Ceiling And Wall Insulation Methods That Work

In loft rooms, in flats and maisonettes, and in houses with flat roofs, it may not be possible to go into the loft to lay insulation between the ceiling joists. The solution is to fix insulation to the ceiling.

The simplest method is to stick expanded polystyrene or insulating board tiles directly to the ceiling. These tiles should be at least 13mm thick — the thicker the better. Wash the ceiling with sugar soap and scrape off any flaking paint. Ensure good adhesion by painting the ceiling with stabilising solution.

Mark out the ceiling carefully so that if the tiles need to be trimmed this can be done evenly around the perimeter. Fix whole tiles first, working adjacent to the longest wall. Spread adhesive over the back of each tile and then press it into place

firmly against the ceiling. With polystyrene tiles, a square of wood makes a useful presser that avoids finger identations being made in the surface of the tiles.

Using thermal board — plasterboard and a vapour-check membrane bonded to an expanded polystyrene backing — it is possible to make a new insulated ceiling directly beneath the old one. Use a bradawl or narrow screwdriver to probe the old ceiling to discover the joist positions, then pencil them in. Simply nail up the thermal board using long plasterboard nails into the joists. Use jointing tape and filler to hide the cracks between adjacent boards.

Another method, which lowers the ceiling further but gives more effective insulation, is to fix timber battens beneath the ceiling, fixing through the battens into the ceiling joists. Battens should be the thickness of the desired insulation and they can be fixed to coincide with the joists, or to run at right-angles to them. A good size for the battens is 50 x 50mm. Screw the battens to the ceiling to avoid dislodging the plaster. When fixing the battens, use a spirit level and straight board to check that the surface of each one is level, and if necessary pack them out with scraps of hardboard.

Insulating material is fixed between the timber battens and can be expanded polystyrene slabs to make up the 50mm thickness, or insulating matting. The matting can be temporarily supported by tacking polythene sheet to the battens. The polythene forms a useful vapour barrier.

Finally, finish off the ceiling by nailing up sheets of thermal board, or use ordinary plasterboard, insulating fibreboard, or tongued and grooved timber boards.

Another method is to fix a suspended ceiling but for maximum insulation the infill panels should be of the insulating type rather than the usual translucent ones.

Heat loss from walls

One third of the heat lost from a house can go through the walls and effective insulation can reduce this figure by two-thirds.

First it is necessary to ascertain the type of outside walls used in the house. Older houses (those built before about 1920) probably have solid walls, distinguishable because they are likely to have half-bricks showing in the pattern of bricklaying. Newer houses are built with cavity walls — a double skin of bricks with a 50mm wide cavity between them. This type will have only full bricks showing in the outer wall. They are better at saving heat than solid walls, but heat is lost due to convection within the cavity; this space can be filled.

Cavity wall insulation

This is not a DIY job, but it can be well worth having the job done in terms of improved comfort and lower fuel bills. The savings in heat will take from five to ten years to pay for the cost of installation.

There are basically three types of cavity infill — urea formaldehyde foam, mineral wool fibre, and expanded polystyrene

timber battens previously fixed to the wall but where the wall surface is flat and firm it is better to bond the thermal board directly to the wall using special thermal board adhesive.

The wall should be clean and dry, skirting boards, door architraves and other decorations removed, and electrical outlet boxes repositioned to take account of the thickness of the boards (22 to 65mm).

The adhesive is applied to the walls in bands, the board is pressed into place and then fixed additionally with nine spaced out wallplugs and zinc-plated screws to assist in maintaining the lining in the event of a fire.

It is well worth using this technique on out-buildings, particularly ones used as workshops, or even on a garage.

Beads. In each case the job involves drilling holes in the outer wall and injecting or blowing the insulating material into the cavity.

Get quotations from reputable contractors who will either carry out the work to British Standards 5617 or 5618, or can show a current Agrement Board Certificate for their work.

Lining with thermal boards

There are ways of insulating solid walls on the outside (insulation under cladding, for example), but generally it is best to do the work on the inside as this is cheapest and does not alter the external appearance of the house. Remember that only the external wall in a room needs to be treated.

One of the best lining materials is thermal board which consists of plasterboard backed with expanded polystyrene, and with a polythene vapour-check membrane between the two. After fixing, the joints have only to be filled to give a flat wall surface equal to that of plastering.

The thermal board can be nailed to Lining with insulating boards by using a gap-filling adhesive or contact adhesive other materials, like plain and painted insulating fibreboards, may also be fixed direct to sound, solid walls using an adhesive.

Gap-filling adhesives are applied in the form of a narrow bead around the perimeter of each board and at regular intervals across it. The board is pressed into place and held for a few minutes until the adhesive hardens. Contact adhesive is suitable for flat walls, and is applied in wide bands on the wall and on the back of the boards. The adhesive is allowed to dry and then the board is pressed on to the wall. The boards can, of course, be cut to shape or around any features.

Lining on battens

A good method of lining an uneven solid wall is to use various wallboards or timber cladding fixed to a framework of timber battens screwed to the wall and lined with insulating material. The method is more costly and time-consuming than using thermal board, but it allows greater flexibility in the choice of wall finish.

Clear the wall of skirting boards, door architraves and other decorations, and also remove electrical fittings after isolating them at the main switch. Using wallplugs and screws, fix up a framework of 50 x 25mm battens to the wall with the 50mm wide face against the wall. The framework should go around the perimeter of the wall, door and window openings, and the vertical battens should be positioned to support the edges of the wallboards when fixed. To ensure the centres of the boards are well supported, also fix a number of 38 x 25mm intermediate battens between the main framework. Improve insulation by covering the wall in aluminium foil or foil-backed building paper held under the battens as they are fixed. If the wall is not flat, pack under the battens with pieces of hardboard. Use a straight edge to check that the face of the batten framework is flat. Fill the spaces between the battens with slabs of 25mm thick expanded polystyrene, or use insulating matting. Now fix in place the chosen wallboards or timber cladding to finish the job.

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