New member looking for advice

[Mscott]

Hi everyone,

 

I’m Matt, a carpenter by trade with experience in timber frame builds and general carpentry. I’ve just bought a 1903 detached house that needs some restoration, and I’ve got a few questions for those with more experience—so apologies in advance for the long post!

 

The house has cavity walls that have had blown-in insulation at some point. I’ve stripped back all the old plaster on the inside of the exterior walls due to previous damp issues around the chimneys from old, poor repairs. I’ve now sorted these problems, but some brickwork is still drying out from years of moisture exposure.

 

I’m looking for the best way to re-skim these walls and possibly improve insulation while I’m at it. I understand how damp works in relation to condensation, but I want to make sure I take the right approach to avoid future issues.

 

Options I’m Considering:

 

Option 1 – No Additional Insulation:

• 2x1 battens for a service void

• Plasterboard and skim

 

Option 2 – Light Insulation Upgrade:

• 2x1 battens on the wall

• Space blanket insulation

• Additional battens on top for a service void (as recommended by YBS SuperQuilt)

• Plasterboard and skim

 

Option 3 – More Insulation:

• 3x2 stud wall set slightly off the external wall

• Flexi-batt insulation between studs

• Plasterboard and skim

 

My main concern is whether any of these options could create condensation issues on the internal brickwork. I’d really appreciate any advice or alternative suggestions from those who’ve tackled similar projects.

 

Thanks for reading, and I appreciate any insights!

[Russell griffiths]

That must be one of the earliest cavity walls around. 

[MikeSharp01]

Welcome to THE forum for people like us. Not my bag but others will be along shortly.

[Garald]

Not my bag either, but:

- use https://www.ubakus.de/en/r-value-calculator/ to spot possible condensation issues,

- consider using an insulating material with good moisture-regulation properties.

 

Others will give much more solid advice than I am able to.

[Mscott]

26 minutes ago, Garald said:

Not my bag either, but:

- use https://www.ubakus.de/en/r-value-calculator/ to spot possible condensation issues,

- consider using an insulating material with good moisture-regulation properties.

 

Others will give much more solid advice than I am able to.

This looks a good website il have to fire up the laptop as it’s abit of a pain to use on a phone. 

[nod]

A better option is gypliner with 52 mil insulated plasterboard 

[Mscott]

3 minutes ago, nod said:

A better option is gypliner with 52 mil insulated plasterboard 

I’ve not seen or used this. Have you got any experience of using it what’s the benefits?

[Temp]

I think I'd check that the insulation in the cavity isnt causing any damp to transfer across. 

 

1 hour ago, Mscott said:

My main concern is whether any of these options could create condensation issues on the internal brickwork.

 

What can happen is that insulating on the inside "moves" the internal brickwork towards the cold side. Then, if warm humid air created in your house can get through the new insulation, water can potentially condense on the now colder surface. That air can get through to new insulation via electrical sockets or any other holes, perhaps at floor or ceiling. So I think careful attention to sealing gaps is important. 

 

I think this is another reason to check the insulation in the cavity wall hasn't all slumped leaving uninsulated areas. 

 

 

 

[ETC]

Granny and sucking eggs - have you asked the insulation manufacturer to do an interstitial condensation risk analysis? Most will do this for free.

[saveasteading]

1 hour ago, Mscott said:

blown-in insulation at

More info will help. Do you know what the insulation material is?

 

Is it plain brick, cavity fully filled,  brick, plaster?

 

Is there damp internally generally or just at some locations?

 

[Mscott]

15 minutes ago, saveasteading said:

More info will help. Do you know what the insulation material is?

 

Is it plain brick, cavity fully filled,  brick, plaster?

 

Is there damp internally generally or just at some locations?

 

I’m not sure of the make it’s a white more fully type over beads. 
 

make up from outside in pebble dash render, 100mm brick, 40-45mm cavity fully filled, 100mm brick.

 

damp was just on 2 chimney breast walls as the lead had been done awfully and no saddle on the ridge, they just put concrete in the chimney pot so was leaking down the chimney beast from the lead then the stack was sealed so couldn’t breathe causing condensation to build up inside. They are all sorted now but the bricks are still drying out. 
 

 

[Mscott]

33 minutes ago, ETC said:

Granny and sucking eggs - gave you asked the insulation manufacturer to do an interstitial condensation risk analysis? Most will do this for free.

I’ve not and didn’t know they did this. I may speak with ybs see if this is something they can do.

[Mscott]

43 minutes ago, Temp said:

I think I'd check that the insulation in the cavity isnt causing any damp to transfer across. 

 

 

What can happen is that insulating on the inside "moves" the internal brickwork towards the cold side. Then, if warm humid air created in your house can get through the new insulation, water can potentially condense on the now colder surface. That air can get through to new insulation via electrical sockets or any other holes, perhaps at floor or ceiling. So I think careful attention to sealing gaps is important. 

 

I think this is another reason to check the insulation in the cavity wall hasn't all slumped leaving uninsulated areas. 

 

 

 

I get exactly what you’re saying that’s why Im unsure of the best route to take? 
 

The cavity insulation seems fine. If I went space blanket I wouldn’t just use the plaster board boxes to not puncture it.

 

The loft will have 400mm of insulation and the floor joist will have 200mm of insulation in. Whatever I do with the walls upstairs il repeat downstairs to match. 

[Temp]

Opinions do differ on this. Some insist that it's not a problem if the wall is vapor permeable or if the permeability increases as you move from inside to out. In my view it's hard to know if the walls are vapour permeable and it's better to add a vapour barrier before plasterboarding.

