Loft Insulation

Roof insulation (as all insulation) generally works by trapping air between fibres or cells and thereby acting as a buffer to slow down the heat transfer. In poorly insulated roofs, 25% of the rising heat from our radiators finds weak spots in the insulation and escapes through the roof instead of heating the house.

Common choices of flat ceiling loft insulation include rolls of mineral wool or sheep’s wool, spray foam and treated, recycled paper. So how do you choose which to use? Firstly find out how effective the insulation is. This is identified by it’s u-value. A u-value is the measure of how quickly a material lets heat escape through it. The lower the u-value, the better it is. Secondly decide if you want to DIY the improvement, based on what is already present in the loft. Thirdly, compare the prices and weigh this up against the other improvements you want to make.

300mm total insulation depth is desired with fibre insulation. Most houses will at least have one layer of 100-150mm mineral wool insulation between the rafters in unconverted lofts. If still ‘fluffy’ and not moisture/rodent damaged, make sure all gaps are filled, but that there is still a 50mm gap at the eaves for air movement through the loft space. This air movement prevents condensation build up.

Spot lights should not be in contact with fibre insulation. Use a simple timber frame around the spot, allowing about 50mm space all round the spot. If your rafters are deep enough, placing a piece of timber across two adjacent rafters will also work. Now place your second layer of 150mm insulation at right angles to the rafters, ensuring no gaps. Start at the eaves (leaving that 50mm gap) and work towards the centre. Do not insulate under the water storage tank, but up to it and even in a frame over it. This will prevent the water freezing in the tank.

Nothing should flatten the insulation as air pockets in the insulation are what make it work. For this reason, it is best to allow for a walkway from your loft hatch to the water tank. There are a variety of good quality rigid board insulations that can be used to insulate the walkway and as they are more efficient, an 80-100mm deep layer placed between the rafters does the same job as 300mm of fibre insulation. Now fix loft boards to the rafters over these insulation boards and you have your walkway. Apply the same technique when creating storage areas in the loft. These rigid insulation boards are not cheap and the walkway can easily cost the same as insulating the whole roof, so if you never go into the loft, use a roll off the 150mm fibre insulation as normal, but be sure to move it out of the way, if access to the loft is ever required, so you do not walk on it.

The benefits of loft insulation will be felt immediately and the typical bungalow can be completed in a day. Measure the outside walls to get your area and then divide by the coverage stated on the insulation to get the number of rolls required (if using fibre/wool insulation).
Don’t forget to insulate the access hatch, else this will become the weak spot. It is also a good idea to place a strip of diy draught proofing around the perimeter and use sliding bolts to secure the hatch in place.
Health & safety precautions must always be strictly adhered to and Ecodev cannot take responsibility for any actions taken as a result of this article. If in doubt, get the relevant help.
Ecodev provides energy efficient designs, energy usage consultations and BER certification.