As she is in so many things, Julie Andrews was right about the hills: they really are alive. And a common way to keep them in place is a retaining wall—a permanent structure, usually made of stone, treated wood, concrete blocks, or gabions (wire, stone-filled cages) designed to hold back a shifting slope, secure the bank you cut into for a new patio, or reinforce an erosion-prone shore.
Back in the day, cottagers could stick almost anything—even old railway ties or the rusting sides from scrapped railway boxcars—along the shore as a retaining wall. “People thought a shorewall would be a good way to mark the end of their waterfront property,” says Meaghan McDonald, the lake planning and shoreline stewardship co-ordinator with the Rideau Valley Conservation Authority. “But they’re prone to failure. Water will eventually find its way through.”
Retaining walls vie with culverts as the cottage’s most under-appreciated infrastructure. When they’re well designed, built, and maintained, they work and they can be ignored. But if you ignore a poorly designed retaining wall, it’s apt to crack, leak, buckle, or tip over. It’s a mess, and repairs can be budget-busting—not among any cottager’s favourite things.
H2O, destroyer of walls
A cubic metre of earth can weigh a tonne or more, placing a hefty strain on even a small wall. But adding water greatly boosts the ground’s shoving ability, says Kim Pressnail, an associate professor emeritus in the Faculty of Applied Science and Engineering at the University of Toronto. Hydrostatic pressure—the pressure from groundwater in the soil pushing against the wall— “is the real killer for these walls.” Gravity increases hydrostatic pressure near the base, especially if the wall is near the water table. Cars and buildings above also add to the load.
To see these forces in action, check out slopes around the lake. Trees growing in an upward curve, like a bow, indicate slow soil movement over a period of years. “As the soil moves, the tree grows upward to straighten itself out,” says Pressnail. If trees are straight but leaning, like the Tower of Pisa, that indicates rapid soil movement. “If I had trees like that near my cottage, I’d be worried. The soil could shift from under the foundations.”
Walls right at the shore have it even tougher—unrelenting soil pressure on one side, constant attacks from water on the other. If high waves overtop the wall, they erode the back side and waterlog the backfill. Meanwhile, the waves’ frontal assault can scour sediment and undermine the base, setting up the wall for failures during extreme storms.
Then there’s ice. In spring 2025, wind-driven ice floes lifted a two-tonne boulder from Pressnail’s Lake Simcoe waterfront and “within the span of two minutes, rammed it into our boathouse,” he says. “That’s the kind of force at work.”
Climate change is weighing in too. A warming atmosphere holds more moisture, and more intensive rainfall means wetter soils, so retaining walls have a tougher job. Meanwhile, reduced Great Lakes ice cover leaves the shore exposed to winter storms. On parts of Lake Huron, this could boost erosion by an extra 30 per cent during the next century.
Signs of wall trouble include cracks, bulges, and leaks, and, with timber walls, rot. These problems are often triggered by poor drainage, insufficient footings, the wrong backfill, or even improper compacting during construction. If it’s a small landscaping wall for, say, a raised garden bed, you may be able to excavate it yourself, install new fill, foundation, and filter cloth, and replace clogged weeping tile with new perforated pipe. For big jobs, you’ll likely need to call a pro. “If you’re trying to restrain a large slope, it’s not going to be easy,” Pressnail cautions.
You’ll likely also require permits, granted by municipal or shore authorities. British Columbia’s Central Okanagan Regional District, for example, requires an engineering report for walls higher than 1.5 metres and those in a “riparian or flood plain area.” The Ontario Building Code gives projects free rein up to a metre high, but in some cases requires a permit after that.
As for vertical walls on the water’s edge, cottagers wanting to build new ones are often blocked by shoreline regulators concerned about impact to the environment and neighbours. The owner of a functional older wall “can do repairs if the wall is in okay condition and needs some work,” says McDonald. But you’ll likely face extra hurdles if your wall is near a wetland or an erosion-prone slope, or within the 100-year flood line.
Whether an old wall is repaired or torn out, the task may require heavy equipment to remove or replace damaged sections, pumping to keep the work area dry, and silt fencing to hold back sediment runoff and protect habitat. Jennifer Cooney, co-owner of Cooney Construction and Landscape in Almonte, Ont., prefers working on waterfront walls after Thanksgiving, when water levels are low and lakes are less busy. Even so, it’s not easy getting an excavator around trees and septic systems—one reason some contractors work from barges.
For big failures, including buckling and collapsed shore-walls, the typical inland-lake fix includes regrading the shore for a sloping waterfront, held in place by a mix of stone and plants. The type of stone varies by location and the level of erosion. “If you put down anything round or too small, it will get picked up by the water and washed away,” says McDonald.
