Internal Insulation - Solid Brick Wall

[jayc89]

I'm starting to think about how we can better insulate the existing parts of our house. They're solid brick walls and external insulation is not an option as we don't want to cover up the existing brickwork, so internal wall insulation it is.

 

The external walls, whilst originally plastered using lime have been at some point skimmed with gypsum and show no signs of damp, so moisture is not currently a problem - externally it's still pointed in lime mortar. The internal plaster build up, in areas, is so thick it's reaching nearly an inch!

 

Whilst are room sizes are decent, we don't want to lose too much internal floor space, so either way I want to knock off the existing plaster first.

 

I'm thinking of two options;

 

Warm Batten

- 25mm PIR direct to wall (taped - acting as a VCL)

- 50mm battens over

- 50mm PIR infill

- Plasterboard

 

Gyplyner

- Gyplyner direct to wall

- Insulated plasterboard

 

I do like how with the warm batten method I can make sure noggins are in place where I know I want to anchor things (like TVs). I'm less keen on insulated plasterboard, but appreciate the void Gylyner provides between the external wall and the insulation.

What would you do? Are there other options I should consider?

[Mr Punter]

I don't like insulated plasterboard.  It is expensive and impossible to recycle and you will need some very long screws to fix it unless you stick it on.  Have you worked out the comparable buildup thicknesses, u values and material costs?  It may be worth having a play with.  You could look at slightly thicker pir on the wall and just use 25mm battens, which still gives enough space for electrics and pipes.

[jayc89]

9 minutes ago, Mr Punter said:

I don't like insulated plasterboard.  It is expensive and impossible to recycle and you will need some very long screws to fix it unless you stick it on.  Have you worked out the comparable buildup thicknesses, u values and material costs?  It may be worth having a play with.  You could look at slightly thicker pir on the wall and just use 25mm battens, which still gives enough space for electrics and pipes.

 

Warm Batten would be a build up of 87.5mm (exc. skim coat) and provide a u-value of 0.28. (50mm PIR direct to wall with 25mm in fill would provide a better overall efficiency.)

Gyplyner, with 25mm cavity, would be a build up of 105mm (exc. skim coat) and provide a u-value of 0.27

 

A difference of 17.5mm wouldn't be that noticeable so I think it comes down to what the most optimum solution would be.

 

For reference, I'd need 150mm PIR to reach a u-value of 0.15

[Iceverge]

Internal insulation is risky. 

 

You will have a permanently colder brick structure which in turn will result in higher moisture levels within the wall, heightening your chances of decay and frost damage. 

 

You need to take every precaution to ensure that moisture can make its way out of the wall as easily as possible.

Choosing a vapour closed internal insulant like PIR risks entirely sealing one side of the wall, halving your potential drying routes.

 

Furthermore the vapour barrier cannot be continuous (unless you cut back the floor joists and internal walls).

 

With vapour barrier penetrations at the end of every joist, the timbers ends sitting outside the heated envelope right at the most lightly point to receive damp air from inside, you're asking for trouble.

 

A safer approach would be to use a very vapour open internal insulant and wall finish.  

[jayc89]

2 minutes ago, Iceverge said:

Internal insulation is risky. 

 

You will have a permanently colder brick structure which in turn will result in higher moisture levels within the wall, heightening your chances of decay and frost damage. 

 

You need to take every precaution to ensure that moisture can make its way out of the wall as easily as possible.

Choosing a vapour closed internal insulant like PIR risks entirely sealing one side of the wall, halving your potential drying routes.

 

Furthermore the vapour barrier cannot be continuous (unless you cut back the floor joists and internal walls).

 

With vapour barrier penetrations at the end of every joist, the timbers ends sitting outside the heated envelope right at the most lightly point to receive damp air from inside, you're asking for trouble.

 

A safer approach would be to use a very vapour open internal insulant and wall finish.  

 

I intend to carry the insulation on through the floor space, cutting back the upstairs floorboards. Joists are the problem though as the insulation would only wrap around the joist ends. I can't think of a good solution to this, other than refitting them on joist hangers inside of the insulation, which I don't really fancy doing, as I'd have to replace the entire ceilings below too. 

[Iceverge]

You have proper 2 choices really. 

 

1. Use a very breathable (vapour open) internal wall buildup tight to the existing wall. 

 

2. Make a complete box within a box and a ventilated cavity all around the internal shell. (Very difficult unless you knock all internal walls and take our the ground floor ceiling) 

 

1. is your only realistic option here.

 

A couple of options are:

 

Gypliner with mineral wool or other breathable insulation. With a vapour open board over the top and lime plaster. 

 

Wood fiber boards and lime render.

 

A thick layer of insulating lime cork plaster. 

