Insulation vs Batons

[mike2016]

I'm aiming for a wall U value of 0.1 and have a build up requiring 360mm of Moy Metac (0.034 W/mK). The Timber Frame is 220mm deep so that gets me 2/3 of the way there and I can put Intello Plus at this point - 2/3 rule where 2/3 of my insulation is on the cold side of the Intello. That leaves 120mm left to insulate.

 

I'm not sure how to counter baton that deep with 120mm batons and if it would even hold? There's a service cavity and plasterboard to add to this also. 

 

I was thinking of a 50mm counter baton and then revert to vertical 100mm batons onto which the plasterboard will go leaving a 30mm gap and space for back boxes etc. While the horizontal 50mm batons can easily fix to the timberframe structure at 600mm centers, the 100mm vertical batons will be trying to fix at the same point on top of the 50mm batons. Maybe I use some type of rafter tie or other side fixing to ensure this connection is solid? 

 

Advice appreciated as always! Thanks. 

[SimonD]

why not just build a second internal stud wall using 38 x 140 studs? Job done.

[mike2016]

It would need to be offset from the outside wall wouldn't it? I like the twin stud concept MBC use but my timberframe provider doesn't supply that. It's just the thermal bridging I need to block.....

[SimonD]

It's far easier to build a second wall with studs offset than it is to counter batten as you've suggested. Why was the wall not fully designed for this before the build?

[Thorfun]

Have you done the calculations to see what benefit getting 0.1W/m2K gives you over, say 0.12W/m2K? 
 

I used Jeremy’s spreadsheet to do the calculations and found it made little difference in heat demand and air tightness had a greater effect. So you could be going through a lot more work and expense for not much benefit. 

[mike2016]

On 05/04/2024 at 22:46, SimonD said:

It's far easier to build a second wall with studs offset than it is to counter batten as you've suggested. Why was the wall not fully designed for this before the build?

It's a case of the only twin stud wall builder won't supply to Dublin anymore, the team I got are excellent but have a preferred approach. As it's my first build I've been trying to get something built rather than getting it perfect first time. 8 year journey so far!! Timing is part of the reason I've ended up where I am today! 

On 06/04/2024 at 08:47, Thorfun said:

Have you done the calculations to see what benefit getting 0.1W/m2K gives you over, say 0.12W/m2K? 
 

I used Jeremy’s spreadsheet to do the calculations and found it made little difference in heat demand and air tightness had a greater effect. So you could be going through a lot more work and expense for not much benefit. 

PHPP dictates U values of 0.1 - I've compromised on the passive floor slab a bit as the pipe run drops were very tight, I hope to hit 0.1 on the walls and roof if possible. Paid a lot for that PHPP design! That's my current aim before I adjust for cost / skills / other reasons. It definitely looks like a second stud wall for fibre insulation or battens on top of more rigid insulation like Gutex to tick the box for me right now. 

I was out onsite today so planning on Gutex still for the underside of the roof and then either stud or battens for interior walls or a mix of both in different areas - the open plan kitchen / living space has very high walls challenging my stud wall skills a bit! Will chat to the builder and get their take on it. 

At least I'm 99% certain the Intello Plus layer is going to be at the 220mm Frame interior wall so can take my time to decide the rest of the build up until the first air tightness test is passed. 

Thanks all. 

[Thorfun]

40 minutes ago, mike2016 said:

PHPP dictates U values of 0.1 - I've compromised on the passive floor slab a bit as the pipe run drops were very tight, I hope to hit 0.1 on the walls and roof if possible. Paid a lot for that PHPP design! That's my current aim before I adjust for cost / skills / other reasons. It definitely looks like a second stud wall for fibre insulation or battens on top of more rigid insulation like Gutex to tick the box for me right now. 

I was out onsite today so planning on Gutex still for the underside of the roof and then either stud or battens for interior walls or a mix of both in different areas - the open plan kitchen / living space has very high walls challenging my stud wall skills a bit! Will chat to the builder and get their take on it. 

At least I'm 99% certain the Intello Plus layer is going to be at the 220mm Frame interior wall so can take my time to decide the rest of the build up until the first air tightness test is passed. 

Thanks all. 

so you're going for Passive House certification? if not then you don't need to do what PHPP says! like you say you might need to do some value engineering to reduce costs in which case lowering your target U-value would be a good way to make savings as it definitely has diminishing returns when adding insulation past a certain point.

 

Also, for me I wanted the AVCL on the inside of all the insulation. I know you're allowed to have insulation inside the AVCL it but it just didn't seem right to me. but there are many ways to build. best of luck. fabric first is definitely the way to go!

[mike2016]

Thanks! I can put the Intello Plus behind all the insulation but it means extending the detailing provided by the timber frame builder and I'm not that confident yet with so many critical junctions in getting them all right. I plan to install 220mm insulation, then the Intello, and test air tightness before adding the extra layers inside this. Not going for the certification as can't afford the Architect any more but wanted to aim high and the fabric is where I'm not holding back cost wise. Thanks for the advice/insight!