Landscape projects these days, both large and small, are placing a higher demand on the professional to address issues associated with moderate-to-steep slopes. Unlike small-sloped sites where a variety of landscape features and materials can be incorporated into an overall design, steep slopes limit a number of these features. One method that can be employed under these conditions is introducing terraces into the landscape design. The following shows you some of the factors involved in planning a terracing project.

Wood, stone, concrete, masonry and other materials can be used to create terraces, but some municipalities have passed laws regulating materials use. For example, the City of Portland has banned use of railroad ties manufactured after a certain date, due to chemical preservatives found to be harmful to groundwater.

Eliminate Erosion

Across the nation more development is occurring in areas that traditionally weren’t thought of as acceptable terrain for a building. This has opened a whole new series of ecological concerns within various municipalities. Properly designed terraces help to manage difficult hillsides by providing definition to the terrain, often reducing or eliminating existing site erosion.

This can be an important design consideration, especially if your local municipality has strict guidelines established to control hillside erosion on new projects.

By effectively using terraces in a project, steep slopes can be reduced considerably and allow more traditional landscape materials to be used. Terraces also open up a hillside to more planting space for yards or gardens.

Built-in value: Benches

When creating terraces on a steep slope for a homeowner, a detail that can be a benefit to you and a convenience for the customer is series of terraces that can also be used as a bench. These benches will create a friendly environment within a yard should your client do a lot of entertaining, and provide a place of rest when they are maintaining the planting beds that these small terraces create.

Small terrace walls -- between 18 and 26 inches high -- are more aesthetically pleasing than one or two large terrace walls, and often are more cost effective too, since they don’t require massive amounts of backfilling or material movement.

Be sure each terrace you build is sitting on a firm, natural grade. Beware of subdivisions where fill material has been piled up or dumped to create the grade, as this material will make for unstable terraces. If your terrace exceeds 48 inches on a slope greater than 2:1, chances are you'll need a building permit.

Material Choices

Several materials are available to create a terrace wall in a landscape project. Each has its own characteristics and skill level required for installation. Traditional products like wood and stone are being reevaluated in several municipalities due to concerns about environmental impact to watersheds from the source of the products. This is spurring manufacturers to create substitute systems that can compete economically as well as aesthetically. Here is a listing of the more popular types:

• Wood

In certain parts of the country, wood has been the staple product for creating terraces. Whether as planks or timbers, this type of material has been rather easy to install. Current economic and environmental concerns are beginning to force this product out of the prominence that it once had. Some municipalities are restricting its use because of the types of preservatives that are being employed and their impact to local watershed. When considering a wood terrace, check with local building officials as to their particular concerns.

• Masonry

Unit masonry has taken a front-row in the terrace arena. Traditional products like concrete masonry units (CMU) and brick are being replaced with larger, stackable units that often don’t require the skill set of a mason for installation. Various sizes and colors create a greater degree of flexibility in the overall design of a terrace project.

Try to design the placement of your terraces so that each wall's excavated soil can be used as backfill for that wall and the terrace area that is being created.

These products are often the most cost effective for a large terracing project. Yet due to their wide acceptance and uniformity in appearance, many newer developments are beginning to put restrictions on their use, especially if there is a lot of terracing that will be required.

• Concrete

Pouring concrete into a form is pretty standard stuff, except when you get into terraces. Issues such as excavation, backfilling, forming and bracing, and site access of material are just a few of the issues that must be addressed with this material. Often this type of material is not economically viable if several terraces are planned for the project.

• Stone

Stone still evokes that "old-world" charm in every terrace project. Stone terraces typically are designed using the "gravity/mass" principle: A large mass is built to resist the force of the gravity being applied against it. The stone mass is built either as a "dry-set" or "mortar-set" wall.

Determining whether to install a dry-set or mortar-set terrace wall is the key to using stone, since each type has its own unique cost and construction requirements. If the project requires removing an existing rockery, it is possible that this on-site stone may be incorporated into a terrace project and keep the hauling costs down.

