An alternative to thermafleece?

[Lime]

I have a reply to my questions from Second Nature. They replied within 2 hours.

Good Morning Ian,

Thanks for your email.There are some interesting clauses in BBA certificates, but, unfortunately, the BBA does not consider 'alternative' constructions like yours. Yours is a fairly standard refurb application where account has to be taken of the nature of the existing system and the age of the components where moisture accessability has been provided over many years. As you rightly say to reduce that facility would be to affect the moisture content levels of the fabric and lead to possible deterioration.I am sure that the system as you envisage, ie without a' control' layer will perform as intended and that there is sufficient breathability to accomodate moisture migration out of the system. The ventilation space you intent to use above the insulation and beneath the breather membrane will ensure that adequate air movement takes place and so minimise any condensation risk.

Ok. He's saying that he thinks you can get away with it.
I could accept that.

But then he says this:

The BBA Certification is sometimes contradictory as, no doubt, the certificate for the breather membrane will indicate that it can be used without a 50mm ventilation cavity.(eg Tyvek Supro, Klober Permo Forte, etc.) Many projects like yours have been successfully completed without any air gaps and give no cause for concern. I hope this is of help. Best regards

Paul Pickett
Technical Consultant
Second Nature UK Ltd

That comment alerted me so I had a look and found this:

5.2 The product may be treated as a vapour
permeable underlay when considering ventilation
of the roof space, and may be laid directly over
the insulation without ventilated air space
provided the passage of moisture through the rest
of the roof structure is controlled, and the system is
convection tight.

I call that bending the truth and I'm being polite.

 

[biffvernon]

The use of a VB on the warm side has nothing to do with a building being breathable or not.

Oh yes it does. Once you've put a vapour barrier in it ceases to be a 'breathing' building.

Paul Pickett is right.

 

[NT]

The use of a VB on the warm side has nothing to do with a building being breathable or not.

Oh yes it does. Once you've put a vapour barrier in it ceases to be a 'breathing' building.

So walls can no longer evaporate their damp? Floors ditto? A VB in the roof insulation has not a lot to do with it. You've still got your eaves ventilation, which is how any small amount of damp getting into the loft from lower floors gets out.

And the sheep wool would still be breathable with the permeable membrane above. All the warm side VB stops is condensation in the wool, a sure recipe for rot.


NT

 

[biffvernon]

I give up :roll:

 

[sarahj]

Hi,

my partner says that b & q are selling a loft insulation made of recycled plastic bottles - do you think this is a good 'green' alternative?

Sarah

 

[skier-hughes]

fleece tops and jackets have been made out of this for quite some time adn they are nice and warm, so if the price isn't too expensive I'd have thought it'd be green.

 

[Ian Bond]

My 'loft' has always been a habitable room. Unfortunately inadvisable 'improvements' have already been made over the years, which I am now reversing.

The eaves were torched with lime mortar, but gaps still let the wind in. So someone had fitted polythene sheets to block the eaves.

Rockwool has been stuffed into the rafter cavities, completely filling them. This was done when the stone tiles were turned in the 1980s. A non breathing roofing felt was also fitted. This has rotted away in places, such as at chimney abutments with defective soakers.

Two layers of plasterboard fixed over the lath and plaster ceiling and walls to the eaves, and covered with plastic emulsion paint.

I am restoring the lath and plaster ceiling and walls - no vapour barrier.

Sheepswool will be placed over the ceiling joists to the eaves, and behind the L&P walls. Care will be taken to NOT block ventilation at the eaves with insulation.

Sheepswool will be placed between the rafters , to a depth of 2 inches, allowing 1 1/2 inches space above.

A breather membrane will be fitted over the rafters, with adequate drape between to allow penetrating water to be channelled away safely, avoiding dumping water on the wall plate.

The tiles will be turned back to their correct face, and hung from oak battens with alloy pegs. Not nailed.

It makes perfect sense to me to take this approach, which closely follows the tried and tested traditional design, by providing adequate ventilation coupled with breathable materials.

