Iwi on a cavity wall

[josefcarpenter]

Hi all,

I'm in the process of significant renovation works on a 1920s bay fronted end of terrace.

Planned works to include:
-Lean-to extension
-wall tie replacement
-iwi / cavity wall insulation/ possibility of under slab insulation if economically worthwhile
-loft conversion
-rewire
-new boiler
-sliding sash window renovation

In it's current state the house gets uncomfortably cold in winter without the heating on full blast; compare the market shows previous occupants energy use was 200% up on neighbours...

House still has the original single glazed sliding sash windows (which I intend to renovate and vacuum glaze). Slab is un-insulated and walls have a 70mm un-insulated cavity. The roof is the original Welsh slate roof with no felt underneath. Apart from what looks to be an early 2000s boiler install, the house has had very little in the way of modernisation - minus the swanky flourescent tube lighting that the landlord installed in most rooms... I plan to build a small extension at the rear under PD to create a more useable kitchen and dining room space, and in time convert the loft.

Lath and plaster ceilings were badly cracked and failing in places... Since the house is in Wales (cardiff) the mortar here is of the messy black coal variety; so I made the decision to remove the ceilings while the house is unoccupied. On the external facing walls I have removed the old plaster as this was a mix of the original lime based, and modern concrete/gypsum.

My main question here is regarding the correct method of wall insulation to use on an older house. I worked in Canada for two and a half years on a mix of new build and renovation; I'm very familiar with the full process when insulating timber framed and ICF passive houses in damp climates...However my work in the UK on older houses is limited to loft conversion, so other than online research, I have little practical experience here.

I was intending to use wood fibre insulation without a synthetic vapour barrier on the external walls with a breathable lime render, returning the insulation a metre on party walls/ partition walls that are touching the external walls to avoid cold spots and trapped condensation.... However, some of the neighbours here have had EPS bead type insulation Installed in their wall cavity and are happy with the results. (research online tends to indicate this is frowned upon generally?)

EPS bead cavity wall insulation would obviously be a much cheaper option, and I would imagine 70mm of EPS would provide a more efficient insulation than 40mm of wood fibre at the cost of being less breathable.

Does anyone here have long term experience of going the EPS bead route? I had the (possibly) bright idea of combining this with a max 25mm of insulating plaster since I need to replaster the external facing walls anyway; with the view that the 25mm plaster would allow some heat transfer to the inner skin of the brickwork... but I don't want to create a condition where moisture is trapped in the wall fabric, without warmth able to pass into the wall and dry out said moisture.

Externally brickwork will be repointed and cleaned/ coated with a breathable sealer like stormdry.

Any practical experience/ input regarding iwi, insulating plaster and retrofit cavity wall insulation would be greatly appreciated.

 

[DampedOut]

Just to say, draught proofing and loft insulation cut the energy needs of this place by nearly 33% a year or two back. I think whatever you do, start there. I don't know how you would insulate the roof itself, but it sounds like you do. Even on your single glazed windows, draught proofing should help a lot if you can't renovate them all in quick succession. Draught proof the front door as well. The letter box was a particular weak point for us.

Curtains will make a difference too. I am still intending to kit out this house with very heavy curtains with heavy linings, but even standard curtains bought on sale a few summers ago make a difference when we draw them at night.

Def following this thread and good luck!

 

[paulc]

The bulk of your heat loss will most certainly be through the windows & doors. So get those sorted as a matter of priority and seal up those cold draughts. I've had all my windows & doors replaced here now, and am slowly adding IWI to the bedrooms. Solid 9" brick walls up there, so no cavity to fill. Just having double glazing and killing the cold draughts has made a massive difference to comfort levels and ability to heat the space. So much so, I'm questioning the need to insulate.... But I've got (most) of the materials now, and some of the plaster is starting to fall off the walls.
When you come to fit a new boiler, replace the radiators as well - Had a new boiler last year and I put in radiators that were some 50% larger than calculations suggest. Plumbing was also redone (bigger bore pipes and more sensible routing) with an eye to the future when heat pumps become the only option. Not had a really cold spell to see how the system performs yet. Most days, it kicks in for about an hour and then fires up for 10-15 minutes every two or three hours to maintain the temperature, and rarely at more than 25% of full capacity - Much of that performance will be down to having the new windows rather than the boiler.

As for insulating plaster, a work colleague used hemp plaster in her little Victorian cottage. She is rather disappointed with the results - Having looked at the specs, a very thick layer is required in order to achieve any worthwhile level of insulation.

