Insulation means saving energy, on every level, from the personal to the global. As people become increasingly conscious of the importance of environmental issues, one of the greatest contributions everyone can make is to cut down on unnecessary waste of fossil fuels, and to reduce the amount of carbon dioxide released into the atmosphere by burning them. This means making more efficient use of energy, and insulation has a big part to play in this. It will save you money too.
Insulation is a means of stopping heat transfer from a warm area to a cold one. In this country, the outside air temperature is below what most people regard as a comfortable figure for much of the year, so we need to heat our homes up to compensate for this.
The problem is that all the materials we traditionally use in house-building conduct heat to a greater or lesser extent. Wood is a fairly good insulator, brick an average one and glass is downright poor, as anyone who has sat next to a window on a cold winter’s day will testify.
Worst of all, providing well-insulated homes has until comparatively recently been a very low priority, both for housebuilders and for the legislators who frame the Building Regulations with which builders must comply.
However, at last the tide is turning, and the latest amendments to the Building Regulations require much higher standards of insulation than ever before for new buildings. They have also belatedly recognized the problems that over-insulation can cause as far as condensation is concerned, both inside the house itself and also within the building’s structure. This means that new houses may cost a little more, but will consume up to 20 per cent less heat.
Unfortunately, this will not help those people living in older properties, many of which were originally built with no thought to their insulation performance at all. Of course, over the years various attempts will have been made to insulate houses like these, but what was deemed adequate ten or twenty years ago is well below par nowadays. Therefore it will certainly pay ory°u to check out your existing insulation, with a view to improving it for the future.
Before thinking about individual types of insulation, it is important to understand the concept of cost-effectiveness. Insulation costs money to install and can benefit you in either of two ways. It can enable you to reduce your heating bills, since your home will waste less heat and you can maintain the same internal temperatures without burning so much fuel. The annual saving that you make as a result will ‘pay back’ the cost of the extra insulation.
If you are also considering replacing your heating system, having better standards of insulation may also mean you can specify a less powerful (and less expensive) boiler and smaller (or fewer) radiators, which will be an indirect one-off saving, but valuable nonetheless.
Alternatively, you can enjoy higher internal temperatures than before without increasing your heating bills, but in this case there will be no direct savings, just a better degree of comfort.
As a guide to cost-effectiveness, loft and hot-tank insulation and draughtproofing score the highest, while double glazing and professionally installed insulation are the least cost-effective. Other insulation measures fall somewhere between the two.
If you have a pitched roof, and you use the loft space just for storage, insulating the loft floor is one of the easiest and cheapest improvements you can carry out. You do this by filling the spaces between the joists with insulation material, either glass fibre or mineral wool, sold as blankets by the roll or in slab form, or else loose-fill material (vermiculite, a lightweight expanded mineral, or shredded mineral wool fibres), sold in bags. You can also have loose-fill insulation, usually mineral wool or fireproofed cellulose fibres, blown into the loft by specialist contractors.
Blanket and slab materials are generally easier to handle than loose-fill types unless your loft is awkwardly shaped, contains a lot of obstructions or has irregular joist spacings. Whichever type you choose, you should aim to lay it to a depth of 100mm if you already have some fairly recent loft insulation, laying it on top of the existing material. Increase the depth to 150mm (6in) in uninsulated lofts, or those with just the old and woefully inadequate lin
thickness demanded by Building Regulations.
Apart from being awkward to handle, loose-fill materials have another drawback. To be as effective as blanket types, they need laying to a greater depth, at least an extra 25mm (lin). With few ceiling joists being deeper than about 150mm (6in), there is nothing to contain the insulation unless you are prepared to fix battens along the top edge of every joist. Therefore, check your joist depth before using this type.
How To Insulate An Attic
Before you start to actually lay the insulation, there are several things to check or to attend to. The first is to clear the loft of stored items so you have room to work; the best practical solution is to stack everything in one half of the loft, lay the insulation, then move the stack to the insulated end while you tackle the rest of the loft.
The second thing to check is that you have adequate loft ventilation. Next, to minimize the incidence of condensation in the loft, you should block up any gaps and cracks in the ceiling below which could allow warm, moist air into the loft space. It is a good idea to vapour-proof the bathroom ceiling, either by painting it with a solvent-based paint, or by laying polythene sheeting on the floor of the loft above it before you put down the insulation.
