An alternative to thermafleece?

[Nemesis]

How 'green' do you feel glass fibre is Biff?

Overall - manufacture, use, disposal etc? And the 'breathability' of the material in a traditional building?

How many house fires are there I wonder where the house has been
'saved' by its use as insulation?

It's not as though Thermafleece is really very flammable, and it doesn't seem that it rains down nasty stuff in a fire as was claimed earlier in this thread.

 

[NT]

[quite]If you want insulation use an insulation material. If you want a fire proof barrier then use material that forms a fire proof barrier. There may be some circumstances when you want to do both these jobs in the same location, in which case a material that is both insulative and a fire proof barrier would be a suitable choice. But this thread did not start off with fire proofing as it's theme. [/quote]

You can always play with logic, but the fact that glass & mineral fibres sometimes act as firebreaks does improve occupant safety.

Lime-ash floors were sometimes used on the top floor and would have given good fire protection, suitable for thatched buildings.

What were those constructed on? A wood structure? Presumably the wood was only needed during settting time.

And the 'breathability' of the material in a traditional building?

Sheeps wool, glass fibre and mineral fibre are all very breathable. They're all open wool structures.

How many house fires are there I wonder where the house has been 'saved' by its use as insulation?

Thats one bit of data I doubt we have any way to find out unfortunately. ODPM's reports give a useful level of info, and quite a lot on smoke alarms, but basically nothing on that question. Turns out smoke alarms are very patchy when it comes to doing the job, but still well worth it. 80% of houses had smoke alarms in 2001 but a smoke alarm only alerted someone in 25.5% of fires. Still doubled survival chances though.


NT

 

[Nemesis]

I don't think that by the time a fire reached my loft I'd be too worried about a smoke alarm.

Reed usually, not wood. Lime ash.

Manufacture of glass fibre - energy used?

Green is a wide, wide remit.

 

[Penners]

How 'green' do you feel glass fibre is Biff?

Overall - manufacture, use, disposal etc? And the 'breathability' of the material in a traditional building?

I have no knowledge or expertise in this area (or any other!) but I would have thought that breathability was rather undesirable in an insulation material. Surely its primary job is to trap pockets of air, not let them pass through.

 

[Ian Bond]

Breathability in terms of letting water vapour pass through, so removing the need for a vapour barrier, as I understand it.

 

[Penners]

But doesn't allowing water vapour through also imply letting air through?

 

[biffvernon]

No.

The rate of air movement is many orders of magnitude different. Breathability is about molecules diffusing. Insulation is about stopping draughts. No connection at all. All fibrous insulations are very 'breathable'.

 

[Ian Bond]

ta for the explanation Biff.

The more I thought about it, the less I realised I understood...

 

[Penners]

Insulation is about stopping draughts.

Surely that's an oversimplification. Draughts imply convection. What about the other methods of heat movement - conduction and radiation?

Here'san interesting explanation of the principles of insulation, from some people who should know.

 

[Lime]

Insulation is about stopping draughts.

Surely that's an oversimplification. Draughts imply convection. What about the other methods of heat movement - conduction and radiation?

Here'san interesting explanation of the principles of insulation, from some people who should know.

Yes you are right.
A draught is a form of heat transfer that wool-like materials are not that good at stopping.
when a wool-like insulation is laid on a plaster ceiling (for instance) the ceiling itself fulfils the function of draught-proofing whereas the insulation reduces radiation and conduction from the ceiling to the air above the insulation.
As a result all three forms of heat loss are reduced.

However I think there is further confusion about just what breathability means.
It is possible to see it meaning two different things, namely the passage of water vapour through the insulation from one side to the other and/or the ability of the insulation material to absorb, hold and release moisture.

While water vapour freely travels through wool-like materials such as Thermafleece or fibreglass it does not pass through Kingspan for example.
Whereas water vapour is absorbed by Thermafleece but is not absorbed by fibreglass or Kingspan.

 

[Ian Bond]

So if I use wool insulation between my rafters, I won't need a vapour barrier between the insulation and the lath and plaster ceiling.

Moisture passing through the ceiling can also pass through the wool and get out through the roof.

I'd also not need to provide 2 inch deep ventilation gap between the top of the insulation and the stone tiles, as there would be no danger of moisture building up in the roof timbers. If I use a 'breather' membrane, I'd just need to leave sufficient space above the insulation to allow it the membrane to drape, and guide any penetrating rain away from the rafters.

If the wool does get wet, it can dry out, but will continue to insulate well in the meantime (according to Thermafleece).

At some point I am going to have to re-lay my stone roof tiles, and at the moment Thermafleece is the firm favourite solution for between-rafter insulation.

Sheeps wool insulation seems to me to fit in with the breathability philosophy in the same way as lime renders and pointing, and as opposed to cement renders, plastic DPCs and so on.

 

[Lime]

So if I use wool insulation between my rafters, I won't need a vapour barrier between the insulation and the lath and plaster ceiling.
Moisture passing through the ceiling can also pass through the wool and get out through the roof.

