Loft Insulation Advice and Tips

Advantages Of Good Loft Insulation

Reduced oil, gas or electricity bills
Reduced carbon footprint
House is warmer in winter
House is cooler in summer
Help prevent internal condensation
Improved home energy efficiency rating
Reduced chance of pipes freezing in winter
Reduced outside noise such as traffic
Cost recovered in between one and two years

General Information

Insulating the loft is one of the best things you can do to reduce heating costs which does not cost vast sums of money. Around 25% of heat is lost through the un insulated ceilings of a house (even more if you have a bungalow) and can pay for itself in under a year. Originally our first house had 150mm of fairly old insulation over most of the roof area. Over three years this was increased to around 350mm using 'Space Blankets' in all areas that were not floored (around half the total loft area). Space Blankets are simply fibre matting encased in a plastic bag with a foil layer to reflect heat These blankets are available in various lengths with thickness of between 100mm and 300mm. Apart from reducing heat loss loft insulation helps achieve a more even heat distribution throughout a room and has the added benefit rooms tend to stay cooler in summer. I am not a great fan of the loose fill insulation that is available since it can blow about in high winds and tends to find any holes in the ceiling. We estimate we recovered the cost of doing this in under two years.

In our second house we started again with around 150mm of insulation with the central part of the loft floored with loose boards. We now have 400mm over two thirds of the loft and 250mm plus three quarter inch chipboard flooring in the central area. Additional insulation was added at the same time to the two water tanks in the loft and all the various water pipes to reduce the risk of freezing. These changes have made a noticeable difference in the bedrooms - being warmer in winter and cooler in summer. The house also takes noticeably longer to cool down when the heating goes off. It took just eighteen months in reduced heating oil consumption to recover the cost..

Which Insulation To Use And How Thick SHould It Be?

This guide on the thermal properties and environmental ratings of loft insulation from the energy saving trust will provide information and guidance.

Installing Insulation

Insulation works best if it is laid in two layers - one layer between the rafters and a second layer across the rafters with a total thickness of around 350mm. Don't push the insulation right up to the edge of the roof otherwise you will stop the roof breathing causing problems with condensation, a gap of 25mm to 50mm is sufficient. Electrical cables should be routed over the insulation, the reason for this is that cables can run warm in use and insulating them will increase any heating effect. Be extremely careful when dealing with cables since it is quite common to come across poorly insulated connections in the loft especially around light fittings as I have found out the hard way. Pipes can safely be left under the insulation. Hot areas (such as down lights) need a safety gap around them of at least 75mm to reduce the danger of overheating and fire. It is possible to buy proper protective screens from major DIY outlets but they are relatively expensive. If the loft has flooring it should have at least 250mm of insulation under the flooring laid between the rafters. Don't insulate under water tanks otherwise there will be an increased risk of them freezing up.

The thicker the insulation the less heat gets through,, the optimum is somewhere around 350 to 450mm of uncompressed insulation for the UK, colder climates will need more.

It is important not to compress the insulation, especially under boarded areas as this reduces the insulation properties considerably since the insulation works by trapping small pockets of air as well as being an insulator. It is vital the loft insulation is kept dry, wet or damp insulation is particularly ineffective.

It is worth making sure all pipes in the loft (especially those not covered by the insulation) are also properly insulated and that tanks are wrapped in insulating jackets since the loft temperature will be lower after insulation with the consequent risk of freezing

Sloping Ceilings And Loft Conversions

If you have a room or rooms in your loft space then it is likely there will be sloping ceilings. It is difficult to achieve good insulation since to stop condensation there needs to be a ventilated air gap of at least 50mm between the insulation and the tiling felt. The best way to get around this problem, assuming there is enough head room is to fit a false ceiling to support a second layer of insulation.

Unexpected Consequence - Water Tanks Freeze!

One often unexpected consequence of improved loft insulation is that water tanks and pipes above the insulation freeze up in winter leading to the possibility of burst pipes or overflowing tanks due o frozen ball valves even though there is no insulation beneath the tanks. All water tanks in the loft need to be properly insulated to protect against this. The best way to do this is build a thin wood box around the tank right down to the loft floor (especially with raised tanks). The box should have a removable lid and there should be a gap of around 300mm (or a close as possible) between the box walls and the tank sides and top. The gap is filled with loft insulation making sure there is no chance of it getting wet. Insulate the lid in the same way by making the lid double skinned to contain the insulation. Do not insulate under the tank. This also has the effect of reducing heat loss through the ceiling a bit. Remember to insulate all pipes above the insulation especially vertical pipes to and from tanks. See insulating pipes for more information on this subject.

Odd Tips

Make sure that all pipes and cables entering the loft from rooms below are properly sealed so that warm air cannot leak into the loft.
Ensure that ceiling mounted light fittings are properly sealed against draughts. Don't forget to insulate the loft trapdoor and seal it against draughts.
If the loft has windows or skylights make sure they fit properly and are sealed against draughts, a thick curtain can work wonders with single glazed windows and skylights.
Leave air vents clear to avoid problems with condensation and damp
Make sure the loft trapdoor has been properly draught proofed

Precautions

Mineral wool insulation can irritate the skin and throat and should be installed with care. Wear a suitable dust mask and protective gloves to avoid irritation.
Be extremely careful when dealing with electrical cables, if in doubt seek advice.
Do not try to work standing on the joists, use a piece of board reaching across three joists that is stable to kneel safely upon.
Light the work area properly, if there is no lighting installed in the loft, run an extension lead up into the void and hang a suitable light from a beam.
Open loft insulation packs in the loft