Insulating a Loft Floor

The current recommended thickness for insulation in new buildings is 250 mm (10 in). If the depth of your joists is less than this, fill to the top of the joists or consider adding wooden battens to the top of joists to extend them. Vacuum the loft before laying insulation - if there is a large amount of dust and dirt, hire an industrial cleaner.

Safety

• Never stand between joists. Lay several stout boards across the joists.
• Always wear a dust mask and goggles while cleaning and insulating. A hard hat is also recommended.
• Ensure the area is well lit.

Laying Rolls

Glassfibre or mineral-wool insulation is made in two widths - 400 mm (16 in) and 600 mm (24 in) - so check the distance between your joists before buying. The rolls are usually 100 mm (4 in) thick and up to 8 m (24 ft) long. Glassfibre can irritate skin so wear suitable gloves and long sleeves when handling it. Run the material under any electric cables on the loft floor, so that the cable will not overheat and is visible. Don't cover downlighter casings or other fittings that illuminate the room below. Don't insulate under the cold water tank. Cold water pipes running between the joists can be covered.

1. Start laying the roll at one end of the loft. If necessary, use a broom to push the end of the roll well into the eaves, but don't block the eaves or any vent.
2. Unroll the material between the joists and press it into the edges, allowing any excess to lap up the sides of the joists. Don't compress the material. When you reach the end of the floor, cut the material with long-bladed shears or a kitchen knife, go back to the other end and start again between the next joists.
3. At the end of a roll, fit the start of the next roll snugly against it.
4. Cut small pieces to fill any odd gaps.
5. Cut a separate piece of insulation to fit the loft hatch and stick it in place with PVA adhesive. Seal the edge of the loft hatch.

Loose-Fill Insulation

Mineral-wool pellets - the only loose-fill DIY product - are useful if the joists are not a conventional distance apart or you are topping up existing insulation but not so good for a draughty loft, as they can get blown about.

1. To prevent the material from blocking the airflow, lay pieces of plywood between the joists near the eaves (enough away from the edge so that the plywood itself does not block the airflow).
2. Pour the pellets between the joists.
3. Level the pellets with the top of the joists by resting a piece of plywood across the joists and dragging it along.
4. The loft hatch is best covered with glassfibre or mineral-wool blanket.