House is B2 Rated
I have a dormer style house , up in one of the rooms (yellow highlighted) , on a windy day the breeze comes through into the bedroom ; it appears to be coming from the attic area at least , maybe behind the plaster board in the room too, under the door you can really feel a strong draft into the bedroom, room is always cold, it has one small radiator , the air leaks overcome the heat
I initially taught by sealing up the access panels below with rockwool , would fix the issue , wind is still coming through (down by the skirting board, rockwool I used to just fill the access panel hole)
As you can see the attic is insulated but I am wondering if it is worth insulating the cavity wall ?
Any advise appreciated, I know it difficult , things are covered up , I have no idea if insulation is present behind cavity walls / plasterboard/ under floors
Cavity wall here on the right
The Access panel above hole is filled with rockwool but the breeze is coming through the skirting below
Your house has a wool jumper but no windcheater!
Your issue is not with insulation but rather a lack of airtightness which is quite common in dormers and is likely an issue throughout the house and not just in the room you highlighted.
Having a targeted whole house heat loss survey will highlight the issues at play and recommend solutions (which can be remarkably cost effective and diyable) but just throwing more insulation at the issue won't solve it.
Btw, from the pics you posted, the fibre insulation between the rafters on the slope is of no benefit whatsoever. You could use this to bolster the insulation thickness between the floor joists on the flat which looks quite thin.
I am chasing leaks / drafts; not trying to achieve a passive house but within reason , I am finding alot of small things like this , rear door no draft proofing , french door not adjusted correctly, big bow in the door creating a gap you can see through ( might as well have a window open), no draft excluder in the cooker extractor pipe, no draft excluder on the external wall vent , it is like having aircon on in the kitchen with a cold wind , front door no insulation around the frame, windows lack of seal between the plinth and frame
It amazes me how these issues even though small and easily fixed , do not impact the BER rating ; its a B2 rated property ; it was freezing when we first moved in, if you have wind passing through; negates the effort and expense of insulation
the fibre insulation between the rafters on the slope is of no benefit whatsoever, I was thinking the same , the attic above only has it between the joists
; I was also questioning these companies that do foam insulation , they are only spraying under the roof and not between the joists ; whats the point, the roof needs to breath, once heat is in the attic it will expel with air moving via the trickle vents; you should be trying to prevent heat escaping into the attic not the roof