From the rolling countryside of Ireland to the mountains of Kentucky, the craft of building dry stacked stone walls has a rich history. Hand crafted stone walls dating back hundreds or even thousands of years can be found around the world. They are usually mortar-less, built of local stone, and reflect each area’s vernacular architecture and cultural heritage.
Dry stone walls are built for many reasons. Some hold back significant amounts of earth, allowing railroads, highways, and buildings to be constructed. Others form the foundations for bridges or provide protective armoring for shorelines. Some are stacked as fences to delineate property limits and others are created for a sense of enclosure and can make a strong architectural statement.
Just within Wisconsin alone, we are truly blessed with a dizzying array of native stone to choose from for our dry wall constructions and would like to share some images and information with you. These projects highlight the dry stone wall building craft as well as the wealth of material riches that there is to choose from. We also invite you to contribute information through words and images including cases where dry stone walls solved a landscape architectural need in your area. Were there any special techniques or unique stone products used to complete the construction project?
Dry stacked stone walls are an important design element in the built environment and it is important that they be properly installed. With modern day technology, there are a few basics that should be taken into consideration when constructing a dry stacked wall:
1. One of the most important factors of a dry stacked wall is what is hidden in the construction of one. What is meant by this is the base preparation for the wall and what is behind it. It is imperative that a sound sub-base be installed. In the northern climates we typically recommend a minimum of 4″-6” of traffic bond but the depth can go as deep as 12″-18” in denser soils. The traffic bond base used can be made up of clear chips to further enhance proper drainage. Whichever sort of traffic bond is used, it should be installed in 2″-3” lifts and compacted using a vibratory compactor. The traffic bond base should extend 6” in front and in back of the wall.
This will ensure the integrity of the wall and will not compromise on the weight of the wall above the stone base. In some instances it may be worthwhile to pour in a concrete trench with reinforcement, but do keep in mind that this will be adding costs to your client. Again, the sub-base is vitally important to the longevity of the wall itself.
2. Proper backfill is also a considering factor when constructing the wall. Typically, backfill is clear stone in order to provide for proper drainage, but it is also dependent on the actual type of stone in which the wall is constructed. When dealing with fieldstone walls, a number of contractors will simply use compacted earth on the backside. However, this should properly be done so that large holes within the fieldstone wall are not present. Large holes may incur water and drainage channels, thus compromising the integrity of the wall itself. Some people do like to install filter-fabric behind fieldstone and other walls – this will be left up to your personal taste.
With walls that have very closed joints (typically Lannon stone walls) it is imperative that you not only backfill with clean stone in the Northern climates but it is also recommended to use drainage tile. With the freeze/thaw aspects of this climate, moisture can get behind the walls. When the moisture freezes, it will expand and thus begin to push the wall forward. This can easily be avoided with the incorporation of drainage tile.
3. Another item to take into consideration when constructing stone walls is the batter or the degree in which it deflects back into the hill. Keep in mind these are gravity retaining walls; they rely on the weight of the material to ensure they do not overturn. Typical batters are generally 2″-3” per vertical foot on fieldstone walls, whereas with more structured walls you can get by with 1″-2” of batter or tilt back into the hill with every vertical foot.
Other landscaping concerns that should be taken into consideration are the type of soils that you are building these walls into. Heavy clay soils have a tendency to store a lot of water which could be problematic in Northern climates. In addition, sandy soils can cause problems with slippage and failure.
With walls that are in access of 24”, you may want to consider installing barriers for the health, safety, and welfare of people. In addition, always check with local codes and ordinances regarding retaining walls and permit requirements. Surcharge on top of the wall is very important and should also be taken into consideration regarding the actual construction, design, and engineering of the wall. If you feel uncomfortable designing and engineering the wall refer to a civil engineer/structural engineer for typical guidelines.
Retaining walls are often installed merely for aesthetic quality, creating a nice texture alongside the landscape, but we should consider – when at all possible – to grade out the landscape with soil, lawn, or garden areas. Although we may feel that our designs may need that structural/design element, a simple slope may do the job with less cut to the land. Take this into consideration when you are designing with retaining walls and it may save time and money.
by Chris Miracle, PLA, ASLA, and Tim Garland, PLA, ASLA, Design-Build PPN Co-Chairs