 

Do you have any plans for ventilation? When you seal up an old house you inevitably reduce draughts that might have been helping to keep the house dry. I think this is more an issue for houses with solid walls and no DPC etc. When we built our house we opted for an MVHR system and I think the constant air flow they deliver does work better than trickle vents in Windows even ignoring the heat recovery part.

[nod]

10 minutes ago, Mscott said:

I’ve not seen or used this. Have you got any experience of using it what’s the benefits?

Yes forty years 😁

Its quite a simple system Takes up very little space and has very little contact with the wall 

This is one of our jobs 

30 apartments in the Lake District that the banks pulled the plug on once built and have stood empty for eight years Of course insulation and airtightness levels have tightened in this time So gyplining and insulation boards was the best option 

[Mscott]

ive been reading up and think an option would be this stuff?

https://www.multifoilsdirect.co.uk/product/ybs-breatherquilt/

 

so vertical batten the wall then the breather quilt then horizontal batten and board and skim?

[Russell griffiths]

1 hour ago, Mscott said:

ive been reading up and think an option would be this stuff?

https://www.multifoilsdirect.co.uk/product/ybs-breatherquilt/

 

so vertical batten the wall then the breather quilt then horizontal batten and board and skim?

Be careful don’t believe the manufacturer, look at independent research. 
it would be the last product i would use. 

[Nickfromwales]

2 hours ago, Mscott said:

ive been reading up and think an option would be this stuff?

https://www.multifoilsdirect.co.uk/product/ybs-breatherquilt/

 

so vertical batten the wall then the breather quilt then horizontal batten and board and skim?

You ever head the phrase “too good to be true”?  

 

Not going to improve your situation with that I’m afraid. That’s the kind of thing you’d use on a conservatory roof to keep the sun from cooking you alive, largely by reflection vs insulation. 

[Mscott]

We use the non breathable stuff on all new timber frame houses and have no issues.

 

What’s the best method people are doing not to cause issue. 
 

At this rate I think I’m just going to batten the wall to give a service void and then just plasterboard, this shouldn’t cause the inner brickwork to condensate and cause damp issues in the future 

[Russell griffiths]

38 minutes ago, Mscott said:

We use the non breathable stuff on all new timber frame houses and have no issues.

 

What’s the best method people are doing not to cause issue. 
 

At this rate I think I’m just going to batten the wall to give a service void and then just plasterboard, this shouldn’t cause the inner brickwork to condensate and cause damp issues in the future 

You might work on those houses, but do you live in one and pay the heating bill. 
I thought you wanted to improve your house, not make it the same standard as the shite being turned out by the mass house builders. 

the non breathable stuff will act as a good vcl but very little in the way of insulation. 
 

im afraid if you want better you need to consider the stuff the mass housebuilders turn out to be very poor. 
we have some of the worst housing in Europe. 
if you want to build something better, stay here and ask more questions and do more research. 
 

aside from that have you had a look at the condition of your wall ties if your place is one of the first cavity walls built, corroding wall ties can be a problem. 

Edited February 23 by Russell griffiths

[Jilly]

I might be mad suggesting this, but as you have pebbledash, might covering that with external wall insulation/render of some kind be an option? 

 

Pebbledash isn’t the most beautiful thing, and EWI doesn’t tend to cause interstitial condensation. The window and door frames would be another issue though. 

[SteamyTea]

11 minutes ago, Jilly said:

might covering that with external wall insulation/render of some kind be an option

It is a cavity wall, probably with failed insulation, so full of thermal bypasses, the biggest one being free air movement.

 

@Mscott

As others have said, best to forget all about the multifoil type thermal barriers.

Everyone wants them to work, especially architects and house builders, so desperate are they, they want a special caveat on the standard material thermal testing regimes that will allow their products to pass with a lower R-value.

[Mscott]

1 hour ago, Russell griffiths said:

You might work on those houses, but do you live in one and pay the heating bill. 
I thought you wanted to improve your house, not make it the same standard as the shite being turned out by the mass house builders. 

the non breathable stuff will act as a good vcl but very little in the way of insulation. 
 

im afraid if you want better you need to consider the stuff the mass housebuilders turn out to be very poor. 
we have some of the worst housing in Europe. 
if you want to build something better, stay here and ask more questions and do more research. 
 

aside from that have you had a look at the condition of your wall ties if your place is one of the first cavity walls built, corroding wall ties can be a problem. 

we have absolutely no issues with this on new build timber frame and probably the most efficient houses there are. 
 

150mm timber frame kit. 100mm sound bat in the frame and then super foil on the inside.  
50mm full coverage externally with pir boards, 50mm cavity then block 

 

I’m not experienced in these older houses so open to suggestions. 
 

[Mscott]

1 hour ago, Jilly said:

I might be mad suggesting this, but as you have pebbledash, might covering that with external wall insulation/render of some kind be an option? 

 

Pebbledash isn’t the most beautiful thing, and EWI doesn’t tend to cause interstitial condensation. The window and door frames would be another issue though. 

 

We already have cavity wall insulation and don’t have any issues with the external pebble dash we have some older features that we wouldn’t want to have covered over. 
 

[saveasteading]

47 minutes ago, SteamyTea said:

forget all about the multifoil type thermal barriers.

OK for taking the extremes off an attic or shed. 

Look at the thickness of the foam layers. Then at the air gaps. Can they combine to the same effect as the same thickness of eps of Pir?

The effect of a shiny surface can only work once. Energy bounces back off the first surface it reaches into the medium it is against. 

There is a distinct lack of independent testing. They seem to have their own.