Open-access content Tuesday 26th January 2016
Advances in polyurethane foam solutions mean that they offer advantages beyond heat insulation, as Leonie Onslow explains
28 January 2016 | By Leonie Onslow
When bringing properties up to the latest standards of insulation and air tightness, facilities managers may want to choose a high-performance insulant to achieve the optimum comfort and energy efficiency.
Polyurethane foam can be installed as insulation in walls, roofs and floors, or to fill voids and other areas to provide seamless thermal insulation.
FMs may not be aware that polyurethane foam can also be used to solve a range of other problems.
1. What is polyurethane foam?
The application of closed-cell polyurethane foams for building insulation has been around for more than 30 years. The polyurethane insulant is a two-component liquid system that produces a highly efficient blanket of insulation with an exceptional thermal conductivity figure. In shops and warehouses, large areas can be installed quickly. Systems can be applied to various depths and have K-values [of thermal conductivity] in the range of 0.025 to 0.028W/mK.
When sprayed to the underside of a structurally sound roof, the foam can achieve excellent insulation values and can be used for the dual purpose of roof stabilisation and to counter nail fatigue, prolonging roof longevity.
2.Open-cell v closed-cell foam
The open-cell option has entered the market in recent years. FMs may well be confused as to the merits of these different systems.
The British Urethane Foam Contractors Association, the trade association representing installers of polyurethane foam, has predominantly represented the closed-cell industry, but recognises that the open-cell alternative has different benefits.
A closed-cell sprayed or injected polyurethane foam material provides one of the highest insulation values commercially available. It also helps to achieve excellent structural stability for a building, adhering to the building substrate, and setting quickly to form a rigid layer. It is widely used for roof insulation and strengthening as well as cavity-wall insulation and stabilisation, which is particularly important where the wall ties are failing.
Air leakage through the cavity can be reduced to zero. With greater thermal performance and
reduced air leakage, polyurethane foam outperforms all other forms of cavity fill. The foam moulds itself to the fabric of the building, sealing out draughts and reducing air leakage. It is increasingly important to improve the structural integrity of buildings, particularly as weather patterns become more erratic.
3. Proof against weather
Closed-cell foams resist driving rain, meaning that the material stays dry with no loss of thermal properties. The insulant can help act as a barrier to stop floodwater entering the building through the walls. The British Board of Agrément certification approves this insulant for cavity walls in all exposure zones. Closed-cell foams that achieve a Class 1 fire rating when tested to BS476 Part 7 are available. Or, where non-Class 1 materials are used on internal applications these must be covered by plasterboard or a similar thermal barrier.
This insulant is often the most cost-effective solution for uninsulated cavity-walled properties, including those classed as hard to treat. Properties with narrow cavities, stone cavities, or of metal or timber-framed construction, or situated in flood plain areas, can be insulated with injected polyurethane foam systems resulting in high-energy efficiency of the walls.
4. Open-cell properties
Conversely, open-cell polyurethane foams, which have entered the market in recent years, do not have the high insulation properties associated with the closed-cell materials, which is a distinct disadvantage if you are trying to save space. They do not have the same fire performance as the closed-cell type, so they should never be left exposed; they have no structural strength to stabilise roofs or walls and are widely marketed to be applied directly to non-breathable membranes. This practice should be treated with a degree of caution as interstitial condensation could occur in the foam, next to roof timbers.
But they are better suited for their enhanced sound attenuation properties. Open-cell foam is also useful in situations that require more air and vapour into a building's interior. Where open-cell materials are used, the installation thickness can be increased for better thermal performance, but if the main purpose is energy efficiency, then the closed-cell option is preferable.
5. Maintenance or service
The polyurethane foam should last for the life of the property. There are usually no maintenance requirements following its installation. But where it is applied to the underside of a roof for insulation and structural stability purposes, the external roof structure should be checked periodically for wear and tear to ensure that the roof remains weather-tight.
6. Choosing an installer
A competent installer - preferably a qualified member of the British Urethane Foam Contractors Association - should carry out installation.
He will carry out pre-installation checks to assess the property's suitability for the installation of polyurethane foam.
Leonie Onslow, executive director, British Urethane Foam Contractors Association