Extension - building for the first time

[Olf]

Hello All,

After weeks of going through the forum content time to surface out

Hopefullly in a few weeks I'll move to a place in Oxfordshire that needs renovating (that I should be ok with), but also extending - to contain new kitchen/diner.

As the extension will be the first structure I'll be involved in building of, expect some newbie questions.

The original building itself is a semi-detached that seems to be Laing Easiform type (in-situ concrete walls with cavity) what I assume brings its own challenges.

I would like the outcome to become more energy effcient and thus more comfortable and eco-friendly house (but I'm not a warrior, can't quite afford that).

I'll try to keep my questions in relevant sections, but to give you a primer:

- one of the walls is on the boundry: is brick&block the only method that can be used without gaing access to neighbour garden?

- assuming I am limited on this side, can I build in different technology on the other side?

- as the existing building will be clad in EWI, am I better off having the side of the extension wall flush with existing wall and put EWI on both (effectively incorporating EWI in extension wall design) or design the extension wall so it sticks out, but after adding EWI to the existing wall they'll end up more or less flush?

- on extension attached to a brick wall a cavity tray would be inserted: in this case, with concrete wall, am I right that after adding EWI its external face (render) will become water barrier and that should be connected with new flat roof surface

 

A picture paints a thousand words: partial view of the back wall of the building, top view of the extension, sketch of a cross section.

[nod]

Yes you are correct in assuming that the render will form a weatherproof barrier 

The EWI will 

The first coat and mesh goes on together and left unscratched for a couple of hours Then topped with a ten mill coat This will be scratched and left pitted Leaving the first mesh coat in tacked to stop any ingress of water