Sorry to jump in, still trying to sort our insulation! So, out of interest, how much more thermally efficient is a wall with a U value of, say, 0.19, compared to one at 0.22? Are we talking a few ££s a year in heating costs or a lot more? 

I'm still trying to get U values calculated for mine, based on 140mm Frametherm between the studs and 25mm PIR inside. Also, is there a thermal membrane that can go on the outside of the kit that may help?

 

 

1 hour ago, davejura said:

how much more thermally efficient is a wall with a U value of, say, 0.19, compared to one at 0.22? Are we talking a few ££s a year in heating costs or a lot more? 

 

Typically this would save about 1.7kWh/m² /yr in Central England 

 

54 minutes ago, davejura said:

I'm still trying to get U values calculated for mine, based on 140mm Frametherm between the studs and 25mm PIR inside

 

Here is a similar wall below, U=0.20. If Protect TF200 Thermo, a low emissivity layer is added to the unventilated cavity the U value will improve to 0.17 

 

 

7 minutes ago, A_L said:

Typically this would save about 1.7kWh/m² /yr in Central England 

Thanks. So about £40 - £50 per year for a 175 sq M floor area 2 story house, at a guess?

 

I'm keen to use Frametherm as it is cheaper and easier to fit. I'll look into using the Protect 200 thermo and also an internal layer of 25mm PIR.

3 minutes ago, davejura said:

Thanks. So about £40 - £50 per year for a 175 sq M floor area 2 story house, at a guess?

 

N.B. the m² is wall area, remember it is energy lost through wall,  allow for any inefficiency in turning fuel into heat, e.g. saving 1kWh of heat saves about 1.2kWh of gas

OK thanks, so a bit more then. Heating will be by ASHP and UFH. Really struggling to get my head around this SAP calculation carry on!

On 17/03/2021 at 08:49, Thorfun said:

agree with @dpmiller and @Russell griffiths. we're simply copying what a lot of the major TF manufacturers do in the factory. here's the MBC example.

 

https://www.mbctimberframe.co.uk/closed-panel-wall-options/

 

I had a look at the MBC examples in that link and I think they've got the 'U' value calculation wrong for this one. I reckon it's somewhere between 0.16 and 0.17W/m2K instead of the 0.14 they are showing on the website.

 

 

Edited March 19, 20215 yr by Ian

4 minutes ago, Ian said:

 

I had a look at the MBC examples in that link and I think they've got the 'U' value calculation wrong for this one. I reckon it's more like 0.16W/m2K instead of 0.14.

 

 

yeah, I've questioned this before (can't remember on what thread though) and also can't comment on MBC's marketing figures.

 

I guess I should have caveated the post with 'make sure you get your own calculations done on the expected U-values'.

22 minutes ago, Thorfun said:

yeah, I've questioned this before (can't remember on what thread though) and also can't comment on MBC's marketing figures.

 

I guess I should have caveated the post with 'make sure you get your own calculations done on the expected U-values'.

not intended as criticism of you in any way....I just thought it looked wrong so checked and I couldn't get it any better than 0.16W/m2K using 2 different 'U' value claculators. It's more likely 0.17W/m2K.

I still find it very strange that MBC seem to have got it so wrong (maybe its me that's wrong?)

Just remember that PIR between studs had to be done very well (foamed AND Taped) if it’s done shite then it’s as much use as an ashtray on a motorbike.... 

Doing it really well is very time consuming (I am doing it right now....) and you should not “assume” your builder is going to do a pukka job if working to a set price or finds this sort of detailing “unnecessary” using a compressible insulation between the studs gives you a much better chance of getting it right and then stick as much PIR as you can (within reason...)on the inside to really bolster up your U-Values. 

29 minutes ago, Ian said:

not intended as criticism of you in any way

none taken! we are in agreement that it's strange MBC seem to have gotten it wrong. I'll see if I can find the previous posts on this wall make up and link them here...

@Ian I found the post I was referring to, although no one actually responded as to the difference as that's probably as I'd answered it myself.

 

@A_L and @ADLIan are both wizards at U-value calculations and they've helped me loads on various posts, but I still find it hard to get my head around all the nuances. I think I need to re-read all my previous threads on this subject for a recap.

