Air Tightness, Internal Plasterboard, and Wall Sockets

[Gaf]

@Iceverge Are the four lumps of adhesive equivalent to dot and dab?

 

Shame there's so much waste with the IWI...jaysus

 

@Mr Punter Yeah I came across a couple of references to using the sand:cement:lime, partly as the lime acts as an antimicrobial and prevents mould growth. 

 

So if I asked to do the parge (sand:cement:lime), does the wall no longer need a specific VCL/AT membrane?

 

I can't just seem to get the ubakus layout right with this wall makeup. The regulation requires the wall u-value to be 0.18. With a 150mm cavity bead with u-value from Kingspan of 0.033. I'll have to play around to see what depth of mineral wool is needed to achieve 0.18

 

Cheers again for the inputs everyone - head is a bit melted trying to work this out. Getting a call from the architect next week but I want to be informed as much as possible before this.

[Mr Punter]

14 hours ago, Gaf said:

So if I asked to do the parge (sand:cement:lime), does the wall no longer need a specific VCL/AT membrane?

 

I can't just seem to get the ubakus layout right with this wall makeup. The regulation requires the wall u-value to be 0.18. With a 150mm cavity bead with u-value from Kingspan of 0.033. I'll have to play around to see what depth of mineral wool is needed to achieve 0.18

 

No need for any membrane.  Knauff do a range of mineral wool slabs with a lamda of 0.035 W/mK.  Could you install 50mm thick?  If you clip electrics to the battens I don't think you will need to derate any electric cable capacities.  This would take you to 0.17 without messing with low e gaps or other fudges.

[Iceverge]

15 hours ago, Gaf said:

the four lumps of adhesive equivalent to dot and dab?

 

 

Same thing. 

 

15 hours ago, Gaf said:

Yeah I came across a couple of references to using the sand:cement:lime, partly as the lime acts as an antimicrobial and prevents mould growth.

 

Lime is an example of a biocide (like bathroom paints, anti mould sealants etc) but relying on them internally is poor practice in my opinion, especially in a new build.

 

Moisture accumulation to the point of providing a happy environment for microorganism growth is the thing to be avoided and this is done simply by tipping the scales in favour of "drying" rather than "wetting". 

 

Airtighness has a very big part in this as it's internal vapour laden air blowing into the structure through cracks and holes that allow almost all moisture get into a structure. 

 

Lime added to a parge coat will greatly assist it's flexibility reducing the cracking and enhancing long term airtighess.  Lime even has some self repair tendencies but my gut tells me this is only really a factor in high moisture environments.

 

 

 

 

 

Edited January 27 by Iceverge

[AartWessels]

Instead of taping around the wallsockets, I would be using mounting boxes like these: https://www.eibabo.uk/kaiser/airtight-double-socket-flush-mounted-box-149x80mm-d-2mm-1656-21-eb10312038

 

I do agree however with others in this thread that the draft should not be there to begin with. 

[Mike]

8 hours ago, AartWessels said:

Instead of taping around the wallsockets, I would be using mounting boxes like these: https://www.eibabo.uk/kaiser/airtight-double-socket-flush-mounted-box-149x80mm-d-2mm-1656-21-eb10312038

They are a great solution - I'm using similar here in France. However, although I think that a single UK switch / socket screw centres are compatible, I suspect that a double wouldn't fit - though worth an experiment. However there are some EU manufacturers that make UK style sockets to fit round EU back boxes (pretty sure Jung do, for one) that you may be able to import / find in the UK.

[TonyT]

Can you not wrap air tightness tape around the box before fitting?

 

then fit and seal cable penetrations

[Iceverge]

On 28/01/2024 at 08:03, TonyT said:

Can you not wrap air tightness tape around the box before fitting?

 

then fit and seal cable penetrations

 

Shouldn't be needed if you moved your airtight layer to a parge coat I'd have thought.

[Gaf]

On 27/01/2024 at 10:34, Mr Punter said:

 

No need for any membrane.  Knauff do a range of mineral wool slabs with a lamda of 0.035 W/mK.  Could you install 50mm thick?  If you clip electrics to the battens I don't think you will need to derate any electric cable capacities.  This would take you to 0.17 without messing with low e gaps or other fudges.

 

Technically we could do 50mm, we haven't started any building works so everything is changeable.

 

Just got speaking with the architect and his proposed plan is mechanically fix the IWI to the block work with no void (services to be chased) and taping around windows, sockets etc for air-tightness with no VCL/AT membrane on the vertical block work at all. The VCL/AT only goes on the ceilings.

 

Spoke to Kingspan technical dept. just to get an understanding of this from another angle. They said directly fixing the IWI to the block work is normally done for our proposed wall make-up because the 150mm cavity bead means the inner leaf is regarded as a "warm wall" so no battens with DPC needed (figure #3 in the K18 brochure below). They said the VCL is incorporated into the insulated plasterboard between the plasterboard and the insulation, so the VCL is on the warm side of the insulation.

