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Two Hybrid Timber-Bale-Cob Houses in Cantabria, Northern Spain
You may remember I visited a rather spectacular natural building complex in Cantabria a couple of years ago. You may remember two straw bale houses in the process of being built. Those houses are now complete (yippee!) Robert Alcock from Abrazo House gives a brilliantly detailed rundown on how they were made, and shows us around.
If you're a regular follower of the Mud Home blog you'll have already read a bit about Abrazo House. At this ecological learning centre in a tiny village in the green mountains of Cantabria, we've spent the past fourteen years building natural homes and doing permaculture with the help of hundreds of volunteers from all over the world. You can read all about the project in our free ebook: (http://abrazohouse.org/en/book/)
In 2016 we decided to apply our hard-won experience to a further natural building project: to create two new, beautiful and efficient eco-houses on another plot of land in the same village, with the aim of attracting like-minded people to live and work in this amazing part of the world. The houses are now complete and are on the market. (http://abrazohouse.org/for-sale/) For all you natural building fans out there, here's a quick rundown on the essentials of the project.
The site is 5000m2 of south-facing terraces with young woodland (planted after we bought the land in 2005) and a stream, in a small village in Cantabria. The "urban" zoning of the land meant we could get permission to build two homes there, and we went down the legal route of architect's plans and municipal permits. (NB We've never run into legal issues because of the unconventional nature of our buildings.)
Because of the steep, south-facing site, we decided to cut away into the hillside and build earth-sheltered houses. A key design element is the addition of a semi-enclosed garage to the north, in between the house proper and the hillside: basically doubling your useful space for just the cost of the roof.
The choice of materials was based on ten years' experience of natural building in this bioregion. Of course there would be loooads of cob: we love working with cob, it's cheap and easy to mix with our well-honed rotavator technique, and it makes gorgeous organic shapes. But we wanted these houses to be completely passive solar—not needing any additional heating in winter—and cob alone isn't quite warm enough to do that even in our mild climate, so we went for a hybrid construction: straw bales laid on edge (35cm thick) with a good 15cm of cob inside and out for protection and thermal mass.
A notable feature of our local landscape is the humungous areas of eucalyptus plantations. These non-native trees are mostly used for making paper, but they actually make a very good structural timber which is very durable if treated with borax solution. So we decided to erect a timber frame structure and green roof first, and build the bale-cob walls afterwards, allowing us to work under cover. We cut and peeled our eucalyptus trunks on a friend's land, less than 1km from the building site. Using them in the round meant stronger beams, and saved us an expensive trip to the sawmill.
Earthmoving and Foundations
On site, our digger crew scraped away the topsoil—which we piled up for use in mixing the cob later on—and found that the underlying subsoil wasn't soil at all, but rock. This meant a lot more expensive digging, but it did have two benefits: a nearly infinite supply of stone for building retaining walls and foundations, and a very solid base for the houses, with no need to pour a concrete foundation. In some areas we could go straight up from the bedrock; in other places we built a brick pier for the posts to rest on.
Timber Frame and Roof
Due to administrative delays we weren't able to start building the timber frame until December 2016, but once we got going it went up in just a couple of weeks. With the main frames up and temporary supports in place, we put on the rafters and the roof during the winter, luckily blessed with good weather, and were ready to start filling in the walls by March.
To keep the bale-cob walls dry, you need a good stemwall. Despite having plenty of stone on site, our stemwalls are mostly built from termoarcilla, a specially insulating type of brick that interlocks like Lego, because it's way quicker: we only used stone on the visible exterior walls. We filled in between the two layers with expanded clay pellets (arlita) — a lightweight insulating pellet that's a bit like Rice Crispies.
On top of the stemwall we put a thin layer of cob, and then it was bale time. It was pretty easy to keep the bales straight and stable by tying them to the post-and-beam structure; in some places, we strengthen them with bamboo poles tied through the wall from inside to outside. At this stage we just left a big enough gap for each window or door, added a wooden lintel and kept going with the straw bales. It's important to take into account that the straw bales will settle over time, so the lintels must be able to move with them. (Our lintels could have done with being a bit stronger, too.) Later on, we would come back and hang the doors and windows from the lintels, filling in around them with slip-straw.
