How to Insulate a Loft – Loft Insulation Guide

Insulating the Loft

Approximately a quarter of the heat lost from an average house goes through the roof, so preventing this should be one of your priorities when it comes to insulating your home. Provided that you are able to gain access to your loft space, reducing heat loss through the roof is simply a matter of laying insulating material between the joists, which is cheap, quick and effective.

On inspection, you may find that your roof space has existing but inadequate insulation — at one time even 25mm (1in) of insulation was considered to be acceptable. It is worth installing extra material to bring the insulation up to the recommended thickness of 150mm (6in).

How to Insulate a Loft
Essential tools:

For blanket insulation:

  • Large pair of scissors
  • Sharp kitchen knife

For loose-fill insulation:

  • Broom
  • Hammer
  • Home-made spreader
  • Scissors
  • Screwdriver


Where to Start

Check roof timbers for woodworm or signs of rot, so they can be treated first. Make sure that all the electrical wiring is sound, and lift it clear so that you can lay insulation beneath it.

The plaster or plasterboard ceiling below will not support your weight – you therefore need to lay a plank or two, or a chipboard panel, across the joists so you can move about safely.

If there is no permanent lighting in the loft, rig up an inspection lamp on an extension lead and move it wherever it is needed — or hang the lamp high up to provide an overall light.

Most attics are very dusty, so wear old clothes and a gauze face mask. It is also wise to wear protective gloves, especially if you’re handling glass-fibre batts or blanket insulation, which may irritate sensitive skin.


Laying Blanket Insulation

How to Insulate a Loft Blanket insulation is made from glass fibre, mineral fibre or rock fibre — it is widely available in the form of rolls that fit snugly between the joists. Before starting to lay blanket insulation, seal gaps around pipes, vents or wiring entering the loft with flexible mastic.

Remove the blanket wrapping in the loft (the insulation is compressed for storage and transportation, but swells to its true thickness when released).

Begin by placing one end of a roll into the eaves — make sure you don’t cover the ventilation gap (trim the end of the blanket to a wedge shape so that it does not obstruct the airflow).

Unroll the blanket between the joists, pressing it down to form a snug fit — but don’t compress it. If you have bought a roll that’s slightly wider than the joist spacing, allow it to curl up against the timbers on each side.

Continue at the opposite side of the loft with another roll. Cut it to butt up against the end of the first one, using either a large kitchen knife or a pair of long-bladed  scissors. Continue across the loft till all the spaces are filled. Trim the insulation to fit odd spaces.

Do not cover the casings of light fittings that protrude into the loft space. Also, avoid covering electrical cables in case they overheat — lay the cables on top of the blanket or clip them to the sides of the joists above it.

Do not insulate the area immediately below a cold-water cistern (the heat rising from the room below will help to prevent freezing during the winter).

Cut a piece of blanket to fit the cover of the entrance hatch, and attach it with PVA adhesive or with cloth tapes and drawing pins. Fit foam draught excluder around the edges of the hatch.

Insulating with glass-fibre blanket

Place the end of a roll against the eaves and trim at an angle or fit eaves vents. Lay rolls between joists, and trim ends to fit with scissors. Clip cables to joists or lay them over the blankets. Don’t place insulation below a cistern. Insulate cistern and cold-water pipes separately.


Laying Loose-Fill Loft Insulation

Loose-fill insulation in either pellet or granular form is poured between the joists, up to the recommended depth of 150mm (6in). Exfoliated vermiculite, made from the mineral mica, is the most common form of loose-fill insulation on the market — but other types, such as mineral wool, cork granules and cellulose fibre, are also available. Run electrical cable over the insulation or along the joists as suggested for glass-fibre blankets.

Seal all gaps around pipes and vents to prevent condensation.

When laying loose-fill insulation, to avoid blocking the eaves, wedge strips of plywood or thick cardboard between the joists, or install proprietary eaves vents as recommended for blanket insulation.

Pour insulation onto the ceiling and distribute it roughly with a broom. Level it with a spreader cut from hardboard. If the joists are shallow, nail on lengths of wood to build up their height to at least 150mm (6in), if only to support walkway boarding in specific areas of the loft.

Cover cold-water pipes with cardboard before pouring insulation.

To insulate the entrance hatch, screw battens around the outer edge of the cover, then fill with granules and pin on a hardboard lid to contain them.

Lagging cold-water cisterns

To comply with current bylaws, your coldwater-storage cistern must be insulated. Buy a Bylaw 30 kit, which includes a jacket and all the other equipment that is required. Insulate your central-heating expansion tank at the same time.

Insulating the pipes

If there are cold-water pipes running between the joists, lay blanket insulation over them to prevent them from freezing. If that is not practical, insulate each pipe run separately with foamed-plastic tubes.

Before pouring loose-fill insulation, lay a bridge made from thin card over cold-water pipes running between the joists, so they will benefit from warmth rising from the room below. If the joists are shallow, cover the pipes with foam tubes before pouring the insulation.

Spreading loose-fill insulant Seal gaps around pipes and vents. Use strips of plywood to prevent insulant from blocking ventilation, or fit eaves vents. Use a spreader to level the insulant, having covered pipes with a cardboard bridge. Insulate and draughtproof the hatch cover.

08. December 2010 by admin
Categories: Insulation | Tags: , , | Comments Off on How to Insulate a Loft – Loft Insulation Guide

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