Thatch and loft insulation

[El Greyo]

Hello all

Last time I was here, I was asked for photos of our lovely 17th century cottage so, hopefully, there are a couple below. Lots of work to stop us getting bored.

Anyway, we've got around to sorting out the loft and putting in some insulation (a bit belated given last month's temperatures). The house is actually thatched only on the front with a tiled roof on the rear (a cost cutting excercise a while ago I assume) so while the thatch provides some insulation, there's not much to stop the heat going out through the back (a friend of ours called it semi-dethatched.)

So what are peoples thoughts on the type of insulation we should put down? The thermafleece products made from wool seem a favoured option - eco-friendly and bring forth images of lambs gamboling on the hillside etc - but is very expensive. Very breathable I believe which is an advantage in a house such as ours. What about the loft insulation made from recycled plastic? It is ecofriendly and also very easy to handle and is resistant to mould and decay. I imagine that it is breathable, but is it more likely to cause condensation problems? We will do what is best for the house but I reckon we could insulate with the plastic for less than half the price of the wool.

Thanks for the advice.

Ok, here goes the photos...

In the sun:

And in the snow:

Yay, they worked!

 

[MdB]

So what are peoples thoughts on the type of insulation we should put down? The thermafleece products made from wool seem a favoured option - eco-friendly and bring forth images of lambs gamboling on the hillside etc - but is very expensive. Very breathable I believe which is an advantage in a house such as ours. What about the loft insulation made from recycled plastic? It is ecofriendly and also very easy to handle and is resistant to mould and decay. I imagine that it is breathable, but is it more likely to cause condensation problems? We will do what is best for the house but I reckon we could insulate with the plastic for less than half the price of the wool.

Celotex / Kingspan - Best performance for its thickness - non breathable - expensive - doesn't burn very well

Rockwool - Needs twice the thickness of Celotex - breathable - very very cheap - doesn't burn

Sheep wool - Needs twice the thickness of Celotex - breathable - expensive - doesn't burn very well

Recycled plastic - Needs twice the thickness of Celotex (i think) - breathable - cheap - burns!

Unless you have a good reason not to, I would go with Rockwool. Most is made from recycled glass I believe however, I think it takes a lot of energy to produce so you can't really call it green. At £3 per big roll, you really have to have deep pockets to consider anything else.

 

[MdB]

I've yet to come across an explanation as to why sheep wool insulation is so expensive. Is it down to the sheering cost?

 

[Lime]

I haven't owned a thatched house but I think I'd fit insulation that would not burn.
Rockwool, glassfibre or vermiculite appear to fit the bill.
I'd plumb for vermiculite if external noise is any problem. It has good sound absorbing characteristics IME. It is also very easy to pour in!

 

[Penners]

I agree with the above comments. I'm a bit unsure about the matter of breathability in insulation, given that the whole principle of insulation is to trap stationary air.

 

[AMc]

I agree with the above comments. I'm a bit unsure about the matter of breathability in insulation, given that the whole principle of insulation is to trap stationary air.

The air remains (mostly) stationary but the moisture can migrate through "wool" materials like sheep, rock etc. presumably by capillary action.
With solid foam like celotex etc all there is no route at all and moisture (as well as air) stays on one side or the other unless it moves around the edges again using capillary action.

My vote would be for either rockwool or the recycled plastic stuff. Local BnQ had knocked massive rolls of insulation down to £3 and some pence from an already low number - I'd get as much as you can move.

 

[El Greyo]

Thanks everyone. My main concern was whether, for an old, thatched cottage, there were any more factors to consider compared to a more modern house.

 

[biffvernon]

Thanks everyone. My main concern was whether, for an old, thatched cottage, there were any more factors to consider compared to a more modern house.

One factor that has not been mentioned is the source of your insulation. You must appreciate the appearance of your environment or you would not be living in such a beautiful house, but for the people living in the shadow of the Danish owned Rockwool factory in Istria life is not so pretty.

It's cheap. but it comes at a price. Thermafleece has the advantage that it supports Herdwick sheep on Cumbrian fells.

