I'm trying to convince my mate to go down the single skin route on his double storey extension. He won't have any of it though.

He wants a cavity wall with 50mm insulation or whatever the current spec is...

I like the first one on your list, it contains recycled aggregate, does not crack or need expensive plaster unlike aerated blocks which should only be used for other people

Ive used fibrolite they are good and not to heavy.
I believe they re made out of aireated clay so dont have the the same ecocredentals as those with recycled content. Might be worth a closer look at claimed embodied energy etc. They're a good half way house and seem stable over time. They also give a very good plaster key.
Fenlite on it side sounds good maybe with a weak lime/cement mortar ?? Youll use a lot off muck though and therefore potentially a lot of cement
a 215 fenlites will be hard on the brickys

Is 150mm ok for two storey? Maybe with a ring beam at first floor or something? Let us know if you find out, good for future reference!

Many thanks to all who have responded - this forum never ceases to impress.

I'm going to propose to my structural engineer that we use one of the more robust blocks listed above, laid flat, and hope that he is happy to support that decision. I'm reasonably indifferent between Fenlite, Hemelite or one of the Plasmor blocks (is it just me or does everyone get annoyed by too much choice?! I may as well as well flip a coin because I'm done trying to analyse them any further).

James, you suggested looking at a 150mm block but the house is two (and a half) stories.

And Mackers, you too asked whether 150mm would be OK. On a quick peruse of regs (always a fun way to spend half an hour) Part A, Section 2C, Table 3, suggests that 190mm is the minimum wall thickness permitted for single skin.

What I haven't managed to find is some firm guidance on block weight. If we end up laying them flat this shouldn't be an issue (since we can use a 100mm block), but for future reference does anyone know whether a 20Kg upper limit is written into regs or whether this is just a 'common courtesy' guideline designed to preserve your brickies backs?!

Thanks again.

Block weight is important. If your brickie is going to lay at max speed, being able to pick a block in one hand is important.

Try picking a 20kg block in one hand, then accurately putting it down at chest height. Then try doing it 200 times!

A heavier block is slower to lay and harder to lay accurately.

Laying the aglite blocks was just doable. When we were using heavier blocks there was a marked slowdown.

Bruno I'd suggest you fully read this thread from an Irish forum on EWI before deciding to go that route on a new build.

http://www.boards.ie/vbulletin/showthread.php?t=2056166150

I think the "recycled" filler is just crushed construction waste from demolition projects etc.

The bits of plastic and aluminium that get in there are probably from the cans and bottles of pop the construction workers are drinking from before chucking them in the rubble pile (pretty common practice).

I don't think they are buying bales of plastic bottles and coke cans as filler (as you say that would be stupid), just that, given the nature of the filler, you get odd objects every now and again. In around 2k of blocks we got 3 or 4 "funnies" with cans or similar.

There's a fair bit of crushed glass in the blocks (they twinkle in the sunlight) and you could argue that glass should be recycled, but unless a glass bottle is washed and reused, simply remelting the glass is nearly as bad as making new glass so using it a aggregate isn't a bad option.

The main effect of using the recycled stuff is to make a "softer" block than a straight aggregate block. If you hit them with a hammer they dent rather than crack. Drilling for fixings is a doddle, and the fixings stick well (we used window screws alot)

Posted By: jamesingramit's got some loading error

If you have any interest in EWI then I would suggest that you make the effort! Try a different browser if it's not loading for you, the link works fine for me in both Chrome and IE11.

There are opposing views expressed on the thread so its really up to you what you take from it.

As for my point of view, I too once shared Bruno's enthusiasm for using block and EWI and considered it for my new build but the more I looked at it the less enthusiastic I became. Lots of links on that thread to German and Canadian references.

I know there are those here who dismiss my concerns and say that with proper detailing these can all be overcome but I am not convinced.

Granted my closest experiences are of EWI'd timber framed houses not block built but many of the issues are the same.

In Ireland I lived next door to a show house for an Austrian house builder and so could see at close quarters how it performed over approx. 7 years. It was constructed from factory finished panels with the windows and doors fitted and the panels rendered with perfect details in the factory. Before the house was 5 years old gaps had opened up between all the frames and the render system allowing moisture ingress.

Here in Sweden I live close to a similarly constructed house which was less than 5 years old when moisture problems occurred and the house had its EWI stripped and replaced with a ventilated timber clad facade.

One of the guys (sas) on the tread I linked to above has built a top spec. 2 storey block and EWI passive house. He employed the very best guys he could find to install the EWI and render system which cost him €42,000 for a 300m² house. So you can appreciate that the detailing is impeccable, I have spoken to him several times and he now actively discourages others from using EWI on new builds.