 

[Lacan07]

Hi all,

I'm in the process of significant renovation works on a 1920s bay fronted end of terrace.

Planned works to include:
-Lean-to extension
-wall tie replacement
-iwi / cavity wall insulation/ possibility of under slab insulation if economically worthwhile
-loft conversion
-rewire
-new boiler
-sliding sash window renovation

In it's current state the house gets uncomfortably cold in winter without the heating on full blast; compare the market shows previous occupants energy use was 200% up on neighbours...

House still has the original single glazed sliding sash windows (which I intend to renovate and vacuum glaze). Slab is un-insulated and walls have a 70mm un-insulated cavity. The roof is the original Welsh slate roof with no felt underneath. Apart from what looks to be an early 2000s boiler install, the house has had very little in the way of modernisation - minus the swanky flourescent tube lighting that the landlord installed in most rooms... I plan to build a small extension at the rear under PD to create a more useable kitchen and dining room space, and in time convert the loft.

Lath and plaster ceilings were badly cracked and failing in places... Since the house is in Wales (cardiff) the mortar here is of the messy black coal variety; so I made the decision to remove the ceilings while the house is unoccupied. On the external facing walls I have removed the old plaster as this was a mix of the original lime based, and modern concrete/gypsum.

My main question here is regarding the correct method of wall insulation to use on an older house. I worked in Canada for two and a half years on a mix of new build and renovation; I'm very familiar with the full process when insulating timber framed and ICF passive houses in damp climates...However my work in the UK on older houses is limited to loft conversion, so other than online research, I have little practical experience here.

I was intending to use wood fibre insulation without a synthetic vapour barrier on the external walls with a breathable lime render, returning the insulation a metre on party walls/ partition walls that are touching the external walls to avoid cold spots and trapped condensation.... However, some of the neighbours here have had EPS bead type insulation Installed in their wall cavity and are happy with the results. (research online tends to indicate this is frowned upon generally?)

EPS bead cavity wall insulation would obviously be a much cheaper option, and I would imagine 70mm of EPS would provide a more efficient insulation than 40mm of wood fibre at the cost of being less breathable.

Does anyone here have long term experience of going the EPS bead route? I had the (possibly) bright idea of combining this with a max 25mm of insulating plaster since I need to replaster the external facing walls anyway; with the view that the 25mm plaster would allow some heat transfer to the inner skin of the brickwork... but I don't want to create a condition where moisture is trapped in the wall fabric, without warmth able to pass into the wall and dry out said moisture.

Externally brickwork will be repointed and cleaned/ coated with a breathable sealer like stormdry.

Any practical experience/ input regarding iwi, insulating plaster and retrofit cavity wall insulation would be greatly appreciated.

So have you got cavity or solid brick walls?

If its cavity you don't necessarily need to follow the rules for older buildings, just continue as you normally would. If you're filling the cavity make sure you use the breathable beads though, the older stuff can cause issues when bridging the gap. Don't bother with insulating lime plaster, its the equivalent of waving a sausage in the Albert Hall, if you want IWI surely you can just stud and Cellotex.

 

[josefcarpenter]

Just to say, draught proofing and loft insulation cut the energy needs of this place by nearly 33% a year or two back. I think whatever you do, start there. I don't know how you would insulate the roof itself, but it sounds like you do. Even on your single glazed windows, draught proofing should help a lot if you can't renovate them all in quick succession. Draught proof the front door as well. The letter box was a particular weak point for us.

Curtains will make a difference too. I am still intending to kit out this house with very heavy curtains with heavy linings, but even standard curtains bought on sale a few summers ago make a difference when we draw them at night.

Def following this thread and good luck!

Thanks, that's a good pointer regarding the draught proofing, the front door here (unsure if my photo has attached) might be left open permanently for all the insulation it provides! I'll definitely be secondary glazing the stained glass, and draught proofing the letterbox as you have suggested.

