1914 House Refurb. - Insulation question

[Tetrarch]

I'm not sure if this belongs here or somewhere else as there are Insulation, electrical, ventilation, aesthetic and other considerations all rolled in.

Below is the layout (subject to planning approval). You'll note that only about 1/3 of the downstairs external wall length is actually solid/original so my concerns about damp/dewpoints etc are here.  
 

 

Upstairs will be like this:

 

                                                  


and this my idea to remedy the uninsulated original 1914 building:

 

The UFH is already done. Everything else is up for grabs. Some explanations/justifications/concerns here:

MVHR - To maintain humidity control without trickle vents or airbricks
Silicone Render - Open to other ideas
60mm Insulation - Balance between insulation and aesthetics
Shadow Gap - No regular doors downstairs - going for super minimal finish
Mains Wiring - Is this allowed?
Hollow Skirting - Where can I source this?
LVT - Amtico Spacia - Me and Mrs Tet agree, so that's sorted

Any thoughts/criticisms/recommendations very welcome

Regards

Tet

PS There are a couple of other windows - those on the floorplan are the full-height openings/glazing

[SteamyTea]

With only 100mm of insulation under the UFH you are going to loose a lot of energy to the ground. Can you increase the wall insulation to compensate for it?

We're is the vapour control layer?

What is being done to improve airtightness?

[Dave Jones]

100mm of celotex is definitely a good start, bump it to 150mm and you will be exceeding new build regs.

[TonyT]

Edge insulation to stop cold bridging at the perimeter of the slab would be beneficial.

Agree with Dave 150mm minimum

pay for insulation once, pay for energy every month!!

[Jenki]

No Solutions - just a few questions. 

 

How does the solid brick wall breathe ?

The mains wiring is questionable.  you will  NEED to run vertically as well.

[jayc89]

There would be a thermal bridge at the wall/floor joint. The 60mm insulation should drop past the 80mm screed to be touching your 100mm floor insulation. (Called a perimeter upstand).

 

Neither wall nor floor insulation is that great, I'd recommend going thicker whilst you're going to all this trouble. 150mm floor (just dig deeper?) and 100mm on the walls. 

 

You need to pay careful attention around things like floor joists, are they pocketed into the existing solid walls? If so they're a thermal bridge and at high risk of condensation and rotting. Best idea would be to remove them, insulate and refit the joists inside the new thermal envelope, this is a lot of work, so an alternative could be to repoint around the joist pockets in lime, to reduce any air leakage, and use a more breathable insulation within the floor void.

For your services, do you have space to batten out the walls by 25mm to allow you to run wiring wherever you need? I did similar; adhered PIR to the walls, mechanically fix 25mm battens through the PIR into the wall, run services, plasterboard over. 

[Tetrarch]

Thank you so much for taking the time and trouble to reply. I have updated the images with some more detail/explanation below and will address comments/questions individually

 

 

 

 

 

[Tetrarch]

 

15 hours ago, SteamyTea said:

With only 100mm of insulation under the UFH you are going to loose a lot of energy to the ground. Can you increase the wall insulation to compensate for it?

We're is the vapour control layer?

What is being done to improve airtightness?

 

Underfloor Insulation - 100mm was to replace removed floor joists/floorboards. Definitely will insist on 150mm when digging out remainder of early 20th century and 1970 solid flooring - thank you

 

VPC - diagram updated - apols

 

Airtightedness - Not tested officially, but house seems relatively airtight. I will check this is as good as it can be as part of the MVHR install

 

Regards

 

Tet

[Tetrarch]

1 hour ago, Dave Jones said:

100mm of celotex is definitely a good start, bump it to 150mm and you will be exceeding new build regs.

 

See above 

[Tetrarch]

1 hour ago, TonyT said:

Edge insulation to stop cold bridging at the perimeter of the slab would be beneficial.

Agree with Dave 150mm minimum

pay for insulation once, pay for energy every month!!

 

Perimeter Upstand - There is a thin (10mm) blue insulation later between 80mm slab and solid wall. Diagram updated

 

[Tetrarch]

55 minutes ago, Jenki said:

No Solutions - just a few questions. 

 

How does the solid brick wall breathe ?

The mains wiring is questionable.  you will  NEED to run vertically as well.

 

Solid Wall - Really good question......I was hoping to use the MVHR to control humidity/dew point. I've seen this on another thread on here - this post was really following up on that.

 

Mains Wiring - The existing wiring ran under the floorboards. I have to either run mains wiring round the perimeter or drop down from the ceiling. My understanding is that if I use a purpose built aluminium channel as skirting board then that is allowable (unlike routing wooden skirting which is ostensibly not). There will of course be upwards tails to each of the sockets. I'm thinking of going "smart" so there may not be any lighting switches at all

 

[Tetrarch]

48 minutes ago, jayc89 said:

There would be a thermal bridge at the wall/floor joint. The 60mm insulation should drop past the 80mm screed to be touching your 100mm floor insulation. (Called a perimeter upstand).

 

Neither wall nor floor insulation is that great, I'd recommend going thicker whilst you're going to all this trouble. 150mm floor (just dig deeper?) and 100mm on the walls. 

 

You need to pay careful attention around things like floor joists, are they pocketed into the existing solid walls? If so they're a thermal bridge and at high risk of condensation and rotting. Best idea would be to remove them, insulate and refit the joists inside the new thermal envelope, this is a lot of work, so an alternative could be to repoint around the joist pockets in lime, to reduce any air leakage, and use a more breathable insulation within the floor void.

For your services, do you have space to batten out the walls by 25mm to allow you to run wiring wherever you need? I did similar; adhered PIR to the walls, mechanically fix 25mm battens through the PIR into the wall, run services, plasterboard over. 

