Insulation and plasterboard between beams.

[9million]

Dear Forum,

I have a grade 2 listed farmhouse with 2 attic rooms that had all the ceiling plaster removed (lathe and plaster + some plasterboard). The oak beams are in a bad state, loads of worm decay etc, but no signs of wet or dry rot, which I have in other areas of the house.

I have spent ages (2months) sanding down the beams so that these will now be shown rather than just plastering over it all. My concern is that between the beams I have placed a thin 25mm layer of celotex board, behind which is old roofing felt (non breathable) and used small battens 1 1/4 inch either side of the rafters in order to apply plasterboard, which I have started to plaster over.

I now have a visit booked by the council, but have read so many different things lately about using lathe + lime mortar etc to let the building breathe, so concerned now that what I have done is either not going to be exceptable by the council or could cause issues with condensation etc.

There is still air flowing between the roofing felt and insulation, not a great deal as this is mainly from a gap where the attic rafters meets the brick wall.

The effect I'm trying to achieve is to expose the oak beams rafters that have now be cleaned up, whilst trying to have some insulation. Any thoughts on how this can be achieved with a minimal gap between roofing felt and rafters (2 - 4 inches thick) or if anyone else has used celotex in an old building roof without issues please let me know.

Thanks

 

[Penners]

When you say "the council" do we infer that the visitor will be your Conservation Officer? If so, did you get Listed Building Consent for the work that you're doing?

The question of whether LBC is actually needed for this work is a moot one. It might be classed as a repair (no LBC requirement) or an alteration (LBC needed). The difference will probably be down to a matter of interpretation by the CO.

As to the practicalities of maintaining ventilation in your roof structure, this is a difficulty that is faced by anyone who requires a ceiling structure between rafters. It's a fact that Celotex is not breathable, but then neither is old-style roofing felt. The best that you can try to achieve, I suspect, is to ensure that you allow as much ventilation as possible between the felt and the Celotex. But I'm afraid nobody is going to be able to guarantee that this will be acceptable to the CO. You'll just have to present the case that this was the best you could do to compromise between ventilation and insulation.

However, try not to be confrontational about this. Your relationship with your CO is an important one, and in my experience you'll get on with him/her best if you explain your needs and ask advice, rather than showing a dogged "what I want" attitude.

 

[9million]

Thank you Penners,

Yes it the Conservation Officer who is due to visit. Have not had any consent for work that I'm doing as its all repair, but my concern is that the old plaster would have covered the beams, whilst the new work is showing the beams, so would this be classed as an alteration. There was no plaster on the attic room ceilings when I purchased the property at Auction as this had been removed at some stage over the past ?? years, but I feel it woud be a shame not to expose the beams and provide some form of insulation.

Regards

 

[Moo]

Wise words from Penners, as usual.
COs are generally nice helpful people who, although their loyalty has to be to the house, understand that it has to be lived in by human beings. If you make it clear that the last thing you want to do is compromise the building's integrity, and ask for his/her advice about the best way of solving your problem, you'll be home and dry ( in both senses).

 

[Zebra]

Or perhaps you're not listed, and when you say "the Council", you mean Building Control.
It is a tricky problem, and one which it might have been wise to consult Building Control about before you decided on a course of action. They may say this is not enough insulation, and that you therefore cannot expose your rafters as you wish.
Or, given that it's an old house, they might let you off. If I remember correctly, there are required U-values for house renovations, which are different to the required U-values for new build. I can't remember the exact requirements, but I don't think that 25mm of celotex would meet the required U-value.
Does the work you're doing actually need Building Control's involvement? I put in Building Notices for the parts of the house which were being completely rebuilt, but didn't apply for one for the renovation of the old house, even though I perhaps should have, strictly speaking.
On the subject of condensation, there'd be little point in using lime plaster in your situation, given that you have a non-breathable roofing felt - it might even be disadvantageous - but I would be worried about condensation on the rafters. It is extremely difficult where you have plaster meeting old beams, to achieve an air-tight seal. If I were you I'd use something like this:
http://www.greenbuildingstore.co.uk/page--pro-clima-airtightness-tapes-options.html to seal where the insulation foil meets the beams, so that none of your warm moist air can reach the void between the insulation and the roofing felt. If it does, it's got nowhere much to go, unless you have a howling gale through the void, and could well settle on your beams. I've used celotex insulation between my rafters, but have not exposed the rafters. They were not originally meant to be, after all. I've put a further layer of celotex underneath, all taped and sealed for airtightness, and plastered over that.
Sorry to be rather gloomy, but it seems you're having some sort of second thoughts about your course of action, so I think you'd do well to get it right now, rather than lay in bed staring at the ceiling in future, worrying about those beams.....

 

[Keith Bowman]

Dear Zebra - he/she does actually start by referring to a grade 2 listed building. (And signs off as 9million!)

Dear 9 million - did you ask the council to visit or have they organised a visit on their own initiative?

 

[9million]

The councils LBC wrote to me about the property which they knew was listed and had been sold at Auction December last year.

I have arranged for them to visit, to see the work that I'm doing on the property which is to try and keep / improve the original features it has, but unfortunately the house was not lived in a for a number of years, which has caused numerous areas that require repair fro wet rot / dry rot / wood worm / damp / holes in chimneys / leaky roof, the list is endless but its taking shape.

The front of the house has had double glazed windows put in at some stage (UPVC) but not sure if this was done before or after it was listed, but I think the LBC people know this as they told me they visited in the past.

Only having second thoughts about the insulation between the rafters as dont want to damage the beams, but feel as I have placed battens between the beams and insulation and all the beams have been treated with multiple coats of wood care, and that there is no heating in the attic rooms, the risk of causing damage should be minimal, but it will be easy to inspect a section in a years time to make sure all is well.

Regards

 

[MatthewC]

Or perhaps you're not listed, and when you say "the Council", you mean Building Control.
It is a tricky problem, and one which it might have been wise to consult Building Control about before you decided on a course of action. They may say this is not enough insulation, and that you therefore cannot expose your rafters as you wish.

Dear Zebra - he/she does actually start by referring to a grade 2 listed building.

But Zebra is right about the need to contact Building Control as you need their approval when changing a element of the roof such as the insulation, even if just adding a membrane when re-roofing. Also, as I found out, you can apply for LBC and no-one in the Council Planning Dept mentions the need for Building Control!!

 

[Flyfisher]

Ignoring any rights or wrongs for a moment, has the CO who will be visiting the house actually seen the house before the 'repairs' were done? Are there any records of the ceiling construction before the 'repairs'? (The auction particulars perhaps?).