Natural Insulation

ABOVE: Natural insulation, such as Thermafleece sheep’s wool from Second Nature (01768 486285; secondnatureuk.com), is better for your home and the environment. However, the natural option tends to be more expensive than traditional measures

Heat is money. The only way to stop that money escaping from your house is to insulate. The Energy Saving Trust tells us that the point at which the energy used to make the insulation is greater than the energy saved by the insulation is around 1m thick. The figure seems likely to vary with the material (there’s very little energy in sheep’s wool) but you get the idea. Furthermore, a US Army study found that insulation gaps amounting to just 4% of the outside area of a structure equate to a 50% loss in energy. These gaps can be either literally gaps or cold bridges. If you can draw a line from the outside to the inside without cutting through a full thickness of insulation, you have a cold bridge. What these studies show us is that insulation is effective and that heat will take the line of least resistance in its struggle to leave.~

As to materials, we are all familiar with the usual rigid urethane foams (Celotex, Kingspan, etc) and with mineral and glass wool, which leads us to the pros and cons of natural insulation.

In general terms natural insulation achieves similar Uvalues to non-sustainable alternatives in a like-for-like situation, and the main types are:

Blanket: perhaps the most common and includes felt, sheep’s wool, hemp and recycled textile waste. These are usually rolls that fit snugly between the joists and all have roughly the same U-values at 0.2 to 0.3 at 100mm thickness.

Loose-fill: including cork granules, wood fibre, loose fleece or cellulose pellets. These are easy to apply and especially useful for areas where joists are irregularly spaced and where pipes or other obstructions make it difficult to lay a blanket. They are also great in helping to overcome cold bridges. U-values vary.

Rigid sheet: includes wood fibre, straw board and cork. Can be used between rafters, underfloor, in timber fames, between joists and in cavity walls. Very low airflow through these materials so always ensure adequate air gaps. U-values around 0.18 to 0.22 at 80mm thickness.

The Cost of Sustainability
If price is your issue, then natural materials won’t work for you, as they will be 20% to 100% more expensive than the non-sustainable alternative. So why use them then? Well for one thing, natural insulation does not come with a health and safety leaflet. You don’t have to don goggles, breathing apparatus or gloves to work with them. And they don’t gas-off. Some of the non-sustainable options are made using a variety of chemicals including ozonedepleting gases. These gases can be released over time and make their way into the property. Unsurprisingly they are not generally considered to do you any good.

Natural insulation also offers better air and moisture management — it ‘breathes’ more. And lastly, you can sit snug and warm in your naturally insulated home content in the knowledge that you have done as little as possible to deplete the earth’s resources.

Further reading:

• Eco Home Insulation
• Choosing Insulation
• How to Install Loft Insulation