DJH:>>>>> "If you did want to do it, it would be quite possible to have a brick dwarf wall at the bottom, outside the EWI, and stand the cladding on that. Yes, it would need some sort of foundation."

ISTR one of the previous discussions of this topic, where someone (maybe even DJH?) mentioned their EWI layer continued down in XPS against the underground bit of the walls, down to the foundation. To protect that underground XPS EWI, they had clad it with paving slabs set on edge. The above-ground cladding then stood on the exposed top edge of the paving slabs.

That sounds like an appropriate solution where there is a minimalist underground masonry structure that both clads the underground EWI and supports the above-ground cladding.


Going back to the OP, if you are using wood fibre as EWI, it has a poor insulation value so you will need a big thickness of it. I don't see a problem with odd bits of timber or OSB projecting through that EWI to support the cladding, because their conductivity is not much worse than the woodfibre over that thickness.

You could have hangers sticking out at the eaves like FT mentioned, or/and projections to support a base rail per Jonti, or/and projections to support horizontal battens every metre up the wall, or/and many projections forming a Larsen truss, or even a continuous fin of OSB sticking out to be the web of a vertical I beam. The thermal bridging might not be much different than if you stuck fat steel screws through.

Posted By: WillInAberdeenThe above-ground cladding then stood on the exposed top edge of the paving slabs

I don't bother with protecting the u/g EWI, as it's up against Terram then v bio-unfriendly sharp clean stone french-drain fill in the trench. But if paving slabs on edge are used, what are they sitting on? If just on the trench bottom, because prob outboard of the strip found, that's prob OK for rough protection, but will surely settle - not good for supporting cladding. Widened strip found? OK, but cost on cost ...

Wood fibre insulation is still 3x better insulator than timber, and 1000x (or something) better than steel. All these kinds of bridging cantilevers or masonry corbels are much better left out, will have a disproportionate effect on degrading the overall performance of your expensive EWI, and fiddly and costly in themselves. People think long and hard about such cantilevering where abs necessary, to support door cills etc.

Hi, I built my brother's Timber Frame Passive House in 2005, it's externally insulated with 120mm of Gutex wood-fiber board. There was a drip of moisture getting in where the cill met the wall and its started to decay, it'll be replaced with EPS. I built my sisters timber frame house in 2003 and externally insulated it with 100mm EPS, there's been no issues with this. EPS is about 1/3 the price of Wood Fiber board, has similar breathability (Mns/gramme) and about half the embodied energy. You could cross batten it and use shorter fixings but double the amount!

Posted By: fostertomYou've come up with some interesting data VH - in
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16791&page=1#Item_22" rel="nofollow" >http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16791&page=1#Item_22
"the Embodied energy of foamed glass on the ICE Database was 2-3 times higher than EPS" and here
"EPS is about 1/3 the price of Wood Fiber board, has similar breathability (Mns/gramme) and about half the embodied energy".

By any chance, any pointers to data on the other eco-footprint aspects of EPS vs a) wood fibre and b) other plastic insulants - thinking of toxins (other than GHG), water consumption etc in manufacture/distribution, and in use?

This study covers some of it but only for eps, mineral wool and woodfibre - https://www.sciencedirect.com/science/article/pii/S1876610216307937 - according to this study eps demonstrates advantages in most areas, woodfibre wins on Co2.

Posted By: fostertomBy any chance, any pointers to data on the other eco-footprint aspects of EPS vs a) wood fibre and b) other plastic insulants - thinking of toxins (other than GHG), water consumption etc in manufacture/distribution, and in use?

I remember looking at it years ago on the ICE Database Tom, the production process requires a lot of heat, the wood's made into a pulp and the boards have to be dried, then there's the transport cost to Ireland, I haven't looked at Embodied Energy recently.
I remember my dad trying to burn some WF off-cuts in his stove, it put out the fire and stank the room.
The Wood fiber for the brothers house was €17k and the EPS for the sister's similarly sized house was €4/5k.
The breathability figures were from a Neil May publication.

Posted By: fostertomBeen searching for this kind of info, never found it. Spot on. Got any more?! Printed off, taking it to awake-in-the-night reading, much to carefully understand.

I spent a lot of time researching ewi several years ago, finally coming to the decision to use woodfibre over eps for my situation. I like to approach these things from a whole of life perspective and I used to be very good at keeping the info but unfortunately, I've moved computers and backups and then packed it all away in our storage unit while I build the house.

