Fine tuning my IWI Solid wall (Warm Batten) design

[lookseehear]

I hadn't heard of gypframe and just looked it up. What do you do if you need a strong wall fixing? The appeal of timber battens is that you can at least screw into it if you need to.

[Annker]

 

3 hours ago, lookseehear said:

I hadn't heard of gypframe and just looked it up. What do you do if you need a strong wall fixing? The appeal of timber battens is that you can at least screw into it if you need to.

Typically you would pattress out areas of wall that are going to have fixtures prior to plaster boarding 

Edited December 16, 2024 by Annker

[Iceverge]

3 hours ago, Annker said:

whatever that means

 

Nothing. 

[Mike]

On 14/12/2024 at 00:54, Mike said:

On 13/12/2024 at 22:17, Annker said:

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.

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...

Just found a pair of images to illustrate the above. This is hemp insulation on a wall about 1m wide x 2.6m high, self-supporting (left) before I put the studs in place (right). The batts here are 100mm thick, but the lowest (out of shot) was sawn through to about half that as the wall behind was out of plumb.

Edited December 17, 2024 by Mike

[ab12]

On 17/12/2024 at 23:44, Mike said:

Just found a pair of images to illustrate the above. This is hemp insulation on a wall about 1m wide x 2.6m high, self-supporting (left) before I put the studs in place (right). The batts here are 100mm thick, but the lowest (out of shot) was sawn through to about half that as the wall behind was out of plumb.

Mike. This is interesting. How did you manage to fix the hemp flexi batts to the walls? With some sort of glue?

Very much like this concept and the following dawned on me. can everyone please critique this:

 

50mm hemp batts fixed to the wall as shown in Mike's photo's with timber battens above instead of the metal studs shown in Mike's photo's to allow for fixing of  either plasterboard with standard gypsum finish or rigidi fibre board with lime finish.

 

Critically will the flexi batts stay in play independant of the studs.

 

Previously was going to fix timber studs to wall and push fit flexi batts between the studs but Mike's strategy is much better as it allows for continous layer of insulation not broke by the studs.

 

In addition electrical socket back boxes can be fitted infront of the flexi insulation batts.

 

Dunno whether this is eureka moment, atleast appears to be so thanks to Mike's suggestion.

[ab12]

On 13/12/2024 at 21:04, Annker said:

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)

 

Don't want to dampen the spirit but a point of observation will the gypsum plasterboard and gypsum  plaster finish NOT contradict the breathable element of the make up?

In addition have you thought about paint finish- certified breathable paint with low SD low?

 

The research that I've done suggests, in order to maintain the breathable aspect, instead of gypsum plaster board to use  rigid fibre board say approx 20mm thickness or wood wool boards fixed to the studwork and finished with Baumit 38 or equivalent product which a standard plasterer should be able to cope with. 

 

Also, just checking Ankerr with your setup, will there be a cavity between the plasterboard and the insulation fibre board attached to the wall?

What sized CLS timber studs are you thinking of using?

Thanks

[Mike]

4 hours ago, ab12 said:

Mike. This is interesting. How did you manage to fix the hemp flexi batts to the walls? With some sort of glue?

No glue required - they're just cut a little over length so that they gently wedge themselves between the walls.

 

3 hours ago, ab12 said:

Critically will the flexi batts stay in play independant of the studs.

Short lengths will stay in place until you put the studs in place, or you can slide the batts behind the studs, or a mixture of both - slide just one end of the batts behind a stud, put the batts in place, then the rest of the studs. It depends on the situation.

 

In this photo there wasn't much space to slide them behind the studs so, as there were walls either side to hold the batts well, it was easier to fix the studs afterwards.

 

3 hours ago, ab12 said:

will the gypsum plasterboard and gypsum  plaster finish NOT contradict the breathable element of the make up?

In addition have you thought about paint finish- certified breathable paint with low SD low?

Plasterboard and gypsum plaster are vapour-permiable, so no problem. Vapour won't move through them over the course of a few hours, but it will over the course of days, which is enough. But but it is necessary to use a vapour-permiable paint over the top - see https://forum.buildhub.org.uk/topic/41776-breathable-paints

 

[lookseehear]

I've been looking more into this after taking some plaster and old newtonite off the walls at home. As expected the stone is pretty uneven, but looks pretty dry. This is about 2 feet above the ground.

 

 

I'm thinking about making up my own base layer of lime plaster as a levelling and airtight coat, rather than a cement based parge coat. I was thinking that a 3:1 mix of sharp sand and lime putty (slaked quicklime) with some synthetic hair added is probably the 'best' thing for the walls.

 

I assume this would suffice from an airtightness perspective and would likely be cheaper than bagged alternatives like Baumit and better than a cement based parge from a drying and wall-health perspective. If I'm only using this to roughly level, hopefully I can get it done in one coat and it won't have to be particularly neat.

 

Over this I'd do the aformentioned wood fibre or mineral wool with ~50mm battens or a 63mm CLS stud wall creating a service cavity, then plasterboard and skim. If the plasterboard turns out to be problematic down the line, it would be possible to swap these out for a wood fibre board with lime skim, but I'd hope not to have to do this obviously!

