Sorting out token effort insulation

[Jdwood38]

Evening folks,

We've got a double garage that has had one side converted into habitable space (adjoining the house) and the loft above converted into a room with rear dormer - works were done c.2010 (before we bought the house), all signed off by building control, all finished to a decent enough standard inside.

Anyway, last winter the loft/dormer room was really cold so over summer I started doing a bit of investigation. To say that the overall insulation installation is a token effort would be an understatement! Hopefully the photos show what I mean.

So, the question is how to go about fixing this, ideally without completely stripping all plasterboard off the room as the quality of that bit seems fine. The floor installation appears to be mostly non-existent. The wall installation appears to be varying thickness PIR between studs, all being poorly fitted > plastic vapour barrier (but not everywhere) > some plasterboard backed with 20mm PIR (at least this bit seems to provide at least some continuous insulation), some standard. It may well be that once the floor is sorted the 20mm compensates at least a small amount for the gaps in the 90mm and the room is significantly warmer - not going to be as good as it could or should be though.

I can sort the floor easily enough - chipboard up, 100mm PIR with all gaps foam filled and then all joints foil taped with new chipboard down on top.

I can also get to the back of the 'dwarf' wall in the eaves and foam the gaps in the insulation from behind which will make some difference, however there doesn't appear to be a vapour barrier on this area as I can see the back of the plasterboard.

Where the insulation is fitted into the rafters, it appears to be right up against the roof felt, no gap for airflow.

And I've no idea what it's like in the timber frame dormer, but I imagine a similar sorry story!


So, with apologies for the rambling, any ideas?!

 

[^woody^]

Take the plasterboard down, re-do it properly.

If you foil tape all joints or fit a vapour check layer behind the plasterboard, and fill all voids, then you won't need to worry about an air gap below the roof membrane.

Consider adding a layer below and across the underside of the rafters - even if it's only 10-12mm. Likewise the eaves wall on the back.

 

[Jdwood38]

Thanks Woody, as always.

My thinking was that would be the only real route to solving it, was just trying to avoid if possible.

So suggestion would be to strip all plasterboard off, remove any vapour check layer that is currently there (where I can find it, it’s a green plastic sheet - sounds like vcl?) so then just left with exposed timbers and comedy insulation job. Foam all gaps around insulation, trim back and foil tape? I trust my ability to do tape than any sort of sheeting as I’ve not used that before. Then finally reline the whole room with insulation backed plasterboard?

Thanks again

 

[Mr Chibs]

Make sure you leave a ventilation gap under the roof membrane, in your second picture, looks like the membrane has mould spores on it (condensation?) that piece of insulation bodged in shouldn't be touching the membrane.

 

[^woody^]

Yes your plan is correct. If it's as

Make sure you leave a ventilation gap under the roof membrane, in your second picture, looks like the membrane has mould spores on it (condensation?)

Thats because of the air voids and lack of an effective vapour check layer. Those are more important than a ventilation gap.

 

[^woody^]

Thanks Woody, as always.

My thinking was that would be the only real route to solving it, was just trying to avoid if possible.

So suggestion would be to strip all plasterboard off, remove any vapour check layer that is currently there (where I can find it, it’s a green plastic sheet - sounds like vcl?) so then just left with exposed timbers and comedy insulation job. Foam all gaps around insulation, trim back and foil tape? I trust my ability to do tape than any sort of sheeting as I’ve not used that before. Then finally reline the whole room with insulation backed plasterboard?

Thanks again

Yes you are on the right track.

If you concentrate on the principles of
- insulation across the timber (no thermal bridge/pattern staining)
- preventing moist air from getting into the roof structure (vapour check layer/foil tape),
- no air voids within the roof structure (no condensation/mould on cold surfaces)
you'll be fine.

 

[cdbe]

.

 

[Jdwood38]

Yes you are on the right track.

If you concentrate on the principles of
- insulation across the timber (no thermal bridge/pattern staining)
- preventing moist air from getting into the roof structure (vapour check layer/foil tape),
- no air voids within the roof structure (no condensation/mould on cold surfaces)
you'll be fine.

Going to proceed like this, thanks as always Woody.

 

[Jdwood38]

Well I can now confirm that this is definitely a worthwhile exercise. There are gaps and cold bridges all over the place! This is now the current state of affairs (obviously a lot of clearing up still to do):

Now left with a new quandary; protecting steel from being a cold bridge at the same time as providing fire protection. I'm assuming the latter takes precedent so any thoughts on how to potentially achieve both? If I was to go across the whole ceiling (including the steel) with 12mm (if can be found) or 20mm PIR to prevent cold bridging and then board and skim the whole lot with 12.5mm plasterboard, would that meet fire requirements? Previous install was just 12.5mm plasterboard across the whole lot, no cold bridge layer, no additional boarding around the steel and all was signed off by BC, but now realise that certificate isn't work the paper that it's written on. I know often it is a requirement for 2 layers of plasterboard to protect a steel, but reviewing table b4 from building regs, it suggests that for a building that is less than 5m in height then the requirement is 30 minutes protection - given this is a room above a garage and the ridge line sits c.4.9m above ground level then I think that 12.5mm plasterboard jointed and skimmed is sufficient? But grateful for thoughts.

Thanks in advance.