To salvage a section of toppled concrete wall, Cooney’s firm dug out the rear of the bad section, improved fill and drainage, replaced filter cloth, poured a new reinforced concrete backing, and then tied it into the rest of the wall with rebar and concrete. With any shoreline work, she says, the goal is leaving clients and regulators happy, and that’s not always easy. Cottagers want a useable, stable shoreline, while the regulators want safety, minimal environmental impact, and no knock-on erosion happening to your neighbours. “We work with the client and the conservation authority to find a balance that is sustainable,” she says.
Difficult slopes further complicate the work, sometimes requiring geotechnical engineering and a stability study, with boreholes and lab work to analyse and map the earth and groundwater. None of this is cheap. Even a small retaining wall repair can cost between $15,000 and $20,000, says Cooney. Big jobs, with quarried blocks of armour stone, mixed-size riprap stone, and engineering can go into the six-figure range.
The demanding nature of this work means “there are very few DIY jobs” near the shore, says McDonald. “Rock is heavy, and usually there’s a lot of earthwork involved when you’re regrading. Most likely, you’ll have contractors involved.”
Diagram By Taylor Kristan
Concrete block retaining wall
Diagram By Taylor Kristan
Pressure-treated timber retaining wall
Build your own
For cottagers who want to try their hand at building a retaining wall, the best option is a modest project away from the shore, ideally one that doesn’t require a permit. “I’d keep it to a metre or less of exposed wall,” Cooney advises. “Once you get above that, you’ll probably need engineering.”
The easiest and most durable approach is a precast block wall, with segments that stack and slot like giant Lego blocks. Blocks range from small hand-hefted units for about $15 a piece to massive blocks such as StrongWall’s two-tonne units that retail for $185 and up. Manufacturers supply detailed instructions for assembly, but these are no substitute for proper engineering on difficult sites, or where regulators demand it.
No matter the size of the project, “the best way to manage the water pressure is to get rid of the water,” says Pressnail. Drain moisture from the wall’s rear and foundation with a base of clean crushed stone (3/4″ ASTM#57 aggregate is recommended by some suppliers), properly compacted and screened with geotextile filter cloth to prevent plugging by fines. Run a four-inch plastic perforated pipe behind the wall to help whisk water away. If the wall is impermeable, add weep holes to let water through the face. For timber walls, drainage has the salutary benefit of reducing rot and boosting lifespan.
Appropriate fill also counters the threat from frost-active native soils, such as silts and fine sands, in which pockets of ice can heave or jack the wall horizontally. Cottagers with frost-susceptible soils should consider “a sheet of vertical insulation on the inside of the wall, between the wall and the earth,” says Pressnail. This insulation absorbs some of the horizontal pressure when the ground freezes and expands.
The other option is to avoid a wall. “A lot of the time, retaining walls should be minimized,” says Neil Turnbull, a landscape architect based in Sunderland, Ont. He prefers working with local stone to build walkways, steps, and landings on cottage hillsides, rather than terraces.
“Try to find a safe and simple route through the area,” he says. “What I really look for are opportunities,” including level areas hidden by foliage. “Sometimes you can cut an area back a bit, and suddenly you have space where people could sit.”
Edge cases
At the shoreline, you can take a similar, low-intervention approach. Worried about continual erosion along their oceanfront Northumberland Strait cottage, Christy and Andrew Carlyle hired Helping Nature Heal in LaHave, N.S., to slow the loss. The firm staked logs, hay bales, bundled brush, and root wads along 90 metres of the eroding bank, then added resilient plants including willows, red osier dogwood, and alders. The treatment also extends upland, replacing much of the lawn with natural cover. HNH follows the Green Shores program—a bicoastal initiative that helps property owners address issues such as shoreline erosion and flooding in an environmentally responsible way.
“In the old days, you put up a rock wall and you walked away. When it failed in a big storm, you rebuilt it,” says Rosmarie Lohnes, president of HNH. Now the goal is to absorb rainfall around the cottage and dissipate wave energy at the shore, in an organic system that’s “like raising a child,” says Lohnes. “You have to keep adding to it and managing it and recovering and responding to storms.”
The Carlyles have spent about $100,000 on shoreline landscaping over the past dozen years, including repairs after 2022’s Hurricane Fiona. But that’s still less than some area landowners have spent on rock walls. “In this part of Nova Scotia, there’s no hope of doing anything but slowing the erosion down,” Andrew says. “This is as good as any other alternative.”
“You have to be open to a different idea of what a cottage property looks like. It’s not a golf green. It looks naturalized and a little unkempt,” Christy says. “But I don’t think there’s any other option. And we love it.”
Soil movement is one of waterfront life’s essential risks. When your hills are alive, as Ms. Andrews proved, how do you solve problems like erosion, hydrostatic pressure, and ultimately gravity? Especially when it’s not placed at the water’s edge, a well-designed retaining wall can handle all of the above. “If you build it well,” says Pressnail, “you can forget it. It’s done. It will work for you.”
This story originally appeared in the Early Summer ’26 issue of Cottage Life.
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