Out of my depth - Air Tightness and Insulation....

[Mulberry View]

18 minutes ago, saveasteading said:

The best thing I have learnt on BH is to build a service void inside the walls. Benefits in airtightness and happy service contractors. But it also adds insulation in itself from the basic air gap and surface benefit, to any amount of additional insulation you wish.

 

My architect specified an air gap, which I had suspected was to add to the thermal performance (as well as for services). Some on here said that it was not necessary from a service standpoint because services can of course be cut into the EPS layer.

 

I do not intend to have the service void on the ground floor ceiling because it seems pointless with the Posis, but as I said, will aim for a 50mm void above the top floor ceiling.

 

 

 

It's already been mentioned on here that the roof detailing is not ideal as it shows a mix of materials at the outer layer. My building is currently committed from an ICF standpoint, so I can't change that, but I'll be exploring ways to give me an EPS layer all the way up to the top of the outer skin. I think I'll be setting the outer roof timber and the edge of the Plywood deck 50mm back from the outer edge and adding an layer of EPS at the top. It's ironic because this could have been done with the Nudura but I built the ICF as drawn so that ship has sailed unfortunately.

Edited February 16 by Mulberry View

[Mulberry View]

4 minutes ago, Post and beam said:

I very recently had a price of £2200 for my Potton 200 sq metre project in North Herts.  They did say that they would stay and keep spraying until we got the airtight figure we needed/wanted. I think i will be taking them up on this offer.

 

I don't think that's a bad price really.

[Post and beam]

When you take into account that increased insulation thickness is a 'diminishing returns' thing. And that airtightness becomes more relevant as the level of insulation increases i think it will be money well spent.

[Meabh]

On 15/02/2024 at 20:29, Mulberry View said:

 

Yes, I've seen Aerobarrier. Luckily my 'kid' is all grown up and not biting at our ankles. Well, actually that's a lie. At 29 years old, she's more dependent that ever, but that's how it goes!

 

Did you do Airtesting after the wet trades? I'd love to know what Aerobarrier costs. I feel as though the cost will be linked to the result it brings and not to the amount of work in applying it. I'm shocked to hear of your unexpected air 'leaks', particularly the windows.

The airtesting was done as part of the Aerobarrier install - you watch the numbers change on a computer outside the building while the spray is on inside. We are currently getting rendered and plastered (and a temp front door) so haven't done our final test yet. They guarantee to get you below 1.5 and if you can guarantee no holes bigger than a certain size (I couldn't) they can get you below 1.  We were £3.4k for a 300 ish sqm house and we have some high ceilings....they can calculate a cost based on stage of build (shell, plastered, finished - they have to protect surfaces that are finished) and the volume of your building (from plans/elevations). Easy to get a quote and then compare to the cost of all the tapes and membranes. For us it worked out very similar in price with more accuracy - we are totally new to building a house!

[Islay]

Re airtightness - not sure if you've seen these guys:
https://www.aerobarrieruk.co.uk/

 

They might be able to help you with advice and bring down air leakage? 

 

Edit: just seen they've already been mentioned! 

Edited February 19 by Islay
other member already mentioned what I spoke about

[saveasteading]

I hadn't come across this before but have now looked at the website. 

It doesn't give much technical information, which always worries me.

 

Is it a spray of expanding foam that sticks at air leak points? 

Or a sort of fuzzy felt that does the same?

 

So it is for where the intended airtight structure isn't working properly?

Either to get building reg's or as a permanent improvement?

 

Does anyone know...Is it messy?

Is it permanently flexible?

 

Is it ever used as the intended airtight barrier rather than a problem solver?

 

Being a combination of cynic and innovator I'm confused and need more info.

[Sparrowhawk]

35 minutes ago, saveasteading said:

Is it a spray of expanding foam that sticks at air leak points? 

Or a sort of fuzzy felt that does the same?

According to an earlier thread it's a "water based acrylic" not that that tells us much. I'm picturing acrylic sealant in droplet form, pushed into gaps.

 

[Russell griffiths]

I’m afraid I consider it a solution to a problem that shouldn’t exist if the job was detailed correctly in the first place and the work carried out accordingly. 
 

if your doing a re- furb or trying to fix others work then that’s fine, but building something from scratch there’s no excuse for poor details. 

[Roger440]

3 hours ago, Russell griffiths said:

I’m afraid I consider it a solution to a problem that shouldn’t exist if the job was detailed correctly in the first place and the work carried out accordingly. 
 

if your doing a re- furb or trying to fix others work then that’s fine, but building something from scratch there’s no excuse for poor details. 

 

In which case, they have a great product, as, by and large, away from build hub and self build, piss poor workmanship is standard.

 

Im guessing they are going to be millionaires!

[saveasteading]

5 hours ago, Sparrowhawk said:

it's a "water based acrylic"

Then it dries?

I appreciate that not everything with water in it is wet.

I'm all for this being great. But they test it themselves while it's being applied. Next day? Independent testing would be comforting too.

[SteamyTea]

On 16/02/2024 at 09:35, Post and beam said:

When you take into account that increased insulation thickness is a 'diminishing returns' thing. And that airtightness becomes more relevant as the level of insulation increases i think it will be money well spent.

