Advice for warm roof design for new build.

[Nickfromwales]

11 minutes ago, Dave Jones said:

 

my concern would be if it gets damp or clumps on wall ties etc reducing its U value. Much of an issue ?

I wouldn't put it in cavity walls tbh. Blown in, bonded beads for that AFAIC.

[Nickfromwales]

11 minutes ago, ProDave said:

For me, not until surveyors have got over their fear of it.

 

I have just been organising the home report for our old house, and one of the very first questions the surveyor asked was "is there any spray foam insulation in the house"  the implication being it would be a problem if there was.

Yup. But its all about pushing back and standing your ground for a better "tomorrow". The BCO's I am meeting on my PH ( or thereabouts ) builds have not got the slightest clue of what they are looking at.

Most are very curious though, and usually spend most of the visit marvelling at this new 'phenomenon' vs doing any BC content. They do a few laps, smile and nod, and then leave. And then we all look at each other and say, "nice chap, why was he here?".

[Dave Jones]

14 minutes ago, Nickfromwales said:

I wouldn't put it in cavity walls tbh. Blown in, bonded beads for that AFAIC.

 

i did look at eps beads but the u value is poor in comparison to tongue and groove recticel meaning a larger cav. Could be argued a larger cav could pay for itself in reduced brickie work though.

[Nickfromwales]

7 minutes ago, Dave Jones said:

 

i did look at eps beads but the u value is poor in comparison to tongue and groove recticel meaning a larger cav. Could be argued a larger cav could pay for itself in reduced brickie work though.

Yes, I was referring to a retro-fit, as would injected foam be. Cavity batts always number one choice in a masonry build, with cavities as big as you can facilitate / insulation beefed up to suit.

All goes out the window ( literally ) though, as these types of builds are just so inherently, massively dogshit for ventilation heat loss vs fabric heat loss ( with the former an insulation killer ). 

[JohnMo]

2 hours ago, Nickfromwales said:

Did you cap the open cell layer with a layer of closed cell, or did you go for an internal membrane instead?

We used an airtight vapour tight membrane, double sided taped to battens and stapled, all joints and staples aluminium taped.  At the wall the the membrane was glued to wall with airtight mastic.

 

We then added 50mm battens to form a service void and plain plasterboard .

 

[Nickfromwales]

4 minutes ago, JohnMo said:

We used an airtight vapour tight membrane, double sided taped to battens and stapled, all joints and staples aluminium taped.  At the wall the the membrane was glued to wall with airtight mastic.

 

We then added 50mm battens to form a service void and plain plasterboard .

 

Seems very neat, and looks like you had minimal amounts to clean back? Are you happy to share who the installers / suppliers were?

[JohnMo]

We had about 10 bags of trimmings from over 250m2 of roof.  Job was completed in around 2 days.

 

I did all the battens and vapour control layer.

 

Yes very happy to share.

 

The same company built our roof and did the foam (although as two separate contracts).  JHJ Joinery and JHJ Insulation.  They are based near Aberdeen. The guys on site had a really good work ethic, nothing was to much trouble, they got on with it.

Edited April 2, 2023 by JohnMo
Added missing details

[Nickfromwales]

14 minutes ago, JohnMo said:

We had about 10 bags of trimmings from over 250m2 of roof.  Job was completed in around 2 days.

 

I did all the battens and vapour control layer.

 

Yes very happy to share.

 

The same company built our roof and did the foam (although as two separate contracts).  JHJ Joinery and JHJ Insulation.  They are based near Aberdeen. The guys on site had a really good work ethic, nothing was to much trouble, they got on with it.

Fantastic review of them, and thanks for sharing. Always great to mention troopers like those chaps on here for others to possibly then get support from.

Doubt they'd want to travel to the M25 region?

[dabba]

Many thanks for the replies,

With the new building regs in mind would anyone know the likely 'over the rafter' insulation thickness for a warm roof, the company doing the building regs drawings are showing some reluctance (they had designed for between & under the rafters) the reason they have reservations is "it would raise the roof height" which could be an issue with planning. If anyone has a idea of possible over the rafter insulation thicknes along with between the rafter insulation (the attic truss design is 197mm for truss & ceiling timbers) it would be most helpful.         

[ProDave]

19 minutes ago, dabba said:

the company doing the building regs drawings are showing some reluctance (they had designed for between & under the rafters) the reason they have reservations is "it would raise the roof height" which could be an issue with planning.

As I said before if they truly believe that I would sack them.  You have to design the rafters to sit slightly lower so when the external insulation is applied the finished roof height is correct.  If they cannot grasp that simple fact then they would not be detailing my house.

[Dave Jones]

32 minutes ago, dabba said:

Many thanks for the replies,

With the new building regs in mind would anyone know the likely 'over the rafter' insulation thickness for a warm roof, the company doing the building regs drawings are showing some reluctance (they had designed for between & under the rafters) the reason they have reservations is "it would raise the roof height" which could be an issue with planning. If anyone has a idea of possible over the rafter insulation thicknes along with between the rafter insulation (the attic truss design is 197mm for truss & ceiling timbers) it would be most helpful.         

 

you need 250mm of celtex to meet new build regs or 150mm for a refurb. Issue putting it externally on the trusses (warm roof style) is how are you going to fix the tiles ? Putting it between 8 x 2 trusses and then 50mm again under that works. You then have the issue of making it vapour tight which is very hard as you are left nowhere to run cables unless you batten again to make a service void but it wont be deep enough for downlighters unless you use 4x2 at which point you have now lost 150mm of headroom all over the roof.

 

No easy wins.

 

[JohnMo]

3 hours ago, Dave Jones said:

service void but it wont be deep enough for downlighters unless you use 4x2

You only need 50mm battens for downlights, if you select the right ones. The transformer comes seperate and will slip in the void and the lights are slimmer than that.