1930s semi retrofit

[retrophit]

Hi everyone!

 

I recently bought a 1930s semi and after stripping off several layers of wallpaper and ripping up the carpets, I've discovered that the house needs a lot of work. Given that I'm already tearing down ceilings, pulling up floors, and removing blown plaster, I think it makes sense to do some retrofit work at the same time.

 

The front wall of the house is solid brick (side and back walls have cavities), and in the process of reading up about internal wall insulation I've gone down a rabbit hole of learning about the risks of interstitial condensation. I think I'm going to go for a "moisture open" buildup of a lime parge coat, woodfibre insulation, lime plaster, and clay paint - not sure if I need to go as far as hygrothermal modelling (e.g. WUFI).

 

I've also been trying to figure out the best way to improve airtightness in various areas, and the trade-off of needing MVHR if I go too far with it. I was originally considering PIV for ventilation, but the government's best practice guide on IWI warns against mixing it with PIV. Installing MVHR would be tricky as the unit would probably have to live in the cold loft, and all of the walls are either solid brick or made of what appears to be cinder blocks. I could potentially knock down some non-load-bearing walls and replace them with hollow stud walls that I can run ducting through. If I'm going to go this far though, I wonder if I ought to aim for getting EnerPHit certification eventually, and involve a certified designer from the start.

 

I'm just trying to decide upon the best way of renovating each part of the building, with the added complication of living in the house at the same time. There's a lot of dependencies, and I want to do things in the right order to avoid having to tear things up again later! I also don't have the money to pay for it all to be done by the trades, so I'm hoping to do most of it DIY.

 

Thanks in advance for any advice!

[PeterW]

14 minutes ago, retrophit said:

I've gone down a rabbit hole of learning about the risks of interstitial condensation. I think I'm going to go for a "moisture open" buildup of a lime parge coat, woodfibre insulation, lime plaster, and clay paint - not sure if I need to go as far as hygrothermal modelling (e.g. WUFI).

Not quite sure why you’ve headed down that route but there are better options using PIR and a vapour barrier - this will give you much better insulation levels and be simpler assuming the old front wall is just brick and not rendered ..?

 

MVHR can go through floor voids - you only need to use a cupboard somewhere as a riser and then plan carefully.

 

Biggest issue you will have with a semi is next door, and also the floors as they tended to be suspended timber and a pig to insulate properly but there are options. 

[Redbeard]

Agree with OP re WF and parge coat, and would encourage you to get a WUFI calc. I would encourage you to get a WUFI calc even if you were going for PIR/anything else IWI. My 'route to wood-fibre' is based on concerns re long-term integrity of VCLs. If I use a method without a VCL the vCL cannot be compromised and fail to do its job.

 

Of course we don't have to agree with it (there are certainly parts I would not agree with) but the latest BEIS Best Practice guidance on solid wall insulation recommends that where 'hard-to-the-wall' internal insulation is done a vapour-open insulant must be used. Where a vapour-closed insulant is used they recommend a ventilated cavity (which, if the cross-ventilation is good, makes the wall behave like a vented loft, where a 'howling gale' purges the space behind into which any errant WV may escape).

[Ando]

1 hour ago, retrophit said:

I'm just trying to decide upon the best way of renovating each part of the building, with the added complication of living in the house at the same time.

 

I can relate to this - currently suffering from paralysis by analysis I think 😂

Good luck with it all! 

[retrophit]

21 hours ago, PeterW said:

Not quite sure why you’ve headed down that route but there are better options using PIR and a vapour barrier - this will give you much better insulation levels and be simpler assuming the old front wall is just brick and not rendered ..?

 

Thanks @PeterW! There's no external render on any part of the house - I initially looked into things like PIR and insulated plasterboard, but as @Redbeard mentioned, the BEIS guide suggests that you need a ventilated cavity for "moisture closed" construction?

 

21 hours ago, PeterW said:

MVHR can go through floor voids - you only need to use a cupboard somewhere as a riser and then plan carefully.

 

Yeah, if I go for MVHR then I'd like to hide all of the ducting in the ceiling/floor voids and walls. It might be possible to fit an MVHR unit in the utility room of the ground floor rear extension, but I'm not sure how I'd route the ducting to the front of the house as the floor joists run from the party wall to the side of the house.

 

21 hours ago, PeterW said:

Biggest issue you will have with a semi is next door, and also the floors as they tended to be suspended timber and a pig to insulate properly but there are options. 

 

There are some big gaps in the brickwork where the floor joists enter the party wall! They will certainly need blocking up for airtightness, but also soundproofing.

 

The ground floor seems to be an uninsulated concrete slab - also weighing up the benefits of excavating the floor to install insulation. I'd like to install wet UFH on both floors, but not sure if I can live with the disruption of screed drying times on the ground floor.

 

21 hours ago, Redbeard said:

Agree with OP re WF and parge coat, and would encourage you to get a WUFI calc. I would encourage you to get a WUFI calc even if you were going for PIR/anything else IWI.

 

Thanks @Redbeard - I'll see if I can find someone to do a WUFI calc!

 

19 hours ago, Ando said:

I can relate to this - currently suffering from paralysis by analysis I think 😂

Good luck with it all! 

 

Thanks @Ando! I keep thinking I've settled on a solution, but then find some conflicting advice that changes my mind 🙈

[Ferdinand]

On 06/11/2022 at 10:28, retrophit said:

 

I recently bought a 1930s semi and after stripping off several layers of wallpaper and ripping up the carpets, I've discovered that the house needs a lot of work.

 

I conclude that this was a day with a "D" in it 🙂.

 

Welcome.

  

On 06/11/2022 at 10:28, retrophit said:

I was originally considering PIV for ventilation, but the government's best practice guide on IWI warns against mixing it with PIV.

The statement in the 'Best Practice' doc seems strange:

 

Quote

58. Positive Input Ventilation (PIV) should not be installed with internal wall insulation. The risk of interstitial condensation between the wall and the IWI is increased when using a ventilation system such as PIV, that actively pushes warm, wet air into the building fabric.

 

My standard approach is to pair a PIV with a continuous trickle ventilation fan or two downstairs (preferably an HR, though sometimes DMEV).

 

That may be combined with an IWI reno, including a warm-side vapour barrier, and perhaps underfloor insulation too, plus the usual 250mm rockwool in the loft.

 

That ensures that warm wet air is ventilated rather than "pushed into the structure".

 

Is that not blatantly obvious that a PIV setup needs outlets, given their comments about sometimes incorporating a vapour membrane and sealing the place from draughts?

 

I've been doing this for 10 years, and it has proved robust.

 

F