Luckily at present I'm able to not live in the house while renovating as I'm staying with the parents, hoping to do all of the windows in (fairly) quick succession... The wall cavities are open around the windows, so I'm looking to close those off when I remove the windows. I can imagine the curtains will help a lot around the windows also

 

[josefcarpenter]

The bulk of your heat loss will most certainly be through the windows & doors. So get those sorted as a matter of priority and seal up those cold draughts. I've had all my windows & doors replaced here now, and am slowly adding IWI to the bedrooms. Solid 9" brick walls up there, so no cavity to fill. Just having double glazing and killing the cold draughts has made a massive difference to comfort levels and ability to heat the space. So much so, I'm questioning the need to insulate.... But I've got (most) of the materials now, and some of the plaster is starting to fall off the walls.
When you come to fit a new boiler, replace the radiators as well - Had a new boiler last year and I put in radiators that were some 50% larger than calculations suggest. Plumbing was also redone (bigger bore pipes and more sensible routing) with an eye to the future when heat pumps become the only option. Not had a really cold spell to see how the system performs yet. Most days, it kicks in for about an hour and then fires up for 10-15 minutes every two or three hours to maintain the temperature, and rarely at more than 25% of full capacity - Much of that performance will be down to having the new windows rather than the boiler.

As for insulating plaster, a work colleague used hemp plaster in her little Victorian cottage. She is rather disappointed with the results - Having looked at the specs, a very thick layer is required in order to achieve any worthwhile level of insulation.

It's promising to hear regarding the replacement windows and doors... I think in your situation, if you have the materials and your plaster is failing, then the extra insulation can only be a bonus... What are you planning to use for your IWI?

I have just replaced all of the windows and doors at my cousin's house (20-30 year old uPVC replaced with modern) I made sure to comprehensively seal and draught proof around the windows when installing, and they have said the difference in warmth due to the lack of draughts has been noticeable.

When you say sensible routing of plumbing, do you mean insulating pipes etc? The larger bore pipes definitely make a lot of sense!

Good to know regarding the hemp plaster, with the amount I would need here, that stuff is super expensive... I'm looking for the best option with minimal loss of space so a thick layer wouldn't be desireable

 

[josefcarpenter]

So have you got cavity or solid brick walls?

If its cavity you don't necessarily need to follow the rules for older buildings, just continue as you normally would. If you're filling the cavity make sure you use the breathable beads though, the older stuff can cause issues when bridging the gap. Don't bother with insulating lime plaster, its the equivalent of waving a sausage in the Albert Hall, if you want IWI surely you can just stud and Cellotex.

Cavity walls on all of the external walls (had a peek in the side of the poorly fitted bathroom window and I can see two rusted and snapped wall ties...) , double skin solid brick on the party wall.

By older stuff do you mean the blown in mineral wool insulation? Stud and cellotex I've heard conflicting info regarding fitting to older houses... Seems like any voids between the cellotex and exterior walls could be a good spot for trapped moisture?

 

[paulc]

It's promising to hear regarding the replacement windows and doors... I think in your situation, if you have the materials and your plaster is failing, then the extra insulation can only be a bonus... What are you planning to use for your IWI?

When you say sensible routing of plumbing, do you mean insulating pipes etc? The larger bore pipes definitely make a lot of sense!

For the walls upstairs, I'm using Kingspan type PIR/PUR boards. Multiple layers with joints taped - The foil facing should act as a vapour control membrane and stop moisture getting in. The outside of the walls have been rendered in a very hard layer of cement from new, so I'm not overly concerned about penetrating damp. 75mm of insulation on the walls and 25-50mm around the window reveals has improved comfort levels in the areas I've done so far. It has also resolved an issue with damp caused by condensation (and not helped by inadequate heating).

The original central heating was from a back boiler - The main feed/return pipes (22mm & 28mm) ran up the party wall into an airing cupboard in the bedroom above. From there, they went half way across the bedroom (in 22mm) before branching off front to back in 15mm. These puny little pipes fed radiators under the windows before dropping down to the radiators downstairs. Suffice to say, heating was never very good..
The new pipework runs from front to back in the void above the hallway ceiling (all in 22mm and lagged), with short spurs feeding radiators mounted on internal walls - With decent double glazed (and draught free) windows, there is no longer reason to put radiators under the windows (in my opinion). Having 22mm pipes going from front to back, I now have the option to fit a boiler or heat pump at either end without any major upheaval or masses of ugly pipes on display. A new gas boiler is installed in the hallway and the pipework for the CH boxed in where it runs up the wall and across the ceiling.

Oh, and being able to see in to the cavity around your windows has a small advantage - Have a look to see if there is any support for the outer leaf of brickwork. The timber frames are probably providing support (they were on my house), so if the ever get replaced, lintels should be inserted. I was fortunate that after removing a brick at the top of the opening either side, it was possible to wriggle a length of steel angle in to support the soldier course above.

 

[Stevers]

When filling cavities I've been given to understand that there's a world of difference between polystyrene beads and blown fibre. It seems that the latter settles and can transmit damp, whilst the former (beads) was installed in my Parents house (1934) and sister's house (1906) transforming them into lovely cosy homes.

