Dryfix News

Spray Foam Insulation

April 3rd, 2019

All posts, Condensation, Energy Efficiency / Insulation Improvements


Thankfully it’s not often we’ll come across retrofit spray foam insulation however, it is still important to understand its impact as there are still a large amount of properties who’ve employed this insulation technique in the past.

Spray foam insulation is a polyurethane spray applied foam which sets to form an insulating barrier. It’s available in two different types open cell and closed cell.

Closed cell foam sets rigid into a solid mass which has been used historically to provide support to parts of structure where integrity has been impaired. I’ve never seen it used this way myself although understand this is one of its apparent benefits. Closed cell foam is a better insulator than open cell because it contains separate pockets of closed air which slow down the movement of heat through the material, therefore, it’s a very good insulator but also a vapour barrier.

Open cell spray foam is less dense and can usually be compressed by hand. The cells in the foam are open to atmosphere therefore it’s not as good an insulator as closed cell and is often used simply as sound insulation.

Spray foam insulation can be used in walls, floors and roofs although in a retrofit manner on existing dwellings this is most commonly seen on the underside of roof coverings.

Nearly in every case I’ve seen this insulation installed retrofit to the underside of a roof covering the homeowners understanding of its impact is misguided, sold only by the positives, it’s cost effective, clean, keeps the roof warm, doesn’t impede storage space in the attic, helps keep the slates in situ meaning less roof repairs. Best of all there’s no itchy fibreglass so, what’s not to like?……………..….You can clearly see the sales tactic!

Thankfully not many people choose this as a viable option for insulting the loft space and here’s why it’s a bad idea:

1: The insulation can dramatically reduce ventilation within the roof space especially if its closed cell material. Even though the insulation may keep the underside of the roof tiles warmer, the absence of air movement within the eves and apex of the roof can mean during winter humidity levels will increase. Sure enough problems with condensate and mould will arrive which inevitably place the roof timbers at risk of decay.

2: The foam adheres the roof tiles or slates in situ. Whilst this may sound appealing meaning less chance of slates slipping due to nail fatigue, if repairs are ever need these become almost impossible to undertake as the tiles/slates cannot be separated from the insulation. If the roof covering is ever in need of renewing, a re-roof I.e. using the existing tiles or slates is almost impossible meaning he only viable option of a new roof I.e. full replacement of the roof covering. This means the cost considerably increases.

I’ve have seen spray foam insulation used in new build properties where to be honest I’ve been impressed. In a new build scenario, however, spray foam is more suited. The construction is designed for this application, materials when needed are protected and levels of ventilation meet building regulation criteria. It is messy when you see it applied requiring floor and wall cavities to be filled before being allowed to set and the cut back as necessary. In a retro fit scenario such as this, spray foam insulation should be avoided.  

Many thanks for taking the time to read my article and i hope you found it useful. If you have any questions regarding the damp diagnosis or timber decay, please don’t hesitate to get in touch.

Russell Rafton – Dryfix Preservation Ltd – Director / Senior Surveyor

Dryfix Preservation, Yorkshires Leading Damp & Timber Specialists.



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