Building natural dry stone retaining walls in a garden.
If you have a steep garden that's making garden maintenance or mowing your lawn difficult, especially when the surface is wet, you may be thinking about constructing dry stone retaining walls. Depending on how steep the garden is, this can be fairly simple.
It's impossible to learn the practical skills on a webpage but these tips, providing you have got the time, may help as you build your own dry stone wall in the garden. If it all falls down, providing it's not yet retaining anything, all you will have lost is time. You will still have the stone to try again and maybe again. Or to call me in build it for you.
Retaining walls have been built and used to retain sloping earth for thousands of years. Almost all early retaining walls were, dry stone walls, built using stacked stone without any mortar to hold the retaining wall together. Instead of mortar the walls were held together by the weight of stone. They were also held together because the stones were matched and fitted together in such a way, that as they settled over time they became stronger and more closely bound.
Get your dry stone walling right and it is more durable than breeze blocks, pre-formed concrete stacking stones and even cropped and cemented natural stone. This is because it contains no mortar that will crack and will never need pointing or rendering. Dry stone retaining walls look better too, especially in a natural setting like a cottage garden. If you are sourcing the stone locally and not transporting it half way round the world it also becomes the most sustainable and eco friendly way to retain your garden.
When planning to retain earth, bear in mind that retaining walls need to be able to withstand gravity and frost because this effects all retaining walls. You will need to build the retaining wall strong enough to offset the pushing force of the soil it's holding back. A single cubic foot of wet soil can weigh up to 100 pounds. Large stones that have lots of surface area touching one another survive because the friction of the stones rubbing against one another works against the pushing force exerted by the soil.
Retaining walls built about 3-feet high are fairly easy to construct as the force of gravity against them is not too great. You counteract this force on the dry stone wall by building the wall so it leans back and is not perfectly plumb. This offsets the centre of gravity of the stone wall, making it harder to topple over.
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High dry stone walls can fail. It is important to be aware that as the retaining wall height increases, the force trying to topple the wall increases by a large factor. For example, if you double the height of a wall, the tipping force can increase by a factor of three or four times.
Frozen soil expands as it freezes and can seriously damage retaining walls. So in areas where frost is likely this is minimised by backfilling the wall with gravel. The soil and area itself needs to be well drained so that water can't build up behind the wall.
If it's not possible to drain the water away from the wall because the slope in the garden behind the wall is to severe, the water can be drained through the wall by installing weep holes at the base of the wall.
Depending what is built under the wall, you then may have to think about where this water is going to be drained to. Garden Drainage information can be found on my garden drainage page
Whilst natural stone is still the best material to build garden walls, as it looks attractive in cottage gardens and other natural looking gardens, it is expensive and may not match the design of the rest of your garden.
Garden walls can be built using wood, railway sleepers, breeze blocks, house bricks and specially designed decorative stackable concrete block that will match your patio.
The choice of material, although important, is not as important as getting the design of the wall right. The base of the retaining wall cannot be laid directly onto topsoil, a concrete or compacted stone foundation is essential to avoid soil creep.
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