Posi rafter roof insulation

[Nickfromwales]

4 hours ago, Rishard said:

@Nickfromwales could I get Gordon’s number also? 

I'll ping it over by PM mate  

[Rishard]

I’m the joiner fitting so shouldn’t cost much 🥴

 

Which option roof build up are you favouring then? Any wood fibre on yours? 

[SBMS]

5 minutes ago, Rishard said:

I’m the joiner fitting so shouldn’t cost much 🥴

 

Which option roof build up are you favouring then? Any wood fibre on yours? 

I was the OP and the first post on this thread is my makeup 👍

[Rishard]

Ah yes of course. Are you having a service void? I had a calculation done similar to your build up with a 45mm mineral wool filled service void and using a 40mm woodfibre externally and got to 0.10W/m2K 

[SBMS]

5 minutes ago, Rishard said:

Ah yes of course. Are you having a service void? I had a calculation done similar to your build up with a 45mm mineral wool filled service void and using a 40mm woodfibre externally and got to 0.10W/m2K 

Yes 38mm service void probably. 22mm steico woodfibre board. Haven’t thought of stuffing mineral wool in the service void… that will probably get me to 0.11 actually 👍

[SBMS]

7 minutes ago, Rishard said:

Ah yes of course. Are you having a service void? I had a calculation done similar to your build up with a 45mm mineral wool filled service void and using a 40mm woodfibre externally and got to 0.10W/m2K 

This is my makeup if it helps 

 

[JohnMo]

4 minutes ago, SBMS said:

This is my makeup if it helps

The plan is vague stating slate or concrete tiles. But they both have a different roof build up. Concrete Tiles need the battens and counter battens on sarking boards, natural slate on the other hand, just needs the breather membrane on sarking boards and then the slates directly attached to sarking boards.

[Rishard]

You can’t hang slates off a 22mm woodfibre sarking board. Depending where this is, Scotland slate roofs differently to the uk. Uk on to tile batons which is what this plan refers to I believe.

Edited April 7 by Rishard

[SBMS]

13 minutes ago, JohnMo said:

The plan is vague stating slate or concrete tiles. But they both have a different roof build up. Concrete Tiles need the battens and counter battens on sarking boards, natural slate on the other hand, just needs the breather membrane on sarking boards and then the slates directly attached to sarking boards.

We are using slates and counter battening. Warmcel (cellulose provider) recommended counter battens.

[JohnMo]

9 hours ago, Rishard said:

Scotland slate roofs differently to the uk

Geography lesson 

United Kingdom, made up of England, Scotland, Wales and Northern Ireland.

 

UK I take it you mean England?

 

9 hours ago, Rishard said:

You can’t hang slates off a 22mm woodfibre

No you can't. But as I said the roof build up is vague at best, at the wood fibre layer, there seems to be 3 options (OSB, wood fibre or sarking boards), which is pretty poor, there should be no options, it should state what is expected.

[Rishard]

I love a vague plan. Thanks for the geography lesson, must have needed more sleep. 

[SBMS]

2 hours ago, JohnMo said:

Geography lesson 

United Kingdom, made up of England, Scotland, Wales and Northern Ireland.

 

UK I take it you mean England?

 

No you can't. But as I said the roof build up is vague at best, at the wood fibre layer, there seems to be 3 options (OSB, wood fibre or sarking boards), which is pretty poor, there should be no options, it should state what is expected.

I asked the architects To pop the options on for contractor quoting because we hadn’t settled on a roof makeup 😉We have now.

 

We are using steico wood fibre sarking boards which do not recommend direct tile

fixing and recommend battens fixed through to rafters to pin the board on. So that’s what we are doing. 

[Rishard]

21 hours ago, SBMS said:

I got a quote for this - was nearly double cellulose for some reason for the same thermal performance. 

Just worked out for mine, the same thickness of Knauf Omni fit slabs 0.034 come in around 2k cheaper than the blown cellulose to the same thickness. Cellulose - 0.038. Bit more time installing but not drastic work if rafters set out to suit the slabs. 

[SBMS]

3 hours ago, Rishard said:

Just worked out for mine, the same thickness of Knauf Omni fit slabs 0.034 come in around 2k cheaper than the blown cellulose to the same thickness. Cellulose - 0.038. Bit more time installing but not drastic work if rafters set out to suit the slabs. 

Yeah that sounds about right. I priced it up and it was around 5k for the glass wool slabs without fitting. I like the fact that the cellulose blows into all the nooks and because I’ve got posi rafters will blow into the metal webs as well further reducing thermal bridging. 

[Rishard]

59 minutes ago, SBMS said:

Yeah that sounds about right. I priced it up and it was around 5k for the glass wool slabs without fitting. I like the fact that the cellulose blows into all the nooks and because I’ve got posi rafters will blow into the metal webs as well further reducing thermal bridging. 

Yes it’ll work well with posi joists. I saw the green building store had to rip PIR to flush up the web on their posi rafters which would be a bit of a pain. 

[JohnMo]

Pozi rafters and anything manually fitted for installation would be a utter pain. To get it done well expensive and not likely to happen. Blown in gets everywhere (when done well - will slump over time, when not done well).

 

We did spray foam, really quick hardly any mess, vapour stop membrane below, breather membrane above. Not the same job as a cowboy installer spraying under a vapour stop old membrane in a cold roof.

[Mr Punter]

2 hours ago, JohnMo said:

We did spray foam, really quick hardly any mess, vapour stop membrane below, breather membrane above. Not the same job as a cowboy installer spraying under a vapour stop old membrane in a cold roof.

 

The trouble is that lenders, insurers and surveyors do not see it that way and spray foam is considered high risk.  They don't differentiate between idiot cowboys spraying badly onto the underside of slates and perished underlay on an old knackered roof and an install to a new building, properly detailed, designed and applied.