Retaining walls for pool yards on a slope

A pool is a level box of water. The deck around it has to be close to level too, with just enough pitch to shed water. On a flat lot you dig, set the pool and pour the deck. On a sloped lot something has to make up the difference between the high side of the yard and the low side, and that something is usually a wall.

There are two basic moves. You can cut into the hill on the uphill side and hold the cut back with a wall, so the pool sits into the slope. Or you can build up the downhill side with fill and hold the fill in place with a wall, so the pool sits out on a terrace. Most real yards get a bit of both, because balancing cut and fill keeps dirt from being trucked in or out.

Northeast Ohio has plenty of these lots. Houses that back onto a creek or ravine, walkout basements with the yard dropping away behind them, and newer subdivisions graded to push water toward a swale at the back of the lot all show up on our site visits. None of them rule out a pool. They just change where the money goes.

Segmental block walls are the most common choice for residential pool yards. These are dry-stacked concrete units that interlock and step back slightly with each course. Poured concrete walls and natural stone walls are the other options, and on bigger grade changes we sometimes pair a block face with an engineered structure behind it.

The industry group for block walls, the National Concrete Masonry Association, separates them into two kinds. A gravity wall holds the soil back with its own weight and the lean of the stacked units. It works for short walls, generally a few feet of exposed height. A soil-reinforced wall adds layers of geogrid, a strong plastic mesh laid between courses and run back into compacted fill, so the wall and the soil behind it act as one heavy mass. NCMA's installation guide says reinforced walls are the right call when the gravity height is exceeded, when the wall has a slope above it, when the foundation soils are poor, or when the wall carries a surcharge.

A surcharge is any extra load sitting on top of the retained soil. A driveway is one. A house foundation is one. A pool full of water and the concrete deck around it are a surcharge too, and NCMA lists pools by name among the loading features a wall designer has to account for. So the short, simple wall you might build to hold back a flower bed is not the wall you want three feet from the edge of a pool.

Water, not soil, is what pushes most failed walls over. When the soil behind a wall saturates, the pressure on the wall climbs, and in winter that wet soil can freeze and heave. Much of this region sits on glacial till with silty clay soils that drain slowly. The USDA's description of Mahoning silt loam, one of the most widespread soils in Northeast Ohio, notes a perched water table within about a foot of the surface for much of the fall, winter and spring in most years. A wall backfilled with that same clay and no drainage is holding back a wet sponge.

A properly built wall has three drainage parts. Clean crushed stone goes directly behind the block, and NCMA calls for this gravel zone to be at least 12 inches thick. A perforated drain pipe runs along the base of that stone and exits somewhere lower on the property. And the ground above the wall is graded so surface water runs along or away from the top of the wall instead of pouring over it. On a pool job, we also plan where the pool's own overflow, the deck runoff and the roof downspouts go, because one badly placed downspout can undo the rest.

The wall also needs to sit on a compacted base below grade, not on topsoil. NCMA's best practices guide gives a minimum buried depth of about one tenth of the exposed wall height, and never less than 6 inches, with more when the ground slopes away in front of the wall. That buried course is what keeps the bottom of the wall from kicking out.

Tiered walls, two or three shorter walls stepped back up the hill with planting beds between them, often look better than one tall wall and give you usable ledges for plants or seating. They are not automatically easier to build, though.

NCMA's rule of thumb is that if the upper wall sits closer to the lower wall than twice the lower wall's height, the upper wall loads the lower one. Two 3-foot walls set 4 feet apart behave more like one 6-foot wall than two separate 3-foot walls. Building departments know this, and some will look at the combined height of a tiered system when deciding whether it needs a permit and an engineer. If you want the look of terraces, plan the spacing so each tier really is independent, or design the whole system as one structure.

It depends on your city, and the state code is less help here than people expect. The 2019 Residential Code of Ohio added an exception that takes retaining walls, walkways and site stairs out of the residential code unless they are tied to the house or its exits. Before that, walls under 4 feet, measured from the bottom of the footing to the top of the wall, were simply exempt from approval. The effect is that local rules now carry most of the weight.

Akron is a good example of how that plays out. The city says a retaining wall under 48 inches does not need a permit, while a wall 48 inches or taller needs a permit from the Summit County Department of Building Standards, and the city also wants a site plan showing where the wall goes. Other towns set their own thresholds or route everything through zoning review, especially near a property line or in a drainage easement. Because the pool itself needs a permit anyway, we draw the walls into the same plan set and ask the building department up front which parts they want to review.

Height is not the only trigger. A wall that holds up a pool deck, a driveway or a structure is carrying a surcharge, and those walls usually need an engineered design no matter how short they are. That is a good thing. You want someone to have run the numbers on a wall that sits beside several thousand gallons of water.

A tall wall creates a drop-off, and a drop-off next to a pool deck is a place where people walk barefoot and wet. The Residential Code of Ohio requires guards on open-sided walking surfaces more than 30 inches above the grade below, measured within 36 inches of the edge. Whether an inspector applies that to a particular site wall varies, but we design for it whenever a deck or patio ends at a real drop. A fence or rail set on or behind the wall handles it.

That same fence can often do double duty as part of the pool barrier your town requires. A wall can also work against you here: if the ground on the outside of the fence is higher than the ground inside, a child can use it as a step. We look at the barrier and the walls together on the plan so one does not defeat the other.

A fiberglass shell arrives in one piece and sets into a prepared hole, so the finished water line is fixed by the shell. On a slope we set the pool elevation first, usually tied to the back door or an existing patio so you do not end up with steps down to the deck, and design the walls around it. Where one side of the pool ends up partly above the natural grade, the backfill and the wall on that side have to be designed together so the shell has the support it needs.

ICF concrete pools give more freedom on hillside lots. The walls are built on site from insulated concrete forms filled with concrete, so the pool can be shaped to fit the slope and one wall of the pool can double as a raised edge with a spillover or a sheer descent into the pool. That approach turns the grade change into a feature instead of something to hide.

Either way, we model the yard and the pool in 3D before anyone digs. On a sloped lot that model is where you see how tall each wall really is, where the steps go and how the deck meets the house.

Walls are priced from the design, because the numbers swing with height, length, material and how much reinforcement and drainage the engineer calls for. A few feet of block along one side of a deck is a modest add. A reinforced wall system that creates a terrace on a steep lot can cost as much as a large patio. Our packaged fiberglass pools start at $68,400 installed, and retaining walls, extra decking, fencing and spoils haul-off are priced on top of the package after we see the site. Outdoor living and hardscape projects on their own start at about $15,000.

One place slopes can save money: if the cut from the uphill side can be reused as fill on the downhill side, less dirt leaves the site. Clay is poor structural fill, so it goes where it will not carry a load, and the reinforced zone behind a wall gets proper granular fill. We work that balance out on the grading plan.

If you are budgeting, get pre-approved early. We work with lenders including PoolLoan.net and HFS Financial, and a known budget makes it much easier to decide between a terraced design and a simpler layout.