How Much Loft Insulation Should I Install to Make My Home Energy Efficient?

Energy Performance Certificate (EPC) ratings give an idea of how energy efficient your home is. Insulating (lagging) the loft space of your home is one of the cheaper and easier ways of improving the dwellings energy efficiency and gaining a higher Energy Performance Certificate (EPC) rating. This article looks at how much insulation you need, and at some of the different materials you can use.

About 25% of total heat loss is transmitted through a properties roof, yet the loft space is one of the easiest areas to retro fit insulation to. Everyone is aware that lagging your loft is a good idea, yet people often underestimate the thickness of insulation that is required to significantly increase energy efficiency.

The amount of heat transmitted through a building’s roof/floor/wall is described by its U-value. The U-value records the energy lost in Watts per metre squared per degree Celsius (kelvin), and is recorded in units of W/m2.k The lower a materials U-value the better an insulator it is. To meet current Building Regulations a properties roof must have a U-value of no more than 0.16W/m2.k

For the EPC survey any property that has less than 150mm of mineral wool (or equivalent) lagging will be recommended to increase this to at least 250mm, however current Building Regulations call for at least 270mm of mineral wool insulation for new builds (to achieve a U-value of 0.16W/m2.k). When retrofitting insulation it would be quite reasonable to aim for somewhere between 300mm and 450mm thickness to achieve a high level of energy efficiency.

These measurements are all based on mineral wool insulation, such as Rockwool, however different types of lagging have different properties, so the required depth will vary. For example phenolic foam insulation such as Kingspan only needs to be half the thickness of mineral wool insulation such as Rockwool to achieve the same U value.

Nowadays there is a wide range of different insulation products available on the market besides the standard mineral wool and phenolic foam stuff. Many people are now opting for lagging made from natural fibres instead of oil based synthetic products.

Sheep Wool is rapidly growing in popularity as a lagging material, and is now available in many of the big high street DIY stores. It is a natural and sustainable product is totally non-toxic and does not irritate the skin, making it much nicer to work with than mineral wool. It is hygroscopic, meaning that it can absorb and then release up to 35% of its own weight in water from the surrounding atmosphere, helping regulate humidity and protect surrounding timbers. Whilst absorbing water wool releases energy in the form of heat, warming the surroundings. The reverse happens as it releases moisture during warmer seasons, generating a cooling effect. On top of this it is naturally highly fire resistant.

Hemp lagging such as Hemcore provides all the same benefits as sheep wool, and on top of this it is extremely good at absorbing sound, making it particularly good for insulating between floors, or in urban areas where noise pollution is an issue.

There are many other products on the market today, both natural and synthesized, so if you spend some time looking around you are bound to find something to suit your individual circumstances. The key thing is to make sure that you use enough of it to be really effective and to leave your roof with a U value of 0.16W/m2.k or less. The manufacturer of your product of choice will be able to advise you on the depth of insulation required to achieve this. When purchasing your insulation you should really see it as an investment, as once installed it should last for as long as the house, and will be reducing your energy use and therefore saving you money the whole time.