IsoSpray applied polyurethane foam has a very low propensity to create a condensating surface due to its extremly low thermal conductivity. When warn air gets to a cold surface there is a likelihood of condensation occurring. To prevent this IsoSpray is therefore routinely applied to areas prone to condensation; typically a 20 to 30 mm coating of IsoSpray will eliminate condensation under all normal conditions. Roofs and industrial steel clad buildings are routinely treated with IsoSpray to eliminate condensation and also to create a high level of thermal insulation.

We are often asked if spray foam affects the breathability of timber especially when applied to roof timbers. The undelying concern is that if the roof timbers cannot breathe and the timber absorps excess moiture, perhaps through condensation, then wet rot and even dry rot may be caused which will cause substantial structural decay, obviously to be avoided! But does appling spray foam cause timber to decay?

Clearly roof insulation must not lead to creating problems in roof timbers; all structural timber must be kept dry and hence ventilation is seen as a way of ensuring this. But ventilation per se is not always needed if the risk of condensation is so low as to be ignored.

The point about 'breathability' is to prevent condensation risk that could lead to excess moisture in vulnerable materials like timber that could lead to structural decay and failure. Clearly roof insulation must not lead to creating problems in roof timbers.

Polyurethane foam is cellular (90% closed, 10% open, very similar to timber itself) and allows breathing. It and does not lock damp against timbers so they 'breathe'. The point about foam is that the condensation risk is considerably reduced to the point of insignificance and the modern way is to only introduce ventilation in heavy water vapour areas such as kitchen and bathrooms. It must be remembered that ventilation per se is not energy efficient and takes heat out of a building in the same way an open window or door does. Modern building technology works on sealed envelope systems so that ventilation is not random and only used where required so the property is more energy efficient.

Modern ventilation systems also attempt to harvest the heat energy extracted and use it for heating up the in coming air but clearly it is better to avoid extraction of expensively heated air if the propensity for condensation is insignificant.

The building industry has already reached standards in commercial new build where the whole building must be sealed and this is being introduced to new build domestic properties to reach code level 6 by 2016, absolute zero carbon emissions from the property. I believe we are on code 4 at the moment having started on code 1 in 2006 as the building industry was given 10 years to adjust to very stringent new standards for energy efficiency and carbon reduction over a period of 10 years. Polyurethane spray foam is recognised as very much part of the solution in helping achieve code 6 as it seals and insulates like no other product known whilst still allowing breathability. It is interesting that the US and Canada have been using these building methods for the passed 20 years or more and we in the UK are now beginning to adopt these ideas and technology. More information on building codes is here: http://www.foam-insulation.co.uk/0-carbon-technology.htm

The BBA certificate for Duratherm Polyurethane Spray Foam confirms that it is both an efficient method for roof stablisation, the control of heat loss and the prevention of condensation. Foam presents a 'warm' surface so does not contribute to condensation build up and would in fact act as slow draw 'blotting paper' if timbers got excessively damp. The foam is also British Class 1 fire rated so does not exacerbate any fire risk. All in all, the BBA certificate covers the points raised on 'breathing' and condensation risk. Please see Duratherm Spray Foam BBA certificate here: http://www.foam-insulation.co.uk/duratherm-bba-certificate.htm

The retired architect may have a well founded nagging doubt in the back of his mind concerning foam because of the way formaldehyde foams were used in the 60's and 70's and early 80's; often inappropriately specified and applied and with potential health risk due to toxic off gassing over time. It is ironic that even now formaldehyde is still being used in some building products such as mineral/fibre wool as part of the 'binders' that hold the product together that has been banned in countries like Sweden! In the 1980's Canada, for example, ruled against formaldehyde foams leaving many houses unsaleable and contractors would spend several weeks or even months internally stripping the house to remove all trace of the foam so the property could be marketed. Bad press indeed for 'foam' but that was formaldehyde based foam which also may have had breathability issues too as it was 100% closed cell.

So your retired architect is right to question but needs to be introduced to modern polyurethane foam technology which is now used as a whole house method in new build, floors, walls, and roof to create a sealed envelope. We use polyurethane foam, an inert product with no toxic off gassing issues and is in fact a completely different product to formaldehyde foam but shares the same name 'foam'! IsoSpray has completed many projects for creating sealed envelopes and we have been awarded contracts by local governments, MOD, Plc's, NHS hospitals, schools, listed buildings etc. Clearly the award of these type of contracts are not done on a whim; excellent resources are in place to vet company, product and solution and must meet the requirements of the project and the method accepted prior to starting the contract. These contracts would not be awarded if the industry view at the professional level had grave doubts of polyurethane spray foam.

An interesting article that may help is dispel any false beliefs on polyurethane spray foam is here:

http://www.foam-insulation.co.uk/spray-foam-roof-tales.htm

On the Isospray proposed method there is no real issue here on 'breathing' or risk to the structure of the property. Further, because the spray foam presents an air tight barrier, warm air cannot excape and come into contact with a cold surface those will likley induce condensation. This property, being air tight as an insulator, is the major reason why spray foam is specified over any other competing insulator.