Partially insulating house externally, - waste of tone?

ravendude

Hi,
We are planning to build an extension to the rear of our house. It is all to the first floor, adding new bedreom and increasing bathroom size etc The extension would have a high/current insulation spec..The house is a dormer built in the late 90s. As part of blending the extension with the existibg structure, we plan to strip some pebble dash from the ground floor external wall and render so the upstairs extension will fit in. The cavity walls have already been pumped with bonded bead, about 50 or 60mm I think.

So, I'm wondering if it would be worth the cost to add external insulation to the rear ground floor, since we are rendering it anyway. Wondering if doing this to just part of the houae is just a waste of money? This way all the rear would have a decent insulation spec, but obviously not the front which would be pumped cavity wall.

Any thoughts?

Calahonda52

Hard to follow: any chance of a sketch, showing old and proposed.

ravendude

Calahonda52 wrote: »

Hard to follow: any chance of a sketch, showing old and proposed.

Will try to upload a sketch.
To be honest I probably added a bit too much detail that may be irrelevant.

So, to simplify the question...
We need to render part of the house anyway, which would happen to be the downstairs kitchen and living area .

Is it worthwhile to add externap insulation on top of the existing cavity wall insulation while we are at it?

Could we expect that part of the house to warmer at least? (in which case it is probably worth doing)
...or, is it a waste of time if we are not going to add external insulation to the rest of the house

ravendude

Assume the rear wall would be fully externally insulated but not the gables...( which would be just cavity bonded bead)...
I am thinking thermal bridging from the table walls could be a problem...