Cold loft insulation in period property Information, help, tips and advice on cavity walls, ceilings and lofts etc....

[berimitsu]

Morning all,

I'm currently cleaning out an old loft of rubble in order to properly insulate the space. The rafters extend quite a way down below the loft floor, forming sloping ceilings in the bedrooms (see pics). Should I push insulation as far down into the voids between the rafters as I am able or do I need to consider ventilation?

Many thanks!

[stoneyboy]

Hi berimitsu,
Try to get a layer of insulation down in the sloping part but leave a gap above for ventilation. You may find expanded polystyrene easier to fit.
Regards S

[berimitsu]

Thanks stoneyboy,

I understand that Celotex might do the job?

[stoneyboy]

Hi berimitsu,
Yes Celotex will work but a 1.2x2.4 sheet 50mm thick will cost around £26, the same sheet in EP will cost around £17.
What you are doing is a compromise because you will never get a good fit sliding insulation panels down into place so is the extra expense worthwhile? Your choice.
Regards S

[ghh]

Hi all...just joined to see if the issue I have has been raised in the past...which it has in this post....not sure if my post will come to the top of the list or lie lost in an unseen email thread from months ago...
Anyway, that aside, I have the same issue in that I have a section of sloping cieling to the front and back of the house following the slope of the simple dual pitch roof which runs laterally across. So at the moment am looking to upgrade the insulation in that area...despite being c 1990 I believe there was very little if any insulation provided in this gap when built...but it looks like the last owner tried to fit some PIR board into the small space ...but as stoneyboy predicted the fit is very poor and in this draughty area I suspect they are doing virtually no good at all...
I am contemplating stuffing loft roll down the gaps, after removal of the PIR boards, which I think is doable...what will be problematic is keeping a gap for ventilation...the ovelal depth of the sloping cielings is about 1.5 metres and I haven't found a bespoke product to suit the circumstances....at the moment I think my options are:
1) do nothing, not very satisfactory
2) Stuff rockwool down the gaps, make up for loss of ventilation by putting some air bricks in the two gable walls (its detached) or getting those devices which allow ventilation in the laps of the sarking felt
3) Use profile box section plastic roofing sheets to put under the felt prior to filling with insulation, either between every rafter (expensive) or say every 3 or 4,
4) Sod it, just fill the gaps with earth wool and then monitor to see if condensation occurs on the roof space at the most likley times (winter)...i.e. inadequate ventilation.
Access to the gaps is even more of a problem as there are large purlins at about the point.
Anyway any advice very welcome and thanks for your time in reading this...
Regards
Graham

[stoneyboy]

Hi ghh,
However you try to insulate the gap from within your loft you are likely to end up with gaps which may allow cold bridging on the ceiling below.
You will have most success by stripping off the tiles battens and felt and then fitting PIR insulation sealed in place with expanding foam. PIR slabs have much better insulation properties than Rockwool. You can either use slabs 20mm thinner than you rafter height to maintain ventilation or fill gap completely and fit air bricks in the gable ends.
An alternative is to insulate inside the rooms with the sloping ceilings using PIR backed plasterboard.
There is no easy solution.
Regards S