How to Build Flagstone Steps

ock gardens offer a good way to landscape difficult sites. Sloped areas or sites with sandy soil, for instance, are unfavorable for traditional lawns but are ideal for rock gardens. A rock garden is also a good choice if you’re looking for an alternative to traditional ground covers and garden beds. Rock gardens traditionally feature hardy, alpine plant varieties that typicallv require infrequent watering.

Building a rock garden requires excavating the site (preferably a sloping or terraced area) and preparing the soil, placing the rocks, and planting. Moving and positioning large rocks is the most difficult task.

[f your rock garden site is large, consider hiring a landscape contractor to deliver and place the rocks for you.

Rock gardens will look more natural if they’re built with stones that are all the same variety—or at least with stones that are similar in appearance. Using stone like that found in natural outcroppings in your area is a good idea. On the other hand, gardens with a larger variety of stone types have more visual variety and high potential for a very dramatic appearance when arranged with some skill.

Common Rock Garden Plants ►

Hens-and-Chicks Snow-in-Summer Coral bells Sedum Dianthus

Wheelbarrow Shovel Work gloves Eye protection Mulch

Eye protection and work gloves

Course sand Pea gravel or rock chips Moss

Buttermilk or yogurt Putty knife Alpine plants

A rock garden is an accessible first natural stone project. Rock gardens make a statement in a landscape and they are an attractive alternative to traditional garden beds.


Thread a line level onto a mason’s string and tie the ends of the string to stakes at the top and bottom of the stair installation site. With the string level, measure the difference in distance from the string to the ground at the top and bottom of the steps to find the total run. See pages 58 to 59 for more help on designing steps.

Excavate for the first step and the stone walls risers and returns. Dig deep enough to accommodate 4" of compactable gravel and 1" of sand throughout. This means you’ll be excavating a shallow area for the tread and a deeper U-shaped trench for the wall stones.

Pour a layer of compactable gravel into the U-shaped trench for the wall stones. Compact the gravel with a tamper or post and then top it off with another layer that should not be compacted.

Position the riser stones and the return stones in the trench and level them. Add or remove gravel as necessary and then rap them gently on the tops with a hand maul to set them. Use a wood block to protect the stones from the maul.

Line the area under the first tread with landscape fabric, drawing it up to cover the insides of the risers and returns. Add a layer of compactable gravel and tamp down to within 1" of risers and returns. Fill with sand and level with a 2 x 4. Slope gravel slightly from back to front for drainage.

Measure the step/run distance back from the face of the first risers and set a mason’s line across the sand bed. Set the second course of risers and returns as you did the first, without digging risers on to the bottom (the bottom tread will reduce risers’ effective height).

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Begin laying out flagstone treads. First, position them like a puzzle to determine if cuts are necessary. Leave a consistent distance between stones. Allow steps to hang about 2" over risers.

Fill in gaps between larger stones by trimming smaller pieces to fit. Fill smaller stones near the back. Don’t allow stones to touch one another when in place and do not cut stones too small. Ideally, each should be at least the size of a dinner plate.



Pack wet sand underneath low areas and remove sand underneath high areas until all the flags on the tread are basically flat and even. Use a level as a guide.

Use thin pieces of broken stone as shims to raise wall stones to their required level. Make sure shims are sturdy enough that they won’t flake apart easily. Use block-and-stone adhesive to hold the shims in place. Make sure there is no path for sand to wash out from beneath the treads. Do not use sand in place of shims to raise wall stones.


Continue adding steps and making your way up the slope. You shouldn’t need to trench for risers, but you may need to move some dirt so you can pack it in and install the return stones. The bottom of the risers should be at the same height as the bottoms of the tread on the step below. The top step often will not require returns.

Fill the joints between stones with coarse sand to bind them together and for a more finished appearance. Granite sand works well for this purpose, or choose polymeric sand that resists wash-out better than regular builder’s sand. Inspect steps regularly for the first few weeks and make adjustments to height of stones as needed.

Steps made using natural stones most frequently are found in locations where the setting is fairly wild, or at least very casual. Whenever you design and build steps, you should be aware of safety issues, but the fact is that in a rustic setting away from permanent structures you have a little more latitude when it comes to design. This works out quite well with natural stone steps, because in many cases the natural sizes and shapes of the stones will inform the dimensions of the steps.

A stairway built using natural or cast cobbles, such as the left photo below, can be manipulated pretty easily to manage the rise in a fairly uniform way. However, it often makes sense from both a practical and an aesthetic point of view, to design the steps as a series of landings. Here, uniform landing depth is desirable, but it is not required and you may want to vary it a little bit so your step accommodates a slope more naturally.

A series of large, flat stones can make very striking steps, with each flat stone making up a single tread. In such situations you’ll need to do more grading and modification of the slope terrain to fit the dimensions of the stones.

In either of the cases above, adding a handrail is probably not required by codes. But it is always a good idea and it will be much appreciated by your visitors.

Updated: 11.05.2013 — 05:04
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