LOFT INSULATION

Loft insulation is almost certainly the most cost effective energy saving home improvement. If your loft is completely uninsulated it most certainly will be and even doubling or trebling the amount of insulation to the current recommended standard will bring significant improvement in comfort and cost savings. The Energy Saving Trust estimates that a quarter of the heat in an average UK home is lost through the roof.  Insulating your loft is a simple and effective way to reduce your heating bills and you can even do it yourself.  Loft insulation will pay for itself over and over again. There are grants and offers available to help pay for loft insulation - you can search the grants and offers database  on the Energy Saving Trust website  to see what's available or call your local advice centre free on 0800 512 012.
Your house will need an accessible loft with no damp or condensation problems.

Amazing fact from the Energy Saving Trust: If everyone in the UK installed 270mm loft insulation ( the currently recommended amount), we could save around £520 million and nearly three million tonnes of CO2 every year. That's enough to fill Wembley Stadium nearly 380 times.

How insulation works
Heat will always flow from a warm area to a cold one. The colder it is outside, the faster heat from your home will escape into the surrounding air.
Insulation makes it much more difficult for heat to pass up through your roof by providing a layer of material which has lots of air pockets in it. These pockets trap heat, cutting what is known as the U value of the loft.
The U value measures how quickly it loses heat so the lower the U value, the less energy you need to keep your home warm. Loft insulation cuts your loft's U value from around 2.3 (for an un-insulated loft) to 0.16 W/m2K, a reduction of around 95%.

How to insulate a loft

Insulation for lofts will be in the form of mineral fibre or fibreglass matting, loose-fill loft insulation materials which are blown into the loft (usually mineral wool or cellulose fibres- this is  a job for a specialist contractor) or loose-fill loft insulation materials, such as vermiculite and mineral fibre. This is sold in bags and is poured between the joists to the recommended depth.
Mineral fibre (eg Rockwool) or fibreglass matting  (or quilt) usually comes in rolls 400mm (16 inches) wide as this is the standard spacing for ceiling joists in the UK. The quilt can be obtained in various thicknesses most commonly 100mm(4 inches) and 200mm (8 inches). TIP for DIYers: look out for special offers- rolls of 200mm quilt can be cheaper per square metre than 100mm.
The insulation value of loose fill insulation which is sold in bags for DIY use, is similar to quilt. DIY loose-fill loft insulation materials, such as vermiculite and mineral fibre, are sold in bags and can be poured between the joists to the recommended depth. They are easier to install than the quilt  if easier if the joists are not regularly spaced or spaces are irregular.
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Watchpoint 1:
Ceiling joists in UK houses are generally 100mm (4 inches) deep. This was fine when insulation of 100mm or less was the norm. But current standards  of 270mm mean that insulation will not sit between the joints. Professional installers will often lay 100mm between the joists and the additional rolls of quilt at right angles to the joists. This makes access to the loft difficult and there is a very real danger of accidents from falling through ceilings which are not capable of carrying a person's weight. The answer is to lay additional timber joists over the old ceiling joists to increase the depth, but this is more expensive. A compromise is to put extra depth of joists around the loft hatch in an area that might be accessed for storage and to simply roll out quilt over the rest.
Watchpoint 2:
Your loft will now be colder than before so make sure that any cold water tanks and pipes are insulated, but ensure that there is no insulation under the tank, so that heat from below can prevent freeze ups.
Watchpoint 3:
Electric wiring was usually laid loose over ceilings. Cables give off a very small amount of heat which can be dissipated in the loft. But if they are covered by insulation, they could become hot and possibly start a fire. With insulation between the joists, there was often enough slack cable to move them to the tops of the joist which were still visible. If there is not enough slack cable, an electrician will have to adapt the wiring.  Many house also have recessed low voltage downlighters. These also dissipate heat upwards and covering them will cause them to over heat. Proprietary  covers should be fitted or boxes made up from plasterboard  to form an airspace around the light fitting.
Watchpoint 4:
The loft above the insulation should be ventilated to avoid condensation. Some roofs have gaps at the eaves which provides cross ventilation. Most roofs have felt or boarding under the tiles, but if the underside of the tiles is visible there is usually plenty of ventilation. Care should be taken to ensure that the insulation does not block ventilation at the eaves and if no vents exist, it may be necessary to install proprietary eaves vents.
Watchpoint 5:
Installing loft insulation is within the capability of most DIYers, but fibre quilts will cause irritation to the skin. Always wear a suitable dust mask (ask at the builders merchant of DIY store for the correct mask for the job) and overalls and gloves. Tip: put elastic bands around the cuffs and wash clothing separately after use.

What about flat roofs?
An insulated flat roof will either be a ‘cold roof' or a ‘warm roof' depending on the position of the insulation relative to the construction of the roof. In a cold roof, the insulation will be at the ceiling level, meaning that the structure of the roof will be above the insulation, on the cold side. In a warm roof, the insulation is placed immediately below the roof covering, so the roof structure is warm. Most modern flat roofs are  ‘warm roofs' because these are less prone to condensation within the roof deck. If the insulation s at ceiling level, the spaces above should be ventilated to prevent condensation. Special care should be taken in flat roofs over kitchens and bathrooms.  Condensation can lead to rot and premature failure of roof timbers.
It is very disruptive to insulate an uninsulated flat roof and the opportunity to insulate is usually taken when the waterproof roof covering needs to be replaced, although some insulation can be laid above the waterproof covering.