Stick built wall build up

[Thorfun]

3 hours ago, Kelvin said:

Have you spoken with your electrician to make sure they are happy putting the oven on the ring main. While some electric ovens can go on the ring a lot of manufacturers state in the specs they need their own protected circuit. What else will be on the ring main? 

+1. 

for our induction hob we needed a 10mm cable. that's one chunky (expletive deleted)!

[Thorfun]

3 hours ago, G and J said:

I used to put built in ovens on a separate circuit till I was told not to bother by the sparky certifying a refurb that included full re wiring.  That’ll be part of the planning I’ll do when I engage with a sparky.  If needed it’ll be easy enough to run in at first fix.

 

Re what else is on the downstairs ring, we’re pretty light on electric around the house, so not much in amperage terms.  We will be having a quooker tap but from memory I think they’re lighter than my kettle.

we have 4 ovens. if running all at the same time there's no way a standard 2.5mm ring would handle it. each oven is on it's own cable and RCBO.

[IanR]

1 hour ago, G and J said:

I wonder if I’ve specified an inappropriate membrane on layer 9 then?

 

No, breather membrane is correct, it's your cement particle board I believe. It's for wet areas, so assume vapour closed. Between it and your vapour barrier (@ 5) no moisture can get out.

[saveasteading]

2 hours ago, G and J said:

you have further insulation within the frame?

That is within. Then there is some on the inner face. We've got about 10 construction details because it is 3/4 convert and 1/4 replace.

[Kelvin]

Worth reading this as it explains how humidity changes over the year and the impact on your building. Obviously it’s flogging their product too. 
 

https://proclima.com/building_science/why_airtight/intelligent_airtightness

[Thorfun]

2 hours ago, G and J said:

I wonder if I’ve specified an inappropriate membrane on layer 9 then?

or is it the cement particle board? I think the external build up looks different to most timber frames I've seen. definitely different to ours! from out to in we have 

 

vertical timber cladding

45mm batten and counter batten

breathable membrane

osb

140mm timber with

140mm frametherm 32

80mm PIR

AVCL (IntelloPlus)

25mm battens

12.5mm plasterboard

skim

 

I pretty much copied MBC https://mbctimberframe.co.uk/closed-panel-wall-options/

 

didn't read @IanR's response before I posted. he got there first! 😉 

Edited June 20 by Thorfun
didn't read earlier posts before posting.....idiot.

[Kelvin]

I think you need to shift your focus from maximising a few mm of floor space to the best wall build up for moisture mgt, air tightness, and insulation. Those are the three most important factors. 

[saveasteading]

47 minutes ago, Kelvin said:

shift your focus from maximising a few mm of floor space

Agreed. We fretted over losing 100mm of the effective width. As finished it doesn't cross our minds that it might have been wider, especially sitting in the cosy space.

Yes optimise the space if there are no other constraints, but build quality comes top.

[IanR]

You've specified 600 centres on your studs, what happens to your U Value if you specify 400 centres?

[saveasteading]

4 minutes ago, IanR said:

what happens to your U Value if you specify 400 centre

The area of wood increases and of insulation decreases. Prorata the area to get the 2 values.

[G and J]

3 hours ago, IanR said:

You've specified 600 centres on your studs, what happens to your U Value if you specify 400 centres?

 

3 hours ago, saveasteading said:

The area of wood increases and of insulation decreases. Prorata the area to get the 2 values.

Yep, my u value gets worse with reducing centres.  I only know this because I wrongly put 1200mm in to start with.  Thankfully I’m used to feeling dumb and can smile about it. lol 

[MikeSharp01]

6 hours ago, Thorfun said:

if you're using the OSB as an airtight layer then you're penetrating it and making it pointless

You can get away with this while you make sure the screws pull the board down tight and the screw gets covered with skim. The screws will relax a little over time but even then the gaps around the threads won't add up to much on the scale of things. 

[G and J]

3 hours ago, saveasteading said:

Agreed. We fretted over losing 100mm of the effective width. As finished it doesn't cross our minds that it might have been wider, especially sitting in the cosy space.

Yes optimise the space if there are no other constraints, but build quality comes top.

I suspect you may be misunderestimating (with a nod to George W) my capacity for fretting.  I can fret about it all at once (it’s my version of multi tasking!). 
 

Being serious my thinking is that as a basic principle one sets the ideal as a goal.  One gives ground unwillingly, and at times, one appears intransigent.  But at the end of the process enough of the right info is gleaned then a good decision can be made.  And yes quality comes top.  Now all we need to do is identify what quality means.  🤷‍♂️

[G and J]

6 hours ago, IanR said:

 

No, breather membrane is correct, it's your cement particle board I believe. It's for wet areas, so assume vapour closed. Between it and your vapour barrier (@ 5) no moisture can get out.

Oddly, if I swap the cement particle board for Osb it makes no difference.   Boy am I out of my depth.  
 

I'm working hard to understand stuff so that we can make informed decisions when the architects pick things up, and I am learning lots, I think, but I feel a long way from having a good handle on all this.  I do appreciate the time you are all putting in.

[SteamyTea]

1 hour ago, G and J said:

Oddly, if I swap the cement particle board for Osb it makes no difference.   Boy am I out of my depth

The hard part is often getting the vapour permeability numbers for different products, it is even harder getting them in the same units.

 

20 seconds of googling got me here.

 

https://efficiencymatrix.com/common-building-materials-vapor-permeance-table/

 

I wonder if an inverse square rule is what works best i.e. each outer layer needs to allow twice as much vapour though.