When building stone terraces, you might choose to recycle any existing stone that is removed (such as driveways, patios and walks). Properly designed terracing can all but eliminate site erosion problems.

• Alternative Materials

New products are being introduced every day. Each is created to deal with a specific site condition. Their cost and benefit must be reviewed against more traditional materials. Other types of product to consider are recycled materials, such as concrete slabs. Numerous municipalities are looking for ways to reclaim this from their limited landfill space. This product can be effectively used to construct attractive "stone appearing" walls at a fraction of the cost of stone. An added benefit is that if the project site has a driveway, patio or walk that is going to be replaced, a quick source is readily available, keeping your hauling and disposal costs down.

Site considerations

Site conditions effect all terrace projects differently, even when they are right next door to one another. The primary factor that must be addressed in a terrace project is soil condition. Since a structure is being built to support the soil behind it, each terrace wall has to be sitting on firm, natural grade.

As easy as that is to say, it can be difficult to find in some subdivisions where fill material has been piled up, dumped and/or regraded from surrounding development. An additional excavation expense should be included if there appears to be a chance that fill material may be present on a project site.

Once this natural grade has been established, then comes the critical question: How many terraces and how high should they be? Most jurisdictions allow terraces to be constructed under 48 inches in height without a building permit. But should your project exceed the 48-inch limit or retain a slope that exceeds a 2:1 grade, then a building permit often is required along with appropriate structural and/or soils engineering.

For example, let’s say that you have a bank that from the toe to the top is 7 feet, 0 inches in height. What are your options?

Option #1: Your could create one terrace, 7 feet, 0 inches tall! This will require a building permit and engineering in order to build it. In the overall design of a project, you need to know that this will create a "fortress" look that won’t be easy to hide with other landscaping features.

Natural stone is always a good look for terraces, though its use is being reevaluated in several areas due to concerns about environmental impact to watersheds from the source of the products. Always check with your local municipality before making terrace material decisions.

Option #2: You could create two or more terraces using shorter walls. This option will work provided that you have enough room to allow space between each terrace. The general rule-of-thumb is that you need to have a minimum distance between two terraces that equals the height of the upper wall. If there isn’t room available then an upper wall will create a surcharge weight that will require the lower terrace wall to be engineered to support the upper wall.

One additional site consideration in the design of a terrace project is backfill. As mentioned previously, excavation is an integral part of any terrace. Try to design the placement of your terraces in such a manner that each wall’s excavated soil will be able to be used as backfill for that wall and the terrace area that it is creating. If this is possible, you can keep your backfilling -- as well as hauling expense -- to a minimum.

Equipment Issues

In new construction, there aren’t a lot of concerns about what equipment to use to create a terrace project. But in an established neighborhood, selecting the right equipment to complete the project is critical. Often, accessibility to the project site will be the main obstacle to overcome. This generally limits the use of larger pieces of equipment.

A small trac-hoe is beneficial in projects of this sort since they don’t require a significant amount of space to maneuver around. A skid-steer loader is also ideal for moving material in and out of the site. With both of these pieces of equipment make sure there is enough clearance for them to move throughout the project. Additionally, verify the location of any utilities and sprinkler systems that might be in the direction of travel or within the area of work.

If you are doing a lot of unit masonry wall construction then a must-have is a plate compactor. Most of these systems require that the gravel footing base be compacted. Also, there are the standard tools of the trade that we just can’t seem to get rid of: A pick, shovel and wheelbarrow. While you may try to keep away from manual labor as much as possible, some projects just can’t be done any other way.

After reviewing all the above factors, it might appear that creating terraces might not be worth the trouble. Yet as with most processes in the construction industry, it takes longer to explain it then to "just do it." A successful terracing project will surely propel you on to creating more diversity in futue projects.

Richard McCutcheon is president of The WALL, a retaining wall company in Portland, Ore., that specialize in using recycled materials in its projects. Mike Hillebrecht is the vice president of marketing for The WALL.