Open cell spray foam vs alternatives

waqasahmed

So, pending review, mortgage companies may be fine with open cell spray foam. 

https://www.mortgagesolutions.co.uk/news/2022/10/27/rpsa-retracts-spray-foam-guidance-pending-review/

Let's say that mortgage companies find that 

- Open cell is fine
- Closed cell isn't fine

Which is potentially likely given open cell is breathable, and closed cell spray foam is the type that rots your roof. I believe currently, mortgage assessors are treating all forms of spray foam as one and the same 

Would that mean open cell spray foam would potentially be better than other forms of insulation? 

Reed_Richards

waqasahmed said:

Would that mean open cell spray foam would potentially be better than other forms of insulation? 

How does it compare in terms of Thermal Conductivity?

waqasahmed

Reed_Richards said:

waqasahmed said:

Would that mean open cell spray foam would potentially be better than other forms of insulation? 

How does it compare in terms of Thermal Conductivity?

"For our Icynene spray foam insulation material, the thermal conductivity is 0.039 W/mK which shows a good level of thermal conductivity"

That's what I've found on the interwebs

https://www.sprayfoam.co.uk/insulation-terminology.html#:~:text=Spray Foam Thermal Conductivity,good level of thermal conductivity.

Reed_Richards

I've been adding insulation to my loft lately.  The fibre roll insulation seems to come in three grades, 0.044 W/m.K, 0.035 W/m.K and 0.032 w/m.K.  So it looks as if 0.039 W/m.K is respectable but not the best.  

waqasahmed

Reed_Richards said:

I've been adding insulation to my loft lately.  The fibre roll insulation seems to come in three grades, 0.044 W/m.K, 0.035 W/m.K and 0.032 w/m.K.  So it looks as if 0.039 W/m.K is respectable but not the best.  

Is that breathable? 

Reed_Richards

Oh yes certainly, these are glass or mineral fibre "wool" materials so air passes through very slowly but there is no physical barrier.  I am laying these on the floor in my loft.  If you wanted to insulate between the rafters immediately below the roof tiles you would need some means of holding the insulation in place.  I imagine spray foam is attractive to installers because it sticks to the rafters and to the roofing felt so can be applied very quickly

In your case, you have a timber-frame house so if you insulated the roof rafters under the tiles you would also need to insulate the gable end walls.

waqasahmed

Reed_Richards said:

Oh yes certainly, these are glass or mineral fibre "wool" materials so air passes through very slowly but there is no physical barrier.  I am laying these on the floor in my loft.  If you wanted to insulate between the rafters immediately below the roof tiles you would need some means of holding the insulation in place.  I imagine spray foam is attractive to installers because it sticks to the rafters and to the roofing felt so can be applied very quickly

In your case, you have a timber-frame house so if you insulated the roof rafters under the tiles you would also need to insulate the gable end walls.

Thanks. I'll get in touch with a company called "efficientloft" one I reinforce my flat roof 

waqasahmed

Reed_Richards said:

Oh yes certainly, these are glass or mineral fibre "wool" materials so air passes through very slowly but there is no physical barrier.  I am laying these on the floor in my loft.  If you wanted to insulate between the rafters immediately below the roof tiles you would need some means of holding the insulation in place.  I imagine spray foam is attractive to installers because it sticks to the rafters and to the roofing felt so can be applied very quickly

In your case, you have a timber-frame house so if you insulated the roof rafters under the tiles you would also need to insulate the gable end walls.

Also out of interest, does what you're doing create an air tight barrier?

Thanks 

Reed_Richards

A lot of the things we do inside a house create moist air.  You want this excess moisture to get out so you don't have problems with mould.  But for insulation purposes you want your house to be as airtight as possible.  These two requirements conflict.  Unless your house has active heat-exchange ventilation you don't want the barriers to the outside air to be completely airtight, you just want the air to pass through very slowly but to carry away excess moisture.  And even the best heat-exchange ventilation will cause you to lose some heat.     

waqasahmed

Reed_Richards said:

A lot of the things we do inside a house create moist air.  You want this excess moisture to get out so you don't have problems with mould.  But for insulation purposes you want your house to be as airtight as possible.  These two requirements conflict.  Unless your house has active heat-exchange ventilation you don't want the barriers to the outside air to be completely airtight, you just want the air to pass through very slowly but to carry away excess moisture.  And even the best heat-exchange ventilation will cause you to lose some heat.     

Essentially I'm wanting to go "PassivHaus" with some heat recovery too, hence the requirement for air tightness 

Reed_Richards

Good luck with that; I think a "PassivHaus" retrofit could be really difficult.  I hope you are getting some expert guidance on this because some of the ideas you have had (such as spray foam insulation) would be ineffective unless other insulation is applied elsewhere in the roof space.