowns at 200mm centres. Secure one side of the roll before gently pulling the roll taut and securing the other side, working your way along the roll.

  • A clearance of 100mm should be left around all waste water pipes.

  • When abutting dwangs or nogs the roll should be installed 75mm longer in order to create a turn down, this is then fixed with staples.


  • Complete a final check of the installation ensuring all areas have been insulated and that you have an even and consistent layer of insulation.

  • Finish your project by removing all packaging from the underfloor and disposing of all rubbish and excess insulation responsibly.

For more installation advice watch our underfloor install video and read our electrical safety information before doing any work in the underfloor.