Fine tuning my IWI Solid wall (Warm Batten) design

[lookseehear]

I think IceVerge covers this in the video, with the main points being you can use standard gypsum plasterboard but don't use latex based paints that will seal it all up.

 

On the point of only insulating 1st and 2nd floor, it would probably make sense to try and remove and refit the coving if you can.

[Redbeard]

On 22/11/2024 at 19:59, Roger440 said:

On 21/11/2024 at 21:02, Redbeard said:

 

Not if (as I usually do) I'm using rigid (140-180kg/m3) WF. If I were using flexi WF (c50kg/m3) I would (and indeed did) use Intello.

 

Can i ask what the logic is that drives that decision?

Moisture-buffering due to the density.

[Mike]

10 hours ago, ab12 said:

When I say issue I mean risk of condensation to ground floor externally facing walls as the IWI is not continuous from ground floor to 2nd floor.

 

Ground floor has some beautiful age old coving which other family members want to retain.

It's theoretically possible, but may make airtightness harder to achieve and, of course, you loose the benefits of the insulation downstairs. It may be possible to buy the same cornice pre-made and install that, but if not then there are companies that will cast an identical replacement for you.

 

10 hours ago, ab12 said:

would you cover this with standard gypsum plasterboard OR wood wool board?

Standard plasterboard is OK provided you don't paint it with regular vinyl paint.

[Annker]

Finally IWI has commenced onsite.

The good advice given here has me sold on the benefit of a parge coat.

I think no matter which IWI system you select a parge coat will sit very comfortably in the mix, its effectively the same material as a victorian brick wall (sand and lime) so  little concern about introducing non-compatible materials that the building may reject.

 

We have spent a few day pointing up the bigger gaps in the jointing, will parge now and expect much like a mist coat it will show up which areas need further attention.

 

I'm mixing 3:1 Sharp sand to NHL 3.5. This mix seems broadly accepted to be OK, however I've seen @Iceverge add a shovel of cement and elsewhere others say NHL 3.5 is too strong, so again noo hard and fast rule it seems.

 

I will say that its not as easy to put on as I thought, not in terms of hard physical effort but getting it from the bucket to the wall.

I'm applying with a soft sweeping brush, the mix in the bucket need to be constantly agitated to keep the sand in suspension, or else you end up just whitewashing the walls.

A lot of material goes on the floor, which when gathered and put back in the bucket dries the mix and so more water is required to bring the mix back to a brushable consistency.  

 

@Redbeardsuggested a pre-bagged mix which certainly would be an easier material to work with, but I figured I'd need 50+ bags so it works out to be a much more expensive option for my project.

 

Here's how the first gauge is looking.

 

[Iceverge]

Good work, keep us posted. 

 

We're all learning. 

[Roger440]

6 hours ago, Annker said:

Finally IWI has commenced onsite.

The good advice given here has me sold on the benefit of a parge coat.

I think no matter which IWI system you select a parge coat will sit very comfortably in the mix, its effectively the same material as a victorian brick wall (sand and lime) so  little concern about introducing non-compatible materials that the building may reject.

 

We have spent a few day pointing up the bigger gaps in the jointing, will parge now and expect much like a mist coat it will show up which areas need further attention.

 

I'm mixing 3:1 Sharp sand to NHL 3.5. This mix seems broadly accepted to be OK, however I've seen @Iceverge add a shovel of cement and elsewhere others say NHL 3.5 is too strong, so again noo hard and fast rule it seems.

 

I will say that its not as easy to put on as I thought, not in terms of hard physical effort but getting it from the bucket to the wall.

I'm applying with a soft sweeping brush, the mix in the bucket need to be constantly agitated to keep the sand in suspension, or else you end up just whitewashing the walls.

A lot of material goes on the floor, which when gathered and put back in the bucket dries the mix and so more water is required to bring the mix back to a brushable consistency.  

 

@Redbeardsuggested a pre-bagged mix which certainly would be an easier material to work with, but I figured I'd need 50+ bags so it works out to be a much more expensive option for my project.

 

Here's how the first gauge is looking.

 

 

Why the NHL 3.5. Thats not particuarly permeable. Its not like you need the strength.

[Annker]

36 minutes ago, Roger440 said:

 

Why the NHL 3.5. Thats not particuarly permeable. Its not like you need the strength.

As I said there is seemingly no consensus on the correct mix, but the majority suggest NHL 3.5 so that's what I went with.