 

 

 

 

[jayc89]

As I understand it, there are two potential problems;

 

Moisture moving out to in, such as driving rain, would should never really happen in our location with well maintained gutters, pointing etc, but is what introducing a cavity (such as Gyplyner) is meant to mitigate.

 

Moisture moving in to out, such as interstitial condensation, as the internal warm, moist air, hits the cold external wall. Isn't the introduction of some sort of continuous VCL meant to mitigate this concern? Of course, the joist ends are still some concern here as you could tape any VCL around them, but there's still the potential for moisture to travel through them. Sufficient ventilation might be a secondary mitigation though?

 

I assume a VCL will also go some way to making the property airtight too?

[nod]

I wouldn’t fix anything directly to the walls 

By far your best option is gypliner either Boarded with insulated pb or wool batts and boarded with 12.5 PB

Or depending on your budget A combination of both 

[SimonD]

Best practise guidance now recommends against using moisture closed insulation systems on retrofit iwi. Where it is used, a ventilated cavity is recommended. If you're going to below u-value of 0.30 then you have to have a good look at cold bridging, not just interstitial condensation and moisture.

 

If you were to go with a moisture open insulation you can fix this directly to the wall, not worry about your vcl, just air barrier.

 

Government guidance here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf

[Iceverge]

2 hours ago, jayc89 said:

Moisture moving out to in, such as driving rain, would should never really happen in our location with well maintained gutters, pointing etc, but is what introducing a cavity (such as Gyplyner) is meant to mitigate.

 

Not exactly. Old walls internal humidity can vary significantly season to season, related directly to the RH of the ambient air, internally and externally. Invariably, in any house in a damp climate without air conditioning, the internal humidity will map the outside, even a passive house. 

 

An old wall ( brick lime stone etc) , as long as it can stay dry, can have a good contribution to the overall insulative value of the total build-up as long as there isn't any cavities or thermal bypass.

 

https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationId=7fc3d5f6-5992-4106-92bf-a59400bf430c

 

However if the wall becomes damp (kept cold and cannot dry) the internal moisture builds up leading to degradation of the structure and a much poorer overall U-Value. 

 

http://www.tara.tcd.ie/bitstream/handle/2262/79420/CERI draft RW SP final.pdf?sequence=1&isAllowed=y

 

@nod Suggesting gypliner I'd be concerned about how to deal with the breach of the continuous thermal and vapour envelope at floor joists and abutting walls. These would be very tricky to seal 100% and most of your buildup would be still gypsum. With low vapour permeability my fear is that you could end up restricting any moisture movements in the house out through the joist ends and abutting walls leading to rot. 

 

Nice explanation from Tomás here. 

 

 

 

 

 

[Roger440]

There have been a couple or three very recent threads on exactly this. Id recommend you read them.

[Temp]

11 hours ago, Iceverge said:

You will have a permanently colder brick structure which in turn will result in higher moisture levels within the wall, heightening your chances of decay and frost damage. 

 

I don't think this is any different to filling a cavity wall with an injected foam insulation. Similar risks?

[Iceverge]

It is a little as the external leaf would never have been warm in the first place. 

 

Also I reckon that cavity walls were after lime morter by and large. Much less critical to allow cement to breath.

 

If you're injecting foam into cavities it'll be closed cell type forming a very effective vapour barrier too. 

[George]

I went with wood fibre boards and lime plaster.

 

Calculated a u-value of 0.5, may well be performing better than that but only have 1 year of numbers to look at and it'd be a very very rough estimation (calculated heat losses vs actual heat demand).

[jayc89]

22 hours ago, SimonD said:

Best practise guidance now recommends against using moisture closed insulation systems on retrofit iwi. Where it is used, a ventilated cavity is recommended. If you're going to below u-value of 0.30 then you have to have a good look at cold bridging, not just interstitial condensation and moisture.

 

If you were to go with a moisture open insulation you can fix this directly to the wall, not worry about your vcl, just air barrier.

 

Government guidance here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf

 

That's pretty useful, thank you. Using something like Aerogel around the floor joists is also an interesting idea, although I don't fully get the detail of where the the vapour open and vapour closed insulations would meet. Surely that would at risk of moisture in itself?

 

What's the deal with going below 0.30? Not that I can afford the space required to go below that figure!

[jayc89]

On 09/04/2022 at 13:47, SimonD said:

Best practise guidance now recommends against using moisture closed insulation systems on retrofit iwi. Where it is used, a ventilated cavity is recommended. If you're going to below u-value of 0.30 then you have to have a good look at cold bridging, not just interstitial condensation and moisture.

 

If you were to go with a moisture open insulation you can fix this directly to the wall, not worry about your vcl, just air barrier.

 

Government guidance here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf

 

I spent some time reading this.

