Internal wall insulation - 1st floor 1930's Semi.

25 Nov 2009
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United Kingdom
Semi-detached house built in the 1930's. All houses in the area are of the same construction.The ground floor has a brick cavity wall which has been insulated with polystyrene beads. The loft is insulated to current regs. The first floor however has a single skin which is not insulated and is internally plastered. The external wall of the first floor has a rendered/roughcast finish painted with masonary paint, therefore not sure what the first floor wall is built of. There are no obvious signs of damp anywhere.
What is the best method of internally insulating the first floor without using up too much space? Celotex bonded to the wall then battened and boarded, or an insulated studded wall to create cavity and boarded? Cheers!
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Thanks amwc
Do you recommend a damp proof membrane behind the battens?
How can you have a cavity wall construction that reverts to a single skin at first floor level?

Are you saying that GF is cavity wall construction and filled with poly bead insulation then at 1st FL level the wall construction reverts to single skin? How does that detail work? How is the cavity closed? The wall plate at eaves height must be on your external skin :confused:
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There are a couple of hundred houses on the estate all with similar construction. There are three designs, some with cavity wall up to GF window sill level. Some with cavity wall up to 1st Floor level and some with cavity wall up to bedroom window sill level. But all designs culminate in a single skin up to eves level. There is a course of bricks laid across the top the cavity wall but due to the render/roughcast finish on the out side and the plaster on the inside, I am unable to see how the cavity is closed. The single skin on each design however is slightly set in from the outer skin of the cavity wall below and the render/roughcast is applied so it angles out above the outer skin of the cavity wall.
If the walls are damp then I'd probably use a dpm otherwise not as long as the house is lived in and warm and theres no damp penetration.

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