Problems with loft insulation and thatch?

[TimB]

Hello,

New forum member, here - though have read as a guest from time to time and found the forum very useful, thankyou!

I'm hoping you can reassure us regarding loft insulation under thatch, and whether there are any gremlins we should be aware of. In particular, my partner was warned by a work colleague that there could be issues with damp and mould resulting from putting loft insulation under a thatched roof, and that we should do some research before putting insulation in. The implication seemed to be that we might want to avoid loft insulation altogether.

Having read some threads here discussing which type of loft insulation to put under thatch I got the impression that it was a common installation, hence wondered if anyone here knew what my partner's colleague might have been referring to? We were intending to insulate using B&Q recycled plastic bottle insulation as I tend to be very bad with anything that can cause breathing irritation, and rockwool looked like a bit of a nightmare for that.

I gather you like photos of period cottages so here's one of our cottage in the December frost and a couple from inside the roof.





Thanks in advance for any help!

Tim

 

[AMc]

I don't have a thatched roof, but I do know a bit about insulating.

Your basic types of roof insulation are 'warm roof' and 'cold roof'.
Warm being where the roof structure is enclosed and insulated i.e. the rafters are kept warm.
Cold is where you isolate the external roof structure from the internal habited area with insulation and allow the roof structure to become/remain cold.

Your roof structure mean you'll be needing a cold roof unless you were suddenly considering rethatching

Problems with condensation occur between the warm, heated and occupied part of the house and the cold surfaces on the inside of the roof. When the warm moist air in the house meets the cold roof structure water vapour condenses and makes the roof wet, if that stays wet then it will encourage rot.

The solution to that is to minimise the amount of warm wet air coming from below into the roof which is also good for thermal efficiency and to ensure that there is ventilation to remove any water vapour that ends up there and dry out any condensation that occurs.

When you are putting in the insulation you need to be sure that you leave adequate ventilation above the 'wool' and below the thatch to allow it to deal with any moisture in the air coming up from below or in from outside.
You also need to avoid bridging between the warm parts of the roof and the cold parts ensuring that the insulation you install doesn't block any ventilation at the edges of the roof.

Some people may suggest a plastic membrane underneath the loft insulation to prevent warm moisture laden air entering the roof, but I would be concerned about trapping moisture underneath it where it could cause problems.
'Wool' insulation (rock, sheep, plastic bottle) is "breathable" in that it is vapour permeable, it will allow moisture to move through it and dry out providing there is a source of ventilation.

Assuming there are some points of ventilation in the gable ends and/or at the edges where the roof meets the ceiling I can't see any reason not to use a thick layer of 'wool' insulation across the floor of the roof - laid between the joists then at 90 degrees to them. I would be tempted to get yourself a mask, gloves and disposable boiler suit as I would expect there to be a fair amount of dust from the thatch that might cause you difficulties. I would also consider removing the debris that's in there now first- even though this will be a pain it will be harder to do once you've started lugging in insulation and discover it gets in the way.
Also make sure you draught proof the loft hatch to discourage warm, wet air going up into the loft in winter.

Once you've insulated then stick your head up there once in a while, esp. in cold weather to check there are no problems with patches of condensation or mould.

Finally before you start laying the insulation I would look at fixing some blocks of scrap wood onto the main beam down the middle of the roof so once you've laid insulation between the joists and then at right angles to that you can lay scaffold planks over the blocks and access the roof space safely. I've insulated our roof which has completely covered the joists and it makes it quite difficult to work out where its safe to stand to move around the loft, you also end up compressing and moving the insulation which isn't great - if I were doing it again I would provide myself with some walkways.

 

[Penners]

100% agreement with what AMc says (assuming, as he does, that your plan is to insulate the "floor" of your attic). Just to reinforce his point - do make sure that your insulation doesn't block off whatever ventilation the attic is currently receiving from gaps around the sides. There needs to be an air flow above your insulation.

And don't forget to insulate and draught-proof your loft hatch.

I bought some plastic bottle insulation from B&Q recently for an amazingly low price. See if their offer is still running.

 

[MdB]

I bought some plastic bottle insulation from B&Q recently for an amazingly low price. See if their offer is still running.

If you fancy doing a little test, I would be interested to know what happens when you put a match to a bit of it. I suspect it could burn rather well but maybe they have found a way of fireproofing it.

 

[AMc]

I guess with thatch you may want check your house insurance doesn't have any stipulations about fire ratings on the insulation.

 

[Penners]

I bought some plastic bottle insulation from B&Q recently for an amazingly low price. See if their offer is still running.

If you fancy doing a little test, I would be interested to know what happens when you put a match to a bit of it. I suspect it could burn rather well but maybe they have found a way of fireproofing it.

I'm not able to do that at the moment. But I seem to remember that the packaging said something about it being fireproof.

