Email from a reader: Hello, I am trying to put together a design for an earthbag dome built into a hill in New York, and for a few reasons, I would like to have some of it underground. Actually, there are two adjacent domes, one with a diameter and height of 14′, and the other 8′. The frost line here is at least 48″, and I’ll probably go down further.
I was looking to the design on Jovoto.com for inspiration. Does encasing the entire bottom of the dome in a waterproof membrane mean no foundation is necessary? Is there a better alternative? I worry about moisture leaking in through the seams of the polyethylene, but if I bind them (using an iron?), or alternate where they overlap, can I avoid this problem?
Slightly off-topic, but there’s a lot of slate on my property, and I’m wondering if it would be too much weight to cover the exposed part of the dome with it?
Thank you so much for your input, Georgie
Owen: This design is most suitable for small, low value structures such as vacation cabins, temporary shelter, etc. and if that’s what you’re planning then yes it can work. Just realize that domes evolved in deserts, and they are vulnerable to water damage in temperate climates. Building below grade increases the risk of water damage. A better option is to build above grade with earth berming.
I would fill the lower courses with gravel or preferably some type of insulating fill such as porous volcanic rock (scoria). The gravel bags act as a foundation. Plastic sheeting punctures very easily and most likely one layer will leak. I recommend heavier duty bituthene rubber. Shop around and you can find lower cost brands.
Adding slate on top is not a problem because domes are extremely strong. The main concern again is protecting against water penetration. Just imagine all that melting snow in NY.
A longer lasting option is to build small roundhouses with roofs made of wood poles and bales covered with bituthene and sod.