Open to correction but with the parge coat thickness on the wall ranges from 1mm to 3mm I imagine at that thickness using NHL 2 or 3.5 is a moot point.   

 

[Mike]

Looks good!

 

1 hour ago, Roger440 said:

Why the NHL 3.5. Thats not particuarly permeable. Its not like you need the strength.

HCLs are significantly more vapour permeable than cement-based mortars. To say more would require an analysis of the particular lime brand and mortar mix as permeability isn't directly rated to the NHL classification (which only defines compressive strength at 28 days). Although using a lime putty would provide superior performance I've not heard of anyone using it for the purpose, though there must be some who have.

 

Edited December 12 by Mike

[Annker]

Update on applying the parge coat.

We were applying using a sweeping brush to apply direct from a tub but finding that each dip pulls a greater amount of water and lime out of the tub which results in the mix remaining in the tub becoming progressively sandier.

Initially mix was a full belle mixer gauge worth at 3:1, however we are having better results with a sightlier more lime rich mix and mixing smaller batches with a paddle mixer in the tub. Now the sand stays in suspension in the tub almost long enough to get it all used.

 

Still undecided about which insulation to use.

I'm actually now reconsidering using wood fibre boards now, for a specific reason

 

I want the insulation layer positioned behind the studwork so the insulation is a continuous layer, however the difficulty is then how to keep the installation tight against the wall, as the studs only will only hold what is directly behind them.

 

As wood fibre boards are typically bonded to the wall with adhesive they will stay in place against the wall regarding of studwork.

Does anyone know is rockwool batts can similarly be bonded to the wall and if so with what type of adhesive? 

 

 

 

 

 

[Redbeard]

4 hours ago, Annker said:

Does anyone know is rockwool batts can similarly be bonded to the wall and if so with what type of adhesive? 

EWI-grade Rockwool, yes. The adhesive is usually cement-based (I used EWI Pro). It allegedly has 'some breathability' but I have no figures. Given that I would not trust the adhesive alone, for EWI and for 'straight-to-the-wall IWI' you use hammer-fixings (Ejot or similar), so no reason why you could not use them here too. I have not read back through the whole thread, but why do you even need studwork? Is it already there? Is the wall 'wibbly'?

 

Edit: Looked at the pic: No, the wall is not 'wibbly', therefore more than ever I feel you do not need the studwork. I have no experience of IWI with rigid Rockwool, but others may. Subject to a condensation risk analysis I do not see why you could not use it like WF. Can't remember the density but go to one of the EWI suppliers' sites - it'll be on there. 

 

Your parge coat at the thickness shown may perhaps crack and thus not be airtight, but as long as it is airtight I would just 'butter' the back of the WF boards with lime plaster with a 10mm toothed trowel and push it on', followed by the mechanical fixings described.

Edited December 13 by Redbeard
added 'buttering'

[Mike]

8 hours ago, Annker said:

Still undecided about which insulation to use.

I want the insulation layer positioned behind the studwork so the insulation is a continuous layer, however the difficulty is then how to keep the installation tight against the wall, as the studs only will only hold what is directly behind them.

Unless your wall is wet, my recommendation would be to either use flexible wood fibre (SteicoFlex or similar), or a similar product made from hemp (IndiBreathe Flex or similar). As mentioned in my post on the previous page, many natural insulations handle moisture vapour in a superior way compared to others.

 

I'd use metal studwork and position this so that the insulation is gently squeezed behind the studs against the wall, to hold it in place in contact with your parge coat. It may be possible to fill the space between the studs with another layer of insulation; it's safest to ask the insulation manufacturer to advise on the thickness, but potentially that may be two 45mm layers, giving you 85mm thick overall (including 5mm compression on that 1st layer) from the wall to the face of the studwork.

 

The manufacturer may also be able to advise on whether or not a vapour barrier is recommended over the top of this; making the structure airtight + installing MVHR (which will help control winter humidity) + the extent of potential rain penetration through the wall are also factors that affect this. If the insulation manufacturer can't give advice, you may need to commission someone to carry out a WUFI analysis. If you do need a vapour barrier, then you'd want to add a service cavity to the face of the studwork to run pipes and cables in.

 

FWIW, this is more-or-less what I've done on my current project in France.

 

Edited December 13 by Mike

[Annker]

4 hours ago, Redbeard said:

I have not read back through the whole thread, but why do you even need studwork? Is it already there? Is the wall 'wibbly'?

