Q&A - Footings

It is always fun and interesting to hear from wallers from across the world - thought I’d share this question that recently came from a waller in Japan.

Q:  “I am a member of the DSWA, trained and qualified with the South Wales branch in the UK but currently living and working in Japan, where I am trying to advocate the magic and wonder of dry stone walling.  I haven't been walling long and am consequently always trying to improve my techniques and learn as much about the art as I can, which is one of the reasons that I bought both the books you have written.  Not only was the work included in them astonishing, I was quite blown away by the accompanying prose.  I am myself useless with words, but as I read what you had written, especially with regard to the way you see what you do as an close interaction with the environment and nature, I found myself nodding my head saying "Yes, yes, that's it!".  It made me feel somehow reassured.  It was also reading your books that makes me write this inquiry to you...in your book "In the Company of Stone", there is a section at the back which catalogues each project, giving location, dimensions, description etc.  It is here that I was interested to read the for some bases you simply built straight onto the subsoil, like the traditional field walls back in the UK, but for others you were building on 2ft deep bases filled with 1.5 inch crushed stone.  I was hoping that you could let me know the reason for this latter base preparation.  Is it to do with drainage or to combat permafrost or to distribute the weight of the wall or something else?  Also, how do you decide whether to use the deep crushed stone base or just to build on the subsoil?”

A: Thank you for writing, it's fun to hear of wallers and dykers traveling with the craft to far flung parts of the globe.  I hope your experience in Japan is as rich and gratifying as I imagine it to be.  I've never been further west than Hawaii and that was a geographical and cultural awakening for me. Regarding foundations (bases, footings) for dry stone walls, as you pointed out from analyzing the project descriptions in "In the Company..." I'm all over the map with that.  Here's an excerpt from another response to a comment on my blog that explains why I do sometimes use a crushed stone base. Wall failure due to tipped foundation stones is sometimes the result of cyclical frost heaving.  It's the let-down as much as the heave-up that creates the settlement.  As frozen soil particles thaw, they are suspended in liquid (water).  The weight of the wall squishes them out, right along with the melt water, allowing the wall to settle into the resulting voids.  Best to use a base material that doesn't absorb water.  I most often use 1.5" crushed stone.  The spaces between the crushed stone may fill with water and freeze but the crushed stone stays put during the freeze/thaw cycles.  For depth of footing I use - "1/2 height of wall."  So, for a 4' high wall, a 2' crushed stone footing. The reasons I might NOT do a crushed stone base include difficulty in bringing materials to the site, a high, dry, well drained site, height of finished construction, scale of stone used, or just in a rush to start building.