 

As I understand it, moisture-open insulation is the recommended approach, with moisture-closed being 2nd best;

 

Quote

41. The risk of interstitial condensation with internal wall insulation can be high due to warm internal air passing through or around the insulation and airtightness layers and condensing on the cold wall, and/or from external moisture within the masonry. The addition of a vapour barrier inside internal insulation (IWI) on solid walls used to be regarded as essential, partly due to inappropriate moisture risk assessment methods. However, it is now agreed that, in many cases, this may cause more harm than good. Therefore, a moisture open internal wall insulation build-up is recommended in the insulation of solid walls, or alternatively a moisture closed system with a ventilated cavity (of at least 25mm) on the cold side.

 

Where moisture-closed insulation is used, a ventilated cavity should also be included on the cold side, however when that is not the case, a wind barrier should be used instead;

 

Quote

48. Moisture closed systems with a ventilated cavity enable the use of high- performance insulations, however the presence of the cavity will increase the thickness of the build-up and this may result in an unacceptable reduction in floor area. In these cases, a wind barrier should be installed on the cold side of the insulation.10 In general, when specifying materials, the vapour permeability of materials should decrease from inside to outside, with the most vapour impermeable layer on the internal surface and most vapour permeable layer on the outer surface.

 

So in a warm-batten method would that be;

- solid wall

- wind barrier (is this like an airtight vapour control membrane?)

- couple of layers of PIR sheets overlapping and tapped (effectively the VCL)

- battens

- optional PIR infill (taped)

- plaster board

 

When it comes to floor joists, ideally the should be refitted on hangers on the warm side of the insulation;

 

Quote

53. Where IWI is being installed around joist ends that are embedded into a wall, the lowest risk option is to entirely remove the joists from the wall and rest on wall hangers or a thermally-broken steel joist. This will eliminate the risk of rotting or deterioration from a cold wall due to the installation of the IWI. Bringing joists away from the wall may also allow the IWI to extend down the wall uninterrupted and thereby avoiding thermal bridges.

 

That's just not possible, I can't rip out upstairs floorboards up (again), the Mrs would go nuts  As such, certain mitigations like injecting the ends with boron paste and wrapping + taping them in vapour permeable insulation instead;

 

Quote

53. If joist ends are left in existing walls then injection of boron paste may be considered. Boron paste inhibits mould and fungus growth, and prevents the joist ends from rotting.

54. Vapour permeable thin internal wall insulation (TIWI) of less than 40mm will help reduce moisture risks in joist ends. If necessary, TIWI may be placed only between joist ends, with thicker insulation above and below the joists.

55. Joist ends embedded in walls should be made airtight using vapour open products such as some airtightness tapes or lime render.

 

Should the joist ends still be wrapped and taped using vapour permeable materials of the wall is covered in PIR? There seems little point if it's behind an airtight wind barrier. I'm not really sure what that detail should look like here.

 

Doing all this, plus replacing our windows/doors, should result in a pretty airtight building too. I assume at this point we'd need to be considering MVHR?

[SimonD]

On 10/04/2022 at 19:25, jayc89 said:

Where moisture-closed insulation is used, a ventilated cavity should also be included on the cold side, however when that is not the case, a wind barrier should be used instead;

 

On 10/04/2022 at 19:25, jayc89 said:

So in a warm-batten method would that be;

- solid wall

- wind barrier (is this like an airtight vapour control membrane?)

- couple of layers of PIR sheets overlapping and tapped (effectively the VCL)

- battens

- optional PIR infill (taped)

- plaster board

 

You've got to be a bit careful with reading these documents as the reference note in paragraph 48 points to this:

 

Quote

Note that achieving a well-ventilated cavity with wind barrier may be difficult in reality, and will
require careful design.

 

You really need someone who can run it through a proper analysis like with WUFI before arriving at a buildup for yourself. You still have the challenge of how to create and maintain a fully sealed and effective vapour control layer throughout the building if using PIR. The detailing thus being imperative.

 

I personally don't understand the popularity of PIR in these circumstances because of the detailing and added risks, particularly when you have a preferred option of moisture open solutions available to you. The alternatives will not only reduce your risks but also tend to provide a nicer indoor air environment because of their breathability. This can in turn reduce the demands on additional ventilation requirements.

 

[jayc89]

1 hour ago, SimonD said:

 

 

You've got to be a bit careful with reading these documents as the reference note in paragraph 48 points to this:

 

 

You really need someone who can run it through a proper analysis like with WUFI before arriving at a buildup for yourself. You still have the challenge of how to create and maintain a fully sealed and effective vapour control layer throughout the building if using PIR. The detailing thus being imperative.

 

I personally don't understand the popularity of PIR in these circumstances because of the detailing and added risks, particularly when you have a preferred option of moisture open solutions available to you. The alternatives will not only reduce your risks but also tend to provide a nicer indoor air environment because of their breathability. This can in turn reduce the demands on additional ventilation requirements.