I've not checked through any of the above U-values but remember the calculation will be different between England & Scotland. Timber frame in Scotland requires a ventilated cavity behind the brick/block cladding which means anything external to the breather membrane is ignored in the U-value calculation (but external resistance is altered). In England this airspace is vented so the cavity and external masonry can be included - particularly important when using reflective breather membranes.

39 minutes ago, ADLIan said:

In England this airspace is vented

 

Can I ask, are you using <500mm² per m length for vertical air layers as defining vented but unventilated, if you see what I mean?

That would be classed as unvent surely. Even if slightly vent, 500-1500mm2/m, the software I use still gives resistance of 0.18 m2K/W for the cavity. Suppose it depends how you define this airspace in TF - weep holes are left but any ventilation from these is fortuitous and probably can be ignored.

How does this look guys? Thanks in advance

I questioned MBC at the self build show about this.

Guy said it was to do with the staggered studs, and something else I cannot remember.

@Ian  When we modelled the 140mm option alongside the 300mm twin-wall, we were advised to use 0.17W/m2K

 

Few reasons:

- MBC calculation assumes external 100mm concrete.

- MBC calculation assumes external 50mm unventilated external cavity.

- Value of foil breather membranes is questionable.

 

 

like @Cpd said I would caution putting PIR in a stud wall. it’s a tricky slow job to get right ( which means it almost never is). 

 

Add to that the shrinking of timber and board  insulation  and you’ll have a wall full of gaps and a cold house. 

 

Save your builder some heartache and your pocket some cash and use a good quality insulation batt. 

 

Doing much to boost U values beyond building regs isn’t near as useful as getting really good airtighness, MVHR and triple glazing. Worrying about the third decimal place in U values (although it is a pastime of mine!) won’t get you a warm house. Good detailing will.

7 hours ago, Iceverge said:

Add to that the shrinking of timber and board  insulation  and you’ll have a wall full of gaps and a cold house. 

 

Does spray insulation like Icynene have the same issues? The fact it goes in wet and super sticky, does it not adhere to the surrounding timbers/boards and guard against timber shrinkage/expansion?

6 minutes ago, Onoff said:

 

Does spray insulation like Icynene have the same issues? The fact it goes in wet and super sticky, does it not adhere to the surrounding timbers/boards and guard against timber shrinkage/expansion?

If it stays flexible (I think Icynene is flexible) then it should.  PUs over expand during curing and continue to shrink for months, this can cause problems if the bond between timber and foam fails.  Water is often used as the foaming agent.

6 hours ago, Onoff said:

 

Does spray insulation like Icynene have the same issues? The fact it goes in wet and super sticky, does it not adhere to the surrounding timbers/boards and guard against timber shrinkage/expansion?

 

Much better option. Not cheap though. 
 

I think Peter Stark ( if i remember correctly) used it without any membrane and had passivhaus airtightness. Either I can't use the search correctly or he's disappeared? His blog was very useful. 

 

If I had a choice for timberframe I'd use blown in cellulose everytime. It's got a great decrement delay, C02 negative, vastly improves airtightness, is non toxic, leaves little mess to clear up and is cheaper than PIR. If you have good installers It gets into all the nooks and crevices that board and batt insulation can't.  

15 minutes ago, Iceverge said:

 

Much better option. Not cheap though. 
 

I think Peter Stark ( if i remember correctly) used it without any membrane and had passivhaus airtightness. Either I can't use the search correctly or he's disappeared? His blog was very useful. 

 

I visited Peter's house, fantastic it was too. Warm and very well insulated against sound too. Way back he helped me out with some bits for my Geberit WC when I was as green as green doing those things.

 

Incredible attention to detail on his house. The finished article looked like his CAD renderings! The Icynene installers came in a horsebox sized truck with tanks of the two components if I recall correctly. Lots of waste with it. They infill between the joists and leave you to trim it flush with a saw they give you and to bag all the trimmings up.

 

Seems he's changed his username and is in fact on the move.

 

@Gone West is the name he's going by now I think.

 

I too looked for the blog but it seems to have disappeared.

Glad to hear it. @Gone West was one of the original blogs I drew much knowledge from over the past 6 years of this process.