Part inspired by pictish wheelhouses, this is the latest in a long line of house designs. Keen for feedback and thoughts!

This approach relies on the generous use of foam glass aggregate - for all round insulation, drainage and use as rubble trench foundations for lime mortared walls. The entirety to be covered in a waterproof membrane, a "geosynthetic clay liner" and a good topping of soil and turf.

The space between the walls can be filled with more stone/gravel.

The "hogan" roof is designed using 200mm diameter logs, capable of supporting 1000kg/m2 at a 3.4m span when butted against each other.

What is the benefit of such a design over a simple circle or spiral? If the walls curved in a circle rather than cutting back in, the interior space would be much greater and the surface area of the walls would be much less meaning lower costs in materials.

Daniel Ray wrote:What is the benefit of such a design over a simple circle or spiral? If the walls curved in a circle rather than cutting back in, the interior space would be much greater and the surface area of the walls would be much less meaning lower costs in materials.

Primarily to add a large amount of thermal mass, compartmentation and structural stability. These dimensions and spans permit the use of relatively small diameter timber in construction. A large amount of light is also able to enter the structure through large glass doors/windows from all six perimeter rooms.

I have struggled to find a way to build an equivalent with natural stone and timber using a circle or spiral. Are there examples you have in mind?

I don't have any specific design in mind although there is a really nice one here http://www.balewatch.com/895spiral.html

However that design is not built to withstand the type of weight in a bermed structure. A circular building with the same window/glass placement would allow better light distribution without the walls. Of course any circular home would stI'll need interior walls that would block light.

Support for a living roof could come with a reciprocal roof, but I'm unsure of the diameter to bearing loads for round diameter timber.

It is a cool design, are there any real life examples of this anywhere you know of?

Daniel Ray wrote:I don't have any specific design in mind although there is a really nice one here http://www.balewatch.com/895spiral.html

However that design is not built to withstand the type of weight in a bermed structure. A circular building with the same window/glass placement would allow better light distribution without the walls. Of course any circular home would stI'll need interior walls that would block light.

Support for a living roof could come with a reciprocal roof, but I'm unsure of the diameter to bearing loads for round diameter timber.

It is a cool design, are there any real life examples of this anywhere you know of?

I should have mentioned our location - the Isle of Lewis. The occasional 130mph winds put the need for such a sturdy structure into context. I'm trying to draw upon the vernacular with all the stone and turf - see the following images for real life ancient examples. Here is a more modern take using shipping containers.

As a self builder I am wary of using a reciprocal frame roofs due the inherent issue known as progressive, or disproportionate, collapse. The structures rely on interlocking of the main members, which means that the accidental removal of one member can potentially mean the collapse of the entire structure. A corbelled roof is a simpler, more predictable approach which doesn't suffer from the same problem.

I have the same reservation about reciprocal roofs. They are an ingenious idea and very cool, but I wouldn't want to live under something that, if one part failed, the whole thing would fall on me.

Glenn Herbert wrote:I have the same reservation about reciprocal roofs. They are an ingenious idea and very cool, but I wouldn't want to live under something that, if one part failed, the whole thing would fall on me.

I've been underneath a few structures and have noticed a disconcerting bounce in the wind... not to say that they can't be constructed safely - but I don't feel confident building a foolproof one myself!

Neat design! I like the looks of that clay based membrane; do you have a notion of what it will cost you?


I like the idea of the compartmentalization... to a point. It would certainly be nice to have that degree of sound insulation between bedrooms and living areas. But doing it for 6 spokes, sure, it lets you use 8" logs of relatively short length... but man, you're going to need a lot of them with all those walls!

As far as wind resistance goes, it seems like once you add in the sloped, outer portion of berm extending out past the 'spoke' ends, you're starting to form a partial wind-trap; the ability of the building to let the wind flow past, was better as a simple dodecagon...

As far as energy efficiency goes, I`m not sure you`re doing yourself any great favours with spokes in all 6 directions, especially not if the intent is for full height exposed outside walls on the end of every spoke. Why not either skip the 2 northern spokes in favor of a semicircular rear wall bermed all around, or berm around the spokes? Either entirely, or enough that only a window opening remains? You're still going to pick up lot of light from windows starting 4 feet up. I think I would try for at least 1-2 windows, quite short but as wide as practical, around the bottom edge of the central hogan. I think you could lose a lot of your outer spoke glazing and still 'feel' brighter/more open with a fraction of that glazing in this location. Do you have much snow to worry about?


(And if you're berming around them... why not use the in-between spaces for additional interior space..?)


My limited experiences with structures with lots of thermal mass, suggest that it's not that necessary to have so much surface area, to see the benefits. And if you don't need the surface area, its more time/money/hassle/risk than the same space, with less surface area, all else being equal. You can pick up thermal mass outside the structure, with your membrane, drainage, and maybe some insulation...


..I guess I should note, I'm picturing an excavator and ground that is possible to excavate. If you've got a mattock/wheelbarrow, and bedrock, I don't think my suggestions apply very well unless you can find some dynamite...

Dillon Crew wrote:Neat design! I like the looks of that clay based membrane; do you have a notion of what it will cost you?

Thanks Dillon! Depending where you get it and in what quantity, geosynthetic clay liners can cost $2 a m2...

You're right - it's a huge amount of 8" logs. But these can be sourced at a reasonable price, the total for this structure would be around $10,000.

Interesting point about wind resistance, makes sense - thanks.

I hear you on the windows, there's plenty of tweaking to be done here. Thing is, we've amazing views out to sea in the North - with lots of light reflected back. It's a fairly mild climate, rarely drops below freezing - and there's never any real snow to speak of. Just have the wind to worry about, need some pretty bomb-proof glazing...