Of course thatch is a pretty good insulator in itself but take care that there is a draught-proof breathable layer.

 

[Flyfisher]

One factor that has not been mentioned is the source of your insulation. You must appreciate the appearance of your environment or you would not be living in such a beautiful house, but for the people living in the shadow of the Danish owned Rockwool factory in Istria life is not so pretty.

There are many rockwool factories around the world - is there some sort of specific problem with the Istria factory?
Anyway, I assume that the Bridgend factory, which has to meet strict UK emission regulations, provides all the Rockwool for the UK market?

It's cheap. but it comes at a price. Thermafleece has the advantage that it supports Herdwick sheep on Cumbrian fells.

Perhaps the very limited availability of sheep's wool is reflected in its relatively exhorbitant price. I'd say that anything with such a limited supply is not really a good candidate for being truly sustainable. Another example of 'green living' being a rather elitist activity perhaps?

The Greenspec website provides an interesting comparison of rockwool and sheep's wool insulation. Its range of figures suggest that Rockwool is about the same or better at insulation and has about the same or lower levels of embedded energy than sheep's wool.

As far as I can tell, sheep's wool costs around ten times more than rockwool.

Herdwick sheep on Cumbrian fells may indeed be a pretty sight but if this is the sort of price we must pay for them, then it's a very high one. Frankly, I doubt they are dependent on this particular inflated niche market, else they would have disappeared many decades ago.


From the GreenSpec website: http://www.greenspec.co.uk/insulation-plant-fibre.php#sheep
Sheep’s wool is a waste product from renewable sources
[plus points]
Wool sequesters CO2 during animal growth
Hygroscopic – provides a degree of humidity control
Can absorb moisture without loss of thermal efficiency
Reusable if in a suitable condition
Recyclable
[minus points]
Contains non-renewable material (polyester binder)
Contains boron-based flame retardant and biocide
Imported wool adds to embodied energy
The possible use of pesticides in imported wool
Thermal conductivity can be increased by compaction 5

Thermal conductivity: Typical: 0.039 W/m°K
Density: Typical density: 25 kg/m3
Embodied energy cradle to gate:
Various figures:
- 20.9 MJ/kg
- 12 – 36.8 MJ/kg dependent on the use of waste wool and scale of production.


From the GreenSpec website: http://www.greenspec.co.uk/insulation-mineral.php#rock
Rock mineral wool is made from quarried diabase rock and recycled steel slag. The insulation is produced in a variety of densities according to format and function. Varying densities result in varying levels of thermal conductivity. Applications include masonry cavity walls, timber frame walls, roof rafter insulation, loft and suspended floor insulation.
[plus points]
Can include around 23% of secondary industrial waste
Some brands include recycled mineral wool
Reusable if in a suitable condition
Some companies have initiated ‘take-back’ schemes
Recyclable
Inherently non-combustible and resistant to rot
A formaldehyde-free binder is available in some brands
[minus points]
Quarrying of material can result in land-degradation
Production emissions include carbon monoxide, formaldehyde and phenol. The release of these emissions is reduced through use of an afterburner. UK emissions are within legally defined limits
Though mineral wool is no longer classified as a skin irritant, exposure can cause temporary irritation
Thermal conductivity can be increased by either compaction or wetting

Thermal conductivity: Typical: 0.031 – 0.040 W/m°K
Density: Typical density: 24 - 40 kg/m3
Embodied energy cradle to gate:
Various figures:
- 16.8 MJ/kg (cradle to grave)
- 15.7 MJ/kg
- 22.4 MJ/kg (Flumroc AG, Switzerland)

 

[Penners]

Sheeps' wool....Hygroscopic – provides a degree of humidity control

Is that really a desirable characteristic in an insulation product? Presumably a hygroscopic material will continue to absorb atmospheric moisture until it's at equilibrium with the ambient air - and that could be a considerable amount of wet.

I'm not sure that I'd want damp insulation lying in my attic.

