In one of the bedrooms in my house (1930s), there is a sunken alcove where an old window used to be, the internal sill is still there. Whoever bricked up the window used bricks much thinner than the rest of the wall, resulting in the 11cm deep internal alcove.

Because it's so thin, the wall here gets really cold resulting in condensation ruining the paintwork. I'm planning on blocking up the alcove with some stud work, but I was wondering what kind of insulation I should use? Should I be concerned about the condensation, or is that likely to go away once the insulation and stud work is done? Is there a better way to fill the alcove?

1 Answer 1


Skip the studs - there's nothing structural here.

  • Use (roughly) 9-10 cm of rigid foam insulation and 1-2 cm of plasterboard/drywall or plaster, depending on internal finish of the rest of the room.
  • Glue the foam in place with a construction adhesive meant to work with the type of foam you get (should come in a caulking tube.)
  • Use some canned polyurethane spray foam ("minimally expanding" type) to fill in the edges around the rigid foam sheet, allow it to cure, trim back any excess, and finish.

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