With blanket types, start work at the far side of the loft. Place the roll near the eaves and unroll the end, pushing it into the eaves as far as the wallplate on which the ceiling joists rest. Then roll out the blanket, tucking it lightly down between the joists but not compressing its thickness unduly. At the other side of the loft, simply tear the blanket across with your hands to the length you want. When one roll runs out, butt-joint the next up to it, and carry on as before.
With slabs, use a kitchen knife to cut each one down to match your joist spacing, and then simply lay the slabs between the joists, butting them tightly together. The slabs are 50mm thick, so add a second (or even a third) layer on top of the first to get the thickness you need.
With loose-fill material, simply pour the insulation out on to the loft floor and spread it evenly between the joists. Fluff mineral wool types up with your fingers; use a spreader to level off granular types.
As you lay the insulation, lift wiring above it wherever possible to prevent the risk of the cables overheating underneath it. If polystyrene granules have been used in the past to insulate the loft floor, it is a good idea to move them from any areas where cables are present, since contact with the granules can cause eventual deterioration of the cable sheathing.
When you have completely insulated the loft floor, secure a piece of insulation blanket to the top surface of the loft hatch, and draught-proof the rebate on to which it closes. Remember to insulate the cold-water storage tank, the feed-and-expansion tank that tops up your heating system, and also any exposed pipework within the loft.
As the importance of loft insulation became apparent during the 1960s, installation instructions exhorted householders to stuff the blankets well into the eaves to eliminate draughts. Thousands of householders did so, only to discover years later that doing so had caused totally unforeseen problems with rot in their roof timbers. Because the natural ventilation of the loft space had been cut down by stuffing insulation into the eaves, the warm, moisture-laden air rising into the loft from the house below was trapped. Fitting the insulation had made the loft space considerably colder, so the moisture vapour was condensing to water on the roof timbers (and also on the insulation, saturating it in many cases and so making it useless as insulation). There was no ventilation to dry the timbers out, and it did not take long for rot spores to begin to develop, leading in some cases to serious damage to the roof structure.
It is now realized that good ventilation is essential for all roof spaces, and the current Building Regulations contain de-
tailed provisions for ensuring that all new pitched and flat roofs are adequately ventilated. Existing roofs should be checked to ensure that they are ventilated to the same standard if rot problems are to be avoided.
Pitched Roof Insulation
With pitched roofs, ensure that insulation is pulled back clear of the eaves. It is a good idea to install small V-shaped eaves vents at opposite sides of the roof, to hold the insulation away from the underside of the roof slope and allow air to circulate over the timbers.
In addition, you should create ventilation openings in the underside of overhanging eaves, either by drilling holes in the soffit with a wood bit and covering them with fine mesh to prevent insects from entering, or by making larger cutouts so you can fit proprietary slot ventilators into the holes. It is also a good idea to install air-bricks in gable walls.
If you have rooms in your loft, or plan to have a loft conversion at some future date, it is obviously a waste of effort and materials to insulate the loft floor. Instead, you should insulate the underside of the roof slope and the walls of the loft rooms themselves, so that you can benefit from heat rising into the loft from the house below.
You can insulate the roof slope in an unconverted loft in one of three ways: by fitting loft insulation blanket, insulation batts or rigid polystyrene boards between the rafters; by stapling paper-faced insulation mat to the underside of the rafters; or by fixing insulating plasterboard directly to them. If you use insulation blanket, batts or boards, you need a polythene vapour barrier on the room side of the insulation to prevent moisture vapour passing into the cavity behind it and possibly causing rot in the roof timbers. You then have to fix up sheets of plasterboard to form the walls and ceiling of the loft rooms. Insulating plasterboard, which can also be used to line the walls of the new loft rooms, contains a vapour barrier between the board and the insulant, and so kills two birds with one stone.
The vital point to remember when insulating a roof slope is that ventilation of the roof slope timbers — the rafters and tiling battens — is just as important as having good air flow over eaves timbers. This means leaving an air gap 50mm (2in) wide between the insulation and the underside of the tiles, slates or roof underfelt open at eaves level.
If you already have a loft conversion, adding insulation is more difficult, especially above sloping ceilings. Here, so long as you have access to the eaves, you may be able to slide cut-to-width slabs of rigid polystyrene up into the space between the room ceiling and the roof slope, and also to insulate the room walls from the loft side with slabs of polystyrene set between the wall studs. If you do not have access to the eaves spaces, the only practical solution is to line the walls and ceilings of loft rooms with insulating plasterboard.
