​Domes have been an integral part of human construction for a long, long while. From the mosques of Istanbul to the basilicas of Rome or Moscow, from adobe vaults in Mexico to the snow igloos of the Arctic Circle, the curved roof can be found in an awful lot of places. So that must mean it’s great, right?
 
Hmm. There’s a lot to like about the dome. There’s a lot to be wary of, too. And there’s a very good reason it was only the Inuit of certain areas who built igloo snow domes. Others further south used other techniques. It's not just coincidence that the mud dome was traditionally built in places like Cameroon or Mexico, but not in Cornwall or Galicia. Dreaming of a mud Sistine Chapel in your back garden? Read on.

The dome became something of an architectural darling in the ’60s. A lot of this has to do with Buckminster Fuller, who began pioneering geodesic dome structures and biospheres in the ’40s and ’50s. A decade later domes became popular on a more individual homeowner level, when space-age architecture became trendy. This is also when the limitations of the dome as a house became clear.

The Good
Domes are beautiful for sure, and they feel extremely calming to live inside. They are like wombs or caves. And heck, for an artist they're both original and funky. With their soft lines and circular form they soothe both eye and spirit. But beware, like most sexy things, they come with some potentially costly drawbacks.
 
The Bad
Lloyd Kahn of The Shelter Blog wrote two books on domes. They were his most popular and lucrative publications. Yet he pulled them off the market because, to quote him, they were “smart but not wise”. Here’s a list of reasons why:
 
1. Impractical
One interesting issue Lloyd Kahn has with domes is that they are impractical. You can’t dissect them easily into sub-quarters, meaning they’re great for meditation centres or lecture halls, but not so great for a house, where you might want to cut the space up into separate rooms.
 
Solution: Well, I suppose here I’d say if everything had to just be practical in this life, I’d probably hang myself from boredom. That isn’t to say Lloyd doesn’t have a good point. I experienced the same issue on a lesser scale with my roundhouse. Pretty much all building materials are designed for squares. And you’re probably going to be making your own furniture if you go dome. But as far as the separate rooms are concerned, if your heart is set on round then the solution is to build multiple smaller round spaces that are linked, like Rhonda did here in Mexico.

2. Leaking
One of the more serious disadvantages of the dome is they are notoriously difficult to waterproof, because unlike most housing structures, there's no roof, and therefore no 'hat' to protect the structure. This is fine in a desert, and even more fine if you only have soft powdery snow sitting on ice blocks. But bring in some serious rainfall, and you’ve got major problems. For the geodesic domes there are masses of joints where the triangular panes all tessellate, all of which are potential leak points. That’s a lot of sealant you’re going to need, and a lot of potential maintenance.
 
For mud domes, in particular earthbag domes, water-protecting is the thing you absolutely have to wrap your head around. Because what you really don’t want to do is what every mainstream builder will tell you to do, namely coat it in Portland cement.
 
Don’t cement over a mud dome!
If you slap Portland on, you have basically stuck an impermeable crust over your lovely breathable walls. So you’ve just killed the airflow. Boom! This will lead to an increase in mould and damp. The house won't be as cool in summer (or warm in winter) as it would have been if it were all mud.

Also, there’s a reasonable chance the cement will crack and fall off too, as clay walls expand and contract with humidity changes, while Portland can’t. See this experience kindly shared by Gautam. Please note this was lime render not Portland, but basically it's the same issue (though at least the lime render will breathe). http://www.themudhome.com/.../gautam-and-kims-earthbag..

Proper solutions:
There are two main ways to keep a dome dry:
 
1) Do what Jehane Rucquoi did at 3 Moons and build a deck on it, or add some sort of cap over the top. This is easily the best way to protect the dome. Jehane's design was ace if you ask me.
 
2) Use shingles. See more about them here: https://en.wikipedia.org/wiki/Roof_shingle
 
Yes, domes are a tough one. But I'm not going to lie, I'll probably make one before I die, because for a creative soul they are beguiling structures.

Related links:
 
Kelly Hart’s interview with Oliver Goshey, all about earthbag domes. A must-listen if you are considering building one! https://abundantedge.com/abundantedge-xzmogh2g479mqg866e0v765lb804l6
 
Lloyd Kahn interview, where he discussed the limitations of the dome: https://www.buildingsustainabilitypodcast.com/45-years-of-building-inspiration-lloyd-kahn/
 
Rhonda’s dome world in Mexico: http://www.themudhome.com/mudbuilding/rhondas-sculpted-earthbag-dome-home-in-mexico
 
Jehane’s earthbag domes in Nevada:
http://www.themudhome.com/mudbuilding/the-85-year-old-dome-builder-of-arizona
 
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The type of roof you choose for an earthbag house is important. No matter whether you construct a circular house or a rectangular one, you want to take into account your roof before you build (or be prepared to alter your roof style at the end).

I won’t deny it. When it came to my earthbag roof, as is so often the case with me, I skidded to success by the seat of my pants. It was sheer luck I chose the right type.

Roofing structures exert a lot of pressure onto earthbag walls. This is fine if the pressure is in the right direction because earthbag walls are strong. What you want is the pressure exerted downwards. What you don’t want is it pushing outwards.

The safest roof type for earthbag
If you are a beginner, the safest, most foolproof roof to stick on your earthbag house is a flat or skillion (pitched) roof, utilising horizontal joists running the length of the building. The joists act as a type of grid that pulls the structure together and prevents the walls falling outwards. What’s more, if you’ve built a smallish round house, you won’t even need a bond beam! You could top the joists with a number of materials: Corrugated iron, ply/strand board with a membrane. Any weight on the roof will be distributed by the joists and easily supported by the earthbag walls. The pressure exerted by such a roof is downward.

The link below shows another example of an alternative reciprocal roof on an earthbag house. Notice how this team combined two styles here. While the main structure is reciprocal, a web of rafters has been inserted into each facet of the roof. Those rafters then form the all-important grid through the top of the earthbag wall which locks the whole structure together.
http://mylittlehomestead.com/ep12-undergound-earth-bag-construction-reciprocal-roof-facia-frame-complete.html

Why you don’t want a compression roof
Compression roofs are typically used for yurts. The design of a compression roof means the strength of the roof structure is derived from the compression between an outer ring or wall, and an inner ring. Such a roof is exerting a lot of outward pressure on your earthbag walls.

If you know what you’re doing, there are of course a whole gamut of other wacky and exciting options for earthbag house roofs, and you'll be able to customize many to work for earthbag. But presumably, if you know all about roof construction, you're not reading this post.

Do you enjoy The Mud Home?
If you find these articles inspiring or useful please consider joining us on Patreon. Your support pays for the running of this website, my virtual help, and my sustenance. A big thank you to all The Mud Sustainers, and everyone chipping in and keeping these posts and articles coming.