About three-quarters of all heating in an uninsulated house is lost to the atmosphere, much of it through the roof. Insulating your roof space is a cheap way of counteracting this loss and will noticeably cut your heating bills.
Although insulation against heat loss or gain is now considered an essential requirement for all homes, most houses are not as well insulated as they should be for maximum economy and comfort. Also remember insulation helps keep the house cool in summer.
Regardless of the exact type of material used by the house builder, there is nearly always room for improvement. And because of fast-rising fuel costs, in the long run you will save money whatever the actual cost and quantity of your insulation.
The cheapest and simplest way of insulating the loft is to place insulating material between, or over, the ceiling joists. Various types of natural and man-made material are available, either in rolled blankets or in granulated form. But as there is little to choose between them in terms of effectiveness you should base your choice on the cost and selection of what is available locally.
Mineral-fibre or glassfibre matting and blanket comes in roll form, cut to fit the average space between floor joists. On its own, this is normally adequate for insulating a roof: awkward nooks and crannies can be filled with off-cuts from the rolls once the main insulation is laid.
However, in older houses, where the ceiling joists are likely to be more narrowly spaced than is usual today, laying a standard-width roll material is a laborious task – every bit has to be tucked in at the edges. In this case, loose-fill insulation is much easier to work with.
Loose fill comes in bags, either in granule form or as pieces of loose fibre. Among the materials used are polystyrene, vermiculite – an expandable mica – and mineral wool (rock wool). The latter is also available made up into blanket rolls.
Besides being handy where the space between floor joists is narrow, loose-fill insulates inaccessible corners more effectively than offcuts of rolled material. In draughty lofts however, the granules blow about unless the floor joists are covered over. Insulation problems are often best solved by using roll for the main body of the floor and loose-fill around the edge of the loft. The roll form makes laying an easy job if the separation of the joists is not too narrow.
Whichever type of material is chosen and however this is laid, depth of insulation is the crucial factor. About 100mm is considered a satisfactory compromise between cost and effectiveness. Roll materials are available in thicknesses of about 75mm or 80mm for topping up existing insulation, and of about 100mm for dealing with a loft which has no insulation.
Inspecting the loft gives you a chance to estimate both the quantity of material required and the extent of work involved. To help you move around, and to avoid accidentally damaging the ceiling below, place stout planks across the floor joists.
Under the provisions of this Act, UK residents may qualify for a grant of 66% or £50 – whichever is the less – towards the cost of insulating a loft. The grant is payable by your local authority providing certain straightforward conditions are met. One of these is that application for a grant is made prior to starting any work. The application procedure is simple and approval is normally very quick. Full details can be obtained from your local Council offices.
Of the loft then calculate the overall floor space. Against this, allow for the space taken up by obstacles such as storage tanks and large beams.
If you are considering adding to existing insulation, think in terms of bringing it up to the 100mm depth of loose-fill or blanket insulation recommended for uninsulated roofs.
A typical roll of blanket material of 100mm depth measures about 6.25m in length. ‘Topping up’ rolls, with depths of about 75mm or 80mm, are slightly longer at about 8m – and usually more expensive. The easiest way of working out your needs is to add together the total length of the strips of ceiling to be covered, and divide this by the length of the roll material you are using to do the job.
Add to this number of rolls a generous surplus to take care of trimming and overlap. Remember to allow for the turn up at the eaves if you think this is advisable, and add any extra for the water tank, its piping, and the trapdoor.
If you are using loose-fill material, your requirements are best based on the manufacturer’s own tables and recommendations – on the assumption you will be adding insulation up to the depth of 100mm.
While you are in the loft, inspect the flashings which exclude water at the junction of the roof and other surfaces, such as around the chimney.
On no account should you proceed with insulation if there is any evidence of roof leakage or wet rot, as loft insulation can aggravate both these problems considerably.
At the same time, take a look at the electrics. Wiring perishes in time – especially the older cloth-covered rubber-insulated type – and in any case may not take kindly to repeated knocks while you are laying the insulating material.
All types of fibre insulation give off fibre-dust and some people handling the material may experience skin irritation. This is normally a temporary nuisance and its effects can be minimized by not wearing tight clothing. By rinsing off the hands and body prior to soaping when washing down, you can avoid rubbing the fibres into the skin. Use additional protection, such as gloves and a handkerchief face-mask, when ripping and shaping material in confined spaces.
Planning the work
When laying blanket insulation, it is infuriating to find that every roll ends short of the mark or repeatedly needs cutting at, say, a particularly large roof member – leaving an almost useless off cut.
The most convenient place for rolls to end is away from the eaves – it is difficult enough having to stretch into these inaccessible areas just to push the insulation home. You should therefore plan on working away from the eaves wherever possible. Any off-cuts can be used up later to insulate a more accessible strip in the middle of the loft area.
When you come to lay your insulation, simply follow the set pattern of joists across the roof. Loose-fill material can be levelled to the correct depth using a template made from thick card or wood off-cut. Shape this to fit the space between joists. Like roll materials, loose-fill should be laid working inwards from the eaves. Level the filling towards a clear space in the middle of the loft where addition and removal will present far less of a problem.
Roll material can be cut to length and shape with large scissors or slashed, carefully, with a handyman’s knife. Awkward shapes are more conveniently torn from a supply length. Be generous in the cutting length so that you can tuck in the surplus at the end. Allow 100mm overlap when continuing with a fresh length. Where the two lengths join, either tightly butt the two ends or leave the excess to overlap by about 100mm. Offcuts can be used to fill small gaps between lengths.
In order to prevent the possible build-up of condensation, ventilation space must be left around the edges of the loft. Even so, strong draughts can be prevented by arranging for the roll ends to be turned up between the rafters – allow extra material for this if necessary. In most cases you need insulate only as far as the wall-plate – the barrier between the joists and eaves.
The loft area is finished off by insulating the access trap or door with spare lengths of rolled insulation, glued, tied or tacked in place. Allow the material to overspill when closed, so that any draughts are excluded.
Partial loft conversions
Boarding over the joists and rafters after you have insulated the loft will reduce heat loss still further. Use chipboard to form the new floor and tempered hardboard or fibreboard on the ceiling.
Before covering the rafters, tack or tie lengths of blanket roll to the tile battens in between. If this proves difficult, simply trap each length of roll in place as you pin the ceiling panel over it.
Where the loft has already been partially floored or panelled, remove as much as you can for access then force in loose-fill material.