 

Edited June 20 by SteamyTea

[G and J]

Soooo, I think I’m at a point where I do need to wait for my architect input.

 

I have various wall build ups of various thicknesses, none of which I can yet be confident about moisture control.  I don’t know that there’s a problem with them, but I need to know there won’t be.

 

I have a wall build up made of lots of PIR which fits my desired thickness and has a good u value, but opinions have been shared about the acoustic properties of that design (and how nice a house built such will be to live in).
 

Alternative insulation yields designs which are either a bit thicker, have a lower u value of both.  I like the 140mm rockwool batts idea in terms of acoustic attenuation but I don’t yet know if we can trade off the insulation level with other elements.

 

The idea of some PIR part filling the frame, then rockwool filling the rest of the frame, then another layer of PIR sounds like a good compromise but it makes a PIR/rockwool/PIR sandwich and that sounds like a recipe for trapped moisture, unless PIR will allow moisture through - maybe the non foiled stuff will.

 

For me, having built a blockwork house, concerns about wall solidity play straight to my anxieties, so if anyone has a timber clad, PIR insulated house I’d be very grateful for you sharing your thoughts on my concerns and whether they are reasonable.  
 

On the brightside, yesterday I bought a shiny new tailored boiler suit.  Tailored meaning I cut 8’ off of the legs (I’m short and round) using pinking shears (it is pride week).  So I may not have a wall design yet but I do now look like a navy blue Tinky Winky.   

[Kelvin]

SIP builds are essentially timber kits with PIR. Loads of them in Scotland many of which are timber clad. You don’t need to worry about the strength of them. 
 

On the acoustics. I have a SIP metal garage where the insulation is 80mm thick. Now you can’t compare that directly with a house but whatever noise is happening outside is almost as loud inside. Noise attenuation doesn’t rely on a single material anyway and making that material thicker doesn’t necessarily help either. You need multiple materials and for it to be well sealed. SIP houses I’ve been in haven’t been as quiet as ours though. 

[SteamyTea]

Can you fit your internal plasterboard onto resilience bars, rather battens, that will reduce noise transmission and not cost much?

[MikeSharp01]

32 minutes ago, SteamyTea said:

Can you fit your internal plasterboard onto resilience bars, rather battens, that will reduce noise transmission and not cost much?

That will give you only 17mm void (They are normally 17mm deep), so 42 assuming a 25x50 counter batten as well or you will need to cut slots in the resilient bars to get any cables through them.

[saveasteading]

9 hours ago, G and J said:

unless PIR will allow moisture through

No it will not. Try  some held under water. It will pop up and be as dry inside as when it went in. 

 

9 hours ago, G and J said:

I don’t yet know if we can trade off the insulation level with other elements.

 

you can, in that it is allowed as long as a minimum level is maintained for he each element.

 

7 hours ago, Kelvin said:

whatever noise is happening outside is almost as loud inside.

I have not found this, so I suspect some flanking path.  But you are right that a sandwich PIR will not be as absorbent as a mineral wool one.

 

9 hours ago, G and J said:

sounds like a recipe for trapped moisture, 

I have to admit that dew point is not something I've ever calculated, so must have been lucky every time.....or it isn't much of an issue in real life and normal room conditions.

[saveasteading]

20 minutes ago, SteamyTea said:

Can you fit your internal plasterboard onto resilience bars, rather battens,

Rather than battens? How about the resilient bars fixed to a cleat or block of some sort, so that there is rom for cables?  I might think this through and patent it.

[G and J]

6 minutes ago, saveasteading said:

I have not found this, so I suspect some flanking path.  But you are right that a sandwich PIR will not be as absorbent as a mineral wool one.

So if we work hard on being airtight then it sounds like a fully PIR solution should yield a nice place to live.   It’s not a noisy environment, and we are close flanked both sides by neighbours with the narrow alleyways in between very rarely used (except by me carting loads of greenery from front to back for tip runs).  

[SteamyTea]

17 minutes ago, MikeSharp01 said:

you will need to cut slots in the resilient bars to get any cables through them

 

13 minutes ago, saveasteading said:

I might think this through and patent it.

Resilience bars are normally shown fitted horizontally, but they will perform the same if fitted vertically, which is the way that cables are normally run down walls.

[Iceverge]

Given the constraints of your circumstance you must decide where to compromise. 

 

In opting for a rigid U value target for a given width you may have missed the wood for the trees a bit. 

 

Say you get your approx 150m2 of wall to a theoretical 0.12 instead of a realistic 0.18. that's a difference of 0.06w/m2K

 

150m2 x  dt20⁰ x 0.06w/m2K. That's about 180w in the peak heating load over say a floor area of 120m² it's 1.5w/m². 

 

At another guesstimate that's about 200kWh/annum or £32 per year. 

 

Now account for the poorer airtighess performance, material wastage during building, additional cooling load due higher decrement delay. Poorer noise and fire performance. 

 

Be very careful about putting PIR In a stud wall. 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Thorfun]

24 minutes ago, SteamyTea said:

 

Resilience bars are normally shown fitted horizontally, but they will perform the same if fitted vertically, which is the way that cables are normally run down walls.

They’re run perpendicular to the timbers to reduce contact points as they’re mostly for reducing impact noises. 
 

so you could run horizontal battens across the TF and then run the resilient bars vertically. But then you might as well run vertical battens and horizontal resilient bars and can run cables behind the bars!