 

Your parge coat at the thickness shown may perhaps crack and thus not be airtight, but as long as it is airtight I would just 'butter' the back of the WF boards with lime plaster with a 10mm toothed trowel and push it on', followed by the mechanical fixings described.

Studwork as required as the current preference irrespective of insulation choice is to plasterboard and gypsum skim finish the walls.

Reason being I can do the boarding myself and then it should be easy to find a decent plasterer to do the relatively straight forward job of skimming (verses finding a lime plasterer)

 

Ahhh, you think the parge coat may crack, is that because you think its too thick or too thin?

[Annker]

47 minutes ago, Mike said:

I'd use metal studwork and position this so that the insulation is gently squeezed behind the studs against the wall, to hold it in place in contact with your parge coat. It may be possible to fill the space between the studs with another layer of insulation; it's safest to ask the insulation manufacturer to advise on the thickness, but potentially that may be two 45mm layers, giving you 85mm thick overall (including 5mm compression on that 1st layer) from the wall to the face of the studwork.

 

The manufacturer may also be able to advise on whether or not a vapour barrier is recommended over the top of this; making the structure airtight + installing MVHR (which will help control winter humidity) + the extent of potential rain penetration through the wall are also factors that affect this. If the insulation manufacturer can't give advice, you may need to commission someone to carry out a WUFI analysis. If you do need a vapour barrier, then you'd want to add a service cavity to the face of the studwork to run pipes and cables in.

 

FWIW, this is more-or-less what I've done on my current project in France.

 

I think this is a good build up.

One potential issue I'm trying to get my head around is how/will the stud work keep and maintain to keep the insulation against and in full contact with the wall.

The perimeter edge of the insulation boards wont always align with the stud centres and where they dont line up wont the whats keeps the insulation against the wall?

Perhaps the second layer of insulation between the studs is necessary to ensure the first layer closest the wall stays against the wall.

 

I've nothing against the cost of doing a WUFI analysis but I'm concerned it will be another case of "this or that" "may or may not" work.

I'd rather just assume a vcl is needed and fit it.

I imagine it could be double sided sticky taped to the metal studding and then plant on batten on the metals studs to create the service cavity?

[Iceverge]

35 minutes ago, Annker said:

One potential issue I'm trying to get my head around is how/will the stud work keep and maintain to keep the insulation against and in full contact with the wall

 

Stand the studs off the wall a little. If you're feeling really picky you can jamb a little fluf behind them, but the batts will fill the gap, espically if you space the studs close enough as they're a little hairy at the edges. The batts will just stay there all by themselves if you get the spacing right. 

 

 

Here's one my mate is doing at the moment. These batts are only 50mm too. Even where they're 2 batts in one bay they stay there fine. 

 

Use a slightly thicker batt than the depth of your cavity and it'll take out the imperfections. 

 

Wufi and other programs are only as good as the data they get and renovations of old houses are full of incalculable variables. 

 

Beware manufacturers will typically spec a buildup that achieves two things. 

1. An "on paper" safe buildup that, 

2. Uses lots of their product. 

 

For example try any of the PIR manufacturers and they'll oblige but I hope my lengthy video might have explained why I think it's a bad idea. 

 

The fundamental points are that it needs to be able to not get WET. Think airtighess, and it needs to be able to DRY. Drying onwards is no issue so long as you manage the ventilation, an imperfect VCL is worse than no VCL.

 

Your plan is sound. Keep the course. 

 

 

[Redbeard]

1 hour ago, Annker said:

Ahhh, you think the parge coat may crack, is that because you think its too thick or too thin?

Possibly a bit thin, as shown in your pics. Thinner than I'd do, but then I trowel on, not brush, so can get it a bit thicker in one pass.

 

57 minutes ago, Annker said:

I've nothing against the cost of doing a WUFI analysis but I'm concerned it will be another case of "this or that" "may or may not" work.

I'd rather just assume a vcl is needed and fit it.

Don't assume that just because you have a VCL you don't need a condensation risk analysis. VCL works well with assumptions that all moisture in a wall comes from the room, and also assumptions that the VCL is perfect. Neither case necessarily applies. 

 

EDIT: Was typing that while @Iceverge posted. We are in agreement re VCL. (Perhaps less so re WUFI, which has done well for me).

