No: I don't think their proposal is very good.

Wood-based products are not good insulants. "Real" insulation materials are much better. I accept you can render over the wood-based stuff, but putting mesh over modern insulation boards is not (I believe) that difficult.

Hollow clay tile is great if you just build single skin and then render directly to both sides. Unfortunately, to get a low enough u value for the UK (rather than for the Med), you will need to put more insulation on, ideally on the outside, as the company you mentioned suggests. However, if you're going to do that, why pay extra for a material that combines structural properties with insulation (and hence isn't very good at either)? Why not get a cheap structural material, such asthe cheapest 150mm blocks you can buy (these would also have more heat capacity), and then fit phenolic or PIR boards to the outside. This will be thinner, warmer, and (I predict, although I do not know the costs of your proposal) cheaper.

Thanks chaps,

As expected some high quality feedback, unfortunately confirming my concerns.

Looks like plaster on dense block, 150 full mineral fibre cavity, lightweighgt block, 50-70 EPS insulation with render on mesh for eg. would be much cheaper, better/ equal performing albeit at a higher impact, although at the mo' they're imported from Germany, so careful choice of local block supplier could mitigate the difference.

Also have heard suggestion of solid masonary w/ external insulation on this site... (I suppose: plaster-215 light block-120-150 Rigid PU insulation-polymer render on mesh...?) ...thoughts gentlemen/ladies...?

J

EDIT

Thought I'd better amend "thoughts gentlemen" to "gentlemen / ladies".

J

As I understand it, one of the reasons NBT advocate this way of building is the vapour openness and hygroscopicity of the blocks and the wood fibre insulation, together with the recommended lime mortars and plasters.

The idea is that these features will reduce the likelihood of interior humidity problems and also of any problems from interstitial condensation and protect the structural integrity of the wall.

An important point is that all the elements of the build are similar in these respects, and so support each other.

Some details in this document

http://www.naturalinsulation.co.uk/cms_items/20060607164406.pdf

eg

“When a render goes onto a capillary open material such as soft brickwork, and water for some reason penetrates that render, the soft brickwork will diffuse the water and relieve the pressure on the render, ensuring that there is no frost damage, or separation of render from substrate. When a render goes onto dense concrete, or plywood, or polystyrene, this is not the case, and the render is more vulnerable if there are any cracks in the surface, as the amount of water it has to deal with is far greater. “

“The hygroscopicity of a material may also help to relieve pressure on renders, as
many are vapour open but capillary closed. Mineral renders are hygroscopic and this means that they will absorb moisture hygroscopically when relative humidity is high outside. This could increase the chance of moulds on the render surfaces. However if the substrate is also hygroscopic (as in the case of woodfibre boards as an external insulation system) this risk will be reduced.�

“The web site www.dimagb.de is full of case studies from Germany, Switzerland and Scandinavia illustrating the under-performance and health problems of External Wall Insulation systems utilising polystyrene. The performance of many of the buildings is usually at least 30% worse than the designed (theoretical) thermal performance. This is due to several factors including bad application (incomplete insulation, cold bridging etc). However the main cause is identified as being due to the fact that the polystyrene and render systems are relatively vapour impermeable and thus increase the amount of moisture in the original solid masonry. This is particularly critical in the ground floors of solid wall buildings without damp proof courses. This moisture is also trapped because the effect of the sun and wind in drying the outer face of the masonry is also eliminated. The consequence is that the thermal resistance of the masonry reduces, giving an overall reduction in the wall U value. Combined as EWI often is, with new windows and draught
proofing, there is the consequence that moulds also grow on the inside of the now damp wall.�

I’m wondering if anyone has any opinions or counter experience?

Peter

Or rather, I do not see how a reduction in resistance from the masonry being damp could be very significant if the insulation is not damp.

Breathability is a term which promotes moisture within the wall/roof fabric and reduces the thermal performance of a building envelope.