Or am I above my scientific pay-grade again?

 

[Flyfisher]

I also have some doubts about that, and the other "plus" point: Can absorb moisture without loss of thermal efficiency

Damp insulation in a wooden structure such as an attic or within timber frame walls doesn't seem like a good idea to me. Not that I'd claim any particular experise, just that it doesn't 'feel' right.

 

[El Greyo]

OK thanks, I'm learning stuff. I think.

To be honest, as thermafleece is so expensive, I'd only really consider it if it had some magic property that was significantly more beneficial for the house than the other options. It doesn't appear to be the case. Thanks for your time.

But on another tack: nice cottage don't you think?

 

[Penners]

nice cottage don't you think?

Oh yes - lovely!

 

[biffvernon]

The hygroscopic properties of wool are a Good Thing in an old building with 'breathable' construction. It doesn't get damp, like a pile of salt, but rather acts as a buffer in the water transfers.

Sheep on hillsides are pretty, and the OP clearly appreciates prettiness or he would not live in such a pretty house. Yes, it's expensive. So is a pretty house.

To say that it's production is not sustainable is nonsense. It is essentially a by-product of the sheep meat industry, would otherwise be wasted (folks don't use as many wool carpets and clothes as they used to) and the relationships between ewes and rams leads to a never-ending supply of replacement production units bouncing about come springtime.

 

[Flyfisher]

To say that it's production is not sustainable is nonsense.

That's not really what I said was it?

I'd say that anything with such a limited supply is not really a good candidate for being truly sustainable.
Meaning that, because of it's limited quantities and exhorbitant price, it's not a particularly good global solution. Thus, the few who can afford it may bask in the glow of their sustainable insulation while the rest of us have to make do with something less expensive and more widely available.

Similar, in many respects, to lower yielding, more expensive, organic produce. Wonderful for the few who can afford it, undoubtedly more 'natural', but not a practical way of feeding the world.

Hence my other point: Another example of 'green living' being a rather elitist activity perhaps?

 

[biffvernon]

Why say 'sustainable' when your really mean 'expandable at a low price'?

 

[Penners]

The hygroscopic properties of wool are a Good Thing in an old building with 'breathable' construction. It doesn't get damp, like a pile of salt, but rather acts as a buffer in the water transfers.

With apologies for my ignorance, I don't really understand the phrase "acts as a buffer in the water transfers".

Surely the word "hygroscopic" means "likes to absorb water". How can wool absorb water without becoming damp or even wet?

 

[Lime]

More to the point, is it a good idea to have a material next to timber that holds moisture?

The arguments used to support wool being used as loft insulation rely on added chemicals to act as a fire retardant, to stop rot and to prevent infestation.
What strange "green" credentials.

 

[biffvernon]

Ok think bathrooms. The mirror is not at all hygroscopic. When you shower and the humidity increases to 100% drops of water condense onto the mirror misting it up. Later, when you've opened the window and the humidity drops, the mirror's surface dries and the mist clears. There was a sharp spike in wetness, though it did not actually store very much water. It didn't matter; it was only a mirror. But some things don't fare so well on wetting and drying. Now think of your towel. It is hygroscopic. Apply it to your wet torso and it wicks the the water away, storing it harmlessly until hung up to dry. It is acting as a buffer, temporarily taking care of a large volume of excess water.

Sheep's wool insulation acts more like a towel than a mirror. In humid conditions it absorbs water, stopping more vulnerable materials from getting wet. When humidity drops it releases the water harmlessly.

And Lime, the moisture will preferentially be absorbed into the wool keeping the neighbouring wood, which is less hygroscopic over short time scales, drier. Wool does not burn easily and is not classed as a fire hazard. Thermofleece is, it believe, treated with borax. This is a salt that is not a hazard to humans but stops moths eating it. It happens to also be a fire retardant but that's not the primary reason it is used here.

 

[Flyfisher]

Why say 'sustainable' when your really mean 'expandable at a low price'?

Because scalability is essential for practical solutions. We need sustainability for the masses, not the elite.