[Strawbale] OSB or Not? (rendering versus sheeting) (dirk witvrouwen)

[asbn]

just an addition...
> The question comes back to the basics; too much protection
> against moisture movement sounds dangerous.

No, I don't agree to this. This is building physics standard and can be
calculated easily.
You can eventually plaster directly on the inside but the problem is, that a
direct plaster on the outside without a folie or other prevention against
water & humidity (rainfall) on the facade often leads to problems within the
insulation-layer.
The reason is, that (in our areas) limeplaster is used, and this plaster
sucks the rain, gets wet and so the insulation layer, if you have no really
big overhangs in the roof.
Earth-plaster on the outside in our rainy/snowy areas leads to a wash-out of
the earth-plaster, as it can be seen on the loadbearing house in St. Georgen
/ Carinthia.
First there are small hairy cracks which freeze in the winter and grow to
big cracks, where the water runs in...
So if you limewash your plaster every year (as you often see it in Greece)
and have big roof-overhangs, you maybe will get no problems. But if you want
to be sure and safe, that nothing happens especially in our areas (and
especially on the weather side), you have to install a rainproof layer
(folie or Agepan board or similar) on the facade under your plaster (or if
the facade is shadowed by trees better use a ventilated wooden facade). You
need this folie and board also for your windproofness...

Mit lieben Grüßen
Herbert Gruber
-- 
asbn - austrian strawbale network
Österreichisches Netzwerk für Strohballenbau
3720 Ravelsbach, Baierdorf 6
Email: asbn at baubiologie...
http://www.baubiologie.at


> Hi Jure and others,

This story tells me nothing in favor of OSB.
Max, Tom are
> presuming that after years, OSB is as much sensitive on moisture as any other
> natural material.

The question comes back to the basics; too much protection
> against moisture movement sounds dangerous.

The fact that the plaster started
> coming off with this man in Austria could as well be of too dry....
A certain
> amount of moister in the air is necessary to keep natural plaster sound, if
> there is no binder extra added.

Maybe to be safe in 20 years we should add a
> binder to the plaster, and make sure that enough breathing is guaranteed...
> 

?

The fact is also that earth buildings were "reworked" every few years
> with a sponge and clayslip to refresh the walls and to close small
> cracks.

This is in any case a serious matter, and hope to hear
> more.

Greetings.


Michel.


On 6 dec 2010, at 06:10, Sport Hotel, Jure Pozar
> wrote:

> Dear All,
> 
> I have in interesting information. I have spoken to a
> guy who does 
> natural plastering for over 20 years and he said that the
> houses in 
> Austria which he worked on 20 years ago show problems now. The
> plaster 
> which was applied directly to the strawbales on the outside is
> cracking 
> and falling off and they found out because over the years some
> moisture 
> got inside the straw and made it crumble and dissolve. So the
> house is 
> no good now and there is no easy way to repair it. I wouldn`t like
> my 
> house to live the same misfortune in cca 20 years time. This is why 
>
> vapour barrier and wind proof facade is a good solution. I can`t wait to >
> hear your comments.
> 
> Cheers
> 
> Jure
> 
> S, Max Vittrup Jensen piše:
>>
> Hi Dirk,
>> 
>> If you'll join the ESBG 2011, you'll see my approach, which I
> believe is
>> fairly generic:
>> Earth plaster straight on vertical bales,
> sloped ceiling made from beams
>> with rough wooden boards with about 10 cm
> spacing to hold the bales
>> above; the boards covered with reeds below and
> plastered. (The bales are
>> also plastered on top, and ventilated below a
> vapor barrier, which again
>> is covered with roof tiles, after another
> ventilation space.
>> I don't usually consider myself 'conservative', but in
> this respect I
>> suppose I am; it's a fairly old proven approach. I'm still
> waiting to
>> hear from people who'd gone in and inspected OSB boards after
> 5-10 years
>> use above a kitchen (used by a family with children in a country
> with
>> plenty of wet and cold days outside). I'd like to see what's hidden
>>
> behind the nice plaster below and covered with straw etc. above.
>> Perhaps
> it's my simple pragmatic mind, however I can't grasp why the OSB
>> don't turn
> black with fungi...
>> 
>> I'm aware of a CZ-Austrian funded project which
> made such insulations
>> about 5 years ago, but apart from the architects
> showing they could do
>> it (and profiling themselves at conferences and
> media), then there's
>> never been a follow up research about the long term
> effect...
>> 
>> As we also reside in a forested part of Eastern Europe, where
> rough cut
>> wooden boards from local forests/mills are still significantly
> cheaper
>> (despite the export to Austria!!!), then it makes a lot more
> economical
>> sense than OSB.
>> There's been enough well articulated points
> about several other
>> downfalls to OSB, especially from Derryl and Rob Tom,
> so I'll simply
>> summarize it with Rob's statement: "OSB Stinks!"
>> [Which
> might be why, at the ESBG, you're only likely to find OSB used
>> for the
> composting toilets ;o)  (We were given some which had been water
>> damaged in
> a flood)]
>> 
>> Cheers,
>> Max
>> 
>> All,
>> 
>> I read people objecting
> agains using sheet material instead of rendering the bales directly. The
> reasoning seems to be mainly relating fire protection and sealing air leaks.
> Yet, lot's of people use bales in their roofs. I'm assuming none of them would
> render the underside of these bales. So why do it for wall's if it's not done
> for the roof?  Any thoughts?
>> 
>> Thanks,
>> Dirk
>> 
>> 
>>
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> 
> 
> -- 
>
> 
> 
> 
> Jure Požar, dipl.org.tur./ general manager
> 
> HOTEL SPORT&   MTB
> park Notranjska
> Kolodvorska c. 1, Postojna
> Slovenia
> Tel.: +386 5 720 22
> 44
> Fax:  +386 5 720 22 40
> Mobile: + 386 51 630 575
> www.sport-hotel.si
>
> e-mail: jure at sport-hotel...
> www.dos-extreme.si
> skype: jure.pozar
> 
> Bodi
> resnicoljuben: nikoli se ne pretvarjaj. Resnica vedno zmaga
> Be truthful:
> never pretend. The truth always wins
> 
> 
>
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> ____________________________________________________
> 
> 

Michel Van
> Mulders
Gregorčičeva 5
1000 Ljubljana
Slovenia
Tel.
> +38631341964
michelvanmulders at siol...

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