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Spray Foam Roof Insulation : a good idea or not?

There are Growing Concerns about 'Sprayed Foam' insulation to underside of roofs.

The surveying industry is getting very 'jittery' about the use of retrospective 'sprayed foam' being applied to the underside of roofs in the loft. Some mortage companies will now refuse to loan on houses that have had this 'treatment' applied.

Let's start with the driving force of why it might be used...

Mainly because homeowners are told it will "improve thermal insulation and save money in heating bills". It can also be sold as a 'fix' to older roofs that have loose slates or tiles, or where the sarking membrane (roofing felt) has degraded.

Let's tackle this logic!!!

On the "insulation benefit"... they are insulating to the underside of the main roof, that means all the loft space and cold air is between the ceiling insulation and the sprayed foam .... which means when heating your house you have to heat all the loft space as well, before the foam insulation will have any effect. BUT Your heating system will not be designed to heat the volume of the loft - so your rooms below will loose the same heat as they always did... you might have a slightly less cold roof (but probably not even that).

On the "fix solution"... fundamentally it's not fixing anything. If the outer coverings were leaking, they are still leaking because the foam is inside, it's just now the sprayed foam is hiding it and probably trapping water against the roof timbers... not a good combination. It also means that if you do need to change one cracked or damaged slate/tile - you now can't do that either because it is 'glued' to the others by the foam.

All in all... the "benefits" are not really there!

It is much better to add additional thermal insulation above the rooms at ceiling level. This way the rooms will keep warmer in the winter and you will spend less on heating bills. Most houses we look at only have about 50-100mmm (2"-4") of fibre-quilt insulation ...the best results are given by 250mm (10") or more.

Ok, so it might not be a benefit, but is it bad?

That's the real problem, it is possible that it will be bad. The main worry is the ability of the roof to keep ventilated to allow condensation and moisture to dry-out. Most lost spaces are designed to be 'cold' space, with free-flowing air to carry away natural moisture & humidity (whether from weather conditions or normal house activity). If you seal the underside of the roof slope covering the roof timbers, the timbers are now encased and separated from the ventilation. The timbers are now on the slightly colder side, so any humidity (vapour) could condense against them and could lead to structural decay or rot of timbers. The extent of this impact is likely to vary depending on the manufacturer and the type of foam ... some are 'open cell' (meaning some vapour permeability) and some are 'closed cell' (no vapour permeability). Vapour permeability is often referred to as the building's ability to 'breathe'.

We want and need buildings to 'breathe' through the ventilation provisions.

**** So what if you already have sprayed foam?

- first off we are looking for local case studies for us to investigate further and monitor the amount of adverse or detrimental effect (i.e. to see if not only it is adding no benefit, but if it is actually being harmful too);

- second, if you are trying to sell your house and the buyer's mortgage lender will not loan, then you may have to look at removing the sprayed foam - which could potentially mean a new roof. Again we are looking for local case studies to see whether this is actaully needed in every case or if alternative ways of removal is possible.

**** If you already have foam insulation installed, or are considering adding foam insulation, then please fell free to message us.

If anything that you have read hear concerns you, we do not want you to panic or immediately over-worry, the downsides of foam insulation are often slow to occur or will be longer-term issues that can be resolved before becoming a massive issue. Just contact us!


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