Internal insulation - Wood fibre vs dry lining

[thebadger7]

Hi all

I've been looking at adding internal insulation whilst refurbishing a solid brick extension on a 1880s property.

I've come down to two choices:
- Woodfibre boards finished in lime
- Dry line wall with insulated plasterboard, leaving an air cavity with vents to outside (through ceiling or air bricks)

Any thoughts on pros/cons? I feel like the second option would be better as the bricks are fully exposed to air, whereas firs option might be impacted by wall being covered in kitchen units etc

Cheers

Luke

 

[Dumsey]

Afraid I have no useful knowledge on this subject, but would be interested in the replies from those more knowledgeable

 

[a twig]

Plenty of fans of option 1) on here, myself and numerous others have posted threads on here about how we did it etc

 

[Lacan07]

Hi all

I've been looking at adding internal insulation whilst refurbishing a solid brick extension on a 1880s property.

I've come down to two choices:
- Woodfibre boards finished in lime
- Dry line wall with insulated plasterboard, leaving an air cavity with vents to outside (through ceiling or air bricks)

Any thoughts on pros/cons? I feel like the second option would be better as the bricks are fully exposed to air, whereas firs option might be impacted by wall being covered in kitchen units etc

Cheers

Luke

The usual objection to rigid foam board is firstly the gap between the wall and the board whether its fixed via dot & dab or batons, but you've obviously made allowances for this with ventilation. This would reduce the effectiveness of the insulation I would imagine though. The other thing to watch for would be condensation on the cold side of insulation board, all joints and junctions would need to be taped for air and moisture tightness.

The other problem with the internal insulation of solid brick walls is the removal of the heat that would usually pass through the walls in winter which can lead to freeze thaw in damp brick work. They say with wood fibre you should only use between 40 - 80mm thickness otherwise your taking out too much heat from the wall. With rigid foam board being a better insulator than wood fibre I would go even less.

 

[simonjamesm1]

Hi all

I've been looking at adding internal insulation whilst refurbishing a solid brick extension on a 1880s property.

I've come down to two choices:
- Woodfibre boards finished in lime
- Dry line wall with insulated plasterboard, leaving an air cavity with vents to outside (through ceiling or air bricks)

Any thoughts on pros/cons? I feel like the second option would be better as the bricks are fully exposed to air, whereas firs option might be impacted by wall being covered in kitchen units etc

Cheers

Luke

Hi Luke. Did you get anywhere with this? We are looking at the same, either wood fibre or cork with lime. We have a quote for a living room wall (hall external facing wall) to be insulated and lime plastered. Internal wall and ceiling to be multi skimmed.

 

[simonjamesm1]

Should have added quote was £6,000

 

[Lacan07]

Should have added quote was £6,000

How many walls in total is that?

Either wood fibre or cork is good in an old house. Are you sure your ground internal wall will be ok with multi finish / gypsum? I assume thats what you meant when you said multi skimmed.

 

[simonjamesm1]

1 one lime and insulation. Ceiling and internal walls multi skimmed. There multi skim on other internal walls so seems to be performing ok, very keen to allow the walls with external faces to breath though.

 

[Lacan07]

1 one lime and insulation. Ceiling and internal walls multi skimmed. There multi skim on other internal walls so seems to be performing ok, very keen to allow the walls with external faces to breath though.

So thats 1 wall to be insulated with wood fibre / cork and lime skimmed and how many internal walls multi skimmed?

Does the wall to be insulated have the original lime plaster, is it painted, wallpapered, etc. Or perhaps its back to brick?

 

[malcolm]

I've used both systems. I've got Cellotex in a stud wall with a 2 inch gap to a timber frame. It made sense as I wanted to keep a bedroom operational while the timber frame on the other side of the stud wall was replaced. I did the same downstairs and it seems to work. The downside is the cavity needs to be ventilated.

For my kitchen I went for woodfibre boards with lime. I don't think cabinets will be an issue so long as exterior ground levels are lower than inside and the outside of the wall can breathe. A dry brick wall is pretty good for insulation - it's worth at least 40mm of woodfibre board and the wall will be better preserved if it is heated slightly in the winter.

 

[CarolineTheChemist]

We’re doing something similar on a solid brick wall building. It was originally plastered in modern plaster (70s refurb) and we had it battened and gypsum plasterboarded (but not skimmed) in the summer. When the rain finally came in the autumn, the black mould came too - for the first time ever! We soon realised we needed to ensure the breathability of the wall.
So we’ve taken it all off and gone back to the (wet) brick. We’ve let that dry as much as possible and are now doing a lime scratch coat (NHL 3.5). That’ll be followed by 40mm wood fibre boards and a lime finish. As part of this work, the external brickwork has also been repointed in lime.

We did discuss the idea of making a kind of ventilated cavity wall with the plasterboard but we didn’t think the ventilation would be enough to keep the cold, damp and mould out of the solid wall. Also, ventilating the new cavity kind of goes against the point of insulating. Either warm damp air goes in there from indoor ventilation or cold air from outdoor ventilation - both seem like a recipe for condensation, rodents, wasp’s/hornet’s nests, etc etc.