 

 

The thing I don't really fully understand is how this works when the IWI is punctured/pierced for sockets etc. The taping won't overlap with the VCL within the plasterboard, so surely if any moisture/vapour gets into the inner leaf block (from the outside even?), then it has the potential to enter the plasterboard. Image below of what I'm thinking - do I have that right? This is where the airtight sockets come in?

 

 

Going to chat to the builder to make sure he's on the same page because if the sockets are chased, then I don't understand how there could be any breeze there. The architect didn't specify the method of fixing the IWI in the spec. but implied it from the construction drawings by not including any battens, so maybe the builder is planning to D&D and creating a void.

 

So as it stands, the proposed wall make-up is below:

 

 

 

[joth]

56 minutes ago, Gaf said:

The thing I don't really fully understand is how this works when the IWI is punctured/pierced for sockets etc. The taping won't overlap with the VCL within the plasterboard, so surely if any moisture/vapour gets into the inner leaf block (from the outside even?), then it has the potential to enter the plasterboard. Image below of what I'm thinking - do I have that right? This is where the airtight sockets come in?

 

 

Note that you're assuming the VCL is airtight. Nothing in the K18 technical documentation states it is. Indeed, it doesn't state what the air permeability of the product is at all

https://www.uvalue.ie/images/uploads/product/28037_Kooltherm_K18_Insulated_Plasterboard_(2).pdf

 

That doc continues the same vague hand-waving wishful approach to airtightness ("draft reduction") as architects use. e.g.:

 

 

so no systematic taping between sheets, unless there are "air gaps" (determined how? eyeballing it?)  No specific direction on how the sealing is done - does it need to reach to the VCL of both sheets? Or, just plug up the hole any old how with squirty foam?

(I'm not convinced by they use of "thermal bridging" when discussing air gaps either.)

 

 

- no statement as to where exactly the sealant is sealing to what. Just "the insulation"

 

 

LOL. Perhaps you can write that into your contract standards of workmanship .

 

 

 

 

 

Compare to a product that is certified and tested for airtightness: https://files.mutualcdn.com/medite-smartply/files/SMARTPLY-AIRTIGHT-Datasheet-V19-0923.pdf

This give airpermiability figures, and methodical way to join sheets for airtightness.

 

 

Edited January 30 by joth

[Iceverge]

Airtighness is really really important, much more so than insulation. Not only for energy use and comfort but also for the integrity of the structure. Gaps and cracks allow air to carry vapour into the walls and roof where it condensates. Apart from water ingress from outside this is the cause of all building decay. 

 

 

Insulated plasterboards are terrible for airtighess. I've never seen an example to get anywhere near a good airtightness score. 

 

 

 

 

 

 

Edited January 30 by Iceverge

[saveasteading]

1 hour ago, Iceverge said:

Insulated plasterboards are terrible for airtightness

 Any idea why that might be?

[Iceverge]

1 hour ago, saveasteading said:

 Any idea why that might be?

With the best will in the world how do you successfully seal the edges to eachother and then to the ceiling and the floor? It's hit and hope in the dark. 

 

Airtighness isn't difficult but it does demand a solid plan and some rigour. Our 0.31ACH figure was equivalent of a credit card sized hole in a basketball court. 

 

[saveasteading]

1 minute ago, Iceverge said:

how do you successfully seal the edges to each  other and then to the ceiling and the floor?

I'd expect the exposed plasterboard face to be sealed as normal and that is what matters.

I see your point though that the eps may be poorly cut which wouldn't be ideal. Cutting it nicely as opposed to the normal snapping will be a slow job.

[Gaf]

@joth @Iceverge Great points and led me to calling two air tightness testers for thoughts. Both instantly commented on the planned wall make-up as having no proper airtightness treatment for the inner leaf blocks. Both suggested a sand cement internal render for air tightness on the inner leaf before fixing the IWI. Both said not to use any kind of VCL/AT membrane but I forgot to ask why; I asked about intello as an example and they both said not to do this.

 

I forgot to ask how thick the SC render would need to be on the inner leaf and have found some posts her suggesting 15-20mm thick will be needed. Then I've found posts suggesting using the VCL/AT membrane instead of SC render (e.g. https://forum.buildhub.org.uk/topic/3622-rendering-and-airtightness/)

 

So (currently) the wall makeup is now this:

 

 

They were very helpful with advice on the first floor concrete slabs also, with both suggesting the internal render would need to be overlapped with a membrane that wraps around the concrete slabs because the slabs are hollowcore. Both advised to try to ensure the edges of the floor slabs don't go 'into' the cavity as they will be a major cause of air leak. The construction drawings indicate the slabs do not go into the cavity.