Edited December 13 by Redbeard
Cross-posted with @iceverge

[Annker]

20 minutes ago, Redbeard said:

Possibly a bit thin, as shown in your pics. Thinner than I'd do, but then I trowel on, not brush, so can get it a bit thicker in one pass.

 

Don't assume that just because you have a VCL you don't need a condensation risk analysis. VCL works well with assumptions that all moisture in a wall comes from the room, and also assumptions that the VCL is perfect. Neither case necessarily applies. 

 

EDIT: Was typing that while @Iceverge posted. We are in agreement re VCL. (Perhaps less so re WUFI, which has done well for me).

Re the parge coat I had in my mind that it would show up any gaps in the mortar joint we had missed with our initially pointing pass, and it has illustrated a few so perhaps we will give apply a second parge coat over what has been done and apply thicker going forward.

 

Perhaps I should have specifically stated my plan was to use the Itello plus membrane rather than saying a vcl; is Intello Plus a vcl?

Regardless I had in my head the inclusion of the Intello Plus as a supplementary layer, added in the understanding that it will not completely eliminate vapour diffusion into the buildup, it will leak but it will also allow drying to the inside.

[Mike]

1 hour ago, Annker said:

One potential issue I'm trying to get my head around is how/will the stud work keep and maintain to keep the insulation against and in full contact with the wall.

The perimeter edge of the insulation boards wont always align with the stud centres and where they dont line up wont the whats keeps the insulation against the wall?

Perhaps the second layer of insulation between the studs is necessary to ensure the first layer closest the wall stays against the wall.

Provided you use semi-flexible insulation batts you cut them a little oversize and compress them a little, so that they push gently against each other from floor to ceiling and wall to wall, holding each other in place when supported by the studwork (at least once you get to 40 or 50mm of thickness). If any additional support is required (for example I had to do a mansard roof + a ceiling so everything was trying to fall in on me), then you can cut them to join behind a stud, and double up on studs to give them extra wide support if necessary. If you're careful, you can use lots of the offcuts, so that there's not much waste.

 

BTW, talk to the manufacturer / supplier about suitable power saws to cut them with - you don't want to be using a hand saw if you have lots to do.

 

1 hour ago, Annker said:

I've nothing against the cost of doing a WUFI analysis but I'm concerned it will be another case of "this or that" "may or may not" work.

I'd rather just assume a vcl is needed and fit it.

I imagine it could be double sided sticky taped to the metal studding and then plant on batten on the metals studs to create the service cavity?

Yes, you can certainly create a service cavity that way.

 

However, as mentioned by @Redbeard & @Iceverge, VCLs don't give you a get-out-of-jail pass - not all moisture comes from inside, it's difficult to seal VCLs perfectly and an imperfect VCL can indeed be worse than no VCL. 'Smart' VCL membranes (those that change their vapour permeability from winter to summer) do allow moisture that would be otherwise be trapped by a traditional vapour barrier an escape route, but you still have to be sure that the structure dries out sufficiently in summer, rather than accumulating additional moisture each year - which would be catastrophic.

 

Re the WUFI analysis, the usual computing adage of 'garbage in = garbage out' applies. And getting that right can be tricky too.

 

This is why internal insulation can be difficult, and a key reason why external wall insulation is normally preferable where it's an option.

 

56 minutes ago, Annker said:

Intello Plus a vcl?

Yes, Intello is a smart VCL.

 

[Iceverge]

11 hours ago, Annker said:

Regardless I had in my head the inclusion of the Intello Plus as a supplementary layer, added in the understanding that it will not completely eliminate vapour diffusion into the buildup, it will leak but it will also allow drying to the inside.

 

Vapour diffusion is a thing, but it's the scale VS airtighess that gets lost on people. 

 

In this example a 1m² piece of wall allows 0.5g/M2/day to diffuse through it. 

 

Meanwhile a 1m x 1mm gap on a day with a gentle breeze will pass 1600 times more moisture through it. 

 

 

 

A badly sealed layer of Intello will do little to nothing for airtighess and that's the big battle you are fighting. 

 

[Iceverge]

Excellent series of video this.  Nice and concise too. 

 

https://youtu.be/Xud4bC1SWDc?si=awXQYIgSo8GX1Oh_

[Iceverge]

Once again to emphasise. 

 

Diffusion is absolutely insignificant compared to air leakage and obviously liquid water . 