 

Window reveals would also be lime plastered, then lined either with some PIR or somthing like Bosig Phonotherm (https://www.ecologicalbuildingsystems.com/product/phonotherm) or maybe a wood fibre reveal board.

 

Any thoughts on the above? If the lime putty based plaster is sufficiently airtight I wouldn't bother with an intello membrane, and instead would focus on getting the details of the lime plaster and taping to joists/floors etc right.

[Bemak]

On 17/11/2024 at 20:10, Annker said:

 

That's an interesting project/thread you'd linked above, I hadn't come across that one.

To me the source of the dampness seems to have been the condition of the roof line and those cracks in the render, and the cement render largely contributing to its persistence.

     

 

this is my project - sorry have been offline for a while. Just as an update, over Christmas I had a builder friend call and run through the plan of attack. In short, new floor slab with UFH - for the walls we're going to dry line internally with a metal stud set off the wall by 10mm or so. The insulation between the stud will be either a hemp combi jute, or gutex thermoflex. wall will be slabbed with a gutex thermoroom board on a finsa vapourstop. skimmed with a breathable lime render. 

 

when we reviewed the floor joists, they weren't too bad. any bad sections were tight to the external wall. so the metal stud approach will also act as a support for the existing floor joists.  

[lookseehear]

On 15/12/2024 at 14:52, Annker said:

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.  

how was it with the sand mix vs sharp sand?

[Annker]

On 16/06/2025 at 14:42, lookseehear said:

how was it with the sand mix vs sharp sand?

Bit more workable with soft sand, just as it would be in a regular mortar mix.

Mix up a few different ratios and see how it goes, you can always recoat and the materials are pennies worth.

[Annker]

I found a video on Youtube of a method of IWI installation that maybe of interest to some.

 

Notwithstanding the absence of a airtight layer/parge coat and the inclusion of a vcl, otherwise it seems like a good arrangement to achieve a quality finish.

 

The gyplyner stud keep the rockwall nicely in place, however one concern is cold bridging risk from the gyplyner brackets. 

I wonder if the brackets were separated from the wall with some manner of rubber gasket would that solve the cold bridging risk? 

 

[Mike]

5 hours ago, Annker said:

I found a video on Youtube of a method of IWI installation that maybe of interest to some.

It's more-or-less the same system that I described in my various posts above. Though with thinner insulation (that could be fitted a little tighter in places) and, as you mention, without parging the wall first (disappointing but not unusual) and with the addition of a VCL that may / may not not be advisable.

 

5 hours ago, Annker said:

one concern is cold bridging risk from the gyplyner brackets.

On the walls these are unlikely to be needed if the manufacturer's sizings are followed. On the ceiling they're needed.

 

Edited July 25 by Mike

[Annker]

1 hour ago, Mike said:

It's more-or-less the same system that I described in my various posts above. Though with thinner insulation (that could be fitted a little tighter in places) and, as you mention, without parging the wall first (disappointing but not unusual) and with the addition of a VCL that may / may not not be advisable.

 

On the walls these are unlikely to be needed if the manufacturer's sizings are followed. On the ceiling they're needed.

 

Yes similar setup to your arrangement.

The brackets are needed for that particular system though, as the studs are gyplyner type not  C or I type. 

 

I actually called Rockwool tech dept with a couple of questions.

The fella I spoke to recommended/was insistent that in IWI usage the rockwool batts are friction fitted between studs and that the studwork (and batts) are both stood 25mm off the existing brick wall. In effect creating a 25mm (unventilated) cavity space.

 

@Iceverge in the example you shown earlier I understood that the rockwool batts were pressed up tight against the existing brick work.

That arrangement makes sense to me, as otherwise the unventilated cavity is created and that seems like an environment where condensation could potentially form.

Whenever I speak to product tech depts I invariably think I should not have bothered calling!

 

 

   

[Mike]

3 hours ago, Annker said:

The brackets are needed for that particular system though, as the studs are gyplyner type not  C or I type.

Must have skipped that bit. I used the European equivalent on my mansard, but here there are several types of nylon brackets available to cut heat transfer; I've not come across them in the UK.

 

3 hours ago, Annker said:

I understood that the rockwool batts were pressed up tight against the existing brick work.

That arrangement makes sense to me, as otherwise the unventilated cavity is created and that seems like an environment where condensation could potentially form.

Yes, that's the recommended method and reason :)

[Annker]

34 minutes ago, Mike said:

Yes, that's the recommended method and reason

I find it strange then that Rockwool require the cavity space, although I think there is more joined up comprehensive knowledge in these forums than the technical departments of some of these companies!

 

Furthermore I'm now leaning towards using wood fibre board instead of rockwool.  

Just monitoring RH levels in the house atm, and despite it being well dried out RH is at 70%, which is at the upper end of the scale.

So I'm thinking the £1k extra opting for wood fibre over rockwool may be a worthwhile expense.

 

[Mike]

Yes, I'm surprised that that was their suggestion too. As you'll know, having read the thread, I was happy to pay the extra for hemp insulation, but I'd have chosen wood fibre if it hadn't been readily available.