If you plan to use insulation blankets or batts to insulate the underside of the roof slope, the most important thing is to maintain the 50mm air gap between the insulation and the underside of the roof slope.
So choose a thickness of material that is at least 50mm less than the rafter size (50mm thick for 100 x 50mm rafters, for example).
With semi-rigid batts, it is usually possible to wedge the slabs firmly in place between the rafters, and then to fit the polythene vapour barrier when all the insulation has been placed. However, with the more flexible blanket types, it is simpler to work downwards from the ridge and to fix insulation and vapour barrier at the same time. Start by securing the top end of the first length of blanket to the side of the ridge, unroll it down to the eaves and cut it to length. Fix a second and third length alongside it in adjacent bays. Then staple the top end of the vapour barrier to the ridge board, and work down the rafters towards the eaves, stapling the vapour barrier to the rafters to hold the insulation blanket in place between them.
Paper-faced insulation is easier to handle than plain blanket, since it has paper flanges at each side which you staple to the undersides of the rafters. You again need a vapour barrier over it.
With polystyrene boards, careful cutting and regularly spaced rafters may allow you to wedge individual slabs in place between the rafters. However, it may be quicker to staple slim battens to the sides of the rafters first, and then to secure the slabs in place against the battens with nails tapped into the rafter sides. Then, you can staple the vapour barrier in place as before.
Insulating Room Walls
You can use the same techniques for insulating the walls of rooms built in the loft, by placing blankets, batts or polystyrene boards between the timber studs forming the walls. Make sure a vapour barrier is included on the room side of the insulation, and check that insulation is lifted from the loft floor as the rooms are constructed.
Alternatively, you can line the ceilings and walls of loft rooms with insulating plasterboard. Cut individual boards to size, then nail them directly to the room’s timber framework.
Insulating Flat Roofs
Existing flat roofs are more difficult to insulate than pitched ones because you cannot get at the voids in the structure very easily. You can tackle the job in one of three ways; the one you choose depends largely on the state of the existing roof surface and the ceiling beneath it.
As with pitched roofs, the new Building Regulations lay down strict requirements for both the insulation and ventilation of new flat roofs, but there are a great many flat roofs in existence that have both inadequate insulation and non-existent ventilation. Therefore, if you have a flat roof as part of your property, it will pay you to consider ways of improving its performance in both of these categories.
What to do
You have three main options as far as improving the insulation of an existing flat roof are concerned.
Option 1 involves laying insulation above the existing roof surface and adding a new waterproof surface, creating what the ex-
perts call a warm roof deck. You can buy special composite insulation boards for this, complete with a bonded-on layer of roofing felt. These are simply bonded to the existing roof decking and then felted over to complete the new roof surface. It is worth considering this option chiefly if your roof is in need of resurfacing anyway. An alternative is to lay insulation boards over the existing roof surface and then to top it off with lightweight slabs to hold the insulation in place.
Option 2 involves fitting insulation batts or polystyrene slabs between the roof joists. If the fascia boards around the edge of the roof can be removed to allow access to the spaces between the roof joists, then rigid polystyrene boards can be slid into place from the eaves. It is unwise to use batts in this situation, since there will be no vapour barrier above the ceiling and moisture vapour could rise into the ceiling void, condense and saturate the insulation. If the fascias cannot be removed, the existing ceiling below the flat roof will have to be taken down so that insulation can be placed between the joists. A layer of polythene is then stapled to the underside of the joists to act as a vapour barrier. Finally, a new plasterboard ceiling is fixed to the joists. With this method, it is essential to leave a 50mm airspace between the top of the insulation and the underside of the roof deck itself, and to provide ventilation holes on opposite sides of the roof; this guarantees a cross-flow of air through the airspace, preventing condensation from leading to rot in the roof timbers. Choose this option if the roof is in good condition and you do not mind removing the fascia boards or the room’s ceiling.
Option 3 is the least disruptive, and involves adding insulation beneath the existing ceiling surface. You can do this in one of two ways. The first is to nail up battens, place insulation blanket, batts or polystyrene slabs between them, add a polythene vapour barrier and then fit a new layer of plasterboard. The second (and the simplest of all) is to fix a layer of insulating plasterboard directly to the existing ceiling.