 

 

I would go so far as to say, that so long you have a mechanical ventilation system and don't use impermeable materials, you can completely ignore it. 

 

 

Edited December 14 by Iceverge

[Annker]

Thanks for all the input @Iceverge @Mike @Redbeardand all others, very appreciated.

 

So WRT a smart VCL,  the jist is that even small gap in the VCL will leak much more domestic bourne moisture into the wall buildup through air movement, than the VCL can return back into the room through vapour diffusion?   

Therefore an imperfectly installed VCL* (smart or standard) hinder the drying ability of a vapour open wall built up.

 

*Agreed here the reasonable assumption that a perfectly retro-fitted VCL is a unicorn.

[Mike]

6 hours ago, Annker said:

So WRT a smart VCL,  the jist is that even small gap in the VCL will leak much more domestic bourne moisture into the wall buildup through air movement, than the VCL can return back into the room through vapour diffusion?

Almost, but it's necessary to distinguish between the airtightness layer and the vapour control layer.

 

With a perfect airtightness layer, then there will be nothing to drive moisture through the vapour control layer into the insulation - see my text on the 3 purposes of airtightness on page 2. You won't achieve perfection but the airtightness layer is the most important of the two layers. So:

 

- Where air can leak through a VCL into the insulation but get no further due to airtightness layer, the moisture transfer will be limited

- Where air can leak through the insulation (through the gaps in or the absence of an airtightness layer) to the outside, the moisture transfer can be dramatic, as per the illustrations above.

 

With time + care + testing, you can achieve very good airtightness. Using service cavities you can likely get a pretty well sealed VCL too, but its positioning means that it's more vulnerable to damage.

 

On 13/12/2024 at 13:20, Annker said:

[for the parge coat we are] finding that each dip pulls a greater amount of water and lime out of the tub which results in the mix remaining in the tub becoming progressively sandier. Initially mix was a full belle mixer gauge worth at 3:1, however we are having better results with a sightlier more lime rich mix and mixing smaller batches with a paddle mixer in the tub. Now the sand stays in suspension in the tub almost long enough to get it all used.

I meant to comment on this yesterday, but it may also be that your sand is too sharp - try a bricklaying sand instead (or a blend with what you already have).

[Annker]

17 hours ago, Mike said:

I meant to comment on this yesterday, but it may also be that your sand is too sharp - try a bricklaying sand instead (or a blend with what you already have).

Yes I had considered doing that, I have plenty soft sand on site so will mix up a 50/50 sharp/soft gauge tomorrow.

I suppose given that the parge wont ever see weathering soft sand will be OK, it may even fill the finer gaps.  

[Annker]

I called Rockwool tech dept with some queries.

Asking whether Rockwool can be bonded/adhered to brickwork, (specifically to ensure it stays against the wall as wood fibre can) the response was no it can't as it would delaminate. Furthermore the advice was not to use RW in this situation as there would be a condensation risk if the batts were not held tight against the wall, the person I spoke to went as far as to advise to use the "alternative insulation I mentioned" i.e wood fibre.

They did however confirm that Rockwool is breathable and entirely suited to installation in older properties, so a mixed response, maybe even a confused response... 

 

Regardless I worked up the build up below using Rockwool:

 

• Gypframe 48mm "i" studs fixed floor to ceiling at 600mm c/c without intermediate support
•  "i" studs stood off existing brick wall by ~20mm
• 75mm RW45 can only be obtained in 600mm wide batts, hence studs at 600mm c/c rather then the more robust 400mm c/c
• RW45 is fitted tight against the existing brick wall,
• ~20mm of insulation behind studs to eliminate cold bridging,  
• Friction fit of insulation batt around the "i" profile of studs keeps the batts in position  

 

[Annker]

Interesting take on IWI solutions from British Gypsum, (I've based the studwork from this spec).

 

The most recent version of their GypLyner Independent System incorporates Isover Steel Frame Batts; however in a previous version from a couple of years ago they were pushing PIR as the insulation, interesting to wonder if this indicates a move towards a more vapour open solution?

 

I imagine BG are specing Isover Glass fibre (and not mineral wool) is due to them both being owned by St Gobain.

I wonder what are the vapour permeability performance of glass wool,  Isover claim "Achieves Eurofins Gold certification, the highest accreditation for indoor air quality" whatever that means. May give them a call to hear how breathably they believe it to be. 

Edited Monday at 16:49 by Annker