Insulating a thatched roof

[tobydog]

Hi,

This is my first post so please bear with me. I have a timber framed thatched cottage in Suffolk built around 1640. It's thatched with water reed and has the dreaded, but possibly not so bad, impermeable felt underneath. I'm told this is okay as long as the thatch sits on batons and there is an air gap. When we had Economy 7 the heaters pumped out so much uncontrollable heat at the wrong time we didn't know what we were losing through the thatch. We now have new oil fired radiator heating and from the way the house cools down so quickly I'm pretty sure the thatch is nowhere near as good as thick straw. There is currently next to no insulation in the loft so my plan is to rectify this and create a cold roof space. The problem is that upstairs the rooms are vaulted except for a small loft area the length of the house. In addition to the loft space I somehow need insulate the gap between the bedroom plasterboard ceiling (the 45 degree bits!) and the felt under the thatch. The gap between the rafters is about 2m long from loft to eaves and about 15cm high. One thatcher mentioned about ramming 'normal' insulation down the gap and then using regular insulation layers in the lost space. My concern is that I've also read that there should be a gap below the felt in order for air to travel into the lofty space and avoid condensation. Has anyone else come across this issue recently and worked out what best to use in the gap?

Thanks :?:

 

[JoceAndChris]

I don't know the answer to the question Toby but a big welcome to the forum. I'm sure someone will be along shortly who does, and I'll be interested to know what's recommended as my loft is also devoid of much insulation. But well done for addressing the problem of your heating! (we spend a fair amount of time moaning about the price of oil on here so you're in good company)

 

[JoceAndChris]

PS. We really love pics on here.

 

[robgil]

Pics would be good. I have the same kind of thing as you Toby except we have a straw roof. We have come to the conclusion that apart from insulating the small roof space insulating would require boarding out the walls and this would lose all the exposed timbers. Its a trade off really.
We use electric heating upstairs and its not too bad , it stays warm.

You need to look at other things, do you have ceilings down stairs or exposed joists with infill's? This can sometimes be bettered.Is your house listed?

I would also say dont believe everything a thatcher tells you , i have found a lot of them to be rather dishonest to get your work, one of which was a complete cowboy. My local CO put me in touch with an organisation / body of trusted thatchers and we found a really nice guy to do our roof through that, he grows all his own materials and also does long straw, i can put you in touch if you like.

 

[robgil]

Where in Suffolk are you?

 

[tobydog]

Joceand Chris - thanks for the welcome. Bit overwhelmed by all the posts at the moment and finding my way around the site. The price of oil I can live with even though I recently had to get 500 litres at 67p. It's how much I'm getting through that worries me and prompted the insulation issue. What sort of pics are you looking for?

Tobydog

 

[tobydog]

Rob - thanks for your ideas. The joists downstairs are open. I would have considered insulting between the floors but that's too much hassle. Instead the plan is to heat the downstairs, leave the radiators upstairs off and rely on the warm air rising. At the moment it's heading straight to the loft hence the insulation requirement and thw 'cold' roof space. I could consider panelling the roof and making it a 'warm' roof but why pay to keep the Christmas decorations snug?!!

I will need to get a thatcher in at some point to sort the flashing around the chimney but hoping to sort the insulation myself.

We are in Stutton, just south of Ipswich. You?

What sort of pics are you after?

 

[JoceAndChris]

Hi Toby
We're just a really nosy lot who continuously crave pics of people's lovely period properties. The outside, the inside, the thatch, what curtains you've got, anything really.
That probably makes us sound really weird but but seeing your house's problems photographed, and also your style ( when it comes to interior choices) you do get more specific advice.
We're a friendly bunch!
Joce xx

 

[Penners]

We are in Stutton, just south of Ipswich.

Aha - just down the road from Holbrook. I mis-spent a fair bit of my youth in the Monk & Compasses pub. Welcome to the Suffolk chapter of the forum, Toby (we're in north Suffolk, not far from Bungay).

Thatch usually offers quite good insulation values, although you're right that reed tends to be less efficient than straw. This is partly because straw can be over-coated and build up into a really thick layer (whereas reed can't - it has to be fully stripped when it's renewed), and partly because reed allows more passage of air than straw.