Later: I've just googled this and found a thread on the Green Building Forum (starring our own dear Biff). It makes reassuring noises about the fire rating of recycled plastic insulation. Look particularly at the light blue panel well down the page.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=772

 

[Feltwell]

We were intending to insulate using B&Q recycled plastic bottle insulation as I tend to be very bad with anything that can cause breathing irritation, and rockwool looked like a bit of a nightmare for that.

The plastic bottle stuff is much nicer to handle, I've used a load recently. No mask or gloves required unless your loft is so mucky that by laying it you will kick up loads of dust. Probably the only disadvantage over rockwool is that it's harder to tear when you want to "cut" it at the end of a run - not impossible, just needs a bit more effort than rockwool. Thermafleece is sheepswool, and is also supposed to be nice stuff to handle & there are environmental arguments to use it. It was on offer in B&Q at one point, but I haven't seen it for a while - last time I checked with no offers on it was much more expensive, hence why I went for the plastic bottle stuff.

 

[MdB]

I still haven't seen anything indicating that the recycled plastic stuff is fire safe. On the B&Q site, rockwool states its fire rating. Nothing is said for the plastic. I would love to be shown wrong.

 

[robgil]

Just a note on ventilation in the loft space, when a wind is blowing I can feel it coming through our thatch, through the gaps between the daub and the rafters and into the room. From this I can assume thatch has good ventilation in itself.

 

[Penners]

Rob - have you considered renting the house out to aircraft manufacturers as a wind-tunnel?

 

[robgil]

Anything stronger than a breeze would most likely blow it down Penners.

 

[Penners]

Then it's perhaps a good thing that the wind can blow straight through, without encountering any resistance!

:wink:

 

[Feltwell]

I still haven't seen anything indicating that the recycled plastic stuff is fire safe. On the B&Q site, rockwool states its fire rating. Nothing is said for the plastic. I would love to be shown wrong.

If you click on the Green Building Forum link above, there's some comments on this from the manufacturer.

 

[AMc]

This is the technical info sheet
http://www.eco-wool.co.uk/downloads/Eco-Wool.pdf

Last page says
Test Report No: 0316-L-06/7.
BS 5803-4: Thermal insulation for use
in pitched roof spaces in dwellings -
Part 4: Methods for determining
flammability and resistance to
smouldering (1985).

AND

Fire Test BS 5803-4 = Passed

The product descriptions on the B&Q web site are generally pretty woeful seemingly you get a copy paste of what is on the manufacturers web site or the outside of the packaging. They routinely ignore things like the dimensions of items or the quantity in the pack.

I spent a lot of time trying to work out the materials used in a "solid wood" door - I had to go and visit one to find out it was made of solid blocks of wood glued together and veneered with thin sheets of pine. On the other hand the B&Q web site is like the encyclopaedia Britannica in comparison to things like the Travis Perkins one. I guess that's a problem with such a large range of products.

 

[El Greyo]

Hello Tim

Welcome. We've recently insulated our thatched cottage as well and went through exactly the same decision making process. Thanks for the photos of your roof, your piles of straw and debris look even bigger than the 20+ bin bags we removed from our loft. If it's like ours, there will be a lot of fine black dust (decomposed straw perhaps) so I'd wear a good dust mask and clothing you don't mind getting absolutely filthy. We came out looking like coal miners.

I did quite a lot of research, including asking on here, and in the end we went for the B&Q recycled plastic stuff. My only worry about it was the fire resistance but from what I found, and what has been written and linked to here, it sounds like it is fine. It's so much easier to handle than the rock wool, so while it worked out a bit more expensive, I'm very glad we used it. You can wrap yourself up in it with no ill effect.

As others have said allow good ventilation but from what I can tell I agree with Rob that thatch seems to give good ventilation in itself. It certainly feels that way when I've been up in our roof since we've insulated. The surveyor also recommended putting insulation in and I haven't come across any information recommeding otherwise. I'm sure it's best keep an eye on it anyway.

 

[Penners]

The product descriptions on the B&Q web site are generally pretty woeful

If you think that's bad, try finding someone with product knowledge in any of the stores.

The Plumbing (or whatever) Specialist is always on his day off. And if you ask some other "Advisor" ( :roll: ) whether a product has a specific feature, the response is invariably, "Oh, I should think so."

Well has it or hasn't it?!
:evil: :evil: :evil:

 

[El Greyo]

If you think that's bad, try finding someone with product knowledge in any of the stores.

I usually feel I've had a good result if they actually know where a product is. I wouldn't want to push my luck much further than that.

 

[Penners]

B&Q recycled plastic stuff...You can wrap yourself up in it with no ill effect....

...apart from a severe case of hyperthermia. :wink:

 

[robgil]

Nothing quite like wrapping your self up in some plastic, some women find it quite sexy.

Not so if you have just eaten a curry, or some cabbage , or a curried cabbage.

 

[Penners]

I don't feel very well...