 

 

I read it as suggesting a wind barrier when a ventilated cavity isn't an option.

 

I don't have any preference towards PIR, other than the space saving, but where I'm based it's an absolute nightmare finding any plasterer that will work with lime and the ones that do are generally based more towards the Yorkshire Dales, 60+ miles away, as that's where most of the demand is. I've even had plasters look at me funny when I ask about lime - that probably says more about them to be fair...

 

So if the walls end up being skimmed in gypsum, making the rest of the build up seems somewhat pointless. 

[jayc89]

This is a pretty interesting read; https://passivehouseplus.ie/articles/insulation/breaking-the-mould-part-v. Basically saying, without very careful management, IWI is only good up to a u-value of 0.45, before running into problems.

[SimonD]

15 hours ago, jayc89 said:

that probably says more about them to be fair...

 

Yes it does. However, there are now several lime products to go on woodfibre IWI, for example, that are very easy to apply, so much so that a typical plasterer will  find it easy, possibly easier, to work with than gypsum - nicely workable and long set time. An example is Lime Green Solo as part of the IWI system - https://www.lime-green.co.uk/warmshell/warmshell-interior. Baumit also sell products well regarded in this area.

 

12 hours ago, jayc89 said:

This is a pretty interesting read

 

This piece does highlight that local climate is very important, and that driving rain can have a significant effect on the performance of the wall. You're going to find variations in suggested buildups. I would personally like to see an update of this as it's from 2010.  The Bristolians guide to insulation suggest 0.60. https://sdfoundation.org.uk/wp-content/uploads/2018/01/2015_bristolsolidwallinsulationguidance.pdf. There are lots of other links in some recent posts that go into a lot more detail about approaches to IWI.

[jayc89]

3 minutes ago, SimonD said:

 

Yes it does. However, there are now several lime products to go on woodfibre IWI, for example, that are very easy to apply, so much so that a typical plasterer will  find it easy, possibly easier, to work with than gypsum - nicely workable and long set time. An example is Lime Green Solo as part of the IWI system - https://www.lime-green.co.uk/warmshell/warmshell-interior. Baumit also sell products well regarded in this area.

 

 

This piece does highlight that local climate is very important, and that driving rain can have a significant effect on the performance of the wall. You're going to find variations in suggested buildups. I would personally like to see an update of this as it's from 2010.  The Bristolians guide to insulation suggest 0.60. https://sdfoundation.org.uk/wp-content/uploads/2018/01/2015_bristolsolidwallinsulationguidance.pdf. There are lots of other links in some recent posts that go into a lot more detail about approaches to IWI.

 

Given many of these methods have been used over the last 12+ years I'd love to get some feedback from people who have installed IWI using certain methods many years ago to see if it did in fact cause any problems. A lot of what I read on forums across the net seem to be theory, or "because that's how it's always been done". It seems somewhat of a dark art!

[Iceverge]

I agree. Studies are often inconclusive. 

 

This one suggests Brick Cream may be an important factor. 

 

https://carbonlite.net/wp-content/uploads/2016/07/1a-b-IWI-PU-foam-Brick-Cream-Treated-vs-Untreated_version-a_UPLOADREADY.pdf

[jayc89]

This is the make up I'm considering, from outside to in;

 

- Solid Brick Wall

- 25mm PIR, taped

- Overlapping 25mm PIR, taped

- Airtight Membrane/Vapour Check

- 25mm Service Void

- 12mm OSB (not necessary but will makes the walls feel more substantial)

- 12.5mm Plasterboard

- Skim

 

 

According to my calcs this would achieve a u-value of 0.29, which is arguably too good for IWI (with the assumption that some heat should be allowed to escape to aid in keeping the wall dry)

 

 

I toyed with the idea of having a separate airtight membrane on the cold side and using the one on the warm side just as an additional vapour check (as the 2x layers of taped PIR should also do this) - would that be overkill?

 

I like the idea of keeping the service void on the warm-side as it means we won't have to punch holes through the PIR, or airtight barrier, but I'd be keen to hear other opinions on not having a cavity between the wall and PIR. I'm still not entirely sure what an unventilated cavity on the cold side would achieve. 

[jayc89]

Another option I thought of;

 

- Woodfibre direct to the wall

- AVCL over

- Batten over to act as a service void (no services penetrating the airtight layer)

- PB + skim

 

 

 

The wood fibre providing the breathable insulation and the service void acting as a cavity to decouple the breathable materials from the non-breathable ones.

 

It adds approx. 50mm to the depth, which is a shame, but probably worth it...

Thoughts?

[jayc89]

Similar to this, albeit the diagram is using sheep's wool not wood fibre...