This EH publication will, I believe, be of help to you. http://www.climatechangeandyourhome.org.uk/live/content_pdfs/775.pdf

In particular, read the section on energy efficiency measures, starting on page 7. It quotes insulation values as follows:-

Overall ‘U Values’ will vary according to actual thickness and density.
• 300mm thickness of Water Reed – 0.29 W/m²K
• 300mm thickness of Long Straw – 0.23 W/m²K
[Source: Based on conductivities from CIBSE Guide A3]
For comparison, the standard in the 2006 Building Regulations for
replacement roofs insulated at rafter level is 0.20 W/m²K. It is therefore clear
that a typical thatched roof on its own can come close to meeting modern
standards for thermal insulation. A roof that has been over-coated rather
than stripped will often have many layers of thatch and will therefore give
even better U-values and most will require no upgrading at all. This is
recognised in the building regulations which allows exemptions and special
considerations for historic buildings.

 

[robgil]

We are in walsham le willows , not a million miles away.
I would say dont try and heat the whole house with just the downstairs rads, they wont cope and your boiler will be working over time trying to keep up, thus using more oil.
Keeping all your rads on , but at a lower setting might slow things down a little.

Are your first floor floors carpeted? It might be worth chucking lots of rugs down in the winter.


We need a gallery guys , all the photos i loaded up onto the site have been taken down. A photobucket linked gallery and a work in progress section.
Perhaps even a sticky thread titled ''Show us your house'' with instructions on how to use an off site photo bank like photobucket would be a good compromise?

 

[Penners]

Perhaps even a sticky thread titled ''Show us your house''

Don't be boring, Rob. It would attract far more attention if we called it, "I'll show you mine if you show me yours". :wink:

 

[robgil]

Ha Ha! Or ''look i got my moobs out for the lads and thers a photo of it''. :shock:

 

[Penners]

No, I think that's more a case of "how much will it cost me for you NOT to show me yours?".

 

[robgil]

Im wearing a bra?

 

[tobydog]

Thanks everyone for the advice on the heating options in the house and insulation information. Our broadband at home is down at the moment so I only have limited time on line at work. One of the few downsides of living out of town with copper wire.

I will try and get some pics on at some point. I promise no moobs or bra's though!!!

At some point shortly I'll have another post coming up about damp floors, rotting sole plates and the dreaded use of cement, concrete and other unsavoury things. Currently in dispute with the original surveyor who was as useful as a chocolate tea pot!!

 

[Penners]

At some point shortly I'll have another post coming up about damp floors, rotting sole plates and the dreaded use of cement, concrete and other unsavoury things.

By all means post on any subject, Toby. Those are all familiar themes!

But I urge you also to take a look through the archive of PPUK Agony Uncle articles. It's a wealth of useful information of all the usual period property problems.

http://www.periodproperty.co.uk/ppuk_discovering_agony_uncle_archive_2010.shtml

 

[robgil]

I dont think a buyers survey could prepare you for an old timber framed house, ours came back with saturated brick plinths but we should have read into this as ''and probably rotten sole plates and lower studwork''.
The good news is sole plates are a sucking in through the teeth for any builder but as i am finding out to do it your self its not a difficult thing to repair, ive already dont one brick plinth insertion with some timber repairs and it was pretty straight forward.
Your main concern , and one you really need to think about getting expert help with is how to support the rest of the frame above.
Photos say a thousand words though. I shall post some of mine up later tonight showing you some rotten timbers, Middi also has some posted ,it might make you feel better about it all.

 

[robgil]

Here you go , some photos in this thread.

http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=11797


I have to do this sole plate and possibly another when the weather gets better, this one will need the brickwork rebuilt as well.
This was hidden under some cement plaster and the survey didnt pick it up, the photos are being quite kind to it.

 

[Ushy M]

Welcome to the forum Tobydog - good to see a fellow thatch owner out there - I'm surprised there's so few of us. We're thatched in a good deep layer of long straw but still seem to lose heat through the top of the house. We insulated the apex of the roofspace along the length of the house with Thermafleece and it has helped somewhat - Thermafleec has the advantage of breathability and as it is treated with borax (as insecticide), is fire retardant. Look forward to seeing some photos!

 

[simon.d]

I'll be stripping and doing a full re-thatch of the farmhouse I'm doing up, and thinking about insulating above the rafters as I want to keep the timbers exposed in the old vaulted ceiling kitchen and hoping to up the thermal performance. I read that wood fibre board insulation is suitable for this application: http://www.gutex.de/downloads/pdf/en/Datasheet_thermosafehomogen-engl.pdf Anyone Know much about it or other insulating options? Pros/Cons etc?