Retired building air tightness technician Trevor Clark gives his advice on installing your own insulation this winter.

DIY insulation is a simple job. Anyone can do it.

If you have been trained properly on what to do, then as long as you don’t suffer from claustrophobia and don’t mind sweating or freezing, anyone can do it.

Insulating inside the attic can be a DIY job.

Bear in mind the potential for falling through the ceiling between the timbers, so work off as large a board as you can.

Have good lighting, protective clothes, face mask and goggles to prevent the fibres getting into your eyes and mouth.

You must ensure there is little or no air flow through the ceiling. Any existing insulation should be lifted and every hole where a cable penetrates the ceiling or walls below should be sealed with AC 50 caulk or similar.

Any gaps along walls (missing plasterboard) should be sealed with foam.

At the wall plate, the gap between rafters or trusses and the wall plate (where the roof rests upon the wall) has been filled (with an insulation board, and sealed to either side and bottom against the wall plate that will stop air flow getting under the insulation).

It should not fill the gap completely as there must be a minimum of 25mm between the top of the insulation and the underside of the roofing felt.

This gap must extend along the roof length from the soffit to prevent wind washing energy out of the insulation.

If it’s ‘rammed’ into the gap at the end of the insulation it will allow air flow to get in and under the fibreglass and ruin its performance.

To fully insulate the attic, the insulation should be continued into the soffit and down the wall to meet the insulation at the top of the cavity inside of the soffit board and be held against the inner leaf of the wall structure, as this area relies on only a single layer of brick/block to retain energy.

This is a major cause of condensation in the upper rooms of houses as energy is lost through this minimal thickness.

However, it’s only accessible by removal of the lower rows of roof tiles and requires scaffolding to work from.

It may be possible to remove the soffit and insulate from underneath but scaffolding is still required to this tight access.

The attic insulation should be 300mm thick. Test this with a long knitting needle marked at 300mm at a number of places over the entire space.

Ceiling joists are generally 100mm (maybe smaller, 75-80mm), so the first layer should come to the top of this joist.

Subsequent layers should be laid at 90 degrees and have tight joints.

If a third layer is installed this can be rolled out on top of the first layer, but half lapped over the joint below.

Use a semi-rigid slab between joists and for the next layer at 90 degrees but use the cheaper rolled fibreglass as the top layer.

If you use three layers of rolled fibreglass at 100mm thick, when you finish you will only have maybe 250mm as the weight crushes the layers below.

If you intend using the attic for storage, you will need to fit extension legs to lift the floor surface above the insulation to prevent crushing the insulation and reducing its performance.

There should be a gap left between the top of the insulation and the underside of the storage flooring of 50mm to allow moisture vapour to escape and not damage the floor boards.