It is strange how we think of insulation as a diminishing return but do not use the same term for airtightness.

What we really need to do is set maximum targets i.e. no part of walls, floor and roof insulated above a U-Value of 0.11 W.m^-2.K^-1 and a mean of 0.1 0.11 W.m^-2.K^-1 

Set an ACH limit of 0.3.

 

9 hours ago, saveasteading said:

Is it a spray of expanding foam that sticks at air leak points? 

Or a sort of fuzzy felt that does the same?

 

9 hours ago, Sparrowhawk said:

"water based acrylic"

I thought it was a water based latex, bit like self levelling floor 'stuff'.

But I also think that the word 'latex' is generic and the product may not contain any real latex i.e. natural rubber.  A quick google and natural latex is produced in most flowering plants and is part of the defence mechanism.  If made from poppies, then it is known as opium, so get the right type of sprayable latex, put Portishead or Jefferson Airplane on the turntable and enjoy the experience.

[Kelvin]

I contacted them to get a quote for my build but decided against it for two reasons. Firstly I ought to be able to get a decent result by careful detailing given it’s a new build. Secondly there was a lack of technical detail and I had some concerns about the longevity of the product. Great for refurbs or possibly where builders can’t be bothered to do the air tightness detail manually. 

[Gone West]

4 hours ago, SteamyTea said:

What we really need to do is set maximum targets i.e. no part of walls, floor and roof insulated above a U-Value of 0.11 W.m^-2.K^-1 and a mean of 0.1 0.11 W.m^-2.K^-1 

Set an ACH limit of 0.3.

When I was modelling my last house, I ran my house design through the PHPP with a range of air infiltration values to see what the effect would be.

 

Pressurisation Test Result (ACH)    Specific Space Heating Demand (kWh/m2a)
               0.2                                              12.1
               0.4                                              12.3
               0.6                                              12.5
               0.8                                              12.7
               1.0                                              12.9
               2.0                                              14.0

[SteamyTea]

3 minutes ago, Gone West said:

I ran my house design through the PHPP with a range of air infiltration values to see what the effect would be.

I have often wondered where the point is between losses though the structure and losses though the infiltration is.

There is a minimum infiltration for humidity control, so that should be the point to aim for, though MVHR skews that somewhat.

[Susie]

There was an article on this in the Build It magazine they recently went back to their ICF house in Gravern Hill and like mentioned had to cover some bits up and then spray. 
from memory it was more like tripods set up in the middle of various rooms, pressure the house then release the spray and it’s so fine it’s sucked to the air holes. I’m doing ICF but seems a bit much for that as we should be good although could be good for other builds but possibly quite expensive for a very leaky house. 
 

[SteamyTea]

I would think that it really needs to be done before the insulation and VLC is fitted.

Making the inner surfaces does not help wind driven cold air by passing the insulation.

Trouble it doing it that way, is that the trades come along and ruin it.

[Mulberry View]

I will not use Aerobarrier to allow me to be lazy on the air-tight details. I just need to know more about what is needed, I have the time and attention to detail. There is some great info in this post, for which I am very grateful.

 

Reverting to an earlier point I had. How concerned should I be about the standard Nudura blocks and their u-value? What are Nudura doing now if the standard block achieves 0.24 yet current regs require 0.18?

 

I am thinking of adding EWI, but this will screw up all my planned brick coursing and sub floor vent placement which I carefully considered at foundation stage.

[Buzz]

8 minutes ago, Mulberry View said:

I will not use Aerobarrier to allow me to be lazy on the air-tight details. I just need to know more about what is needed, I have the time and attention to detail. There is some great info in this post, for which I am very grateful.

 

Reverting to an earlier point I had. How concerned should I be about the standard Nudura blocks and their u-value? What are Nudura doing now if the standard block achieves 0.24 yet current regs require 0.18?

 

I am thinking of adding EWI, but this will screw up all my planned brick coursing and sub floor vent placement which I carefully considered at foundation stage.

It think you have 3 choices here . Add extra to the outside or 

Add extra to the inside or 

Do nothing. 

Are you going to mess the floorplan layout up if you were to add 50mm pir onto the inside of the exterior walls ? 

[crispy_wafer]

12 minutes ago, Mulberry View said:

I will not use Aerobarrier to allow me to be lazy on the air-tight details.

This is Key, I'm considering Aerobarrier for my own brick/block build, I've been quite fastidious in membranes, taping, painting airtight paints at junctions, but I'm always thinking about how to make the best out of what we are doing, and at this point Aerobarrier does come into the equation for me.

 

I think I'd need to do a pre plaster Airtest first to really work out if I can justify a decision to proceed.

[SteamyTea]

6 minutes ago, crispy_wafer said:

painting airtight paints at junctions

How easy is that to do?

How long does the paint last?

29 minutes ago, Mulberry View said:

What are Nudura doing now if the standard block achieves 0.24 yet current regs require 0.18

That is an interesting point, I suppose you can claw a lot of it back via windows, doors and ceilings.  The walls may only be 30% of the exposed structure.

