How to go about sticking a roof on this cob/gabion house...

Hello all,

Conjuring up plans for a Blackhouse inspired dwelling that will withstand the weather in the Western Isles of Scotland... Sketchup file: https://drive.google.com/file/d/0B48oxCOHD5N_X3ZvM1RkcVVOSW8/view?usp=sharing

It is a single story cob house with an outer skin of rock filled gabions to keep the elements at bay. I firgured gabion baskets are quick and cheap and once they start falling apart after 60 years I can leave it to future generations to do a proper job and throw up a dry stone wall...







You'll have to use your noggin and imagine doors, windows and glazing along the front of the house - big ol' greenhouse.

I'm stumped as to how to go about sticking a mono-pitch turf roof on this. The cob can be load bearing. I've been looking into a roundwood frame roof but can't work it without getting posts everywhere which messes up the design. Alas, I think this is too big a beast for a recipricol frame roof - approx 15m x  23m. Any suggestions welcome!

Right, I've had a good sleep on it and this is the best solution I've come up with so far...







Posts to be go on stone footings. Roof is at slight pitch - 2.4 degree angle. Joists here are 75mm x 200mm.

If anyone out there has an idea of how to go about calculating how much of a load a roof like this could handle it would be good to hear from you! It might be time to seek out an engineer...

I appreciate maximizing sunlight and using cheap, plentiful local building materials, and I understand that a corbelled or monolithic ceiling might be a bit much work.  

The traditional blackhouses seemed smaller than what you're designing, presumably limited in width by the timber available to support the roof.  Though there is this picture/link I'm attaching that appears to be two houses parallel to each other, which may or may not be connected to one another.  Are you married to the idea of a flat roof?  I wonder if the idea of parallel traditional roofs over the different rooms would be practical, with interior gabions to support them, or whether that would pour water inside the house.  (Hm, harvest fresh rainwater delivered right to point of use....)  It rains in Scotland, doesn't it?    For that reason, I would question having a flat roof.  

(And, about a chimney--are you going traditional blackhouse, without one, or am I jumping the gun on details?    )

http://www.photoeverywhere.co.uk/britain/westernisles/blackhouse3712.jpg

Gabion making by hand.

There is a set of hand operated equipment (two actually) for producing gabions from plain galv wire.

The idea is to make one of three types of mesh, then fasten it to a wire frame that is held on a large spindly jig. Then fold it up.

The three types of mesh are Diamond mesh (chain link) and Trinet which has triangular holes and Square Mesh which looks like diamond mesh turned 45 degrees. All three can be hand made under a tree.

The website is www.newdawnengineering.com under fence products.

The Trinet jig product was designed for Dam construction and bad be made with quite thick wire. The others are normally 11 gauge or thinner, 12 gauge being most common (2.5mm).

Regan Dixon wrote:I appreciate maximizing sunlight and using cheap, plentiful local building materials, and I understand that a corbelled or monolithic ceiling might be a bit much work.  

The traditional blackhouses seemed smaller than what you're designing, presumably limited in width by the timber available to support the roof.  Though there is this picture/link I'm attaching that appears to be two houses parallel to each other, which may or may not be connected to one another.  Are you married to the idea of a flat roof?  I wonder if the idea of parallel traditional roofs over the different rooms would be practical, with interior gabions to support them, or whether that would pour water inside the house.  (Hm, harvest fresh rainwater delivered right to point of use....)  It rains in Scotland, doesn't it?    For that reason, I would question having a flat roof.  

(And, about a chimney--are you going traditional blackhouse, without one, or am I jumping the gun on details?    )

http://www.photoeverywhere.co.uk/britain/westernisles/blackhouse3712.jpg

There's much to be admired about the traditional blackhouse.



Here's a good summary touching on why they worked so well... And here is a fascinating document - "a case study of the blackhouse at 42 Arnol, Lewis, its materials, construction and maintenance."

Weston A Price writes about them in great detail in Chapter 4 of Nutrition and Physical Degeneration.

Alas, all that my build will have in common is that the walls will be thick and partly built from the surrounding stone. The parallel roofs would be great but I think I'll try and keep things simple. The roof is at a slight angle to permit water catchment - I'm aiming to keep the profile of the build low so it can handle the wind, be easier to construct and not be too much of a blot on the landscape.

It'll have to have a chimney to comply with building regulations! The plan is to stick in a rocket mass heater/cooker. Some underfloor heating wouldn't go amiss as a dump load for turbines - no shortage of wind.

Crispin Pemberton-Pigott wrote:Gabion making by hand.

There is a set of hand operated equipment (two actually) for producing gabions from plain galv wire.

The idea is to make one of three types of mesh, then fasten it to a wire frame that is held on a large spindly jig. Then fold it up.

The three types of mesh are Diamond mesh (chain link) and Trinet which has triangular holes and Square Mesh which looks like diamond mesh turned 45 degrees. All three can be hand made under a tree.

