Ceiling under tiled roof

[El Greyo]

Hello all

In the process of removing an airing cupboard, header tank and some associated framework, we've exposed this area under the sloping roof.



There is a membrane and then a tiled roof above the hole. Below the hole, the ceiling is plaster board skimmed with plaster. We're not sure what the other panels of ceiling are made of, most likely lath and plaster given both the appearance and because a lot of other walls and ceilings are lath and plaster. At present there is about 60 mm between the existing plasterboard and the roof and this is well ventilated.

So we're wondering how to cover this section and it would be nice to insulate it a bit better (as there is none at the moment). We could put celotex or similar and plasterboard but would it better to use something breathable? Does anyone have any alternative ideas?

Cottage is a 17th C timber frame with brick infill. Thatch on one side of the roof, tiles on the other.
Thanks all

 

[Keith Bowman]

It looks as though the tie beam has been cut through at some stage to make a doorway. Are there any signs of the roof spreading the walls apart? (If not and it has been like that for years, take no notice of me!)

 

[El Greyo]

Hi Keith

Yes, the sawn through tie beam is an interesting feature! The answer is that it has been like that for a long time and there is no sign of bowing but it is quite comical.

The house has been through many incarnations. Originally it was two cottages and that tie beam would have been within the party wall. We also think that the chimney was added at one time and I'm not sure whether the tie beam goes through the chimney anyway. At another stage, the house was joined to next door and was a pub - we can see where doors went though to next door. Thankfully they didn't completely cut through that tie beam.

 

[xanthe]

We're buying a house that sounds very similar to yours - late C16th timber-framed with brick infill and tiled roof.

The surveyor's report states that there is insulation board wedged up between timbers and the tiles and then plaster-board on the inside with no ventilation gaps or membrane - and amazingly no evidence of condensation. The state of the roof generally (tiles, roofing felt etc) means that it is most economical to strip the whole thing and start again at which point it all needs to be remedied.

The recommendation that we have had is fix small timber battens to the rafters to allow for ventilation and/or lay a breathable membrane before retiling. If we lay the breathable membrane we could leave the insulation board that is currently there, but given that nothing 'modern' in the house has been done well, we are looking at replacing it with either sheep's wool, or hemp, or celotex and then replacing the plaster board. I've done some basic research and I'm currently leaning towards the former two as I prefer natural materials, but husband is keener on celotex.

Looking at the roof timbers, at some point they were lath & plaster judging by nail holes, but that is long gone. However, we have some patches of lath & plaster on a downstairs ceiling and an upstairs wall, and we aren't allowed to touch any of them - notes and photos in the CO's file on the house. The whole of the downstairs ceiling needs to come down (fibre-board so big fire risk) but the l&p section between two beams has to stay as is - even though the condition isn't great.

If you are Listed, which I presume you are, you may want to speak to your local CO about what they would like/permit you to do with regards to your lath & plaster.

Would be interested to know what insulation product you eventually go with and why.

 

[El Greyo]

We are also listed and it is my principle to conserve where possible, and where repair is needed use a replace like with like approach. So where we have lath and plaster, we are leaving it where it is in reasonable condition. There are some sections that I think may need some repair at some time but we will still use lath and plaster.

But there are some sections where more modern materials have been used such as stud walls that have plasterboard and skim. The section shown above has plasterboard so I don't necessarily feel constrained to restore it to a traditional construction.

But within those constraints, we would like to improve the insulation of the house as it is very thermally inefficient and cold in winter. I'm treating this section as a bit of a trial section I guess. One problem with natural insulation materials such as hemp and wool will be fixing them in place and maintaining the ventilation gap. A rigid board will be easier to fix.

I've no issue against modern materials such as celotex just because they are modern and synthetic. There can be a particular satisfaction in using traditional materials and methods but the hemp and sheepswool aren't really traditional, more a modern way of using natural fibres. To me it's more about whether it is the best thing for the house and here it is whether breathability is a potential benefit.

This is probably similar in your case. If you are replacing the plasterboard which is non-breathable, then there isn't a need to use a breathable insulation behind it - particularly if it is more difficult to install. But there may be a benefit in using breathable materials - in which case all layers would have to be breathable.

I will have bit more of a think about it and perhaps have a chat with the Old House Store. Will let you know if and when we decide on something.

 

[xanthe]

Regarding the ventilation gap, we are advised that small timber battens should be nailed 2" below the top of the rafters so that insulation can't fill the whole space and allow for ventilation. Currently the insulation board is right up against the rafters allowing no ventilation at all.

I'm not too worried about breathability with the roof - more preventing water ingress. I just obsess about it with walls!

With the sheep's wool I think I'm just rather taken with the idea of giving my house a nice fluffy jumper!