Steve

In a sealed building envelope the wall/roof fabric remains warm and dry similar to a moonbase specification. Moisture does not penetrate the wall/roof.

This dramatically multiples the thermal performance of the envelope.

Steve

Peter

We will have to move to sealed envelopes because this is the only way to preserve building fabric. We already do sealed thermal cladding on buildings and it is no problem to keep watertight. The principle of moonbase is living in a controlled atmosphere with superior air quality and zero moisture penetration into the envelope fabric. A good example of sealed building would be an underground house or earth covered house were the walls and roof have to be sealed against moisture. Some people like living in a sealed atmosphere it is certainly more energy efficient and that is what we are all about are we not.

Steve

So.... how does this relate to Ziegel / thermoplan or other monolithic / solid mehtods of construction...?

Steve's external selaing of buildings is a bit of a hot topic so I think it deserves definitive thread:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1104

...see you all there...

... back to the subject then....

J

<blockquote><cite>Posted By: James Norton</cite>So.... how does this relate to Ziegel / thermoplan or other monolithic / solid mehtods of construction...?

As far as I understand, one of the main points about the Ziegel blocks is that they are completely vapour open. Also the lime/earth plasters and the compressed wood insulation.
So if you use the system as it is recommended, then internal humidity in the house will be soaked up by the walls and transported to the outside.
Likewise, if the walls get an external soaking, the water will not be concentrated in one element by other waterproof elements, the whole wall will be wetted, but will then dry out. This is the way in which traditional buildings made from timber and lime plaster work is it not? That is why a timber frame building with lime plaster infill panels can last for centuries in the damp UK climate.
There are also positive effects on internal air quality claimed.
The whole thing depend upon the various elements of the wall being similar in Hygroscopicity and vapour openness ,U values etc. If you put in a synthetic element like plastic insulation, this will cause problems, as explained in the text I quoted.
It is all explained in the link I gave above. The paper is a bit intimidating at first glance, but I found it very interesting and persuasive upon reading thoroughly.

However this is all theory, it is interesting to read Gervase's practical experience. For example, one reason I am interested is that it is claimed these blocks are easier to build with than ordinary bricks. I had considered, as an amateur builder, having a bash myself, but the experience of actual users is not sounding encouraging.

The document I linked to above is also interesting to me because it seems to be a fundamentally different way of building (tho traditional?), a different 'philosophy' of building from normal in the UK. It seems to address a knot of issues that is arising as a result of our response to the energy crisis and buildings - modern materials/airtightness/insulation/air quality. These are all bound together and I think we need to consider them as a whole.

Peter

Gervase,
Would it be reasonable to say that the problems you describe are down to this being a new way of doing things. So you are comparing an unfamiliar way with a familiar way, and inevitably finding problems. If builders and architects were familiar with this way of making walls, it may be that the claims about speed, and therefore lower cost, might be born out?

Everyone,
My own worry is the idea that the walls will get wet, but we need to design it in such a way that they do not get wet all the way through. How do we do that for sure? I know that NBT recommend over-hanging roofs, and I think that somewhere I saw pictures of some kind of membrane installed outside the blocks.

Almost everyone here seems to agree that we will need to make large changes to the manner of building if we are to respond appropriately to the energy crisis and global warming. So whatever we do is going to be different, and untested at the start. So people like me, private householders wanting to build green, are going to be left with this dilemma - "how can I be sure that this will not be a disaster?"

This method of building appears to have a successful record of use in other wet and cold climates, and appears to be based on the time honoured way of doing things

Peter

Chris,
That is interesting, of course you would not be getting the breathability.

Do you have any figures for U value and cost for these two ways of doing it?

Peter

Chris,

That's a lovely dream mate, (God we're sad...! )

Has anyone come across the Ibstock earth block?

J

Neil,

Not sure I get the Durisol thing, is it a sort of eco becoform, ie permanent concrete formwork...?

J

Neil,

Came across Durisol at Ecobulid interested for myself but a client has also expressed an interest, any look with it yet...?

J