 

[josefcarpenter]

For the walls upstairs, I'm using Kingspan type PIR/PUR boards. Multiple layers with joints taped - The foil facing should act as a vapour control membrane and stop moisture getting in. The outside of the walls have been rendered in a very hard layer of cement from new, so I'm not overly concerned about penetrating damp. 75mm of insulation on the walls and 25-50mm around the window reveals has improved comfort levels in the areas I've done so far. It has also resolved an issue with damp caused by condensation (and not helped by inadequate heating).

The original central heating was from a back boiler - The main feed/return pipes (22mm & 28mm) ran up the party wall into an airing cupboard in the bedroom above. From there, they went half way across the bedroom (in 22mm) before branching off front to back in 15mm. These puny little pipes fed radiators under the windows before dropping down to the radiators downstairs. Suffice to say, heating was never very good..
The new pipework runs from front to back in the void above the hallway ceiling (all in 22mm and lagged), with short spurs feeding radiators mounted on internal walls - With decent double glazed (and draught free) windows, there is no longer reason to put radiators under the windows (in my opinion). Having 22mm pipes going from front to back, I now have the option to fit a boiler or heat pump at either end without any major upheaval or masses of ugly pipes on display. A new gas boiler is installed in the hallway and the pipework for the CH boxed in where it runs up the wall and across the ceiling.

Oh, and being able to see in to the cavity around your windows has a small advantage - Have a look to see if there is any support for the outer leaf of brickwork. The timber frames are probably providing support (they were on my house), so if the ever get replaced, lintels should be inserted. I was fortunate that after removing a brick at the top of the opening either side, it was possible to wriggle a length of steel angle in to support the soldier course above.

Are you using PIR backed drywall? Or studding out the wall and then over boarding?

That makes a lot of sense to route the pipework that way. I have a similar situation here, in that the current pipework is a spiders web of microbore and I will be looking to futureproof.

And I agree with the location of the radiators, I've always felt like since heat transfers to cold, having radiators placed under the window means a good amount of the heat is wasted leaving the room before it gets a chance to circulate around the rest of the room. I could be very wrong there! But that's always been my thinking...


I had a look above the windows this evening and there is a lintel on both the inner and outer skin of brickwork luckily. On the front bay windows however, there's a bath stone lintel on the exterior with just a precariously loose course of bricks above the upstairs window internally (downstairs there's a wooden lintel)

 

[josefcarpenter]

When filling cavities I've been given to understand that there's a world of difference between polystyrene beads and blown fibre. It seems that the latter settles and can transmit damp, whilst the former (beads) was installed in my Parents house (1934) and sister's house (1906) transforming them into lovely cosy homes.

That's good to hear! While I was rooting around in the cavities earlier today; I noticed that close to the party wall, there are eps beads that have travelled through to my house when the neighbours had them installed...

I asked if they'd had any issues, and they also confirmed zero

 

[paulc]

Are you using PIR backed drywall? Or studding out the wall and then over boarding?

Neither. I struggle to handle 8x4 sheets of plasterboard, and maneuvering them upstairs would be a right royal pain. Building a stud framework sounds like too much effort for little gain. I settled on the "warm batten" method where you fix vertical battens (2x1) to the wall at 600mm centres. Infill the space with 25mm thick Kingspan, filling any gaps with expanding foam using a gun, then taping the joints with aluminium foil tape. Fix a second layer of 25mm thick Kingspan over the entire wall, again, foam & tape the joints. To secure the second layer in place, horizontal 2x1 battens on 400-600mm centres are screwed to the underlying vertical battens, and yet more Kingspan cut to fill the gaps (foam & tape). Final step is to fix plasterboard to the horizontal battens and then skim the lot.
My thinking is the multiple layers of foil facing will act as a vapour control membrane, and as there are no fixings going all the way through, no cold spots will form. I've also taken to lining the window reveals with 25mm of the Kingspan and finishing it off with painted timber - Under the window boards, I've upped it to 50mm just to hide the base of the window frame and leave just 25mm showing all round.

It goes without saying that the use of modern materials has thrown any notion of breathability out of the window. But as the outside is rendered in cement (applied when built back in 1928/9), and this is the upper half, breathability is not a major concern. And as a developer pointed out when submitting plans for housing on an old industrial site within spitting distance, these houses are of no architectural merit or value. For a property that does have "value", I'd probably use cork or woodfibre with a lime finish to maintain breathability.