Open cell is extremely vapour open and will allow moisture vapour to pass freely through it allowing the building to breathe naturally.
Because spray foam can create an air-tight yet breathable envelope, it has made it the insulation material of choice in new build homes built to Passivhaus-type standards.
Unlike the urethane foams of 20 years ago, modern spray foams such as Icynene Foam Lite use water as the blowing agent.
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. Real world experience also shows that the more difficult a component is to install, the less likely it is to be installed correctly!
The modern alternative is spray foam insulation, which is applied using a pressurised gun system. Here, foams are applied as a two-component mixture that come together at the tip of a gun forming a foam that expands 100-fold within seconds of application, sealing all gaps, service holes and hard to reach spaces, virtually eliminating cold bridging and air leakage.
When selecting spray applied insulation it is important to understand a number of factors: Unlike the urethane foams of 20 years ago, 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 Foam Lite expands, the cells of the foam burst and the CO2 is replaced by air. Consequently, from an environmental perspective, Icynene has a Global Warming Potential (GWP) of 1 and an Ozone Depletion Potential (ODP) of 0 (Zero). Icynene does not, therefore emit any harmful gases once cured.
OPEN CELL OR CLOSED CELL COMPOSITION
Spray foam insulation can be either open or closed cell in composition. Open cell is extremely vapour open and will allow moisture vapour to pass freely through it allowing the building to breathe naturally. Open cell foam will not soak up or ‘wick’ water.
Closed cell foams tend to be much less vapour permeable than open cell and are considerably more rigid and hard. They resist the passage
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Insulation materials work by slowing conductive heat flow and to a lesser extent, convective heat flow.
of liquid water and although not entirely waterproof, will prevent it from passing through a structure for a considerable period of time. Closed cell foams often have a greater thermal resistance than open cell foams.
Chlorofluorocarbons (CFCs), which were developed in the 1930’s and frequently used in spray insulation many years ago, are recognised as the main cause of the ozone depletion. CFC’s can last for 100 years and 1 CFC molecule can result in the loss of 100,000 ozone molecules. In light of this, when spray applied insulation is used it is important to verify that the material does not contain any chemicals that may potentially cause damage to the environment.
WHERE DOES SPRAY APPLIED INSULATION FIT?
Spray applied insulation tends to be more expensive than conventional fibre based and rigid board type insulation materials and is usually applied by specialist contractors using bespoke equipment. However, its speed of installation, minimal waste and its ability to perform in difficult to treat applications and the fact that it can be injected into voids that would otherwise require invasive tear-out of surfaces, means spray foam is a cost-effective solution when compared to rigid board type insulation for both refurbishment and new build projects.
Open cell spray insulation has been used on many historic buildings where its non-invasive installation methods have allowed the continued occupation of the building with the minimal of disruption to users and negligible impact to the fabric or the breathability of the structure.
At the other end of the scale, the fact that spray foam insulation can create air-tight envelope has also made it the insulation material of choice in new build homes built to Passivhaus-type standards.
*Footnote: As levels of air tightness increase, consideration should be given to the introduction of efficient mechanical ventilation
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