My daughter's new home, a 1930s semi with a decent sized square hipped roof space has 2" of insulation, so I will up this to 180mm of fibreglass.
As I don't want to compromise use of the loft space and she may wish to fit a dormer window I was wondering about both ceiling joist strength and making space for the new insulation. First thought was to add 2 by 4s perpendicular to the joists, fill gaps with insulation and lay boards over that, with the knowledge that the insulation over the joists would be compressed at these points.
Next I thought that adding 2 by 4s to the top of the current joists would give better strength.
Any thoughts?
AJH