Luckily Google scholar seems to have remembered my interest and has thrown up this paper worthy of a read.

https://www.sheffield.ac.uk/polopoly_fs/1.363473!/file/beu_wp1_civil_final_report.pdf

I've just fitted 200mm (and 160mm) of woodfibre. It is _much_ more solid than EPS in terms of fixing things to it. Fischer do 50mm and 90mm spiral fixings which will take a fairly significant load:
https://www.fischer.co.uk/en-gb/products/fixation-on-etics-insulation/fixing-in-insulation-material/insulation-fixing-fid
The downloads link give load data, but only for 15 and 20kN EPS, not woodfibre.
Now it depends a lot what type of woodfibre. I reckon that Udi diffutherm will take 2-3 times the load of belthermo Ultra (which is much more fluffy) I have diffutherm over belthermo on one wall (200mm) and udispeed over belthermo on the other (160mm). So the substrate matters a lot. Belthermo probably has similar loading to EPS.

Actually I have spare FID50 fixings and offcuts of 80mm, 60mm, 40mm top boards and 120mm base boards and some XPS and EPS. I could do some pull-out tests.

It also takes normal (long) woodscrews pretty well for small loads - I used this to hold some edge/reveal boards in place whilst glue sets. important to use stainless so you don't get rusting eventually, if leaving screws in place.

You would need manufacturers advice, or some testing, fora ful rainscreen support deisng, but you could definitely make a pretty solid fixing of battens to the stronger woodfibre boards. And those are fixed through to the masonry with Ejot fixings. IIRC I added 2 tonnes of woodfibre boards to the walls. I expect this could work but I would be very wary of trying the same things with EPS.

It's a very nice material to work with, and you don't need to worry about leaving loads of bits of plastic in the environement, which is inevitable with EPS. Even if you cut boards with a hot-wire the fixing drilling still leaves a lot of bobbles.

It does need to be 10% fatter for same U-value, but on the other hand you get massively improved decerment delay due to significant thermal mass in the boards. It is significantly more expensive at least at the moment as it's relatively uncommon. And as Viking points out, if you don't get your windowcill detailing right you'll regret it in a few years time. But it's not that hard to get right. Acoustically it's much better and it'll be easy to dispose of at end of life. Maybe the world will have proper EPS disposal in 40 years time (all just gets melted back down to a drum of goop?) but at the moment it's a load more plastic in landfill.

I'll tell you in 30 years how the longevity thing has gone i can report that it's been nice and toasty and windtight over this winter. Not quite passivehouse levels in that some heat has been needed when the sun doesn't shine. But heat loss must be at least halved since last year (may drop to 17 (from 18-19) after a cold night, not 14 like it used to). And the house isn't finished yet (floor uninsulated, except for perimeter on 3 sides. half the skeilings and one bathroom wall still to do..

Have you all used a circular saw on woodfibre boards?!
It isn't a pretty sight. Very fluffy.

That's true Tom, but nearly all the installs I see are also using mechancial fixings too (and making a right mess - most installers use a saw not a hot-wire too).

Jfb - yes you'll generate lots of wood-fluff cutting boards but the point is that it doesn't matter - it's just wood not plastic. It goes into the soil, or blows away or gets collected and composted or used to start the stove. Scaled up to millions of EWi installs I think this is actually quite a big deal.

Posted By: fostertom

Posted By: wookeynearly all the installs I see are also using mechancial fixings too

Why is that - any idea?

IMO historical baggage.
Over here mechanical fixings are recommended unless Ytong blocks are used where it is said that they are not needed. What is different about Ytong block in this respect is not mentioned however when I have tried the usual plastic fixings in the blocks they have just pulled out with very little effort.

Certainly Parex, always subject to soundness of the extg substrate. i.e. the adhesive does the job fine, without mech fixings, as long as the adhesive doesn't pull the extg paint off the wall, or pull chunks of the extg render off.
https://www.parex.co.uk/GetFile.ashx?file_id=801
The rep visits site, inspects the substrate, and advises EWI products accordingly (that is, adhesives, finishes, accessories - the EPS insulation itself is bought separately from insulation suppliers).

"Why do Parex only require adhesive to bond the EPS insulation to the substrate?
Adhesive application of EPS* insulation is by far the most suitable way of fixing the insulation boards to either masonry, concrete or suitable render board substrates. The adhesive performs significantly better than mechanical only applications and has been proven to be a far superior fixing application on numerous occasions under test conditions and when realworld severe wind loading weather events have occurred.
Because of this reason Parex does not use or recommend mechanical only fixing applications and this is also not the recommended guidance under ETAG004."

"When do Parex require the addition of mechanical fixings?
Mechanical anchoring is always required in addition to an adhesive layer for surfaces unsuitable for bonding only applications, such as rendered substrates, painted surfaces or water resistive barriers. Always consult Parex for technical advice and a project specific specification.
Due to the make-up of some types of insulation, mechanical anchoring is always required as an addition to the adhesive. This generally applies when using suitable external façade insulations such as Phenolic, Mineral Wool and some PIR boards."

"Can I just use mechanical fasteners and no adhesive?
No."