See:
http://www.buildingconservation.com/articles/pdf_roofsbreathe/roofsbreathe.pdf

 

[Lime]

In your situation Ian Bond I would probably do exactly the same.
Compared to the almost blasphemous treatment previously meted out to your building's structure putting in a natural insulation while allowing for proper ventilation is almost saintly.
However I hope you understand my concern that this method (without a vapour membrane) is not used wholesale in older houses.
Inhabitants who regularly use portable gas heaters and hardly ever open windows or cook a lot with something boiling most of the time or perhaps shower regularly with little ventilation will have very humid conditions within their house.
A house without roof-tile insulation will be able to cope very well but as soon as insulation is fitted a large temperature gradient is created across the insulation. With high humidity within the house air escaping through the insulation (or around it) will condense out on any cool surface it meets. Any drying out is totally reliant on the weather and we all know we can't rely on that to be dry on dull damp Autumn/Winter days.
In such situations the reliance on the wool to properly deal with the moisture is expecting bit too much.
Damp will occur followed by rot of some sort or another.
What appears to be forgotten in most of these discussions is that good insulation and warm houses is a modern thing.
If we insist on living in the modern way (ie without wearing greatcoats indoors) sometimes we have to consider modern methods of combating the problems it creates.

 

[MdB]

IA house without roof-tile insulation will be able to cope very well but as soon as insulation is fitted a large temperature gradient is created across the insulation. With high humidity within the house air escaping through the insulation (or around it) will condense out on any cool surface it meets.

And the first cool surface will be the insulation. Moist air traveling through insulation from a hot side to a cold side will condense inside the insulation making it damp. Putting a VB on the cold side won't stop this but a VB on the warm side will. Obviously putting in a VB will stop the moisture in the room from going anywhere so the room will need more ventilation. i.e. there are downsides to both having a VB and not having a VB.

 

[Ian Bond]

Water vapour is more likely to pass *through* the insulation and condense on the underside of cold tiles (or roofing felt) on the cold side.

This happens in modern houses too, particularly where extra insulation has been added, making the roofspace above colder.

No one is suggesting wearing a coat indoors. Although there are good arguments for dressing appropriately in winter, rather than profligately burning fuel. It's a lifestyle choice that some can afford, but this is not the place for that argument.

The Thermafleece, if installed as recommended should reduce the risk of condensation without the need for a vapour barrier on the warm side. The breather membrane and ventilated rafter and batten cavity should see to this.

Of course, you would need to assess each building individually, consider its design and construction and choose an appropriate solution.

For modern, non-breathing buildings, it may be desirable to retrofit a vapour barrier. How effective it would be in practice is hard to say. Loft hatches, holes for pipework and cables penetrating ceilings? Perhaps it would reduce the passage of water vapour sufficiently. I am quite happy to accept that.

However, in a traditional building, with open fires, lime plaster, stone walls, direct to earth stone floors, lime mortar pointing and so on? I would rather not attempt to seal water vapour out of some places, with the risk of it being diverted and trapped elsewhere. The 'breathability' approach seems logical to me. Plus, trying to install an effective VB barrier retrospectively would be difficult, given the structure of the roof.

If the wool between the rafters does get wet, which I think is unlikely, the limewash on the lath and plaster ceiling should tell the tale. A problem may take longer to show through a VB and plasterboard.

 

[NT]

The place where water condenses out of the air is wherever conditions have gotten cold enough for condensation to occur. Since insulation of any sort insulates relatively well, and (gappy) tiles or slates very little, almost the entire thermal temp drop will be across the insulation itself. Thus if there is any condensing occurring, it will occur in the insulation. Insulation vulnerable to rot with no means to prevent this occurring is not a good choice.


NT

 

[biffvernon]

No...resist...I've already said I've given up.

 

[Nemesis]

This is the same insulation I recall someone saying would drip dangerous stuff down in the event of a fire...

Which wasn't exactly true now was it?