[Russell griffiths]

59 minutes ago, Mulberry View said:

I will not use Aerobarrier to allow me to be lazy on the air-tight details. I just need to know more about what is needed, I have the time and attention to detail. There is some great info in this post, for which I am very grateful.

 

Reverting to an earlier point I had. How concerned should I be about the standard Nudura blocks and their u-value? What are Nudura doing now if the standard block achieves 0.24 yet current regs require 0.18?

 

I am thinking of adding EWI, but this will screw up all my planned brick coursing and sub floor vent placement which I carefully considered at foundation stage.

I believe the standard blocks are 0.22. 
the new blocks are 100mm insulation inside and outside. 
talking to nudura it seems the new blocks have been made for the European market, they are not sold in Canada where I believe it’s slightly colder than here. 

IMHO  you do not need to do anything with your block walls, that item on your list is done, tick it off and forget it it’s finished. 
 

you do however have some details to sort out joining your roof to your walls, this is the area to spend your time. 
 

I would build some mock ups of your roof buildup, and see how it all connects. 
im unsure how your roof sheets fit down if you don’t have a second plywood layer. 
120mm of pir is not enough, I would also say I believe your roof will be noisy, we have standing seam with 200mm of rockwool between the joists, then 75mm of pir under the joists, then a batten with 25mm of rock wool sound slab then 15mm blue plasterboard. 
the rain is definitely noisy, is it unpleasant ? Not really, is it silent ? Definitely not. 
 

 

[saveasteading]

9 minutes ago, Russell griffiths said:

rain is definitely noisy, is it unpleasant ?

I was on a visit to a school once where the sound from the rain on the roof was surprisingly loud. The head and trachers said they positively liked it, as a link to the outside and what sort of day it was.

That wasn't one of my projects but i've done lots of schools and offices with metal roofs. I don't recall noise being an issue except on skhlights, so it must be in the detailing. Standing seam with an air gap may act as a (gentle) steel drum? But then there is the rest of the structure.  Are there skylights?

[Russell griffiths]

2 hours ago, saveasteading said:

I was on a visit to a school once where the sound from the rain on the roof was surprisingly loud. The head and trachers said they positively liked it, as a link to the outside and what sort of day it was.

That wasn't one of my projects but i've done lots of schools and offices with metal roofs. I don't recall noise being an issue except on skhlights, so it must be in the detailing. Standing seam with an air gap may act as a (gentle) steel drum? But then there is the rest of the structure.  Are there skylights?

No skylights, but the whole living area is vaulted ceiling, so there’s only 400mm between you and the outside. 

[Mulberry View]

2 hours ago, Russell griffiths said:

I believe the standard blocks are 0.22. 
the new blocks are 100mm insulation inside and outside. 
talking to nudura it seems the new blocks have been made for the European market, they are not sold in Canada where I believe it’s slightly colder than here. 

IMHO  you do not need to do anything with your block walls, that item on your list is done, tick it off and forget it it’s finished. 
 

you do however have some details to sort out joining your roof to your walls, this is the area to spend your time. 
 

I would build some mock ups of your roof buildup, and see how it all connects. 
im unsure how your roof sheets fit down if you don’t have a second plywood layer. 
120mm of pir is not enough, I would also say I believe your roof will be noisy, we have standing seam with 200mm of rockwool between the joists, then 75mm of pir under the joists, then a batten with 25mm of rock wool sound slab then 15mm blue plasterboard. 
the rain is definitely noisy, is it unpleasant ? Not really, is it silent ? Definitely not. 
 

 

 

@Russell griffiths, What is the build-up on top of the joists? Presumably you have a deck under the metal?

 

Although I haven't looked at it in great detail at this stage, I have planned for a 6x2 wall-plate on top of the Nudura core, the concrete is 2" lower than the top of the EPS. The wall-plate will be bolted down and the top will be level with the top of the Posis.

 

From there, the Plywood deck will sit on top of the Posi and extend out and onto the wall-plate.

 

 

The Architect drew a timber upstand to the edge (4x2 timbers?). Though the mix of materials at the outer face does appear to be an issue (EPS, Plywood and Timber all reaching the outer edge under the render). I think this was not considered by the Architect. I am minded to pull that timber and the Plywood inboard by 50mm and add an EPS infill to the outside edge. Although there will be a join in the EPS, there won't be a mix of materials.

 

The real-world implementation of that detail or a variation of it with the 5° roof angle translated to the timberwork is a little confusing. As is the fixing down of the timbers, these will evidently go through the vapour barrier. Am I overthinking this?!

 

As an aside, I plan to amend the roof service void to 50mm as mentioned earlier and may/may not implement the service zone in the wall. That is to be decided on the basis of whether it adds to the u-value or might be better detailed with an additional internal layer of insulation?

[Russell griffiths]

What I’m not seeing in your drawing @Mulberry View is how the standing seam is fixed down. 
every time I’ve seen it it’s fitted with a clip or bracket screwed down to the wooden substrate. 
 

your drawing to me looks like you have the kingspan insulation and then a separation membrane then the zinc. 
 

how’s this zink fixed down.