The first layer of plaster we added to the bales was a clay slip—just clay soil and water mixed by hand and foot in a pit (an excellent way to make friends and get incredibly muddy), and applied to the bales by hand.
Electricity tubes get fixed straight on to the straw bales. Then it's time for the cob plaster—layers and layers of cob plaster until the walls are weatherproof, thick and straight.
On top of the cob we applied Ecoclay, a commercial earth plaster—basically a much finer version of cob. Then came the finish layer: gypsum plaster inside the West house and an extra fine commercial clay plaster in the East house, with lime plaster on the exterior of both houses for strength and durability.
On the market
The two houses are now on the market, together with 5000m2 of land with wooded terraces and a stream. The East house is furnished as a small family home, while the West house is slightly larger, with a loft and two bathrooms, and would be ideal as a studio space for working, running courses or as a rental property. We believe this is an exceptional property for the right people, who are looking for a place to realise their dreams of a life in harmony with nature. Please take a look at our webpage (http://abrazohouse.org/for-sale/) or check out our promo video (https://youtu.be/mgMiTj5ujCA) and get in touch if you want to know more.
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It was an amazing mud adventure. Kim Siu’s gorgeous hobbit house in Moray is now finished, and it's a showcase of natural building. It ticks every box: a straw bale house with rubble trench foundations, living roof, earthen plaster, wattle and daub/cordwood interior, and a stunning earthen floor. Not only that, but it was built to code. In the UK. Yup, you read that correctly. It’s 100% legit. Building permits In. The. Bag.
But let’s not lie. Clawing your way over those bureaucratic hurdles is anything but a picnic. “I’m not building again,” says a somewhat frazzled Kim this end of the build. “I don’t think my frayed nerves could take it. Two builds is quite enough. I’ll stick to buildings that don’t need permissions such as gazebos or chicken sheds!”
Many thanks to Kim Siu of Get Rugged and the Hobbit Hideaway for sharing with me this honest, warts-and-all story of a phenomenal build.
There really is no better foundation for a natural build than the rubble trench. Tried and true, it beats concrete hands down in terms of cost and drainage. You can read exactly how to build one here, but basically it’s a trench, in this case lined with geotextile membrane, and filled with stones and rubble. That’s it.
As with most straw bale structures, you throw up the post and beam structure first. That includes the roof. The straw bales are basically the infill for the walls. The advantage of constructing your roof first is that you have this wonderful sheltered area to store materials, use as a shelter, and work within.
I asked Kim how she went about obtaining those elusive building permits. This isn’t her first house and we documented the UK permit process in detail in a post on Kim’s other larger straw bale house.
“Getting planning permission and the building warrant followed exactly the same procedures as our other house,” explains Kim. “It was far easier this time though, as we had an architect that not only knew his stuff, but knew how to communicate with officialdom. Sam at Rocket Architects restored my faith in architects! He got us through all the permissions gracefully, without too much stress.”
The Building Team
Kim employed an alternative building firm in the UK called Hartwyn to build this gorgeous house. Yes, you don’t have to do it yourself, and there are some definite advantages for getting a professional in.
“Hartwyn commission Rocket Architects as part of their package. That’s one of the reasons that we chose them for our project, because we knew we needed to jump through many, many hoops. Especially as this build was a hardcore eco-house,” says Kim. “Hartwyn were the natural builders and educators. Another reason why we chose them was because they would recruit and teach students as part of the build. This was such a great fit for my vision of the build and how it could be beneficial to others.”
Yes, it was a wonderful concept. I followed the process online and found it heart-warming to see the next generation of builders being trained in another, more sustainable construction methodology. You can see plenty of photos of the students at work with Hartwyn on the Get Rugged Facebook page. It all looked great fun.
Where did Kim find out about Hartwyn? “Ah from Talking Natural Homes,” she says. When talking to Jeffrey (the Natural Builder) it was very obvious that our values were aligned and it was a no-brainer to choose Hartwyn.”