Yes, it will pass through.

I'd also not need to provide 2 inch deep ventilation gap between the top of the insulation and the stone tiles, as there would be no danger of moisture building up in the roof timbers.

No.
The open ventilation gap is required to allow any moisture to escape from the insulation and also to remove by convection any condensation that may occur on the underside of the stone.
Any insulation held directly against the stone (even with sag) would create trapped air that, when moist, would condense out onto the colder stone in unfavourable weather conditions.
The condensation would then pool and run down the timbers.
The air gap is essential IMO.

 

[biffvernon]

Surely that's an oversimplification. Draughts imply convection. What about the other methods of heat movement - conduction and radiation?

Simplification, for sure. A fibrous insulation, glass wool / rock wool /sheep wool etc., does stop draughts very effectively (except round the edges if not tightly fitted). The air trapped amongst the fibres does not move so the very low thermal conductivity of air can have its effect without being spoilt by mass transfer of warm air.

'Breathability' is a rather non-scientific idea but relates to the material's resistance to the diffusion of water vapour molecules. There is a scientific measure, but it is too early on a Sunday morning to get one's head round it as it is seriously complicated.

Suffice to say that woolly insulations are very 'breathable', foam insulations less so, and sheets of metal hardly at all.

The ability of natural fibres, like Thermafleece and the hemp based insulations, to absorb moisture at times of high humidity and release it during drier conditions, thus regulating humidity, is something else and is best not confused with 'breathability'.

 

[Penners]

Suffice to say that woolly insulations are very 'breathable', foam insulations less so, and sheets of metal hardly at all.

Phew - thank goodness I decided against insulating my loft with sheet steel.

it is too early on a Sunday morning to get one's head round it as it is seriously complicated.

Amen to that.

 

[Lime]

Phew - thank goodness I decided against insulating my loft with sheet steel.

Well, that all depends on how strong your draughts are.
However getting it through the loft hatch would be a problem.

 

[JMartin]

We have recently installed this insulation coupled with some limited draught proofing and have experienced a massive improvement in comfort in the house. Having said that we went from virtually no insulation to 80mm of insulation. We're saving up for the rest. :roll:

Can't comment on it's technical properties though. We chose it because we believed it was the right material for a damp house. It made sense to us to install an organic material which would be more likely to allow the house to breathe.

 

[chuckey]

Ewe lot are talking a load of baa locks.
Frank

 

[NT]

So if I use wool insulation between my rafters, I won't need a vapour barrier between the insulation and the lath and plaster ceiling.

Moisture passing through the ceiling can also pass through the wool and get out through the roof.

I'd also not need to provide 2 inch deep ventilation gap between the top of the insulation and the stone tiles, as there would be no danger of moisture building up in the roof timbers. If I use a 'breather' membrane, I'd just need to leave sufficient space above the insulation to allow it the membrane to drape, and guide any penetrating rain away from the rafters.

If the wool does get wet, it can dry out, but will continue to insulate well in the meantime (according to Thermafleece).

The absorbency of sheeps wool does not mean you can do away with measures to prevent regular condensation wetting. If its wet it will soon rot away, and breed lots of horribilities in the process.

At some point I am going to have to re-lay my stone roof tiles, and at the moment Thermafleece is the firm favourite solution for between-rafter insulation.

Sheeps wool insulation seems to me to fit in with the breathability philosophy in the same way as lime renders and pointing, and as opposed to cement renders, plastic DPCs and so on.

If it were me I'd not use it in a situation where its likely to get wet. I dont know what your roof is like, but many old roofs leak like a sieve, and thats not a place to put water vulnerable products.

All non-rigid insulation products are breathable (except bubble wrap & foil).


NT

 

[Ian Bond]

The reason I looked at Thermafleece was that I was lead to believe by Second Nature that it was 'naturally breathable' and would allow water vapour to pass through, avoiding damaging build-ups of moisture.

I didn't want to use rigid urethane insulation, as this seems to be contrary to the 'breathability' philosophy applied elsewhere. I would much rather use materials and techniques that allow moisture to get out, rather than trying to seal it out in the first place.

I had detailed discussions with the technical people at Second Nature, and was told that I could use Thermafleece between the rafters safely with *just* a 10 to 15 mm gap above to allow the breather membrane to drape correctly.

There's no space for a 2 inch air gap, as the rafters are not deep enough, and I cannot raise the roof level.

Are we saying that vapour barriers and rigid urethane insulation boards are the way to go, rather than wool and lath and plaster?

The roof has survived well (despite the odd leak) for 170 years without insulation or membranes, so I don't want to do something that will lead to rot!!!

Anyway, thanks for the warning NT, I would rather be made to rethink at the design stage than when it's too late.

 

[Ian Bond]

Just to comment on your last point NT:

The concern I had with non-rigid insulation was, that if it is wet with a good breeze across it, that the insulating properties would be considerably reduced. This is something that the sheepswool claimed to avoid.

I do not like the sound of damp anything in permanent contact with roof timbers!

Ian