EPS beads here. They're fine although I am slightly suspicious of the claimed k value of 0.033. I think 0.035-0.037 world be closer in reality. 

 

Over all would recommend.

5 minutes ago, Iceverge said:

EPS beads here. They're fine although I am slightly suspicious of the claimed k value of 0.033. I think 0.035-0.037 world be closer in reality. 

 

Over all would recommend.

Thanks. I will do some research into this. It's likely that I will be doing my own blockwork so there would be no installation cost (just my time) associated with the mineral wool. I would, presumably, have to pay someone else to install the beads so this might be a deciding factor for me.

I've done some calculations. I'll share them here incase they are of use to someone else (or someone can pick me up on any mistakes).

 

I have about 420m2 of external cavity wall area which will sit on a total of 114m of foundations.

 

I have compared the two following options:

 

Option 1 - 20mm external render/100mm dense block/150mm 32 cavity slab/100mm dense block/20mm internal render+skim finish - which will give me a u-value of around 0.20 (not sure I trust the calculator I've used to reach this figure)

 

Option 2 - 20mm external render/100mm dense block/200mm 37 cavity slab/100mm dense block/20mm internal render+skim finish - which gives me a u-value of around 0.18

 

Costings 

 

Option 1 - £11,500

420m2 of 150mm 32 cavity slab ~ £7000 

37m2 of concrete in footings (based on 600mm wide and 550mm deep) ~£4000

1000 wall ties ~ £500

 

Option 2- £10,240

420m2 of 200mm 37 cavity slab ~ £4200

44m2 of concrete in footings (based on 700mm wide and 550mm deep) ~ £4840

1000 wall ties ~ £1200 (not sure about this figure, more research required)

 

I can use concrete lintels on almost all the openings so there are no additional costs there.

 

Unless I am missing something, it would appear that it is infact cheaper to go for the 200mm cavity option which also provides a better u-value.
 

 

 

Edited April 27, 20251 yr by Ben1984

@tonyshouse

 

http://tonyshouse.readinguk.org/

 

Good blog here from tony. Don't know if he's still active or not. 

 

Similarly from Green building store there's a series of videos about denby dale passivhaus, great details for a cavity wall house. 

 

 

5 hours ago, Ben1984 said:

What software/calculator have you used to produce this? 

 

 

Ubakus.de

54 minutes ago, LiamJones said:

Ubakus.de

Thanks, that's seems much better than the calculator I had been using

25 minutes ago, Ben1984 said:

Thanks, that's seems much better than the calculator I had been using

We are doing our second build and have opted for 200mm cavity with eps beads. Coming out around 0.15 u value. We are doing dot and dab however I am going to use aerobarrier for air tightness.  It negates the need for a parge cost on Inner block, performs sealing around windows etc. will be doing it pre plaster. Not commonly used on here so I will be reporting back how it goes when we get to that stage of the build.

4 minutes ago, SBMS said:

We are doing our second build and have opted for 200mm cavity with eps beads. Coming out around 0.15 u value. We are doing dot and dab however I am going to use aerobarrier for air tightness.  It negates the need for a parge cost on Inner block, performs sealing around windows etc. will be doing it pre plaster. Not commonly used on here so I will be reporting back how it goes when we get to that stage of the build.

 

Are you not worried about using excessive amounts of the aero barrier caulk? 

 

Keep us posted. 

52 minutes ago, SBMS said:

We are doing our second build and have opted for 200mm cavity with eps beads. Coming out around 0.15 u value. We are doing dot and dab however I am going to use aerobarrier for air tightness.  It negates the need for a parge cost on Inner block, performs sealing around windows etc. will be doing it pre plaster. Not commonly used on here so I will be reporting back how it goes when we get to that stage of the build.

I think I could hit the same 0.15 u-value by using a better quality mineral wool but it would pretty much double the cost of the insulation. I'm failry certain I would never get that £7000 back! I've re-done my calculations on ubakus.de calculator and they are coming out at 0.17 with 200mm of Knauf 37 - I'm more than happy with that.

 

I've had a quick look at the aerobarrier - seems like a good idea. Have you got a quote for your project yet? I don't think I will need it with a wet plaster finish but i'd be interested to have a rough idea of what it might cost.

 

Here's one of a few technical videos about denby dale. Well worth the view. 

 

I would alter the foundation, thresholds and window detail slightly but it's a great starting point.

23 hours ago, Iceverge said:

Are you not worried about using excessive amounts of the aero barrier caulk? 

 

Not especially to be honest - I did ask them and they said it was ultra low VOC, water soluble and effectively chemically inert. But would be interested if you’ve ready different!

23 hours ago, Ben1984 said:

I've had a quick look at the aerobarrier - seems like a good idea. Have you got a quote for your project yet?

Yes it’s about £3900 for our 380 sqm so around £10 per sqm. Sounds a lot but there’s no need for parging, or taping round windows or sealing floor wall junctions. They are aiming to get to 0.6ACH or lower. 

5 minutes ago, SBMS said:

parging

Sorry can't help myself

 

We did approx 210m² Durisol blocks (so full of holes) with sand, cement and lime parge, 2 off us a day and half and nearer £200 than £4k. Block work would have used half the parge coat.

 

So not very good value for money.

5 minutes ago, JohnMo said:

Sorry can't help myself

 

We did approx 210m² Durisol blocks (so full of holes) with sand, cement and lime parge, 2 off us a day and half and nearer £200 than £4k. Block work would have used half the parge coat.

