An octagonal passive house in straw bales

[jean63]

The wooden formwork, I do not understand, we can no longer coat the boots with lime since they enter a formwork? and for the problem of "breathing" it is not a problem?
No, poorly expressed: error in my sentence; I speak, of course, of straw bales: do they form a rectangular parallelepiped (spelling?) perfectIncluding on the length do not they tend to warp and bend themselves?

The wooden structure is necessary to take up the structural forces because the straw bales have no cohesion between them and cannot support the load (and must not, otherwise they would settle which would cause the plaster to burst and would decrease the insulation (it is the air of the "voids" which insulates).
The straw bales are not precise mechanical bricks, the length and thickness dimensions are approximate the width is more precise and their geometry is also approximate (depends on the settlement and the humidity rate)
Important thing to check: if the boots were made with straw well dry otherwise it will ferment ...
Alas too: very few farmers still use these old balers: practically everyone uses the rollers because it saves time handling ...

OK there I understand ....... there must also be a horizontal wood structure in the walls between each layer of boots ??

[jonule]

The wooden structure is necessary to take up the structural forces because the straw bales have no cohesion between them and cannot support the load (and must not, otherwise they would settle which would cause the plaster to burst and would decrease the insulation (it is the air of the "voids" which insulates).
The straw bales are not precise mechanical bricks, the length and thickness dimensions are approximate the width is more precise and their geometry is also approximate (depends on the settlement and the humidity rate)
Important thing to check: if the boots were made with straw well dry otherwise it will ferment ...
Alas too: very few farmers still use these old balers: practically everyone uses the rollers because it saves time handling ...

in any case, the "wooden formwork" structure is not compulsory.
it is used for walls and undercuts.
but the Nebrasca type (who comes from this US county) does not use any wood structure! like little things what ...

as for the coating it can be put and put back in touches and retouches, the time that the straw is squeezed it passes, time!

of + as I said the baler is adjustable, the pressure too.

We must see this as a real demand from the peasant supplier, who is committed to donenr correct boots, yes we must ensure that the straw is dry in the summer!
which was not easy this summer 2007 ...

so those who have these balers should keep them ... it is found in the ads or discounts?

[johnix]

I guess it's octonome that made the cuts and assemblies.

Yes, on site and open site.

And then you need a hoist (crane or other), scaffolding .....

Coincidentally, there was a crane on the job site when the post was laid. So we used it. But otherwise, we had planned to mount it by hand. Instead, scaffolding was used.

I would like to have details on the dimensions of the elements, spacing ... etc.

Are the elements nailed or screwed together, or with ankles (old carpenters technique)?

The posts are spaced 80 cm and measure 20 cm deep. The boots are stacked flat between the posts. They have been re-cut one by one to the correct length, according to the method illustrated here: http://alysse.org/~thomas/2006_premier_cochon/spip.php?article96

All 2 ranks, we inserted cleats nailed on both sides of the poles, to maintain the boots.

The frame is assembled with screws and nails.

The wood (douglas) was not dry because cut recently, is not it a disadvantage for the straw (contact between the poles and the straw) + deformation of the wood when it does not dry well flat and forced?

The wood is actually green, and it will deform a little while drying. It does not pose any particular problem.

Douglas fir is naturally resistant to insects.

How do we adhere lime on straw and wooden poles? (straw boots that must be perfectly aligned and do not buckle !! a straw boot is not a brick or a block).

On the inside, is there a plasterboard or other board against the straw or a lime plaster directly on the straw?

When all the boots are put down, a mixture of lime and sand, sufficiently liquid, is sprayed directly onto the boots. It's the gobetis. It penetrates between the strands and constitutes a layer of grip.

Then we apply 2 other layers of plaster + sand: the plaster body, which takes the differences in level, and finish. In the end, we have on average 4 cm of coating. The wall is not perfectly flat. In particular, the windowsills or edges of the walls are rounded.

There are no placo plates inside.

As the boots are flat, and they overflow with respect to the frame, the straw strands spread and fill the interstices between the boots, thus covering the frame. In the (rare) places where we had to smear on wood, we screwed pieces of fibragglo. Indeed, the lime does not hold on the wood. At the junctions between plaster and lime (door frames ...), stainless steel nails were planted in the framework, and they were drowned in the plaster, to avoid the appearance of days.

Certain techniques exist, either with a bastard mortar poured against the boots ("GREB"), or with caissons and wooden panels, or cladding.

The historical techniques called "carrier straw" or Nebraska may seem attractive at first glance, but they are neglected today, because they offer few advantages. The wooden frame is probably the best technical solution, except to use "high density" boots (the large parallelepipedic).

How is the central pole fixed on the ground? what makes the house stand upright, its octagonal shape?

