you can fix insulated composite (plasterboard bonded to insulation) panels to the underside of the coombe--about 40mm thick --Kingspan make them but can be expensive.
neil roger, November 2008
Often we use 'cavity battens' - they are slabs of insulation material, well compressed which makes them easier to slide into place. Available at the usual builders merchants.
John, January 2008
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I can answer this question...
How do I insulate coombe ceiling space in my roof?
