External Cavity wall soon to be Internal

[Steveb21]

Extending to the rear of my bungalow.

Black square is existing building
Red is new building which is to be attached to black existing building.

The cavity around the existing black building is approx 70mm - which is NOT filled/insulated in anyway.
The cavity around the new red building is 100mm insulated slab.

The wall where I have the arrow pointing will go from External to an Internal wall.

Questions:
Should I leave the cavity empty? or fill with beads?

The new roof will be pitched and linked to the existing pitched roof. Currently the existing building has loft insulation which stops at the eaves (direction which the blue arrow points). When the roofs are linked will it be OK to run the loft insulation over the cavity wall across into the new extension?

 

[conny]

Yes to the loft insulation. Don't see the need for insulation in your existing cavity unless you want to try and deaden any sound coming from the extension. If you do the it would probably need to be solid boards with sound deadening qualities.

 

[Charlie George]

You will probably be able to take out a skin of the cavity wall if it's not loadbearing to give you @170mm extra space, have done this on many extensions and it can make a difference for little cost.

 

[Steveb21]

Thanks both.