The Toughest Part of the Build
During the building of the main structure, things move along at a nice clip. Motivation is high, and something is blooming out of nothing. That’s the easier part, in my opinion. I think the toughest section of any project is the finishing. Everyone is tired. Money is running out. And plastering and detailing are trickier and more time-consuming than you think. Kim, it seems, would agree.
“I think the final stages where the most difficult as they sapped me of all energy. There was just so much detailing left to finish. We had several months left of sanding, sealing, scraping, painting, fixing and finishing to get it ready and this seemed to take forever. I was under so much pressure at the time as my mother was dying, and we had got into huge debt with the build and needed to get it rented out and bringing in money as soon as possible.”
What would Kim do differently next time?
This is where Kim said there wouldn’t be a next time. :)) “It’s the financial pressures and permissions that took the most out of me. I’m still knackered. Who knows though, a few years down the line and I may well be looking at an earthbag structure. I think if I did build again, it would be with earth and stone...”
He he he, watch this space. :)
5 great lessons to take away from this:
The Hobbit Hideaway now
Kim’s hobbit house is now the most beautiful little bed and breakfast cottage where it gives people the chance to taste what life is really like inside a bonafide natural home. Guests continually come away shiny-eyed and rejuvenated. If you’d like to know more about it, or book a stay, look here. https://www.facebook.com/hobbithideaway/
Photos by Dewi Roberts
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A list of the pros and cons for earthbag building, cob, straw bale, wood, stone, and wattle & daub.
Many people are planning and researching at the moment. January does that to people. If it’s natural homes you’re thinking of then here’s a comparison of a few building techniques you might be considering: earthbag, cob, straw bale, wood, stone, and wattle and daub. I've compared the cost, difficulty of technique, how the buildings fare in extreme weather, heating, and other advantages and disadvantages. This list was written with beginners in mind, so I hope it’s helpful.
Difficulty of Technique
Earthbag is labour-intensive compared to straw bale or wood, but the good news is the technique is fairly idiot-proof. Earthbag homes can be built fast, depending on the energy and organisation of the team. Finishing the interior may take longer though.
If you’re building a round house, the materials are very inexpensive. Mud is free. The sacks are inexpensive. Labour is the key factor for cost with earthbag, so if you have volunteers it’s going to reduce the price tag significantly. If you’re making a straight-walled post and beam structure, then it’s going to be more expensive.
Poor. R 0.2 per inch (still better than concrete though).
One of the attractions of earthbag is the freedom of design. Domes, circles, and wavy lines are all possible.
Earthquakes and Extreme Weather
Earthbag is without a doubt the strongest sustainable building technique out there. It has exceeded earthquake test limits with no visible damage. This is why it has become popular in seismic areas like Nepal. I can personally attest earthbag also performs amazingly in hurricanes.
In the Wet
Earthbag performs better in the wet than any other mud building technique because the bags and wire hold the dirt together in case of a flood. Again, as with all mud buildings, rubble trench foundations, a good stem wall and wide eaves are necessary.
Negligible. Plaster touch-ups, that’s it.
Because it’s a modern technique we’re yet to see how long earthbag lasts. But with decent rubble trench foundations, it’s estimated to stand at least a century.
Fireproof, soundproof, bulletproof. Earthbag is the survivalists’ dream:)
In mixed (wet followed by dry) climates, the clayey earth in the bags will swell and shrink, especially in the first year. This can put pressure on door and window frames, as the walls expand, compress the frames and then contract again.
Difficulty of Technique
Cob can be time-consuming depending on the climate, as each layer needs to dry before laying the next. Patience and some know-how are necessary. It’s a beautifully simple technique though. Perfect for artists, and fun too.
Mud is free. Labour, time and learning the art is where you could spend money. A great technique if you can find volunteers and have no pressing time limit.
Poor. R 0.2 per inch (better than concrete)
The beauty of cob is you can create all kinds of wiggly, organic shapes with it.
Earthquakes and Extreme Weather
Cob is stronger than poorly constructed concrete or brick, but not so great in floods.
In the Wet
It all depends on how high your footings are, and how wide your eaves. Cob can resist a fair amount of rain and weathering, but is not recommended on flood plains.