 

So not very good value for money.

I agree that there are cheaper ways - but parging isn’t the only cost. Liquid membrane at floor and wall junctions, airtightness tapes (we have a lot of glazing) and an overall complex irregular building shape. 
 

I’ve not focused on how much it costs so much as what the return on the investment is. Getting airtightness right makes a large impact on energy savings and that’s what I focused on when looking at the cost of aerobarrier. That and the certainty of knowing, pre plaster what the airtightness is, and outsourcing this part of the build. In the grand scheme of things the 4K is an excellent return on investment if it can achieve the level of airtightness promised. In the context of the whole of the build it’s an effective ROI. But I do get your point John -

in the same way it’d be cheaper for me

to fit my Own windows, lay my Own bricks

or pour my own concrete! This is something I decided to outsource for speed, and certainty. 

2 hours ago, JohnMo said:

Sorry can't help myself

 

We did approx 210m² Durisol blocks (so full of holes) with sand, cement and lime parge, 2 off us a day and half and nearer £200 than £4k. Block work would have used half the parge coat.

 

So not very good value for money.

Also just for devils advocate ive got 385sqm of external walls so about double yours. Plus some horrible full height vaulted areas. If I were to pay 2 lads 4 days at £200 a day to parge that’s still about £1600 Without materials - and it’d probably take longer than that as they’d need scaffolding or towers inside for tricky bits. And then there’s the worry if they got it all 100%. Then there’s the tapes etc for windows and labour for that on top. I think that’s a fairer cost comparison than doing it yourself with free labour. If I had time though I would - and would do a lot more on the build myself as well!  

The other thing this gives you is an air tightness certificate.

 

I think it's pretty neat, especially on a bigger/more commercial project where you are operating to a schedule and just need this 'done'.

24 minutes ago, bmj1 said:

The other thing this gives you is an air tightness certificate.

 

I think it's pretty neat, especially on a bigger/more commercial project where you are operating to a schedule and just need this 'done'.

Not really, it is being done prior to second fix so will not be valid.  So will need to be repeated.  It's more akin to a prior to second fix diagnostic test.

2 hours ago, SBMS said:

Also just for devils advocate ive got 385sqm of external walls so about double yours. Plus some horrible full height vaulted areas. If I were to pay 2 lads 4 days at £200 a day to parge that’s still about £1600 Without materials - and it’d probably take longer than that as they’d need scaffolding or towers inside for tricky bits. And then there’s the worry if they got it all 100%. Then there’s the tapes etc for windows and labour for that on top. I think that’s a fairer cost comparison than doing it yourself with free labour. If I had time though I would - and would do a lot more on the build myself as well!  

Have a look at the Aerobarrier system. https://www.aerobarrieruk.co.uk/

 

Cheaper and better than you think. They say if you just foam the windows and cut it flush they can take over from there. Speak to them and get a quote / do the maths, I think you'll be pleasantly surprised. Certainly an option, and a 1 day sitting and they're done.

Plasmor Aglite Ultima blocks are a good compromise on thermals (K= 0.31 W/mK)/cost and are solid enough to cut fine without crumbling. Versitile too, as can also use them in B&B floors.

 

 

11 hours ago, SBMS said:

the certainty of knowing, pre plaster what the airtightness is,

I think there's a lot to be said for this. While boarding out can be done very well it can also be done very badly for airtightness without that being obvious and post plaster is an expensive time to try and make improvements.

 

 Airtightness is an area it helps to be hands on to ensure it's done well, but if you can't give the time then at least aerobarrier sounds a reliable way of outsourcing for a good result

@zagaboo I agree Plasmore have good compromise options. We used their Fibolite which are 0.28 and still readily take fixings, direct nailing compared to thermalite

13 hours ago, SBMS said:

Not especially to be honest - I did ask them and they said it was ultra low VOC, water soluble and effectively chemically inert. But would be interested if you’ve ready different!

 

It was the cost I was thinking of. Caulk is pretty inert as you say. I assumed they charged on a time and materials basis and concrete blocks are pretty porus a d would need lots of sealing if not wet plastered first. 

 

 

55 minutes ago, Iceverge said:

Caulk

I never come across a caulk that doesn't shrink and leave gaps everywhere after a couple of years. If caulk based I really wouldn't bother, will it last? Will you be airtight in a years time?

1 hour ago, JohnMo said:

I never come across a caulk that doesn't shrink and leave gaps everywhere after a couple of years. If caulk based I really wouldn't bother, will it last? Will you be airtight in a years time?

I think they’ve had independent testing that guarantees for 50 years without deterioration. But that’s their marketing speak!

12 hours ago, Nickfromwales said:

Have a look at the Aerobarrier system. https://www.aerobarrieruk.co.uk/

 

Cheaper and better than you think. They say if you just foam the windows and cut it flush they can take over from there. Speak to them and get a quote / do the maths, I think you'll be pleasantly surprised. Certainly an option, and a 1 day sitting and they're done.

Thanks @Nickfromwales - if You read up a couple posts that’s exactly what I’m going

for and I’ve provided the quote as well. Will Report back Here on how it goes. 

1 hour ago, SBMS said:

Thanks @Nickfromwales - if You read up a couple posts that’s exactly what I’m going

for and I’ve provided the quote as well. Will Report back Here on how it goes. 

I’m lazy, what can I say lol? 🤷‍♂️🤦‍♂️