[Mike]

@Annker - just a follow up to consider how you'll be cutting the insulation. If you're cutting lots then you'll want a power saw, which you may be able to pick up on eBay or hire. For hemp that has to be an alligator saw fitted with wavy-edge insulation blades*; for wood fibre a circular saw may be OK if it cuts deep enough, but check the insulation manufacturer's advice.

 

*For example:

The UK version of the Bosch Professional GFZ 16-35 AC + TF350WM blades (used personally)

Festool 577231 18V (have seen it used)

Dewalt + DT2979-QZ blade (unverified, but the blade looks promising)

[Annker]

4 hours ago, Mike said:

@Annker - just a follow up to consider how you'll be cutting the insulation. If you're cutting lots then you'll want a power saw, which you may be able to pick up on eBay or hire. For hemp that has to be an alligator saw fitted with wavy-edge insulation blades*; for wood fibre a circular saw may be OK if it cuts deep enough, but check the insulation manufacturer's advice.

 

*For example:

The UK version of the Bosch Professional GFZ 16-35 AC + TF350WM blades (used personally)

Festool 577231 18V (have seen it used)

Dewalt + DT2979-QZ blade (unverified, but the blade looks promising)

Thanks for the pointers Mike, considerate of you.

Being a carpenter I have many different types of saws mains, battery and arm powered! 

 

I'm still finalising the spec, only certainty is that gypsum plasterboard & skim will be the finishing layers.

 

In terms of insulative performance and mitigation of interstitial condensation risk,  I'm ranking rigid wood fibre board bonded directly to the brickwork with adhesive number 1.

That choice will require the entire depth of studwork to be in front of the insulation depth, however it also then creates a service cavity of good depth, so this buildup would work well in the kitchen and bathrooms where services and domestic borne moisture will be most prevalent in the house.

 

In rooms and walls where there are fewer services ran and less habitation, (guest bedrooms and hallways), I am thinking that flexie wood fibre or rockwool batts fiction fitted into timber studwork would perform satisfactorily. 

 

I had initially thought of using the same buildup throughout but I suppose I can "upgrade" to utilise natural fibres in the areas of the house where greater volumes of moisture are created.            

 

[Mike]

19 hours ago, Annker said:

I'm ranking rigid wood fibre board bonded directly to the brickwork with adhesive number 1

I'd choose flexible / semi flexible with a friction fit - it's easy to fit free from gaps - unless you have a particular reason for choosing rigid.

 

19 hours ago, Annker said:

I suppose I can "upgrade" to utilise natural fibres in the areas of the house where greater volumes of moisture are created

Not sure what the rest of your insulation plans are, but there are other advantages to natural insulation that may be useful. For example much improved decrement delay to reduce summer heat build-up (useful at ceiling level & in timber frame), good fire behaviour (it will burn, slowly, but won't drip burning plastic or release toxic gas), pleasant to use, negative embodied carbon...

 

Edited July 27 by Mike

[Annker]

3 hours ago, Mike said:

I'd choose flexible / semi flexible with a friction fit - it's easy to fit free from gaps - unless you have a particular reason for choosing rigid.

 

Not choosing rigid specifically over flexi on a material basis; rather that the rigid boards can be bonded to the brickwork in continuously layer as opposed to flexi batts that need to be fitted between studs and therefore the insulation layer missing at every 400mm c/c stud.

Although perhaps the lower u-value of the timber stud vs insulation discounted?

[Mike]

25 minutes ago, Annker said:

flexi batts that need to be fitted between studs

They don't have to be; they can be fitted behind the studs the same as the rigid, as per my photo above.

[Annker]

3 minutes ago, Mike said:

They don't have to be; they can be fitted behind the studs the same as the rigid, as per my photo above.

My concern is that I have some large area walls, 3m high ceiling and almost 5m long.

In such large areas do you think flexi batts would maintain their installed position long term?

 

I have actually just ordered a bag of mushroom head insulation fixings, I was going to experiment with these to see if they may help keep either rockwool or flexi wood fibre boards in place.

[Mike]

2 minutes ago, Annker said:

3m high ceiling and almost 5m long.

In such large areas do you think flexi batts would maintain their installed position long term?

My wall insulation is a just short of 3m high too, and the maximum length similar to yours too and there's no problem. Just cut the batts a little longer & wider than needed, with the stud about 90 to 95mm off the wall for a 100mm batt (experiment - you want a good friction fit without over-compressing), and they won't be going anywhere :)

[Annker]

3 minutes ago, Mike said:

My wall insulation is a just short of 3m high too, and the maximum length similar to yours too and there's no problem. Just cut the batts a little longer & wider than needed, with the stud about 90 to 95mm off the wall for a 100mm batt (experiment - you want a good friction fit without over-compressing), and they won't be going anywhere

Sounds good, thanks it's very useful to hear others experience in the absence of your own.

I think I will still opt for insulation within the studwork for a couple of rooms. 

Namely two rooms that have bay windows. Here it would be preferable to keep the depth of buildup to a minimum around the bays otherwise the proportions of the individual wall panels start to look off.

Here I may keep the studwork 10mm-15mm away from the brickwork and pack a little insulation behind the stud.