 

[Ian Bond]

The place where water condenses out of the air is wherever conditions have gotten cold enough for condensation to occur. Since insulation of any sort insulates relatively well, and (gappy) tiles or slates very little, almost the entire thermal temp drop will be across the insulation itself. Thus if there is any condensing occurring, it will occur in the insulation. Insulation vulnerable to rot with no means to prevent this occurring is not a good choice.


NT

The insulation will not be vulnerable to rot if it is installed correctly, and a vapour barrier on the warm side is not mandatory. The VB is not necessary in a traditional 'breathable' structure.

In a traditionally constructed building, that is well ventilated (sash windows, open fires) with a breathable fabric (lime renders, pointing etc) the volume of moisture reaching the roof will be moderated.

In a 'sealed' modern construction then perhaps more water vapour would reach the roof structure, and a VB would be useful. That has been acknowledged above, and is not in dispute.

The rockwool insulation that packed the rafters in my roofslope was dry, and there was no damage to the timbers. Despite there being no VB, and non-breathing roofing felt.

There were also water storage and central heating cisterns in the attic (now removed), and lime plastered walls had been covered with layers of wallpaper and coated with vinyl emulsion. Even though the breathability of the system had been compromised, condensation had not caused any problems in the roof.

I've now reversed all of the damaging modernization, and would have thought that the risk of condensation is now reduced.

If a problem does arise, the ceilng will become stained and I will know about it.

Vapour Barriers that reduce the breathability of the building envelope, and merely push any moisture elsewhere are not a good choice in historic or traditional buildings.

 

[NT]

The place where water condenses out of the air is wherever conditions have gotten cold enough for condensation to occur. Since insulation of any sort insulates relatively well, and (gappy) tiles or slates very little, almost the entire thermal temp drop will be across the insulation itself. Thus if there is any condensing occurring, it will occur in the insulation. Insulation vulnerable to rot with no means to prevent this occurring is not a good choice.


NT

The insulation will not be vulnerable to rot if it is installed correctly, and a vapour barrier on the warm side is not mandatory. The VB is not necessary in a traditional 'breathable' structure.

In a traditionally constructed building, that is well ventilated (sash windows, open fires) with a breathable fabric (lime renders, pointing etc) the volume of moisture reaching the roof will be moderated.

In a 'sealed' modern construction then perhaps more water vapour would reach the roof structure, and a VB would be useful. That has been acknowledged above, and is not in dispute.

It depends on the interior RH/temp, and that is determined by other factors than the building construction. Bedroom occupancy and occupants' (ventilation) habits make a lot of difference. It may work fine, but in all cases? no.


There is a difference from wall render here in that a roof insulation VB does not cause problems, whereas VBs on walls often do.


NT

 

[Ian Bond]

Who said in all cases? Not me. :wink:

You are of course absolutley right about the behaviour of the occupants being a major factor.

I still prefer to leave the VB out, and see how it goes, with my knowledge of this particular house and how it has performed in the past.

 

[AMc]

Hi,
my partner says that b & q are selling a loft insulation made of recycled plastic bottles - do you think this is a good 'green' alternative?
Sarah

http://www.eco-wool.co.uk/ Looks quite interesting.
Spotted this today at B&Q 150mm deep, 270mm wide and 5.3m long - £15 a roll. 2 for 1 at the moment. Much better value than lots of the mirror finished spaceblanket/multifoil things they had at £100+ a roll
Similar performance to fibreglass but no itching. 85% recycled plastic which is probably greener in your loft than in a landfill.

 

[biffvernon]

Anyone know what "Fire Test BS 5803-4 = Passed" means?

 

[Nemesis]

I feel the name is meant to mislead. Wool it ain't.

It's the same stuff as fleeces wot you wear are made from I presume. They melt into holes at the slightest spark. I assume this stuff has some retardent in it.

http://www.bsi-global.com/en/

 

[biffvernon]

They make a thing about it coming from recycled bottles so I guess it's hard to assume it comes from a sheep. You get glass wool, steel wool, cotton wool, Herdwick wool and now plastic bottle wool.