External wall insulation, or, External Wall?

[JP_]

In a solid wall 1930s bungalow. Still considering external wall insulation, but costs seem very high, according to https://www.thegreenage.co.uk/how-much-does-external-wall-insulation-cost/.

Surely, it would be cheaper to dig a new foundation, and build a block wall, fill with rockwall, and render? Why don't people do that?

 

[Ian H]

Your roof wouldn't fit.

 

[John D v2.0]

Also you'd need a new foundation for the new wall.

It's definitely less work to attach insulation and render it, then to attach a whole new wall with 150mm+ cavity on a foundation and render that.
If you really want to use wool you'd use rock wool between timber framework with a breathable membrane and cladding on top. Basically like a cold roof construction on its side.

Although the way things are going with celotex prices maybe next year it would be cheaper,

 

[m0t]

I'd imagine it's a lot quicker to use EWI than build new walls - our house had the bulk of the work done in 3 days then bits and bobs done over another 3 or so. Also less messy and disruptive.

 

[JP_]

About how much did you pay? I really don't fancy paying 10k for 6 days work and materials - even with the high price of insulation, I don't see how these prices add up.

 

[John D v2.0]

Off the top of my head it could easily be 500 a day for labour plus a couple of k max for scaffolding, then 5k for materials?

 

[tomfe]

A Johnstones system is around £22/m2 thickness of insulation makes very little difference in the final price.
Depending where you are it could be £20-50 /m2 to get it installed.

It would not be cheaper to build a new brick/block wall.

 

[^woody^]

There are massive problems with EWI, and it only takes a slight lack of care when fitting or specifying, or a failure of a simple bit of sealant to allow water behind it to cause problems.

There are now growing industry concerns about the problems with internal dampness and condensation that are developing from the rush to fit EWI over the past few years. It is feared that it will come back to haunt owners and landlords.

There is concern that it will become the modern "Barratt timber frame" fiasco.

I have serious doubts about EWI, and would demand exacting quality control in the specification, fitting, sign-off (including a thermal imaging survey) and very long insurance warranty to cover all the associated problems that could develop.

 

[tomfe]

There are massive problems with EWI

There are massive problems some with EWI.
An appropriate and well fitted system is the best way forward for much of the building stock. Unfortunately a lot of EWI was slung up under green deal by people who would not know one end of a stick to another, no offense woody.

 

[John D v2.0]

As with most things wall related it depends on your exposure too. Much of the rest of Europe uses solid walls and ewi with no issues, we only use cavity because it was the only way to stay dry reliably.
If you're in the east go right ahead but if you're in West Scotland you'll need to tread more carefully and maybe I include a drained cavity.
Even traditional rendered brick can have issues if you get water behind the render, that's why building is a skilled job.
If the alternative is internal wall insulation, I am not sure I'd recommend that either due to thermal bridging and condensation risk.

 

[JP_]

That's why I was wondering about the feasibility and cost of adding an extra wall (and extending the eaves) and filling it. But, I am in sunny Essex, so maybe EWI is a better option. So far, quotes for internal insulation have been way too high. I essentially have 4 rooms that will need insulating, 2 front and 2 back. Quotes for front rooms come to around £4000 (this is strip back, strip wallpaper from other walls, install insulation on external walls, drywall and plaster). So by the time I've done all 4 rooms, unless I find a cheaper builder, I could easily spend £8000. I only have two 9 metre walls to insulate externally - the front of the house is almost entirely window. These walls face east and west and are the least exposed walls really.

One local builder / insulation installer has come back with £80 per metre, so, maybe I can get my walls EWI for less than that!

 

[m0t]

It cost £11.5k but under the green deal I paid £5.5k. They had 4-5 people on site for the days they were working but the price was clearly inflated because government were paying. I did have a section that needed to be covered with brick slips which added about £1k to the cost.

I had to be really fastidious in inspecting what they had done. The majority of it was fine but they hadn't sealed properly at the top of the walls and we quite quickly got damp coming through. I went round and looked at everything, made a list (which wasn't too long) and got them to fix it all before I confirmed to the council that it was done.

My main concern now is that the top of the walls are joined to the EWI with sealant only, if that fails then you end up with damp getting into the wall behind. It's something I've added to the list of things to check semi regularly for maintenance. My house will need re-roofing at some point in the next 10 years so I might see how possible it is to extend the roof over the top of the EWI properly at that point.