Increasing height of old stone cottage walls

[John Scoot]

I am renovating an old stone cottage - walls are about 500mm thick cob (mainly stone, rubble and lime mortar) and appear to be very sound, as do the ground floor rooms and first floor joists etc. The roof timbers are not salvageable and it has asbestos tiles, so a complete new roof is required, however, the bedroom ceilings are barely 2 metres high and I want to increase the wall height c. 450mm to get more head room. One of the gable ends used to have a chimney that was simply stripped out by a by a previous owner leaving just an outer skin of stonework that leaks like a sieve so that will also need to be rebuilt.

My roofer suggests building a timber frame on top of the old walls but as these a rather rough and uneven they will need to be made level in any event, so I was wondering if it might not be better to build up with lightweight block?

Any advice, suggestions gratefully received

 

 

[Gordo]

I would suggest casting a 150mm reinforced concrete ring beam on top of rubble walls and then maybe light weight blockwork.