In the Cold
Earthen walls work well with passive solar construction, and heat up like a battery. But they are not recommended in climates that are subzero for months on end (for more detail on that look here).
Easy and enjoyable. You’ll probably just be patching up the final layer or the lime wash in the areas that see hard rain.
Centuries. Cob houses have been standing for centuries in the UK.
Difficulty of Technique
Straw bale is one of the fastest and least labour-intensive of all the natural builds. Bales are light compared to sacks filled with mud. You can have a house up in weeks. Finishing the interior may take longer though, and you’ll need some basic carpentry skills for a post-and-beam structure.
Usually pricier than mud building because of the post and beam structure. If you don’t have straw bales to hand this will also add to the cost.
Excellent. R1.5 - 2.5 per inch depending on which study you follow. The way to go in cold climates.
Although there are plenty of examples of alternative shapes created from straw bales, you are using a rectangular building block which lends itself better to straight lines when compared to cob or earthbag.
Excellent. Straw bale has been known to survive an 82-ton force on a shake table.
In the Wet
Moisture is the enemy of straw bale, and I’ve seen a few cases of bale rot now, which can be the end of your house if you’re not careful. Yes experts know how to mitigate this, and if you construct a decent rubble trench foundation, a high stem wall and wide eaves, straw bale can stand plenty of rain. But if you’re a newbie, you need to bear this tendency to rot in mind.
Plaster touch-ups. Usually easy and enjoyable.
With the correct foundations and moisture/fire protection, straw bale can last a lifetime.
Soundproof. Very snug.
- We’ve seen a number of fires in straw bale homes (Both Simon Dale’s went up in flames), so you really need to be super careful about your wiring, wood burner pipe exits, and so on.
- Mice can move into the walls if they find a hole to enter by.
Difficulty of Technique
You will need some reasonable carpentry skills to build a nice cabin.
Wood is always the priciest material in a natural build, especially if you’re going for quality, so a wooden cabin will no doubt cost more than a straw bale hut, and definitely more than cob or earthbag.
Very poor. You’ll have to add decent insulation to the walls in cold climates.
Poor. Wooden huts neither store much heat, nor prevent temperature exchange. This is one of their major disadvantages in my opinion.
Wood wants to go straight, so geometrical shapes are going to be the most logical for a wooden structure.
Better than stone. Worse than earthbag or straw bale.
How your hut stands up to a tornado does depend on how well built it is, but generally? Rather you than me.
In the Wet
Raised wooden structures will survive the wet quite well. You can stick them on stilts, for example.
Grrr. I find wood a right pain in the backside to maintain (though it does depend on which wood you’re using, and the amount of weathering your hut will see). Usually you’ve got to prevent it from sun and rain damage, which is expensive and time consuming.
This largely depends on the wood you are using. Some quality hardwoods last forever. Others, like commonly used pine, will need a lot of care.
Super fast to build. If you’re in a tight spot and need a roof over your head fast, wood can get you there.
Not soundproof, nor fireproof.
Difficulty of Technique
You’ve got to know what you’re doing with stone, especially if you’re building with a natural mud or lime mortar.
If you’ve got the stone on site, and you are a stonemason, fantastic! If not...ouch! In most countries hiring a stone mason is going to set you back a pretty penny.
Good. Performs way better with mud or lime mortar than with Portland cement.
Ah, stone is very aesthetic in the right hands. You can create all kinds of shapes, round or geometric.
Stone usually performs badly in earthquakes because the stones shudder and shift, thus loosening.
In the Wet
There’s no real issue with stone houses in the wet.
Very easy. Perhaps a bit of mortar pointing every few years?
With the correct foundations and drainage, stone houses last millennia.
The stones have a personality, an it’s quite wonderful to live with them. Another great thing about stone wall is that mice can’t chew through them.
Wattle and Daub
Difficulty of Technique
I think wattle and daub is quite underrated and underused in the trendier world of natural building. It’s not horribly complex. You will need some basic carpentry skills for the post-and-beam structure (much like with straw bale), but the wattling and daubing itself is wonderfully easy, and enjoyable.