The post is simply placed on a concrete block. For the frame, its basic element, the low rail (piece of horizontal wood that goes around the house) is spited on the wall of foundations.

[jean63]

OKAY. thank you.

I am a little less ignorant about the straw construction.

What happens when the straw is humidified? you can not destroy the whole wall !! ... maybe only the area where the wet straw is?

There can be no settling and micro-cracking in the exterior plaster (or at the junction with the window frames) that could allow water to penetrate during heavy showers?

Inside the plaster is enough to prevent the moisture of the house from entering the straw?

In my MOB, after laying the insulation (rock wool there 20 years we did not find the current bio insulation, except expensive cork), I stapled on the inside a waterproof polyane film before Plasterboard installation, to avoid a risk of migration of the ambient humidity in the rockwool.

Now we are waiting for photos from inside: networks, VMC, etc .....

Good luck for the future.

[jonule]

Hello,
on every house there is maintenance, the concrete walls sag and crack, they are cemented?

on a wall of straw is ditto, it is necessary to think of the maintenance, johnix provided slats fixed to the poteux to limit the settlement.

Yet nothing simple to deal with the settlement: just add it from above!
and the coating is redone in a jiffy ;-)

but do not be delirious either: it does not deform like that!

normally when it is well done, the straw does not take moisture.
already she regulates her properties!
that's why its comfort is appreciated.

then it's like any insulation: it has to be broken down.
that is a coating outside breathable style lime earth, and especially not coated cement !!!

even rock wool in a roll has its vapor barrier: moisture MUST pass through it to escape, ventilated to the outside, it is the circulating air space between the insulation and the roof for the roofs, or for the walls see "insulation from the outside": there is also a breathing air space behind the exterior facing.

[Chatham]

Hello,
on every house there is maintenance, the concrete walls sag and crack, they are cemented?

Yet nothing simple to deal with the settlement: just add it from above!
and the coating is redone in a jiffy ;-)

but do not be delirious either: it does not deform like that!

I do not know where you've seen concrete walls (or mechanical bricks) splitting, unless there is a construction fault (no, or too little reinforcement, bad concrete) or a soil collapse ( especially on clay soil) or an insufficient foundation ...
Well yes, we close the holes as and when: the house under permanent construction is what will rejoice madam
With a supporting structure (for the frame of the roof) in SEC wood the subsidence is contained, but not canceled because the wood and the straw it works, the coating does not.
(when with the use of green wood ... the loaded green wood will deform enormously while drying! and the humidity, the mushrooms and the molds are in love with it)

[jean63]

Chatham wrote:

With a supporting structure (for the frame of the roof) in SEC wood the subsidence is contained, but not canceled because the wood and the straw it works, the coating does not.
(when with the use of green wood ... the loaded green wood will deform enormously while drying! and the humidity, the mushrooms and the molds are in love with it)

On this occasion, I would agree with you.

I do not understand the use of green wood.
Well, the Douglas is theoretically rot-proof (except the sapwood). It must be certain that there is no sapwood in this structure.

For more security, I preferred dry Douglas Fir treated under vacuum (green color) in my MOB and again, I have a pergola beam that has received 2 layers of stain and more, and there I saw that it rotted 30 cms (sapwood in my opinion) after 20 years.
This is what we see outdoors in the playgrounds for children.

On the other hand the cladding in red cedar without any treatment, then he is REALLY rot-proof, it gray or black after exposure.

[jonule]

well if at last chatam, concrete walls crack!
we speak of realization + or - well done, and it is the same case for the house in block, and even the concrete banché can crack, years after the settlement of the ground, the differenets bad weather etc ...
if it's photos you want it's a concern ;-)

I would say even + that on a clay soil, the straw house is + resistant to differential settlements that concrete, it seems obvious ...

the coating on concrete workel with the ebony, but the coating on the straw works alone, it is still an advantage ...

But hey, he returns every year to make a quick tour of the house to check the maintenance, like the foam on the roof for example!
so it is not inevitable ... in addition one can imagine an "insulation from the outside" in cladding leaving a drying air space, like the roofs in fact!
with its vapor barrier also so the water does not come in and moisture is removed ...

for the wood rafters of my structure, I will use chevrons bricodépot ;-)

[BIOMAN44]

At the same time, a back-up on a passive house should rather be of the "instantaneous" type than "inertia"; and an active solar system only makes sense if it allows a significant phase shift (inter-season storage), which is too complicated and expensive for a small backup.

Good evening Johnix!

I take the conversation on the way ...

Can you explain in detail your 2 points of view quoted above?

Thanks in advance

[Woodcutter]

This thread has not been followed for nearly 9 months: it would surprise me that you have a quick answer ...