Yet Another Timber Frame Question

[Thedreamer]

9 minutes ago, BartW said:

Thanks. Trouble is the 32 seems to command double premium compared. 
 

I need 210m2 for external walls, and been working out price difference between TF manufacturer supplied insulation vs PIR (GA4120) vs variables of rockwool, and between PIR and dri35 there was roughly £1500 difference. Let alone, floors, internal partitions, roof, intermediate floors, inner face of external, etc. 
 

 

 

Yeah I expect that would be the case.

 

I used a mixture in my build of PIR and glasswool. If I go could go back I would have just used glasswool. 

 

PIR really is horrible stuff. Dust in your eyes and mouth, a pain to cut and get accurate. Also if you have ever burned PIR it scarily.

Edited December 5, 2020 by Thedreamer

[Oz07]

@Thedreamer I've chucked air in the fire before and it just goes black, doesn't burn whatsoever. You talking about eps?

[Oz07]

air/*PIR

[Thedreamer]

6 minutes ago, Oz07 said:

air/*PIR

 

PIR, Quinn therm in my case.

 

I've burn some on a bonfire and it's produces a lot of heat and horrible toxic black smoke.

 

I was glad when it was all covered up with plasterboard.

 

Zero waste with glasswool, as you can always use bits elsewhere.

[BartW]

With that view in mind, what would you swap the inner PIR anti cold bridge layer with? More rockwool slab, perhaps cross layered and packed as part of the service cavity?

 

[JamesP]

I used 3 layers of Rockwool slabs, cross layered. 140mm,70mm and 50mm in the walls. Also 40mm Pavatherm on the outside of the studs. In the photo you can see the 70mm being fitted horizontally. The slabs are very manageable with zero waste.

[BartW]

1 hour ago, JamesP said:

I used 3 layers of Rockwool slabs, cross layered. 140mm,70mm and 50mm in the walls. Also 40mm Pavatherm on the outside of the studs. In the photo you can see the 70mm being fitted horizontally. The slabs are very manageable with zero
 

 

sounds and looks good

 

 

My target is 0.15. 
 

The plan is to get the TF company to fabricate and erect the structure, lay osb and vcl externally, and then take over from there. Would I do inner layer of earthwool, then inner vcl, then service cavity?

 

I did a quick calculation in a piece of simple ios app, but when I add the “air” layer it reduces the U by quite a bit. All well and good, but timber battens add quite a bit being a cold bridge. 
 

see below for comment please:

 

 

[Oz07]

1 hour ago, JamesP said:

I used 3 layers of Rockwool slabs, cross layered. 140mm,70mm and 50mm in the walls. Also 40mm Pavatherm on the outside of the studs. In the photo you can see the 70mm being fitted horizontally. The slabs are very manageable with zero waste.

interesting birds mouth detail or are they nogs between rafters?

[ADLIan]

Re U value. Thermal bridge in layer 5 at 15% timber will have a big impact. Resistance of 25mm airspace is wrong, should only be 0.18 (not 1.02)

[JamesP]

@BartW  Similar build up to yours, but OSB on the inside. I have enclosed a hand drawing of the wall build up, from the outside its,

Cedar Cladding

Counter batten

Batten

Breather membrane

Pavatherm

3 x Rockwool

VCL

OSB

Batten

PB

 

 

@Oz07  Small birds mouth as I used 3.6m which just fitted.

 

Floor, Wall, Roof Build up Jan 2018..pdf

[Oz07]

It looks like it hooks over the inside edge of plate

[JamesP]

7 minutes ago, Oz07 said:

It looks like it hooks over the inside edge of plate

Yes  it does. 

[A_L]

1 hour ago, BartW said:

see below for comment please:

 

as for ADLIan, only more so, there must be timber in your layers 2, 4 & 5. (or more elsewhere). I have copied your table and added 15% timber to 2, 4 & 5. Result - U value falls to 0.216

 

adding a cavity and brick façade reduces U to 0.205

 

Edited December 5, 2020 by A_L
tidy up

[BartW]

Thanks guys. 
 

How do the TF suppliers manage to back their back up their claims as to uValue then?

 

And is there a more accurate tool I could use to calculate my target U? (PS. mac user here). 

[Thorfun]

31 minutes ago, BartW said:

And is there a more accurate tool I could use to calculate my target U?

Don’t know about more accurate but I’ve been using changeplan. https://www.changeplan.co.uk/u_value_calculator.php

 

[ADLIan]

Get the insulation manufacturer to do them. They tend to have the correct software and know the conventions that must be used

[BartW]

8 minutes ago, ADLIan said:

Get the insulation manufacturer to do them. They tend to have the correct software and know the conventions that must be used

 

Yes, this is on the cards, hopefully won't kick the fuss about it knowing I would want to supply my own insulation.

 

An early comparison for our build as priced by one of the suppliers resulted in savings of nearly £4k + VAT, and that is without shopping around, or optimising the product.

 

Kit supplier price: £8,895 + VAT.

 

Bought individually:

 

[redtop]

On 05/12/2020 at 19:32, JamesP said:

@BartW  Similar build up to yours, but OSB on the inside. I have enclosed a hand drawing of the wall build up, from the outside its,

Cedar Cladding

Counter batten

Batten

Breather membrane

Pavatherm

3 x Rockwool

VCL

OSB

Batten

PB

 

 

@Oz07  Small birds mouth as I used 3.6m which just fitted.

 

Floor, Wall, Roof Build up Jan 2018..pdf 237.97 kB · 9 downloads

Same as mine except I used the smartply for vcl and OSB racking. 100mm rockwool and 140mm pavatherm