30
feature
floors, walls, ceilings & acoustics
upgrading thermal performance
by insulating Neil Turner
When it comes to making energy efficient upgrades to existing homes, addressing heat loss through the floor is one of the first places to start. Approximately 10-15% of heat loss in a typical house takes
place through the floor, according to the Energy Savings Trust. Insulating floors can significantly reduce heat loss and lower energy bills, introducing major savings, especially as energy bills continue to rise. Not only does it help to reduce energy usage, but upgrading the insulation in suspended timber floors increases comfort and reduces a building’s overall carbon footprint. Studies show that there are approximately 10 million suspended timber ground floor constructions in the UK and it is estimated that a large percentage are not sufficiently well insulated for energy efficiency and comfort. Improving thermal efficiency The most effective way to reduce heat loss in suspended timber floors is by insulating between the floor joists. This usually involves lifting the floorboards which, providing they are in sufficiently good condition, can be reinstated when the thermal performance improvements have been carried out. Any compromised floorboards or joists can also be replaced as part of the retrofit project. In some cases, if the floor is accessible from below, such as
from a cellar, it may be possible to partially insulate the joists from underneath.
As anyone who works with older properties will know, joists can sometimes be unequally spaced, making it difficult to match the contours of a rigid board insulation to the existing timbers. This can lead to gaps which allow air leakage, therefore reducing the thermal performance of the insulation. If the gaps are large enough, they could even allow the sections of insulation board to fall through into the crawl space and onto the ground below, rendering the insulation ineffective. Often, the issue is addressed by using an expanding foam to fill the gaps, but this solution may only be temporary as both the installation and the hardened foam lack flexibility, so any structural movement could cause gaps to reoccur. The non-breathability of these materials also means that, if any moisture should penetrate the floor structure over the building’s lifetime, it may not be able to dry out. This is where natural building materials can help, as they combine high levels of thermal performance with naturally hygroscopic properties. When upgrading a suspended timber floor, a windtight
breathable membrane is recommended. The primary function of this type of membrane is to manage moisture and prevent condensation, which indirectly contributes to energy efficiency. This membrane is also windtight and hence prevents cold
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