Where to start insulating and avoiding condensation

[cuthbei]

I need to insulate my roof, but I’m wondering what best approach to take to account for the previous work and not cause anymore issues. The house is from the 1700s, stone and brick built mix, lime mortar, tiled roof. The roof space has been converted from a cold roof to a warm (ish) roof, half of which is still a loft space and the other half is a bedroom. It was converted about 20 years ago and I don’t think the builder did a good job. The fabric of the roof is

Tiles - Waterproof membrane / felt - 50mm foil backed PIR - Roof truss - Plasterboard (in the room half, no plasterboard in the loft half)

The list of problems includes
- No insulation on the gable end walls, just brick, probably single skin
- Air gap between the top of the gable end walls and PIR above
- No insulation on chimney breasts
- Air gap between the top of the chimney breasts and the PIR
- Air gap along the ridge where the PIR finishes slightly too low
- Air gap between wall plate and PIR between roof trusses
- Nothing below the PIR on the underside of the roof between the fascia board and wall (I don’t have any soffits). They painted the PIR with black paint so you can’t see it!
- 50mm PIR is nothing like thick enough
- No waterproof membrane on the inside
- In the loft half, the builder has left two other sets of previous roof trusses from the previous 300 years, so getting anything done in that space is hard
- In the loft half you can’t easily get to a lot of the roof, as the loft floor is quite high in the loft space (they added some RSJs on popped the lost floor on them)

Right now I clearly don’t have any condensation problems, because air flows through the roof like your outside. I just have a gas bill and global warming problem.

As far as I can see my choices are that
- Fill all the gaps with foam
- Add additional insulation under the PIR between the trusses in the loft half (loft roll, I won’t get PIR in)
- Insulate the gable end walls in the loft with something
- Insulate the chimney breasts in the loft with something
- I can’t do much in the attic roof as I can’t get behind the plasterboard, unless I rip it out
- Hope I don’t give myself a condensation problem with the lack of air flow and cold spots I have missed

Alternatively I pay a builder to take off the roof tiles and PIR, fill all the air gaps, add PIR between the joists and then PIR back above the trusses. Basically do the job again properly. It still gives me some challenges with the gable end walls etc, but maybe I can tear down the plasterboard and do that as well, as the job will already create some mess.

I did a smoke test to see how bad the air gaps are and I could barely get out fast enough to see the smoke they are so large.

Thoughts? Is it easier just to move house

Thanks, cuthbei

 

[noseall]

Condensation is a crafty old fox. The minute you remedy the most vulnerable area the next one becomes the front runner. However there is no point insulating/ventilating areas that don't need it.

 

[cuthbei]

Thanks, It definitely needs insulating though, at least in the room half of the roof space. I suppose I could insulate around the loft half and make that part a cold roof, leaving all those nice air gaps.

 

[StephenStephen]

Thanks, It definitely needs insulating though, at least in the room half of the roof space. I suppose I could insulate around the loft half and make that part a cold roof, leaving all those nice air gaps.

My amateur thought is that I think you're right - I'd split it into 2 jobs:
-Insulate the floor of the loft space - use stilts if you need to to raise the floor, and essentially keep it as a coldish loft.
-Insulate the inside of the bedroom

 

[cuthbei]

Thanks. For insulating inside the bedroom I guess I could strip back the plaster, insulate between the trusses and then use insulated plaster board.