 

 

[Iceverge]

32 minutes ago, Gaf said:

forgot to ask how thick the SC render would need to be on the inner leaf and have found some posts her suggesting 15-20mm thick will be needed. Then

 

A parge coat wouldn't need to be that thick. 3-5mm should be fine. Slop it on with a broom. 

 

If you are using insulated plasterboard then you'll still be chasing conduits into the blocks. 

 

These will need to be sealed too. I used airtight paint. 1 dilute coat at about 5:1 as a primer and 2 neat coats. 

 

 

 

Even so when I had my DIY blowerdoor running I could feel some leaks from the back of the conduit.  

 

The blue airtight sealer was used quite a bit even with 3 coats of airtight paint. 

 

Also note my detail allowing the conduit to run up to ceiling level and emerge under the A/T membrane ( not installed) into the ceiling service cavity. 

 

 

40 minutes ago, Gaf said:

They were very helpful with advice on the first floor concrete slabs also, with both suggesting the internal render would need to be overlapped with a membrane that wraps around the concrete slabs because the slabs are hollowcore. Both advised to try to ensure the edges of the floor slabs don't go 'into' the cavity as they will be a major cause of air leak. The construction drawings indicate the slabs do not go into the cavity.

 

 

Also known as a Tony Tray. See @tonyshouse for details. He did a blog too. http://tonyshouse.readinguk.org/index.htm

 

This will work ok if you can fit the hollow core planks yourself. In reality they'll be crowbarred into position by the delivery guys and it'll tear the membrane. Ours was in tatters so I cut it away and painstakingly sealed the house room by room, from the inside out. 

 

As a minimum use some heavy DPC type plastic with a bedding layer of wet mortar on top before dropping the hollow core to protect it. 

 

Realistically it's hard to do a good job on the corners and it's one of the reasons I'd prefer to follow the denby dale intermediate floor detail. Much more robust. 

 

 

 

I would mix standard 220mm timbers with metal web space joists only where they were needed for service's to save cash. The pozis could be deeper in rooms where you needed the service space. Alternative use standard 220mm joists throughout and install a metal drop ceiling for a service space under bathrooms etc. 

 

16mm resilient bars underneath the joists and 2x layers of standard 12.5mm plasterboard +skim  and mineral wool sound insulation in between would make a very quiet floor. Especially with carpet upstairs. 

 

 

 

 

 

 

 

 

 

 

 

 

[Gaf]

@Iceverge Would the blue stuff be Blowerproof Airtight Paint?

[Mr Punter]

Here is a current work in progress with sand:cement:lime applied with a trowel and about 2-3mm thick on medium density blockwork.  If you purse your lips on the surface and suck it is amazing the difference between parged and not parged.

 

[Iceverge]

2 hours ago, Gaf said:

@Iceverge Would the blue stuff be Blowerproof Airtight Paint?

 

Soudal soudatight LQ.

 

4 minutes ago, Mr Punter said:

Here is a current work in progress with sand:cement:lime applied with a trowel and about 2-3mm thick on medium density blockwork.  If you purse your lips on the surface and suck it is amazing the difference between parged and not parged.

 

 

Concrete blocks are the rice Krispie cakes of the construction world. 

 

With minimal care you can pour a bottle of water through a block. 

 

Hopeless on their own for airtighess.

[Gaf]

@Mr Punter Thanks for that. I love seeing the photos of the actual work as I find just reading about these things is hard to get a proper grasp of it all.

 

8 hours ago, Mr Punter said:

If you purse your lips on the surface and suck it is amazing the difference between parged and not parged.

 

I must do this with herself on site and not explain why I'm doing it just to see her reaction 😆

 

8 hours ago, Iceverge said:

Soudal soudatight LQ.

 

Under the "External Walls" heading the architect's spec mentions "Use appropriate joining tape to join the airtightness membrane with Partel Vara liquid airtightness membrane on block walls." From pulling it all together now, he's putting the membrane in the ceiling/roof on the first floor and no membrane on the ceiling of the ground floor, but is putting the Partel Vara (spray/brush) on the inner leaf of all external walls.

 

I wonder what the technical specs are for a parge coat vs. the partel vara liquid. Noticed the partel vara spray version has passive house certification: https://database.passivehouse.com/en/components/details/airtightness_system/partel-partel-vara-fluid-spray-1899as00?

 

Probably costs a fortune though in comparison to a parge coat... maybe better to do the parge coat and use the partel vara in the chasings...

 

[Iceverge]

That Partel spray costs from about €6/M2. However that's only for very smooth surfaces, think spraying one coat over a skimmed wall or a sheet of ply.

 

I would say I brushed on at least 3 coats to be happy with the blocks I did. And Partel say brush application is twice as thick as a spray. 

 

Thats €35/m2 plus application cost. Over a 300m2 building it's well North of €10k. 

