How to Build a Retaining Wall that Lasts
Roger Cook comments on building a stone retaining wall that requires little maintenance
One of the stone retaining walls next to our house is in rough shape, with bulges and loose stones. It looks ready to topple over. How can we rebuild it so it will last a lifetime?
—Anthony Gabrielson, Hollis, NH
Building a stone wall is an art that requires a strong back and the ability to take a random pile of rocks and fit them together into a three-dimensional jigsaw puzzle. I’m not saying you can’t tackle this project, but like any art form, it takes practice to develop stone-wall-building skills, and it’s unlikely that your first attempt will “last a lifetime.”
Lucky for you, New Hampshire is rich in rocks and has quite a few professional stone-wall builders. A pro will bring in his own supply of stones to supplement the ones salvaged from your old wall.
There are three ways to build a wall on-site: with large stones held together by mortar, with thin veneer stones adhered to a concrete-block wall, or with large stones held together only by gravity. This is known as a dry stone wall. The first two methods must have a footing that reaches below the frost line so that soil movement won’t crack the mortar. The base for a dry stone wall doesn’t have to be so deep—because it uses no mortar, a 6-inch-thick bed of well-tamped crushed stone is sufficient—but the building process will go slower and be more expensive than the other two methods. Plus, reputable dry-stone “wallers” are scarce and in high demand, a factor that really pushes up the price of that type of wall.
But in New England, there’s now an alternative: stone walls built off-site. Natural Stone Wall Solutions has developed a patented process in which stonemasons marry real stones to reinforced concrete, forming sections that can be used for either retaining or freestanding walls. The sections, which can be curved or straight, are trucked to the job site, where a crane deposits them on a pad of crushed stone just 24 inches deep. After the sections are set in place, the joints between the sections are hidden with stones that were fitted but not attached to the concrete.
At the TOH Generation NEXT project house in Newton, MA, the company delivered 75 linear feet of a 30-inch-high retaining wall and completed the work in less than 3 hours. Building that same wall on-site with mortared stones would have taken my crew and me more than a week.
This approach saves not only time and lots of heavy lifting but also money. NSWS’s walls run about $50 per square foot, with a minimum order of $20,000. That’s 20 to 50 percent less than standard stone or veneer-stone walls.
Right now, the high cost of transporting these sections limits their availability outside of New England. But this welcome option will likely be more widely available as more factories are established in other parts of the country.
Shown: Roger Cook checks the top of a newly installed stone wall that was manufactured off-site. The wall’s sections were put in place with a crane in just a few hours.