Air leakage accounts for a high proportion of the heat loss from a building and often has a greater impact on thermal performance than conductivity through walls and roof planes, says Paddy Leighton, UK Director for Spray Foam insulation specialists, Icynene.
Here, Housing Association Magazine takes a look at heat loss in buildings and how new, high performance insulation systems can improve comfort levels in both retrofit and new build applications.
Insulation in a building is generally introduced to provide resistance to heat flow. The more heat flow resistance the insulation provides, the lower the likely heating [and cooling] costs. Good levels of insulation not only reduce heating and cooling costs, but also improve comfort.
Insulation materials work by slowing heat transfer from warmer to cooler areas until there is no longer a temperature difference. In a typical home, this means that in winter, heat flows directly from all heated living spaces to adjacent unheated roof voids, garages, cellars and particularly to the outdoors. Heat flow also moves indirectly through interior ceilings, walls, and floors, wherever there is a difference in temperature.
To maintain comfort, the heat lost in the winter must be replaced by heat from a central heating system or other means. Adequate levels of insulation will decrease this heat loss by providing an effective resistance to the conductive flow of heat.
How can we insulate effectively?
Retrospective insulation – which is fitted after construction of the building – has traditionally taken the form of thick layers of glass or mineral fibre placed between rafters in the roof void, or blown in cavity wall insulation such as styrene beads or mineral wool.
In the UK, U-values are the measure of insulation’s ability to limit conductive heat flow - the lower the U-value the better the resistance to heat loss. However, it should be noted that up to 40% of a building’s heat loss can be attributed to air leakage.
Moisture vapour in the air within a building carries heat and moist humid air can support up to 4000 times more heat energy than dry air. As air leaks out of a building it carries with it this moisture vapour and with it, heat.
The most effective way to increase the energy efficiency of a building is not merely to reduce U-values as required by Building Regs, but rather to combine U-value reduction with an air barrier – creating a “sealed box” effect to reduce air [and heat] leakage to a minimum.
Spray applied insulation
Traditional forms of insulation are relatively inefficient in sealing the box, as they cannot completely fill all voids or seal the interface between the insulation and the building structure. This can lead to cold bridging and thermal by-pass, risking localised condensation and inevitable dampness.
Air leakage can be eliminated by the introduction of an air barrier. These can take many forms but must be installed with great care if they are to perform as desired.
The modern alternative is spray foam insulation. Here, foams are applied as a two-component mixture that come together forming a breathable foam that expands 100-fold within seconds of application, sealing all gaps, service holes and hard to reach spaces.
Modern spray foams such as Icynene Foam Lite use water as the blowing agent. This means that the reaction between the two components produces CO2 which causes the foam to expand. As the material expands, the cells of the foam burst and the CO2 is replaced by air.
This creates an open cell foam structure with a soft, yielding texture that provides outstanding insulation and lets the building breath naturally, resisting internal condensation.
Icynene does not emit any harmful gases once cured and, from an environmental perspective, has a Global Warming Potential [GWP] of 1 and an Ozone Depletion Potential [ODP] of 0 [Zero].
Where does spray applied insulation fit?
Spray foam insulation has been used widely on new-build and retrofit applications in both public and private sector housing, particularly in old and difficult to treat stock where its non-invasive installation methods have proved valuable.
In such situations, spray foam has been carefully injected through small holes drilled through studwork, with minimal impact on the fabric or the breathability of the structure.
As spray foam insulation can create an air-tight envelope, it has also made it the insulation material of choice for high specification dwellings built to Passivhaus-type standards. It should be noted however, as levels of air tightness increase in such applications, consideration should be given to the introduction of efficient mechanical ventilation.