Design garden borders with timber sleepers

A simple and effective way to create raised garden borders, is with sleepers. Reclaimed railway sleepers or brand-new treated timber baulks, are an incredibly versatile building material for all sorts of hard-landscaping projects.

Retainers and Planters

For raised beds or low retainers up to 3 or 4 courses high (about 450-600mm), the sleepers can be nailed or screwed together. It’s usual to countersink the nails/screws, to ensure they penetrate the underlying sleeper to a reasonable depth, minimum around 50mm. Typically, these fixings would be positioned about 150mm in from each end of a timber, and one in the centre.

For heavy applications, such as a retainer of 3 courses or more, we prefer to ‘spike’ the sleepers with 20mm diameter mild steel dowels that are fixed through pre-drilled holes, passing through all the courses and into the foundation concrete. This system works for sleeper walls up to 1200mm in height; anything higher than 1200mm needs to be designed by an engineer to take account of local ground conditions and loadings.

On site, the first sleeper is bedded onto a semi-dry or stiff concrete bed, and the remaining courses stacked on top, making sure that the sleepers overlap, especially at corners. Once all are in position, the spike holes are drilled, through the top course and into the underlying course. The top course is removed and set aside, then the holes are drilled through what was the penultimate course into the one underneath that, the course removed and set aside, and so on and so forth until all courses are drilled. This method ensures the drill holes are properly aligned.

The sleepers are replaced in reverse order of removal and then a 20mm steel dowel can be driven through the lot with a sledge hammer or similar, until it penetrates the bedding concrete by 50-100mm. The top of the spike is cut off level with the top course and driven a further 25mm or so to ensure the top of the steel dowel is within the timber. The hole is then sealed with pitch or other sealing compound.
Another fixing method for non-critical applications, is to use steel straps. Right-angled strapping is used to tie the corners together or straight strapping can be used vertically away from the corners.

Sleepers can also be used vertically, as fence posts, or to create the look of a breakwater or groynes in themed gardens. When used in this manner, they should be treated much the same fence posts and installed accordingly.

It’s important that the sleepers are properly “anchored” when used as a vertical retainer. The usual ‘rule of thumb’ is that one-third of the overall height should be buried: So, if a 2400mm long sleeper was to be used, 800mm would need to be inserted into the ground and concreted in place, with 160mm above ground.

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