Ideas for a natural building materials for a first floor floor, and roof

Its my first post so please be gentle.

Hi

Location: La Alpujarras, Granada province, Andalucia, Southern Spain

Some info first: we live in the Alpujarras, Southern Spain and we (I say we but its mostly been build by builders! we will help too) are renovating an old goat shed and making it into a two floor house to live in. It's originally made of stone with a flat roof. We would like to build using traditional local building styles but for the first floor it was hijacked by a 'bio construction' builder and it got out of hand....anyway.


We now start on the second stage after the summer break and we are searching for bio construction/natural building materials and techniques to construct the first floor floor with. Clay, sand, straw, mashed up hemp? But we need to have the perimeter of this floor in concrete as this will provide the support for the pillars which will sit the roof.

Now, the layout of the house is like this. ground floor has a concrete floor (yes, I know, sorry) and it uses a combination of large bricks (also, sorry) and original stone. The building was in bad shape and it needed to be reinforced with steel rods, steel beams etc (the conventional building way) but now we are changing back to the original plan. A bio construction house.

The other thing of note is that after the first floor has been constructed we will probably need to use modern and traditional techniques to make the floor.
Why? The floor will probably (yes a lot of probablys as we are still consulting with conventional and natural builders) need a concrete perimeter and the central part natural to balance the. The concrete perimeter (does it need to be concrete?) will support the pillars which will hold up the roof.
But my rational is that the two different material (concrete perimeter and natural central floor) will shrink at different rates and cracking will occur. This is no good as we will put tiles on top of this.

Plus, how do we get around not using concrete (or reducing the amount) when building the roof. It has to be a flat roof due to local laws.

We are asking for your experiences, ideas and practical advice on the matter.

Many thanks
Daniel

You are a bit confusing.
When you speak of the first floor, I take it you mean the first floor walls?
Why not try straw bale if they are available.

It's a wide topic. Concrete probably is not necessary, but easily helps to reinforce/renovate something that was not build to last. Probably the simple shed was built by someone who did not think about the long lifespan of the building - probably the foundation was inadequate, the walls too thin, etc. Like for example building an adobe (or rammed earth) wall 20 cm thick and too tall and expecting that it will last for centuries. The same for stones that are too small/round and joined quickly. If the foundation and roof allowed for water penetrations eventually it will crumble sooner than later. Also Alpujarras is in seismic zone that will help to disintegrate buildings not sturdy enough. Old (and natural) buildings that survived all of this usually have very thick walls, buttresses that help to resist the forces, very thick timbers and good design.

You already have reinforced concrete frame so now you can choose the infill material for the walls.
You could:
-use modern Porotherm - natural clay and insulating then lime plaster it
-rammed earth (tapial)
-regular bricks - you could build two-wythe wall and fill the cavity with natural insulation; Spain is the kingdom of bricks - the best looking on the planet, great selection of shapes, frequently manually made and also cheap

Alpujarras is almost 1000 m elevation, so having some insulation could help.
Bricks can be laid on lime mortar.
Bricks can be laid to create Mudejar patterns - the part of the wall where the concrete frame is, can be plastered. Since they are small, it will be more expensive to lay them.

How thick are the concrete columns?

Hi Daniel,
Sounds like a pretty cool project. If I am understanding correctly, you have a one story building that is partly stone, and reinforced with steel. And you want to add a second story using natural materials?

Some pictures would certainly help us understand the exact setup better, but I am going to suggest building a timber frame inside the current walls. Just inside the current stone wall, build a two story timber frame. This will allow you have a natural first floor without needing cement for support. It will allow for some good insulation between support posts on the first floor (because stones are awesome except for insulation).

Then you could cover this frame on the second floor with a variety of methods. Hempcrete, cord wood, clapboar siding with a natural insulation. As for the roof, a slate roof is natural but expensive around here. A wood shingle roof might work. Also, in your area, are clay tiles for roofs created in a natural way?

Hola Daniel, welcome to permies!

how do we get around not using concrete (or reducing the amount) when building the roof. It has to be a flat roof due to local laws.

I wonder what the traditional construction of the flat roofs are?

Traditional flat roofs here in Southwestern North America were just earth. A big thick layer of earth, on top of wooden beams, with maybe a layer of sticks or bark involved somewhere. There would ideally be a very slight slope to direct runoff in a desired direction and stop it from forming puddles. The structures built this way that have survived for centuries without maintenance are the ones built underneath a natural cliff overhang; they won't last forever out in the open. But if your climate is dry enough, then you can get away with just building the roof thick enough that a single storm won't soak all the way through, and then fixing the damage after every big storm. These days, few people are okay with this level of ongoing maintenance for their home, but it used to be more common, and in a few places the practice continues to this day for some traditionally important structures. If you live in a wetter climate, I'd be surprised to hear that flat roofs are traditional there, but if so I have no idea what other techniques people might have used.

For that arid or semi arid  region, rainfall is about 14 inches per year. However, I think all flat roofs are a bit problematic

Even in a desert, they accumulate too much heat gain without careful planning.  John has experience with safari roofs, and they can make a huge difference.  Also I have seen rooftop patios using shade cloth and plants, this can protect most of the flat roof.  

If a flat roof is slanted there might not be as many problems as most flat roofs.

I only know USA traditional building techniques using framing.

Yes, the rainfall in Andalucia can be handled with proper techniques like those

But after working one summer on a roofing crew, I saw the intense heat generated (125F one day i checked) could destroy some of the drainage....primarily if the tar and pea gravel method (or roll roofing) was used. That would be my utmost concern if flat roofs were mandated.   A quick search shows Andalucia as a whole averages 97F in summer months, ouch.
 A flat rooftop will normally be much hotter. Perhaps a vented "attic " of 100cm  could be built under it, making a buffer below the roasting hot roof?

Rico,

They can get between 6 and 60 inches of rain depending on location.
Overwhelming majority of houses built in Andalusia has gable or hip roof. I think that requirement for the flat roof in this particular case is caused by some regulation that says that any rebuilt should preserve original building's envelope.