Overview on insulating stone house with new build

Happyman42

Basically we have a semi detached stone house that we will be gutting and removing all existing internal walls and rear wall. Leaving us with front and side walls (4 up and down sash windows in each wall and front door) and the wall adjoining other property.
Is there any where I can get an overview of the issues involved with this type of build, eg. insulation and dealing with 18'' or 19'' stone walls?
Only at the dreaming stage here, so want as comprehensive list of talking points before approaching professionals.
Thanks in advance

UpCork12

Hi, doing the same work myself in a terrace house. Have got 2 different approaches from builders re insulating the 200 year old stone walls. One suggests using felt on walls and then Kingspan insulating boards over that. This is the option favoured by the engineer. Another builder claims there should be a gap left between the old walls to allow them to breathe and would put a sheet of steel and then insulated Kingspan onto that. Engineer doesn't want to hear of 2nd option, says the gap promotes build-up of mould and we would have to drill vents at 5 foot intervals top and bottom of 2ft. thick walls for ventilation. Am totally bewildered by conflicting advice and want to do the best possible for the old building. Any enlightenment anyone?

sydthebeat

theres a few approaches you can take:

the first is to stop any moisture laden vapour from entering the walls. this means trying to create a perfectly sealed vapour barrier all throughout the house on the inside, and then ensuring you have adequate ventilation internally to deal with the build up. This method means you can use "non breathable" materials and insulations such as PIR (kingspan) and non breathable felts as vapour barriers. This method is incredibly difficult to get correct, practically impossible IMHO. You will never get a perfectly sealed barrier internally with a new build because of intermittent floors, junctions of internal and external walls, pipe protrusions etc

The next method is to accept the fact that the house needs to "breathe" ie allow moisture laden warm air to exhaust to the outside. To do this you need to use breathable materials and insulations such as the quilted insulations rockwool, sheeps wool, etc and also to use breathable felts as a vapour barrier. This felt is required to stop moisture entering back inside the house from the outside, which can happen. the 'intelligent' vapour barriers are called 'vapour control layers'.
This method is better than the first in my opinion. The issues with this would be that quilted insulation shave less insulative properties than foam type. However this short fall can be made up by increasing thickness.

The third option is to insulate the house externally. This means applying (generally) polystyrene to the outside as the insulation layer. This then makes the external walls warm and therefore the moisture laden vapour does not condense within the wall structure, negating the issues which are being tackled in the first two options. Performance wise this is probably the best option, cost wise its probably the most expensive.

You could do a cost benefit analysis on all three methods to find out which suits you best.

Happyman42

Any thoughts on marrying new build to old in terms of effective insulation.
Our only option is internal insulation (front listed) would we have to contiue that on the new build or could we externally insulate it?

BryanF

New can be dealt with as your eng sees fit, modern methods etc
Existing build: is consider Syds 2nd option but using hemplime or similar breathable method/ products suitable for old builds as stone external skins tend to be someway porous

UpCork12

thanks to Syd. Your 2nd option sounds best as I can't insulate from outside as house is on street and therefore cannot make any changes there, " architecturally protected area" in council's terms!