I could be wrong, but aside from the breathable properties of lime, I think its alkaline nature means it’s mould resistant.

I hope that helps!

 

[erikwoolf]

We have decided to go with woodfibre boards and lime plaster. There are some tricky parts like around the staircase and inside the bathroom and the external kitchen wall that in theory will have all the pipes running across that we are still figuring out. We did a bit of research around the issue of interstitial condensation as a result of installing IWI. Some of the manufacturers claim that if the property is in an exposure zone 1 (and all external vapour blockers/issues have been rectified) then there is little issue with the woodfibre 60mm product that we are going for. Not sure if this is 100% accurate but apart from carrying out a hygrothermal risk assessment this is the kind of information we have sourced.

 

[Lacan07]

We have decided to go with woodfibre boards and lime plaster. There are some tricky parts like around the staircase and inside the bathroom and the external kitchen wall that in theory will have all the pipes running across that we are still figuring out. We did a bit of research around the issue of interstitial condensation as a result of installing IWI. Some of the manufacturers claim that if the property is in an exposure zone 1 (and all external vapour blockers/issues have been rectified) then there is little issue with the woodfibre 60mm product that we are going for. Not sure if this is 100% accurate but apart from carrying out a hygrothermal risk assessment this is the kind of information we have sourced.

60mm should be fine, I'd say 80mm was pushing it.

 

[thebadger7]

Thanks for the replies everyone, some really good points.

I think we're going to go with the cavity approach for a couple of reasons:
1. It has been difficult enough finding tradesmen to do the project in a suitable timescale (we have to get it done by Spring next year) - very few firms I've engaged with want to do breathable insulation/lime plaster (sad, I know).
2. One of the rooms will be a bathroom, so a lot of the finish won't be breathable anyway with tiles and shower etc. So with a cavity approach at least the brickwork can still breathe.
3. Rooms are kitchen/bathroom so a lot of services it would be handy to conceal in a cavity.

I may regret it, but had to be pragmatic and instead going to focus on replacing the cement render with lime render next summer.

I'll report back!

 

[Lacan07]

Thanks for the replies everyone, some really good points.

I think we're going to go with the cavity approach for a couple of reasons:
1. It has been difficult enough finding tradesmen to do the project in a suitable timescale (we have to get it done by Spring next year) - very few firms I've engaged with want to do breathable insulation/lime plaster (sad, I know).
2. One of the rooms will be a bathroom, so a lot of the finish won't be breathable anyway with tiles and shower etc. So with a cavity approach at least the brickwork can still breathe.
3. Rooms are kitchen/bathroom so a lot of services it would be handy to conceal in a cavity.

I may regret it, but had to be pragmatic and instead going to focus on replacing the cement render with lime render next summer.

I'll report back!

Don't worry about it too much, everything is a compromise at the end of the day and you may be taking the most sensible approach.

 

[DampedOut]

@Lacan07 Out of curiosity, are there similar limitations for the thickness of internal wall insulation when it comes to stone rubble walls? It’s probably even less for cob buildings, right?

 

[paulc]

3. Rooms are kitchen/bathroom so a lot of services it would be handy to conceal in a cavity.

Personally, I'd be reluctant to lose pipework in a cavity. If they spring a leak, you won't know until damage is apparent on the surface. By then, all kinds of horrors could have developed unseen. Pipes could be chased in to the insulation boards just below the plaster surface. Cover with a thin strip of timber, and you'll be able to get to the pipes should you ever need to.

 

[Lacan07]

@Lacan07 Out of curiosity, are there similar limitations for the thickness of internal wall insulation when it comes to stone rubble walls? It’s probably even less for cob buildings, right?

Hi, I'm no expert on stone walls, are they susceptible to freeze/thaw in the same way that a brick is? That's the main issue with brick, especially the old soft variety, if you remove some of the heat they receive in the winter with IWI and the bricks are damp then they freeze internally and the face gets blown off. I think its called 'spalding'? Then they are no longer protected from the elements.

I guess stone walls are a hell of a lot thicker too?

 

[Cubist]

Hi, I'm no expert on stone walls, are they susceptible to freeze/thaw in the same way that a brick is? That's the main issue with brick, especially the old soft variety, if you remove some of the heat they receive in the winter with IWI and the bricks are damp then they freeze internally and the face gets blown off. I think its called 'spalding'? Then they are no longer protected from the elements.

I guess stone walls are a hell of a lot thicker too?

Depends on the density of the stone. Roughly speaking density relates to porosity and as a consequence even the hardest stone can absorb some water through its surface and spalling damage can ensue. Just not as quickly as a manufactured brick I'd guess.

 

[NecessaryWing]

@thebadger7 what county are you based in?

@CarolineTheChemist - we have cement repointing which we want to rectify. How expensive is that process? Did they replace it with traditional fat lime mortar (hydraulic)?