We moved into the house at Easter 1995. From then until late summer, we were drawing up plans and getting them approved. There were last minute additions as the building inspectorate suddenly required U values, (heat loss ratio) for the rubble stone walls which are up to 1m thick. There are no reliable references for this kind of wall, so David Olivier of Hereford firm, Energy Advisory Associates, kidly supplied an estimate and the plans were passed.
Builder, Steve Brook rebuilding Rubble Walls .
At the outset, we decided high levels of insulation would be key factor in reconstructuion. All the walls are internally insulated with a dry lining system. Two methods were used.
Preparing the internal walls for dry lining with recycled timber studding.
On the upper floor, we specified recycled timber studding lined with 15cm of mineral wool and a foil backed plaster board. The ground floor walls are mostly finished in plaster over an internal concrete block skin with an insulating sandwich of slabs of polystyrene and air gaps.
Steve Brook was keen to eliminate cold bridge effects at window and door openings. Cold bridges are caused by rapid heat loss where poorer insulators such as timber, stone and glass, meet heavily insulated walls. The condensation caused by a cold bridge interface is probably the most likely cause of rot in timber framed windows. The theory is that if the cold bridge is reduced, there is no reason why timber frames in softwood should not last as long as more popular hardwood. So at the points where wall meets window frame, 3cm foil backed insulation board made by Kingspan and equivalent to 10cm of rockwool, was fitted to eliminate the cold bridge at window and door reveals. A vapour barrier and foil backed plaster board completed the wall construction.
In the roof and below the floor, we included as much mineral wool insulation as could be managed, this being at least 12" in the loft space. Under the traditional stone slates, was a layer of Tyvek roof membrane which works in much the same way as the Gore-Tex material used to make outdoor gear. ( It lets out condensation, but keeps out rain)