As with any type of insulation you need to make sure that the roof is dry and in good condition before any insulation is added.
Room in roof insulation specification.
Retrofit room in roof insulation is now established as a common energy efficiency measure in the domestic sector.
This document identifies the main viable methods that can be deployed and seeks to offer guidance on appropriate installation techniques.
This guide is intended to supplement annex b12 of pas2030 2017 to offer more specific advice.
If you want to use your loft as a heated room then you need to take a slightly different approach and create a proper room in the roof.
Interior roof insulation desired outcome continuous contiguous and safe thermal boundary that prevents air movement 50 pascals and allows adequate roof deck venting.
Safely access both.
If roof over attic space is not large enough for safe physical access install insulation in original attic from the interior of the dwelling and install insulation in the roof over attic from the roof or gable of the roof over attic.
At a minimum access each end cavity of the original attic to install insulation.
Room in roof insulation riri is ideal if you use your loft space as a room enabling you to insulate the sloping surfaces of your roof using sheet insulation rather than insulating the floor.