Loft insulation

[Bogart]

Probably been asked millions of times before but Ive trawled through the forum and yet to see a definitive answer. Loft space in thatched cottage has no insulation at ceiling level. All people say
is thatch is a good insulant itself, maybe so but why should I be heating that wasted space anyway. So I have 2 options normal rockwool which is poo pooed by some as not breathable and hence
shall not be used. Uncertain as to why I need a breathable layer between bedroom ceilings and loft space! Next choice is natural stuff ie sheep wool which I think would be lovely for mice if
some took up residence and will cost a lot more.
Any suggestions, Thanks

 

[paulc]

So I have 2 options normal rockwool which is poo pooed by some as not breathable and hence shall not be used.

My opinion - Rockwool type insulation is just as breathable as sheepwool and perfectly adequate for insulating loft spaces. Had a water leak recently, and a large chunk of glassfibre insulation got saturated. Once the leak was fixed, the insulation dried out very quickly (a day or two) unlike the timbers which will take weeks,

On the environmental side, sheepwool might be greener than some of the alternatives, but Knauf do a fibreglass insulation that is made from recycled glass (less waste going to landfill).

 

[Flyfisher]

I'm pretty sure rockwool is breathable. I'd be interested in any references suggesting it's not.

 

[wobs]

I don't think there's much difference between Thermofleece and mineral wool with regard to breathability, but I've not explored this link in detail TBH:
http://www.ecotimberframe.ie/pdf/BreathabilityinbuildingsNBT.pdf

 

[MikeG]

Architect here..........mineral wool is a great product, perfectly breathable, and perfectly good in listed buildings or under thatched rooves. It is a thousand times better to work with than the old yellow stuff, and a hundred times better than the successor to that, the pink stuff. It is made from recycled products. Many many things in building become fashionable without good reason on the strength of something on Grand Designs or whatever, but there is no reason to use expensive and problematic sheep's wool, for instance, in place of mineral wool.

The only thing I'd caution you to think about is ventilation in the void between the thatch and the mineral wool If you can get some airflow in there I'd be much happier (given that you almost certainly won't have a vapour barrier at ceiling level). Gable vents, perhaps? As for depth..........pile it in. You need about 260mm, I think, for Part L compliance, but double that if you've got the room.

 

[a twig]

I use the supaloft from thermafleece (recycled plastic) - its half the price of the other Thermafleece products, and lovely to work with, tears/cuts very neatly and nicely as well.

Breathable, no problem with sheep wool smells, vermin resistant etc, and has slightly better performance than a lot of the mineral wools as well.

Cheapest place I founded it was Celtic Sustainables.

 

[bennoa1]

Isn't one of the benefits of sheeps wool is that if it gets damp/wet it retains its thermal performance. Having seen the fibreglass that was behind the walls I decided on sheeps wool as internal insulation - I use Black Mountain rather than Thermfleece.

 

[MatthewC]

Uncertain as to why I need a breathable layer between bedroom ceilings and loft space!

All that moisture that we humans exhale needs to go somewhere, and warm air rises. So unless you like sleeping with your bedroom door and windows open, it's good that it can gently pass through the ceiling.

I have Thermafleece in my loft, fitted five years ago, and upstairs is noticeably warmer than downstairs so I think it works. One of the issues with the old prickly pink stuff was that it collapsed if it got wet and so never dried, whereas (ISTR) Thermafleece has a small amount of plastic in it to retain its shape. Possibly the newer Rockwool stuff is designed to do the same thing, and hence is breathable?

 

[wobs]

As for depth..........pile it in. You need about 260mm, I think, for Part L compliance, but double that if you've got the room.

Correct me if I'm wrong, but wouldn't that reduce the effectiveness of the stuff at the bottom? I read somewhere that the recommended depth is about 260mm because when you get too much, you hit the law of diminishing returns, not just for the amount of heat you'll save, but due to the squashing of the insulation.

Perhaps some rigid breathable insulation at the bottom would be preferable if you wanted to go crazy with insulation.

 

[TheRoost]

Architect here..........mineral wool is a great product, perfectly breathable, and perfectly good in listed buildings or under thatched rooves. It is a thousand times better to work with than the old yellow stuff, and a hundred times better than the successor to that, the pink stuff. It is made from recycled products. Many many things in building become fashionable without good reason on the strength of something on Grand Designs or whatever, but there is no reason to use expensive and problematic sheep's wool, for instance, in place of mineral wool.