The website is www.newdawnengineering.com under fence products.

The Trinet jig product was designed for Dam construction and bad be made with quite thick wire. The others are normally 11 gauge or thinner, 12 gauge being most common (2.5mm).

Thanks Crispin! Solid looking equipment. I'll have a look into it further and figure out if it will be cost/time effective.


Do any cob experts out there envision that putting gabions up against a cob wall would encourage pests to have a go at it?

I can't speak to cob, but I have dry stacked rock walls in the garden, that the dog is always digging into for chipmunks.  And that's outside in the elements, not in a sheltered, heated house!  So my guess is yes, those gaps in the rocks will be great, comfy warren for rodents to hang out in, planning their next attack.  Meow, here kitty-kitty!

The idea of using 'fencing' as a deterrent or structural element is good in that you can make by hand precisely what you need. For example if you are making Square Mesh on site, you can make a single sheet of 'fence' as wide as you want - no joints for example over an entire roof.

You may have seen the Diamond Stucco Mesh on the same website. This was specifically designed to make a wire product that could hold cob or plaster without and backing - sort of like a chicken wire that is sized to hold plaster. It has a thickness of about 5mm meaning if you push it against a mould, the cement still gets behind half the wires and onto the other half.

The purpose is to be able to add a very strong reinforcement to plastered things like hay bales without investing a lot of money.

The Diamond Stucco Mesh machine is also used to make stainless steel mesh for bird cages. Unlike chicken wire (rigid hexagonal holes) it is stretchy so it can form over complex shapes like barrels. The machine is not easy to learn to use it - it takes a few days. Experts make about 25 m^2 per day (14mm holes). There are no machines in North America.

The Square Mesh has been made by hand down to 30x30mm. It is used to make gabions with internal dividers. The usual size is 76mm (3") holes.

The savings over buying fence may not be much where you live - check the cost of plain wire in bulk per kg and fence per kg first. The difference is the available savings. Most places it is 40% but watch out. Same warning for barbed wire.

If there is any interest in making water tanks from cement and mesh I can forward drawings for making a mould based on a galvanised corrugated iron water tank. We made dozens of such moulds for thousands of tanks in Southern Africa. The finished tank is 40mm thick (1-1/2"). Sizes were 1000 and 2000 Imperial gallons (4500/9000 litres)

Maybe I'll have to leave a gap between the inner cob and outer gabions... and say that it's broch, not black-house inspired!

Crispin Pemberton-Pigott wrote:The idea of using 'fencing' as a deterrent or structural element is good in that you can make by hand precisely what you need. For example if you are making Square Mesh on site, you can make a single sheet of 'fence' as wide as you want - no joints for example over an entire roof.

You may have seen the Diamond Stucco Mesh on the same website. This was specifically designed to make a wire product that could hold cob or plaster without and backing - sort of like a chicken wire that is sized to hold plaster. It has a thickness of about 5mm meaning if you push it against a mould, the cement still gets behind half the wires and onto the other half.

The purpose is to be able to add a very strong reinforcement to plastered things like hay bales without investing a lot of money.

The Diamond Stucco Mesh machine is also used to make stainless steel mesh for bird cages. Unlike chicken wire (rigid hexagonal holes) it is stretchy so it can form over complex shapes like barrels. The machine is not easy to learn to use it - it takes a few days. Experts make about 25 m^2 per day (14mm holes). There are no machines in North America.

The Square Mesh has been made by hand down to 30x30mm. It is used to make gabions with internal dividers. The usual size is 76mm (3") holes.

The savings over buying fence may not be much where you live - check the cost of plain wire in bulk per kg and fence per kg first. The difference is the available savings. Most places it is 40% but watch out. Same warning for barbed wire.

If there is any interest in making water tanks from cement and mesh I can forward drawings for making a mould based on a galvanised corrugated iron water tank. We made dozens of such moulds for thousands of tanks in Southern Africa. The finished tank is 40mm thick (1-1/2"). Sizes were 1000 and 2000 Imperial gallons (4500/9000 litres)

Just been checking out the other equipment, some really interesting stuff - I like the air-compressing ram pump. This house build is purely hypothetical at the moment - but should our plans come to fruition I will enquire further about the mesh machines. Would you be able to PM me with a quote for the square and diamond mesh machines and P+P to the UK?

Yes. Quotations come from Thabsile Shongwe. Sea Freight is possible. Air freight is sometimes cheaper. Other times it is better to make your own.

You can click on any of the email links to send an email to Thabsile (a lady).

There are masses of photos available of these technologies in use - just a taste on the web. Many have been on the market for 20 years. For home construction also see the hand operated rock crusher. There are 90 in Haiti.

Thanks Crispin.

If anyone has any comments regarding the design/feasability of this build - especially the marrying of cob and dry-stone gabions - I'd love to hear them!