Post build external wall insulation

[peweuk]

I have some questions regarding external wall insulation and wonder if anyone has had an experience of insulting external wall post-build.

- Is injected cavity insulation any good, and if so what are the likely costs for an average 3-bed detached house Which estimate between £500 and £700, but others have suggested a lot more than that. Any links to companies carrying out such work would be useful (Location, noth of Cardiff by the Brecon Beacons)
- Would surface applied insulation be more effective, and if so which would be your choice, external or internal application. I realise that internal would impinge on space in the room depending on thickness used, but may be easier to install.

Surveyors use a meter to measure heat loss, does anyone know if it is possible to rent/hire these.

Any and all input would be appreciated.

 

[Captain Nemesis]

If you have cavity walls why are you considering EWI?

 

[peweuk]

If you have cavity walls why are you considering EWI?

I am not considering it - it was just an option that was suggested by someone. We mentioned that we were possibly going to consider cladding the exterior with stone slips and it was suggested that external insulation under the stone would be more effective than cavity injection - but that was just one opinion.

 

[Captain Nemesis]

.. possibly going to consider cladding the exterior with stone slips ..

 

[denso13]

We mentioned that we were possibly going to consider cladding the exterior with stone slips

Done a few and it can look quite impressive but very expensive compared with rendered EWI.

 

[peweuk]

Done a few and it can look quite impressive but very expensive compared with rendered EWI.

We were not intending to do the whole house, we budgeted to do just the bottom of front elevation and side elevations and leave the rest as it is - rendered and painted.
If we plumped for the EWI as opposed to cavity fill, we would use rendered EWI on the rest of the house.

It all comes down to the cost/effectiveness comparisons. I can apply the EWI and stone myself, but would have to engage someone to do the render. Obviously, if I go for cavity fill that would have to be a contracted out job and so far I have not been able to obtain a rough idea of cost other than that provided online from various sites, including Which, and one local guy who said it would be a lot more than Which and other information sites suggest.

 

[IT Minion]

EWI can be much thicker than retro fit cavity insulation, which means it can be more effective.

However it's also ten times the price and, even if were twice as good at keeping the heat in, it'll never compete on value for money.

Now location wise you're apparently right on the border between 'Very severe' and 'severe' exposure to wind driven rain. Which is nonsense, the Brecon beacons is a windswept hellhole populated by nothing but the insane and cold rain going horizontally.

The historic reason for cavities is to prevent rain soaking through your walls. One of the experienced builders may be able to suggest if it's enough to make an impervious EWI and render combination a better choice.