 

Wall Insulation - I'd agree that battening and/or 100mm wall insulaton would be best but this is really aesthetic with smallish windows to the original house that I can't change and the fireplace that I can recess a bit, but 100mm+ is just too much IMO. I can probably do 100mm on the upstairs North side as there are no windows on that aspect 

 

My general thoughts that if I go for high spec in the new parts ~(and a new roof) plus the MVHR that this will mitigate for my slightly sub-optimal efforts in the old part of the house

 

Floor joists - Just an upstairs problem. Is this critical? There are no downstairs joists or voids

 

[larry]

We've used 100mm wood fibre onto a solid wall with lime render outside, so far so happy. 

 

Have you got a clear idea on the wall makeup beyond just brick, plaster, render, wallpaper, paint? All may impact moisture transmission and buffering which I'd say is a key consideration if you're whacking a load of celotex on inside. 

 

Will defer to others but can't see relevance of MVHR to the wall if you're sealing the wall from the room (you will improve air quality but how is the dryer air going to get to your wall??)

[larry]

On 08/08/2023 at 09:36, Tetrarch said:

I'm thinking of going "smart" so there may not be any lighting switches at all

This sounds like a complete recipe for future disaster! But maybe I'm a luddite!

[MikeGrahamT21]

Surely external wall insulation would be a far better idea? It’ll stop your masonry from getting blasted by the elements

[Tetrarch]

15 hours ago, larry said:

We've used 100mm wood fibre onto a solid wall with lime render outside, so far so happy. 

 

Have you got a clear idea on the wall makeup beyond just brick, plaster, render, wallpaper, paint? All may impact moisture transmission and buffering which I'd say is a key consideration if you're whacking a load of celotex on inside. 

 

Will defer to others but can't see relevance of MVHR to the wall if you're sealing the wall from the room (you will improve air quality but how is the dryer air going to get to your wall??)

 

External - We have limited scope to install external insulation due to the constructionof the roof. The roof is pitched with low eaves (slopes on all four sides of the house) and the soffit is only ~120mm. We are having a new roof, but we are in green belt and will need PP. You have now made me think about how I could increase the soffit by lowering the pitch of the roof a little - thank you.

 

I could definetely put external insulation on the North side of the house with no real aesthetic cost

 

Wall - Wall of the original house (yellow shaded) is solid brick. Render is a very solid roughcast

 

MVHR - The MVHR will manage the humidity levels in the house. This has dew point and water transmission implications. I'm not any kind of expert on this, my biggest concern is damp avoidance. My current theory is that by sealing the house drum tight from the outside then I only have to control internal humidity to manage any potential damp issues.

 

 

15 hours ago, larry said:

This sounds like a complete recipe for future disaster! But maybe I'm a luddite!

 

You can make the bulbs smart-controlled or the power wiring smart-controlled. I've been playing with a few solutions with mixed success. Power cuts seems to be the bugbear of one solution. British General sockets and Shelly bulbs seem to be OK

 

14 hours ago, MikeGrahamT21 said:

Surely external wall insulation would be a far better idea? It’ll stop your masonry from getting blasted by the elements

 

See - above

I'm now even contemplating both. It's "only" the old part of the house, so there is an element of diminishing returns as well

 

Regards

 

Tet

[MikeGrahamT21]

If you can make the space all round for it, it’s a far better solution, even filling all available space, think of it as a waterproof thick coat for your property.

 

any finish can be achieved, render, pebbledash, brick slip, brick or stone effect render, I’ve done brick slips on mine to match the existing brick, so planning permission even where you are shouldn’t be an issue

[Tetrarch]

Update : Planning Permission granted so we start work in late February

I will be submitting a minor planning amendment to cover the roof as well and the plan is to extend the roof slightly to deliver some broader eaves (more in line with current BR). My new insulation proposal is  to have a hybrid mix of internal/external.

 

Black is new 365mm walls

Red is new insulation

Orange is old 1970's cavity wall

My master plan is to have the South walls (1914, 1972, 2024) lined up in such a way that the internal and external faces will be seamless and "un-stepped". This means using various thicknesses of external insulation and then K-Rendering the whole lot. The reason fo the internal imsulation on the front (West) is to preserve the aesthetic of the current sash windows

 

My "new" question. Is it OK to just insulate and render on top of the existing painted roughcast finish? This finish is absolutely rock-hard and very difficult to remove even a small area.

 

Regards

 

Tet

[MikeGrahamT21]

2 hours ago, Tetrarch said:

Update : Planning Permission granted so we start work in late February

I will be submitting a minor planning amendment to cover the roof as well and the plan is to extend the roof slightly to deliver some broader eaves (more in line with current BR). My new insulation proposal is  to have a hybrid mix of internal/external.

 

Black is new 365mm walls

Red is new insulation

Orange is old 1970's cavity wall

My master plan is to have the South walls (1914, 1972, 2024) lined up in such a way that the internal and external faces will be seamless and "un-stepped". This means using various thicknesses of external insulation and then K-Rendering the whole lot. The reason fo the internal imsulation on the front (West) is to preserve the aesthetic of the current sash windows

 

My "new" question. Is it OK to just insulate and render on top of the existing painted roughcast finish? This finish is absolutely rock-hard and very difficult to remove even a small area.

 

Regards

 

Tet

 

Are you doing the works yourself or contracting it?

 

For External Wall Insulation there is a test which installers do called the pull off test, they will use adhesive on a small piece of insulation, apply it, let it dry, and then pull it off and see which bit fails. It should be the insulation, but if it isn't then other remedial works may be needed before installation. In reality the insulation won't fall off, but you risk it delaminating from the substrate, which causes thermal degredation and bypass.