Spray Foam Insulation - A Good Idea or Not?

Lumen

The one angle that's not really covered is whether any type of rafter insulation is desirable.

I'm sure I've read threads like this where people are being sold a spray foam rafter treatment when some careful but cheap deep joist insulation and ceiling/hatch airtightness would do as good or better a job.

Like, what's the point in insulating an unheated ventilated space?

Muahahaha

This thread is timely for me as Im finally going to re-insulate the attic in a 1995 built timber frame house. Its slightly unusual & problematic as its a 3 bed semi but with 2 bedrooms on the first floor and the third bedroom & ensuite on a second floor up inside the attic. Its not an attic conversion per se as it was built this way. But it means each side of this top bedroom and under the pitch of the roof there are two crawl spaces, triangular in shape sloping down with a steep pitched roof of 40 degrees.

Ive had companies out here quoting in the past but never went ahead with the job as they all came coming with this spray foam solution. Im not an engineer but to me it didnt make sense to spray the rafters and insulate the two crawl spaces at roof level because where the roof and top of the wall meets (so basically near where the guttering is on the exterior) there is a gap of about 10cm with cold air coming in there and sometimes birds too. So it always seem pointless insulating at rafter level when Ive this ventilation that is 10cm wide and runs the width of the building, about 4.6 metres. So even if I went for the spray foam Ive still got this gap with cold outdoor air coming into the attics crawl spaces. Ive never understood if this is normal construction or why it is that way, I know attics need to be ventilated but I would have thought it would be some small holes rather than a 10cm gap running the width of the building? Any comment much appreciated as Ive never understood this about my house.

Im hoping others here can advise but my impression of how to do this job correctly is that I actually have two insulation jobs. One is to insulate the floor of the crawl spaces with 300mm rockwool so the heat in the two bedrooms below them cant escape quickly. And then the other job is to insulate the envelope of the top bedroom which is best described as a cube inside the attic. So the bedroom walls would be insulated from the attic side of it with 300mm rockwool. The tricky part is the bedroom ceiling- the top of that has no access from the crawl spaces because the rafters run close to the apex of the cube. So the only way I can think of it getting done is for a hole to be cut in the bedroom ceiling and the installer to go up there and lay insulation above the ceiling and then to replaster the ceiling. And if I dont do that bit above the bedroom ceiling the heat is still going to escape from the ceiling upwards and the entire job would be a waste of time. Am I correct in thinking like this, i.e that the entire cube needs to be insulated both walls and ceiling?

Is what Im describing do-able? I dont even know where to start here as any company I contact comes running with their spray foam solution which Ive decided I dont want due to uncertainty about insurance and well because even with a 50mm air gap I dont like the idea of never seeing the rafters again because if theres a roof leak they could be rotting away hidden behind spray foam insulation and by the time I realise it the roof has fallen in.

@Calahonda52 I remember you pointed me before to an NSAI document with standards for how to insulate a room in an attic/dormer bungalow situation. I cant locate it or your post due to Boards search not working well. Any chance you could re-link it as Id love to read it again and try to get some understanding of what I need to specify with an installer to get this job done correctly.

mickdw

I received a circular from my insurers I believe basically stating that where spray foam is found during Building inspections, it is to be recorded as a possible defect.

That was about 3 years ago.

Practical experience of opening up existing structures would suggest that it is a very bad idea.

https://www.boards.ie/discussion/2058368235/spray-foam-insulation-a-good-idea-or-not

look up spray insulation in reddit/uk housing. Do not allow it near your house, numerous house sales have fallen through in UK due to this fire hazard. Many have to spend thousands to get it removed, some even have to reroof their houses in order to sell their properties.

https://www.reddit.com/r/HousingUK/comments/1dneesp/spray_foam_insulation_still_being_promoted/

Gerry Sheridan

The amount of misinformation regarding Spray Foam Insulation on this post and in general is incredible, Spray Foam insulation has been around for over 60 years and has been successfully used around the world in all types of properties, the critical factor is that it is installed in accordance with the relevant product certification and manufacturers instructions, it is the safest most effective form of insulation when installed correctly. Spray foam is one of the most tested and certified insulation products on the market and must meet the strict criteria laid down in EN 14315-1 thermal insulation products for buildings.

The situation in the UK arose when cowboy operators used closed cell foams directly to the underside of tiles and slates as a waterproofing and stabilization solution, the effect this had was to trap moisture and expediate the failure of the roof, as a result of this mortgage lenders blanket refused to lend on properties with any type of spray foam, this situation is now easing as lenders and surveyors learn the difference between open and closed cell foams and according to a recent BBC report 75% of the major lenders will now consider lending where a proper paperwork trail and inspection process is on place. this is not an issue in Ireland as virtually all applications in Ireland are open cell either directly or indirectly to roof membranes and felts as per product certification. in a recent Irish Times article the major lenders have confirmed no issues in Ireland with lending

in Ireland we must comply with Building Regulations not technical guidance documents (TGD). TGD are there to do exactly what they say, provide guidance and they do stress the following

" the adoption of an approach other than that outlined in the guidance is not precluded provided that the relevant requirements of the Regulations are complied with. Those involved in the design and construction of a building may be required by the relevant building control authority to provide such evidence as is necessary to establish that the requirements of the Regulations are being complied with".

Therefore some certifications allow for direct application to felts and membranes with the use of vapour control layers where required while others require a 50mm ventilated air gap with through ventilation at the soffit and ridge. In addition there are several studies carried out by the Fraunhofer Institute on WUFI Hygrothermal analysis on the application of spray foam to roofs in Ireland and the UK In Ireland NSAI and KIWA certification demonstrate compliance with Irish Building Regulations, always make sure you use a registered brand with certification and a contractor that is approved by the manufacturer, is part of a third party surveillance scheme and has a robust Quality Management System, never use closed cell foam in your property

For clarification i have over 20 years experience in spray foam insulation with approximately 150,000 installations in Ireland and the UK with a failure rate of less that 0.0001%, i will provide accurate information to anyone that required it

Mod: Advertising removed

SwimFin

https://www.boards.ie/discussion/comment/122597292#Comment_122597292

NSAI Agrément Part 5 Conditions of Certification i.e. 5.1 "This Certificate shall remain valid for five years from date of issue or revision date"…therefore this Certificate is not valid and not acceptable under TGD D3 ©

Technical Guidance Document D – Materials and Workmanship