Similar to straw bale in terms of materials. The post-and-beam structure is where the money goes.
Geometric shapes are best for wattle and daub, as the laths are straight lines.
Not sure. I only know them from the UK where there are all but no quakes. If you know, feel free to add in the comments, and I’ll update the post.
In the Wet
As with the other mud builds, if you have decent eaves and decent rubble trench foundations with a good stem wall, wattle and daub can cope well in the rain.
If lime washed, then the maintenance is pretty straight forward.
Excellent. Wattle and daub houses from the 15th century are still very much alive and well in the UK.
Other related articles:
1. Can you build mud houses in cold climates:
2. Mud Building Techniques Overview
3. Getting to Know Cob (Oliver Goshey)
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The great thing about being on the road is that you finally have the chance to visit other natural homes. Many of them are inspirational. All of them teach me something new.
Abrazo House is a cob/strawbale hybrid tucked away in the sweeping Cantabrian hills. It’s a perfect example of a well-built natural ecohome, with a green roof that flourishes in the wet climate, earth plaster created from clay on site, and a lime wash finish to protect it. The lower floor is made from insulated cob, and the upper floor is straw bale. It is, as you can see, quite beautiful. At 200 square metres, Abrazo House is the largest self-built natural home I’ve seen so far.
Robert, the creator of Abrazo House, has executed a number of impressive eco building projects to date. There is a cob cabin on the land too, and just up the road he has two more fabulous straw bale houses on the go which will ultimately be sold. Indeed this is something of a natural house empire with a view to breathing life and community back into an abandoned Spanish village.
But here’s a little secret just to encourage folk. Something went awry in the build of Abrazo House (which if builders are honest is par for the course in construction). And what do you know? I have something interesting to write about, and we all learn something new.
So what went wrong?
Originally Abrazo house was planned to be completely straw bale. Because the climate was wet and the build took a long time (four years in total), by the time the second floor was reached, the first floor had begun to rot. I don’t want to imagine how Robert and co. felt the moment they realised this. Personally, I would have lay down in the dirt, beat my chest and howled for a day. But Robert seems a mellow chap, so he probably flipped a little more quietly than I would have. And anyway there is always a solution. Many times it becomes the most outstanding feature of the house.
How did he solve the problem?
The issue was resolved by jacking up the first floor, removing the bales and then creating cob walls in their place. The cob easily supports the bales (which are far lighter than the solid earthern walls). Thus this has become a rather magnificent example of a hybrid natural home.
How did he increase the insulation value of the cob?
The reason Robert chose straw bale in the first place was that he was concerned about insulating such a large house. Straw bale has a high insulation value. Cob, on the other hand, has a high thermal mass value but is not particularly efficient for insulation (you can read more about that here). To mitigate this issue, Robert replaced some of the sand in the cob mix with sawdust. The result is a fabulous, attractive and warm family home.
Is this house built to code?
For those ever hungry for information on legalities: This is a natural home built to code. Yup, fully legit (as we say back in Essex). To do this in Spain you must buy an appropriate piece of land (edificable), speak to officials in your local government, get an architect to draw up an official plan, and then have it signed off by various titled pen-wielders in various offices. Obviously, each time you take any of these steps you will need to inhale and exhale deeply, and spend some money too. Patience and persistence are the two characteristics you must cultivate when embarking on a self build project anywhere.
Something else I learned:
Robert was mixing his earth plaster using an unconventional method (at least I’d never seen it done this way before). We laid a large layer of gravelly sand directly on the ground, then added a layer of clay, and finally some straw. Then the ingredients were mixed using a rotavator. Unfortunately I have no photographic evidence of me doing this, which is tragic because it was truly a battle between woman and machine:) To use this method successfully you need a fair bit of experience with earth plaster first, so you know exactly how the mixture should look. It’s quite hard to measure the quantities of ingredients carefully when they are spread on the floor. But because Robert knows his dirt and his climate well, he knows from sight and can assess the state of the mixture just by handling it.
If you want to read more about Abrazo House, or would like to help volunteer, go to www.abrazohouse.org.
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