Starting from scratch...

[Greenbeast]

did a few hours research on rammed earth yesterday, interesting stuff

I'm thinking the internal walls will be put in and then timber frame over the top, as obviously you need access to the tops of the walls for ramming.
Then strawbale infill for the external walls.

I know i could have loadbearing rammed earth, but i think i'll stick with timber

[dhaslam]

How thick are the outside walls and what mixture will you use?

[Greenbeast]

The outside walls would be strawbale thick i guess

Mixture, for the earth? i really don't know, its all new to me!

[noelsquibb]

think Ive already droned on somewhere about building a cob barn.

Just to repeat a bit -

I used the local subsoil which happened to be a flakey almost stone type material, that we call shellet in Devon, and mixed it at 20 : 1 with OP cement and enough water to make it look and behave like concrete.
Machine loaded into the mixer and lifted from mixer into home made climbing shutter. Walls were cast approx 500mm thick and still standing several years later.

Cube tests before I started casting the walls came out at around 3.5 newton / sq mm, about the same as a regular celcon block. So no further structural elements required.  I did cast in some strips of mesh around the window openings, below 1st floor joist height and below wall plate cos I could. Creating boxouts for joists, casting in big old oak beams, tapered window reveals and even cutting in a wooden barrel to create a round opening were all pretty simple.

All you need is a digger ( or two ) -  think Ive said that before as well .....

Don't think straw bales are that exciting as the material is only good for insulating and you've got to build an expensive structure to contain the cheap insulation. No thermal mass and a high degree of protection / encapsulation is needed to stop damp and rodent invasion.

I do rate rammed earth tyre walls but unlike my patent cob mix I don't know how to demonstrate compliance for load bearing.  Would like to find an excuse and the time to build a tyrewall dome.

noel

[dhaslam]

Yes I thought there would need to be some binder in the mix unless the clay is  specially suited to the job.  Clay walls seem to be more suited to hot countries where protection from sun is needed but not  insulation in winter and dampness isn't a problem.   Some way of aerating the clay would be a way round the insulation problem.     

[billi]

Rammed clay building seems to have a renaissance   in Europe  , perhaps i would consider cladding the "weather side "



http://www.lehmtonerde.at/english/w1.html

here  one from Austria

[dhaslam]

This Canadian system  uses insulation on the inside which defeats the purpose of the  heavy structure.    Would it be possible to mix cavity fill beading through the mix?   

www.rammedearth.info/insulated-rammed-earth-Canada.htm

[Greenbeast]

i'm planning on only having rammed earth internals and strawbale externals, seems like the best of both worlds?

[dhaslam]

I would still try to see if the one wall could do both jobs.    There are probably  some naturally occurring materials that would act as an insulator when added to the mixture.   If you have an earth wall and straw  it would need a lot of framing for doors and windows , as well as for the straw There would be a lot of extra roof needed  to cover the extra width.     In Ireland some houses were insulated with peat  in the centre of the wall but that wouldn't be up to modern standards. .

[EccentricAnomaly]

Don't think straw bales are that exciting as the material is only good for insulating and you've got to build an expensive structure to contain the cheap insulation.

Straw bales are often load bearing.

[daftlad]

Have you heard of/seen Rachel's strawbale building in St. Dogmaels (Cardigan)?  I went to see it a couple of years ago and it is a beautiful place.  It won the Grand Designs Eco Home of 2008 competition.

She started out with a masonry stove but replaced it, with a wood burner I think, as she couldn't get enough heat from it.

Here's a couple of photos I took.  The place is well worth a special trip if you are planning something similar.

This is a 2 story loadbearing straw bale house.

[billi]

Are we talking about straw bales  normal harvested or about special compressed strawbales ? to build a two story house?

My timber log cabin one story  3.7 meter high (gable ) 2.8 meter walls ) shrinked about  30 -40mm already  , hope thats all  , but what happens to the plasterwork if a house shrinks   ?

Billi

[noelsquibb]

Yes you can make straw bales loadbearing but youve still got to protect the straw from rodents and damp. Rodents seem to be able to smell a source of food and chew through most non metal building materials.

As Billi points out, settlement / shrinkage is inevitable, which means you have to design flexibility into the structural openings. So a gap might be required between lintels and windows to allow the walls to settle onto the windows, cos the alternative isnt pretty and a very flexible waterproof render is required.  I dont think lime mortars will stop damp ( they actually look to keep cob walls damp )

So not sure how you might create a long term building if the straw has to be structural ?

Be interested to learn how it is done.

 

[EccentricAnomaly]

Are we talking about straw bales  normal harvested or about special compressed strawbales ? to build a two story house?

Yes, normal straw bales though you want the baler set to make them as compressed as possible.

My timber log cabin one story  3.7 meter high (gable ) 2.8 meter walls ) shrinked about  30 -40mm already  , hope thats all  , but what happens to the plasterwork if a house shrinks   ?

The usual technique is to "pre-compress" the walls with tie-downs (wire or plastic tape) before putting the roof on.  Yes, they do settle a bit more and the plasterwork goes on fairly late in the process.

Yes you can make straw bales loadbearing but youve still got to protect the straw from rodents and damp. Rodents seem to be able to smell a source of food and chew through most non metal building materials.

The straw itself is basically woody material so pretty much inedible though it'd be good for nesting, I suppose.

As Billi points out, settlement / shrinkage is inevitable, which means you have to design flexibility into the structural openings. So a gap might be required between lintels and windows to allow the walls to settle onto the windows, cos the alternative isnt pretty and a very flexible waterproof render is required.  I dont think lime mortars will stop damp ( they actually look to keep cob walls damp )

As I understand it lime mortars work fine to protect straw.

So not sure how you might create a long term building if the straw has to be structural ?

There are 100 year old load bearing straw bale houses in Nebraska - hence load bearing is called "Nebraska style".

Be interested to learn how it is done.

I'd recommend "Building with Straw Bales: A practical guide for the UK and Ireland" by Barbara Jones.  A first place to look, though, is her company's web site: http://www.amazonails.org.uk/.

I was interested in the idea for a while though I think the plastering is more labour intensive than anything I'd want to try to tackle.  The whole thing can get a bit fraught with weather and keeping bales dry as the roof and plaster goes on.

[noelsquibb]

Oi
Greenbeast

you fall asleep contemplating your project ?

or was it all just a dream