In September the Government announced a �2bn plan to offer home insulation grants of up to �5,000 per household in England. This is to be known as the Green Homes Grant and has replaced previous schemes such as the Green Deal which largely failed in their key objectives.

Grants can pay at least two thirds of the cost of some energy-saving solutions. The maximum amount available is �5,000, or �10,000 for those on certain benefits.

The new scheme will come as a welcome boost to the home insulation and renovation industry, while at the same time as offering to improve the energy efficiency of homes using approved installers.

Poor quality installations

Previous government schemes have been plagued with poor quality installations which lead to low insulation efficiency and in some cases contribute to other problems such as condensation and decay.

One type of insulation treatment in particular is problematic: spray applied foam insulation. The reason is that most surveyors take a jaundiced view of this material and its application in homes and most mortgage companies don't like it. It means that in some cases loans will be refused when a property has had foam insulation installed.

Quick and easy solution?

Whilst spray foam is quick and easy to apply - either in a loft space between rafters, or within internal walls inside studied partitions or timber frames - it takes a skilled operator to apply it properly to avoid problems [see picture above] in the future.

Once applied, good or bad, it's difficult or impossible to see if it's hiding moisture condensation and wood decay. Therefore, when surveyors value houses for mortgages they will flag this up to the mortgage lender as an issue and loans get refused.

Like many services in the building trade there are rogue and unscrupulous operators who will apply this type of insulation with little or no regard to the quality of the finished product, and as it's impossible to inspect what's going on behind the foam, many surveyors will simply condemn it.

Foam removal

Once installed it's very difficult to remove the foam. It's got to the stage, with spray foam insulation, that companies are now offering their services to remove it when people find they can't get a mortgage '� most likely the service is offered by the same companies that apply it.

Correct application

The application process, when done correctly, solves a lot of problems. It's quick to apply and the chemicals come in two large tubs instead of a truck load of Celotex sheets, which are then very time consuming to install, involving a lot of cutting to size and fitting.

Installing slab or Celotex type insulation needs a lot of care to get the sheets to the correct size, a snug fit to avoid any gaps, where cold bridging could occur. All joints and any gaps should be filled with sealer and all then sealed over with foil tape. A careless workperson can make the difference between a perfectly insulated roof or wall and a far less effectively insulated one with potentially hidden problems.

What is spray foam insulation?

Sprayed foam insulation is not a new idea, its been around for at least 30 years. There are two types: closed cell and open cell. The closed cell acts as a vapour barrier but it must be installed without any gaps where it touches the wood sides. The open cell type allows moisture to seep through but can only be used if there's a breathable vapour barrier on the other side, usually the felt type roof covering.

So the open-cell products are vapour permeable and must only be used in conjunction with a breathable roof covering, a breathable roofing felt. Closed-cell products are often used to stabilise defective roofs with no felt layers, sprayed directly to the underside of slates or tiles which gives them some stability if their fixings have corroded. The problem here is, the foam covers a lot of sin hence why the mortgage companies don't like it.

Closed cell products can undoubtedly extend the life of a defective roof, quickly and without going to the disruption and expense of replacing the roof covering. The closed-cell solution will improve airtightness in a home and depending on how a loft space is being used, this can be an efficient way of insulating the loft and house space, perhaps more so that deep loft insulation, which leaves the loft space cold. However, if the loft space is included in the sealed envelope of the house, to avoid condensation the loft must then have extra ventilation.

Spray foam performance

Truly reliable performance data on spray foam insulation installations is hard to find. The insulation qualities will vary according to the thickness of the application and whether all gaps are sealed. The main problem is that interstitial condensation can occur.

This means that condensation forms on the cold side of the insulation which leads to decay in the rafters, slate battens and slate / tile fixings. The quality of the application is therefore crucial if problems like these are to be avoided. This is not a DIY job, training and a good degree of skill are required by the operative to avoid these problems.

Depending on the situation, a sealed vapour barrier may be required on the warm side of the insulation as any gaps could allow air leakage and cause condensation on the underside of the roof covering. Therefore, spray foam insulation is not usually an option if breathability is required.

Any roof can be affected by condensation if it lacks the correct ventilation, and any type of insulation can cause this whether conventional or spray foam. It would be wrong to blame or condemn spray foam entirely on that basis, it's simply a matter of the correct design and application.

Ventilation the key

Ventilation is the key to preventing condensation in any property, full stop. Structure and fixing decay, or wet and dry rot in timber, whether in roofs, floors and timber frames can all occur when there's insufficient ventilation. Moisture will find its way into sealed spaces or spaces without a good air flow, which never properly dries out, and that's when trouble occurs.

There does not appear to be much evidence of serious decay problems with spray foam insulation when applied correctly, and in the right circumstances, but to avoid problems with mortgage applications it may be wise to stick with conventional insulation types.