The only thing I'd caution you to think about is ventilation in the void between the thatch and the mineral wool If you can get some airflow in there I'd be much happier (given that you almost certainly won't have a vapour barrier at ceiling level). Gable vents, perhaps? As for depth..........pile it in. You need about 260mm, I think, for Part L compliance, but double that if you've got the room.

When you say mineral wool, do you mean just rock mineral wool, or both rock mineral & glass mineral wool? (the latter I believe is the cheap basic stuff).

I find researching insulation very confusing, some of the terms are just brand names too which doesnt help( I.e. Rockwool is a brand name, Ekoroll is a brand that describes itself as 'earthwool' but its actually plain old glasswool!)

 

[MikeG]

As for depth..........pile it in. You need about 260mm, I think, for Part L compliance, but double that if you've got the room.

Correct me if I'm wrong, but wouldn't that reduce the effectiveness of the stuff at the bottom? I read somewhere that the recommended depth is about 260mm because when you get too much, you hit the law of diminishing returns, not just for the amount of heat you'll save, but due to the squashing of the insulation.

Perhaps some rigid breathable insulation at the bottom would be preferable if you wanted to go crazy with insulation.

Hi wobs.

Yes, of course you get the law of diminishing returns, where you spend X amount on insulation to reduce your heating bills by, say £500, and then spending the same again only saves another £200......but insulation is cheap, and super-insulating your house (along with other passive features) can reduce your space heating requirements to zero. Yes, nil. I have 500mm in my loft, and no, the stuff at the bottom is perfectly well "lofted".

All of the rigid insulating boards that I know that are breathable are much poorer insulants than mineral wool, and so even if the mineral wool weren't fully lofted it would still do a better job than any breathable solid board I am aware of.

 

[MikeG]

......When you say mineral wool, do you mean just rock mineral wool, or both rock mineral & glass mineral wool? (the latter I believe is the cheap basic stuff)....

The latter.

 

[GPHouse]

I bunged in 300mm of Thermafleece CosyWool. It made the world of difference but I didnt have a good heft of thatch.

It's easy to work with, quick to install, and I have to say quite pleasant.

I trawled around and did a compare and contrast - At the time (and recently) I found Mike Wye to be cheapest and on the last order I get a good deal (cant remember how but I did get a discount - was either coupon or asking very nicely....).

Mines been in 9 months and I marked depth. It's layed in perpendicular layers and there has been no discernable compression.

Using the Cosywool to meet standard I think I calculated you needed 260mm but it made little cost differecce to go to 300mm, but if you ahve none now, anything MIGHT be better than nothing.....


G

 

[Bogart]

Uncertain as to why I need a breathable layer between bedroom ceilings and loft space!

All that moisture that we humans exhale needs to go somewhere, and warm air rises. So unless you like sleeping with your bedroom door and windows open, it's good that it can gently pass through the ceiling.


Going to install new loft access hatches and find them stating that they are all airtight to stop the migration of moist air into the loft space. Seems a bit of a dichotomy here. Now having had a good rummage up in the loft space I find that half of it has a plastic sheet laid over the plasterboard whereas the other has none. Unsure if I should remove it or not.

 

[Bogart]

Architect here..........mineral wool is a great product, perfectly breathable, and perfectly good in listed buildings or under thatched rooves. It is a thousand times better to work with than the old yellow stuff, and a hundred times better than the successor to that, the pink stuff. It is made from recycled products. Many many things in building become fashionable without good reason on the strength of something on Grand Designs or whatever, but there is no reason to use expensive and problematic sheep's wool, for instance, in place of mineral wool.

The only thing I'd caution you to think about is ventilation in the void between the thatch and the mineral wool If you can get some airflow in there I'd be much happier (given that you almost certainly won't have a vapour barrier at ceiling level). Gable vents, perhaps? As for depth..........pile it in. You need about 260mm, I think, for Part L compliance, but double that if you've got the room.

Been trawling around for prices and there is a big difference. Approximately £1000 for Supaloft (recycled plastic bottles) and £300 for Knauf Earthwool with same thermal conductivity. As regarsd ventilation as I think Ive quoted somewhere else half the loft space has a vapour barrier in place and half not. To ensure I do not mess up the ventilation I am thinking of keeping the insulation a few inches away from the eaves area and not gong to jam it in there.

 

[MikeG]

.....To ensure I do not mess up the ventilation I am thinking of keeping the insulation a few inches away from the eaves area and not gong to jam it in there.

The I can tell you that the only way to successfully do that is to place a barrier first, prior to laying any insulation, to physically form the gap. The usual is some solid insulation boarding, such as Celotex, but you could use boards (such as OSB), battens, or even garden netting.