http://www.natural-building.co.uk/pavadentro_renovation.htm

Anybody have any experience with this stuff? It seems to answer the problem of interstitial condensation when internally insulating existing walls and does not result in the immediate loss of thermal mass attributed to lightweight materials.

And how does one paste a hyperlink....??

Thanks fostertom. Hyperlinked now.

The data for both materials is as follows:

hemcrete: u-value 0.36; density 1120kg/m3; can't find decrement delay (Limetec)
Pavadentro: u-value 0.042; density 180kg/m3; decrement delay 7.9 hours (NBT)

Now, hemcrete has significantly greater mass, so will presumably have a greater mass continuity with its background, assuming masonry construction; but is this significant in areal wor;d situation? A decrement delay of almost 8 hours for the pavadentro suggests a pretty good 'thermal mass effect'; but with a markedly better u-value. See the Viking house web site http://www.viking-house.ie/decrement-delay where identical buildings were constructed with two different insulators to the same u-value but with different densities. One house was insulated with fibreglass at 20kg/m3 and the other with cellulose at 70kg/m3. In response to a change in external temperature of 30 degrees, internal temperatures in the the cellulose house was 3 degrees, compared to 13 degrees in the fibreglass house. The densities of materials here were 20kg/m3 for the fibreglass and 70kg/m3 for the cellulose. Pavadentro, at 180kg, would presumably be better still.

The lining would be internally to solid - err, that is, two skin ashlar and rubble core - limestone wall.

The main attraction of Pavedentro for me is that it can be fixed to the existing wall without removing existing plaster (it is a listed building) and I could do it myself (I am more of perfectionist than the average tradesman). The bonus is that the balance between u-value, decrement delay and breathability looks good. I'd just like to know if anyone has used it.

I hadn't, in all honesty, even considered hemcrete/hemcoat. Have you used this in a historic building?

There seems to be an absolute dearth of research into the behaviour of traditional buildings to improved thermal insulation/air tightness, let alone different types of insulation. A possible PhD topic here!

Hi alant,

The question I woulad ask you is whether any 'dampness' is rising/penetrating damp which I would agree, may pose a risk to the material, or whether it is condensation that use of the material should address.

See discussions passim about whether there is such a thing as rising damp!

I think I might get some and fit it in one room to see what happens. I can also monitor for the supposed risk of condensation/mould that is supposed to occur in adjacent, uninsulated, rooms.

I've seen it for sale on a retail scale by natural building technologies and Mike Wye

Hi All

We used Softboard as Drylining but not the Pavadendro which has a membrane in the middle which is suppose to stop water vapour getting as far as the Cold Wall but there is a break in the Vapour Control layer where the boards meet, which is a bit like the foil-faced plasterboard.
I haven't seen any damp patches in the Softboard wall afterwards, we didn't rip it off the wall to see how it was working, but it seems to be working fine. I think that the Lime Hemp lacks a bit of U-value to prevent heatloss.
A French Drain around the house works well to prevent rising damp and to dry out the footings to reduce heatloss.
In cases where we have to dryline we built a 100mm stud wall lined with OSB and filled it with Pumped Cellulose which seems to be another option for breathable drylining.

Posted By: rogerwhitisn't (interstitial) condensation likely somewhere behind the cellulose, possibly on the original wall surface behind it

Is this not a potential problem for all internal insulation?

The pavadentro attempts to stop this by having a membrane in the middle, but what about the joins at the edge of the boards?

the Pavadendro and the '100mm stud wall lined with OSB and filled it with Pumped Cellulose' are attempting to solve the problem by being vapour open and hygroscopic? If any condensation does happen on the cold side, it will be absorbed by the hygroscopic material, and able to duffuse/permeate out to the room?

I'm very interested in this for the upper floor of my barn (using hemcrete downstairs as it is quite damp) - I emailed my local contact, but had no reply. I'm interested to find out just how easy it is to install, as I may have to DIY. Main issue is the fixings - my walls are rubble and lime, so fixing into them is difficult - or do the fixings just grip into the lime mortar layer?

Hi Roger whit

The OSB (taped) stops the 99% of the water vapour getting into the Cellulose, while the Hygroscopic properties of Cellulose allows the moisture that gets in, to disperse over a large surface area due to its vapour suction properties. The best materials that you can surround your timbers in your stud wall with are Hygroscopic ones because they keep your timbers dry and healthy.

Hi Tom

It not so important how breathable OSB is, only that is 10 times less breathable than the brick. Page 3-4 of this document http://www.viking-house.ie/downloads/Breathability%20in%20buildings%20NBT.pdf shows that regular bricks are 10 times more breathable than OSB, which is what we want here, letting moisture move towards the outside. But OSB is a lot more breathable than a lot of other materials on the list I will admit!
I was recommending SIGA tape, you would need an angle grinder to remove that if you put it in the wrong place.

I'd have thought so too.

hmm

i looked at http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=3255&page=1#Item_0

and used builddesk modeller. But it was lacking; apparently if you wait 2 weeks they will update it and add new types of insulation, ie hopefully hemp, cellulose, sheep's wool.

and had a look at http://www.l-e-s-s.co.uk/Guides/Physics/Psychrometrics.htm#17

and used dp calculator http://www.dpcalc.org/

I think you have to consider where the condensation will arise in your wall. My guess is if it's condensing then it's collecting, not flowing and potential problem. Yes if material absorbs the water then it should spread said water out and aid dispersal. I assume above methods are what BCO/ regs people use?

I understand you make the walls though, you should take one apart and see what's happening! Or fill it full of measuring devices!

can you show me where it says that? i think he recommends internal VCL (Intello mentioned) and then zone for services and then plasterboard. so you avoid piercing the membrane. Didn't see softboard mentioned? Yes I did see breathable ext waterproofer recommended, siloxane compound, ie something which reduces penetration but allows diffusion. I can't see myself painting anything on the outside of my walls! have you considered vcl in your wall system?

I left a Timber Frame wall unplastered for 2 years, when we dismantled it, it was dry as a bone and was in a wet area. I just know Joe Little quite well, his article mentioning drylining with PU will be on next months Construct Ireland, but we often talked about it. The only insulations that keep the wall moisture level are the natural insulations he says. Is there a breathable waterproofer that you can paint onto bricks?

and my last comment is why is fibreboard so expensive? 80mm is approx £30 /m2 +vat, 4 sheets of 18mm OSB is only £15 / m2 +vat. what's so special about fibreboard?