Hello I'm a newbie here and in need of some pragmatic advice please.
We've a Victorian detached house solid walls and double pitch roof in Kingston, Surrey. An energy analysis tells us that after the walls our roof is losing the most energy. We've a 2nd floor room conversion 'room in roof' which we use as an office .
It's very hot in summer and cold in winter. Entered by full staircase but without 2m head clearnance. Ther's no insulation in the roof between the slate tiles/mebrane and plasterboard. We'd like to make it more comfortable and lose less energy.
We've a finite budget to improve our overall efficiency of the house (lets say £25-30K) . The energy analysis says we need to spend £150K to go from F rated (current) to A. Our thoughts include insulating between the roof, replacing some strategic single glazed windows, adding lined curtains and putting a decent PV array on our roof with battery.
Option 1 - Provisional quotes to remove the existing plasterboard, fill the rafter gaps with PIR/Wood Fibre and then line with 50mm insulation are coming in at £15K to £25K (includes rad moving and electrics). This would include 50mm insulation between the rafters and say 50mm on top to cover the rafters. Total insulation 100mm say. We've also requested that we cover the 3 gable walls. Advantages of this approach, gives us 100mm of insulation overall, Disadvantages, potentially blows our complete budget with existing quotes. There's 100+ square meters of plasterboard to carefully remove and rafter gaps to fill. (this alone doesn't get us a fully compliant room as don't have 2m height on stair access).
Below an alternative scheme to hopefully reduce costs and still save energy but the question is how much of an improvement might this make versus Option 1 above.
Option 2 - cover the existing plaster board with say 60-75mm of wood fibre/PIR , and plaster over. (We'd still go with 100mm for the gable ends ) Screw/fix on top of the existing lining. (Nothing to clear or dispose of less mess.) The expectation is this would be much cheaper to carry out and leave monies say to do the PV and Curtains. My questions are simply (a) Is this approach a waste of time with no rafter insulation (b) will it provide useful energy reduction in view of the compromised approach ?
Any thoughts comment please to help steer us forward. Thanks in advance.