Underfloor batt 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 Health and Safety Message. 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: AS3999:1992. 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
  • Suitable clothing (see our Health and Safety message)
  • Tape measure
  • Plastic strapping tape


  • 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.
  • Use our ready reckoner here to quickly calculate the amount of packs you need.

Slice the pack lengthwise down the side. Take out a segment and place one side hard up against the joist and the floorboards. Slide the other side of the batt up into the corner working your way along the joist to friction fit the batt into the joist space folding over as necessary. Fold should come no more than 75mm below the bottom of the product.

Make sure the batt is firmly in place, and each piece butted snugly at all joints. Leave no gaps between the insulation, the joists and the underside of the floor. This ensures there will be no air movement up the joists or underneath the floorboards. When installing insulation around plumbing, pipes and junction boxes, cut the insulation to ensure a tight fit. Take care not to cover any wiring or block ventilation openings. All insulation should be installed in accordance with AS 3999, leaving suitable clearances around underfloor service elements as required.

Using plastic strapping tape, strap the insulation in place to ensure that any movement (from wind or upstairs activity) is kept to a minimum. Whether
the strapping is fixed across several pieces of insulation, or applied diagonally across one segment, use three straps per segment and staple them in place – hard up against the insulation. Make sure straps are within 200mm of the end of each batt.

SAFETY TIPS: EXTREME CAUTION IS REQUIRED when stapling near and around electrical cables. Only apply staples to timber surfaces that are clearly

• Always wear a face mask, eye protection and gloves.

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