Only just realised that this wall is uninsulated

[Radian]

View of a bit of wall in our ventilated (cold) loft:

 

View of inside hallway on the other side of that same blockwork:

 

Been here over 20 years and not grokked that we have an uninsulated wall inside the house. Two actually because there's an identical setup on the other side. A separate loft space is to the right of this link bridge. In fact, that one's worse as it's just one width of dense concrete block whereas at least the main house to the left has lightweight blocks laid flat. No wonder the hallway gets cold in the winter!

[Radian]

I'm obviously crap at thinking in 3D because I'd already understood that the cavity formed by this wall was internal to the house so cold attic air could descend into the walls all the way down to the ground floor:

 

 

The wall plate runs around the top of the cavity and either side of this it's closed with insulation socks but they left this bit open.

[ProDave]

This is what we keep saying on this forum, it is attention to detail that makes a house good or bad.  Clearly a lack of joined up thinking or care here.  It is not like getting the detail right is going to cost much money but builders generally don't know or don't care about such details.

 

It has long made me cringe when working in houses in the winter that you unscrew a switch or a socket and a blast of icy cold air comes out of the hole.  Clearly the cavity and a lot of the house structure, such as partition walls and inter floor void in many cases is open to cold outside or loft air.

[Radian]

45 minutes ago, ProDave said:

It has long made me cringe when working in houses in the winter that you unscrew a switch or a socket and a blast of icy cold air comes out of the hole.  Clearly the cavity and a lot of the house structure, such as partition walls and inter floor void in many cases is open to cold outside or loft air.

 

That's my house right there!

 

I was just about to close the cavity by sawing strips of 50mm celotex that I've got off a skip and foaming them in when I though about what was on the other side of the blockwork. Now I'm thinking I should clad the entire wall in rigid insulation but 50mm won't really be enough. I make 220mm of thermalite and 50m rigid PUR out to have a U-value 0.24 W/(m²K) whereas 100mm PUR gets me down to a U-value 0.16 W/(m²K). So I need to buy some sheets of 100mm PUR but how best to attach it? 

[ProDave]

Attach it with long screws and you can buy big plastic screw heads made for the job to spread the load so they don't pull through.

 

Another stunning lack of detail on a self build I wired, room in roof so dwarf walls at eaves height, cold eaves space behind.  They were "insulated" with 2 layers of 50mm PUR badly cut to be a loose fit and than just propped there mostly with a gap between.  I did point this out to the self builder but he did not do anything about it.

[Radian]

20 minutes ago, ProDave said:

Attach it with long screws and you can buy big plastic screw heads made for the job to spread the load so they don't pull through.

But lightweight concrete blocks are pretty useless at taking screws without plugs and setting up big sheets of PUR and drilling through, placing plugs and finding them again sounds like an almost impossible task. I've tried hammer-in 'screw' fixings but these also seem to blow out the blocks. Usually one is ok but comes loose when hammering in the next.

[PeterW]

47 minutes ago, Radian said:

Now I'm thinking I should clad the entire wall in rigid insulation but 50mm won't really be enough.

It will make a huge difference - I would start there, and also just use low expansion foam with a few EWI fixings through it for stability. 100mm is regs but is overkill as your loft will never truly be at  outside temperatures

[Radian]

16 minutes ago, PeterW said:

with a few EWI fixings

Never seem to find such things in stock in the local sheds. Then when I look online it's a big box of them for big £££!

[PeterW]

4 minutes ago, Radian said:

Never seem to find such things in stock in the local sheds. Then when I look online it's a big box of them for big £££!

£13 for 100..??

 

https://www.tcfixings.co.uk/product/timco-m8-x-50mm-plastic-insulation-fixings-pif50-100/11284

 

[gmarshall]

Or you can just use expanding foam adhesive?

[Radian]

1 hour ago, gmarshall said:

Or you can just use expanding foam adhesive?

I know how that would end 🤣

I'd be standing there not daring to let go. I think I'll be going with @PeterW suggestion of using some EWI fixings with adhesive. They look ideal for a belt and braces approach. Still undecided about 100mm or 50mm though. The rest of the walls are due to get a 50mm EPS bead fill when the contractor finally shows up with a long enough nozzle, so the U-value using 50mm rigid PUR will be roughly the same (0.24W/(m²K) for both external and internal attic wall).

 

Unfortunately we're not going to be able to improve on this figure but it's far better than the unfilled cavity that we've been living with which is more like 0.5W/(m²K)

[Radian]

First step is to make a decent access and work area (something I've been meaning to do for a while).

 

The idea is to make a deck that sits between the water storage tanks and loft hatch. To keep the insulation up to scratch I'm framing up 100mm of PUR bits and pieces I have. To begin with this means extending the 100mm joists that carry the tank platform towards the hatch opening:

 

 

Now the PUR can fit snugly above the minimal glass fibre and mineral wool layer in between the trusses. A good use for some 50mm and 100mm offcuts rescued from a skip:

 

 

Next job is to trim the end with another length of 20mm x 120 wood and infill on top with flooring chipboard. Maybe tomorrow.