Overheating blog

Much has been written recently concerning the dangers of overheating in homes, particularly in connection with loft rooms.

This is clearly an issue, brought to public notice by the Daily Mail articles in July 2013 ‘OAPs could die in Green Deal Homes’  and May this year ‘Summer danger of ‘red-‘hot’ eco homes’.  The articles go through the obligatory scare tactics with very little research or understanding of the issues.

If properties are failing in respect of overheating then that does not discredit the idea of the ‘passive house’ concept. It does, however, highlight the importance of getting the design and detailing of the property right.

We at Urbane Eco have been exploring how to refurbish existing properties and build new ones to a standard where low energy use is paramount alongside comfort and health of the occupants. It is part of what is now being labelled the ‘holistic’ approach to building.

Overheating can be avoided if the right insulation is used in the right way. Adequate ventilation is also essential.

Using insulation products with good thermal mass such as wood fibre, wood flex, sheep and hemp wool (see here) can have a profound effect in ameliorating the problem of overheating, as these products can absorb the build-up of heat derived from solar gain in a roof. Using blinds over roof lights and dormer windows will also reduce solar gain. see here

Lightweight insulation with little or no thermal mass can do a very good job of holding heat in an attic room, with no ability to absorb that heat. If you get heat in an attic room derived from sun streaming through dormer windows, gable end windows, and roof lights, you have a problem if the fabric of the building is insulated with high performing materials such as PIR products, Kingspan, Celotex etc which do a good job of reflecting heat back into the building. Materials such as wood fibre and hemp have the capacity to absorb and store heat, mitigating this issue. Having said that, preventing the solar gain in the first place by using blinds is just as important.

Two other reasons I’m a big fan of these insulation products are:

A) They are produced from natural materials which reduces the risk of pollution in land fill and of chemicals and gas being released in the indoor air of the property. For example, it is thought that PIR insulation loses some of the gas, in the first two years, that is used in the manufacture of the product (also meaning it loses 20% of its efficiency)

B) They have hygroscopic qualities. This means they have the ability to manage moisture. Our indoor areas have varying degrees of moisture present in the air and in the fabric of the building, and humans are unable to feel differences in humidity between 40-70%. However, levels of humidity over 60% encourage growth of harmful bacteria, mould and dust mites, and can have serious health implications. Hygroscopic products allow moisture to pass in and out of the building fabric and help to buffer the amount of humidity in the house. A healthy building fabric for healthy building occupants!

Lots more to talk about, but I’ll leave it there. I will take up the issue of airtightness and ventilation next time.

Nick Lloyd