 

As a comparison I can buy a good quality airtight membrane for about €1.30/m2.

 

Alternatively cement at €7/25kg and sand at €30/ton mixed 5:1 and brushed on at about 3mm works out at 20c/M2 or €60 for the house.

 

 

 

Architects and other people's money.....

 

 

 

 

 

 

 

 

[Gaf]

19 minutes ago, Iceverge said:

However that's only for very smooth surfaces, think spraying one coat over a skimmed wall or a sheet of ply.

Hmmm, I did wonder when the brochure says the spray version is minimum 500ml/m2 but "usage depends on the surface" and they don't provide any details on usage for different surfaces.

 

21 minutes ago, Iceverge said:

Architects and other people's money.....

That's hilarious! That's exactly what some of the builders said when I was first chatting to them about some of the architect's original ideas...

 

And to put it into financial figures, we didn't go with a number of his suggestions, and the difference in tender costs between his estimated costs based on the tenders he said he manages (based on his preferred designs) versus the tenders we've actually received (based on our own preferences + advice from others) is >€90k.

 

Keeping on top of this stuff is like having a second job at the moment but will be worth it in the end.

 

This forum has be invaluable.

[Gaf]

@Iceverge @Mr Punter @joth @ProDave Just thought I'd @ everyone who gave me a steer on this. Chatting to the builder and I obviously walked away from our first meeting with the complete wrong idea. He said that there shouldn't be any air/breeze at the sockets (I mistook him telling me about people who have come to him about this as an issue wondering if it was normal but he didn't do the builds). We covered a lot during that meeting so I misheard him on that one.

 

I just asked a broad airtightness query and without needing any prompting he confirmed everything from you're posts/advice. He doesn't do the partel para fluid (said he could if I wanted but said it's serious money) and does sand cement as standard behind the IWI, he seals the chasing with sand cement (said though if I wanted to go with a painted sealing he'd happily do that either), seals the sockets, seals the conduits, for the first floor slabs he gets the ends filled but also goes on site during the install to supervise and has a membrane setup to wrap around the slab ends for airtightness exactly as @Mr Blobby showed from his construction in this post.

 

I mentioned getting an airtightness test done once the airtightness work was completed and he welcome me doing this. Said it was best practice and had no issues with it.

 

All in all, as much as it was a bit of a pain trying to get my head around this stuff (and realising I was weak link in this) it was great to have my own understanding of what's best and then music to my ears to hear the builder say exactly what you've all been saying.

 

Good result, cheers for all the input.

Edited February 1 by Gaf

[Iceverge]

Sounds like you've a good builder. 

 

 

[Mr Blobby]

@Gaf, I didn't realise you are in Ireland, this should make the airtightness easier for you because builders are familiar the tighter regulations.  When we had our slabs installed we asked hollowcore guy if wrapping the slabs was commonplace.  He said yes, in Donegall he sees it all the time, but our house was the first he'd seen with wrapped slabs in Northern Ireland.

 

If you are going to wrap the slabs then beware that during coonstruction water may run through the ends of the slab and pull the membrane down and the block layers will carry on regardless.  At one place we had to slit the membrane at a GF window opening to let the water out so we could pull the membrane back into place from above! 

 

Also, to protect the membrane the brickies laid one course of block on top of it on the first floor and then (after the mortar had set of course) I taped the membrane to the block and then covered it with dpc to protect it from mortar droppings.  This is almost a full time job.

 

Also, if you are in Ireland, you should be able to get your internal walls wet-plastered for airtightness instead of dot and dab. That's what we're doing, and painting in the chases and back boxes. with pro clima aerosona viscon fibre paint.  It's easier to get in Ireland than blowerproof.  And I prefer it to the other one.

 

 

Edited February 1 by Mr Blobby

[Gaf]

18 hours ago, Mr Blobby said:

If you are going to wrap the slabs then beware that during coonstruction water may run through the ends of the slab and pull the membrane down and the block layers will carry on regardless.  At one place we had to slit the membrane at a GF window opening to let the water out so we could pull the membrane back into place from above! 

 

Also, to protect the membrane the brickies laid one course of block on top of it on the first floor and then (after the mortar had set of course) I taped the membrane to the block and then covered it with dpc to protect it from mortar droppings.  This is almost a full time job.

Ah good to know. Did you tape the membrane to the blockwork within the cavity? Was it something like the below?

 

 

18 hours ago, Mr Blobby said:

Also, if you are in Ireland, you should be able to get your internal walls wet-plastered for airtightness instead of dot and dab. That's what we're doing, and painting in the chases and back boxes. with pro clima aerosona viscon fibre paint.  It's easier to get in Ireland than blowerproof.  And I prefer it to the other one.

 

I hadn't checked about the internal walls actually, good spot. Been so focused on outside-to-inside. Will run that past the builder. Thanks for the steer to the pro clima also.