As Tony often says we should be designing houses for at least a 100 year lifespan and with the Germans estimating that the lifespan of EWI is about 30 years it just doesn't cut it.

I'd be interested in other views on that thread. Was quite an eye opener. The stuff about damaging the wall rang home with me, with a young boy... I fully hope he will learn how to control a football by whacking it against a wall, just like I did (a bit ;) ).

Chris, interesting to hear that "sas" is now against block+EWI after being positive in that thread.

Thanks all.

Chris, you make a compelling case, and I think it's time for me to reassess. I guess the EWI enthusiasts would have better answers than I do but I think I'll go straight to the people who should know and ask Sto (my preferred supplier - absolutely no affiliation). When I asked them previously about failures they claimed theirs never fail, which I was understandably sceptical about - so I asked several installers/applicators, who all said the same: that the jobs they get called back on are never a Sto system.

I was (perhaps incorrectly) under the impression that something like a third (total guess, in honesty) of all German new builds are EWI. Would the Germans really put up with something that performed so poorly? And if theirs don't perform poorly, is it due to more experience, or a kinder climate? (I'm in a sheltered spot in Essex that on average is one of the driest part of the UK, so I'd be surprised if the average German climate is any milder). Sto alone claim to have installed over 500 million sq m of EWI and render - call it two million whole houses' worth for the sake of argument. On that basis, even if I find a few stories of Sto failures (so far I've found none) then statistically we're arguably looking no worse than cavity walls.

In the link that Chris kindly posted, the most common problem cited seemed to be the ever popular 'poor workmanship' which is always a tricky debate because of course any build type will suffer if correctly qualified and supervised contractors aren't used; though almost certainly this risk is worsened by any system which is deemed to be non-standard - and I have to accept that unfortunately masonry + EWI fits into this category.

Another problem cited was potential damage from 'kicking a football against the wall' etc. There are numerous clips on You Tube which seem to suggest that the levels of impact resistance achieved are easily good enough for this not to be a problem.

Lastly, and most worryingly by far IMHO, the assertion that wind loads could cause fixings to cut through the EPS. But the BBA cert does not suggest this is a likely problem and suggests that 'at least 30 years' can be expected and '60 years' with the simple inclusion of an additional mesh to prevent this problem.

If I can get 60 years then it's going to see me out - and let's not forget that doesn't mean the building is shot in 60 years - it just means the prevailing owner will have to shell out for new EWI - which one imagines by then will be somewhat superior.

The above is my guess at what the professionals will say - but I will report back with their answers in due course.

For me, I'm 50/50 on whether to persevere or throw in the towel and go for wide cavity (whereupon others will no doubt start telling me horror stories about the dangers of going down that route)!

Hairydude,

That is a lot of mass to reheat if you get a broken window in the middle of winter.

@Bruno I am glad at least that you are going into it with your eyes open.

FWIW I used STO render on calcium silicate boards for the ventilated facade on our TF build and am delighted with the result.

If you are going to go with EWI I think it really helps that you are going with one of the class leading solutions. I have to say I really cringe when I see people mention that they will DIY their EWI, I really think it is a job that should be left only to the professionals.

Does the STO system use fireproof insulation?

The point about blue tits and woodpeckers causing damage was a new one on me, but appears to be well documented in Germany. Does the STO system use a minimum of 7mm of render as recommended by the Germans?

I readily admit that my direct experiences of EWI failure both involve TF houses. But to my eye at least the same problem of gaps opening up around the window and door frames after 4-5 years could also easily happen with a block house.

The situation here in Sweden is that there has been a number of problems with this type of facade with some high profile court cases and media attention. The result is that every such house has been tarred with the same brush and you couldn't give away a house now that was built with this system.

When we were going to build I considered that it was going to be probably the biggest purchase I would ever make and I wanted to be completely comfortable with the system I was using. For me that meant going with, for Sweden, a more traditional TF build because that is what the local suppliers here are competent with. Had I ended up building again in Ireland I am pretty sure I would have gone with a wide cavity block build.

Do we know about gaps in insulation in wide cavity block builds, at least with EWI when the insulation fails you can see it, so fix it.

We have 200mm full filled cavities between aglite 100mm blocks, telpo thermal ties across the cavity.

The insulation was knapf earth wool. Basically glasswool with a less itchy binder.

It was installed as 2x100mm batts. The vertical joints were broken and each layer of batts was inserted after th inner and outer leaf had gone up. This produced a fill with pretty much zero gaps and no sag. The bats were flown across openings and cut to size after.

I'm a big fan of the wool fill due to it's ability to conform to irregular surfaces and expand to fill gaps. I'm currently working on a retrofit EWI solution using aluminium (i think) larsen trusses, wool insulation and cement bard cladding.