Which Material Should I Use to Insulate My Loft?

In the UK hundreds of thousands of people are insulating their homes each year to cut their energy use. One of the most important parts of the house to insulate is the loft, where the average home can lose up to 25% of its heat. If you insulate your loft well, you can save over a tonne of CO2 each year, and around £110 a year off your heating bill, according to the energy saving trust. With such savings, insulating your loft can pay back the investment required in under 2 years.

There are many different materials to choose from when thinking about insulating your loft. The most popular type of material is mineral wool, which as the name suggests is derived from naturally occurring minerals. Popular brands include ‘Rockwool’. A similar option is glass wool, which is made from recycled glass and sand that are heated and spun into fibres. Popular brands include ‘Knauf’ and ‘Space Blanket’.

You can also use organically derived materials to insulate your loft. An increasingly popular choice is sheep’s wool, which comes in slabs made of fleece offcuts which are treated to make them fire resistant and insect-proof. ‘Thermafleece’ is an established brand. Other options include board from compressed wood waste, material made from recycled and scrap cotton, flax (brands include ‘Isovlas’), rolls or slabs of hemp (brands include ‘Thermo hemp’), and finally cellulose / paper (brands include ‘Excel Warmcel’ and ‘Homatherm’).

With so many options, how should you choose? There are a number of different things you may want to take into consideration:
- Insulation performance: this is measured by the material’s ‘U value’, which is a measurement of how fast the material conducts heat (or cold)
- Cost: in £s per square metre and
- Qualification for government subsidies: in the UK, most people can get large government grants that cover much of the cost of insulating their home, but only when using certain materials
- Renewable source material: is it made from material that will grow back?
- Embodied energy: how much energy has been used to produce and transport the material?
- Ease of disposal: is it biodegradable or recyclable?
- Other considerations, such as its ability to deal with moisture, and also how easy and safe it is to install

All the materials listed above have similar insulation performance, with materials like paper and wood performing slightly better than mineral wool. Sheep’s wool is supposed to be particularly effective at keeping buildings cool in summer, because it releases moisture to keep cool. This can reduce peak temperatures by up to 7 degrees centigrade when compared to other materials.

The prices of these materials are also very similar, with the exception of wood, which can be double the price of the others. Therefore in terms of straight performance and cost, there is not much to distinguish the different materials.

However, in the UK, mineral or glass wool is the only material offered under the various different government grant and discount schemes. Under these schemes you can get your loft insulated by a professional contractor at a heavily discounted price, which often actually makes it cheaper than DIY. Provided your building is suitable, everyone can qualify for these discount schemes in the UK, and so for most people their choice of material is bound up with accessing these grants and using a professional contractor.

For those determined to go the DIY route, there are some other considerations that can help you decide on one material versus another. For example you may be concerned about what happens to the material at the end of its life. Glass wool is the hardest to dispose of, being neither recyclable or biodegradable. Mineral wool is recyclable but not biodegradable. All the organic materials mentioned above are the easiest to get rid of, being both recyclable and biodegradable.

Another consideration is the amount of energy used in the material’s manufacture. Glass wool is again the worst performer here, compared to all the other materials. You might also be concerned whether the material is made from renewable resources: all the organically derived materials are, but mineral wool and glass wool are not.

Finally you may also want to think about other considerations, such as ease of installation, what happens if it is burnt, and ability to deal with moisture. For example, glass wool causes irritation when it comes into contact with skin (as does mineral wool), releases toxic smoke if burned, and does not perform well when wet. By contrast sheep’s wool insulation can be installed without gloves or protective clothing, is not irritating to the skin, and will naturally help prevent condensation.

To sum up, the option that most people will find attractive is to install mineral or glass wool using a professional contractor, so that they are able to access government grants, and make sure the job is done properly. However, those going the DIY route should consider the benefits of one of the organically derived options, such as sheep’s wool.