Winter’s toll: Fixing seasonal wear on Cotswold properties

Robert Hamilton of Central Surveying on counteracting the effects of the British climate on our Cotswold limestone walls and roofs

"My drystone garden wall has developed an alarming bulge this winter. What do I do?"

This last winter has been a really horrid one! First there was interminable damp, then there were several heavy dumps of snow accompanied by some bitterly cold weather. Then there would be one or two suddenly warm days followed by plummeting temperatures again, and then more wet…not surprisingly the garden has been sulking and the poor birds don’t know if they are coming or going.

This type of weather really takes its toll on Cotswold limestone. Many of you will have noticed loose slates on stone roofs caused by the weight of snow or laminated tiles caused by the frost. Often, the tiles or slates hang on and then drop off when the weather has suddenly turned warm. This is a real case of ‘last straws and camels’ in that the natural movement caused by the warming and drying of timbers and stones in the sun will cause a slate or tile to break free.

Similarly with your drystone wall. These are a real craft to build and one which is fortunately not lost. ‘Drystone’ means that there is no cement or mortar holding the stones together, but the friction of the stones themselves. Large foundation stones are used at the base of the wall and are partly below ground to ensure a level area. The walls are then built up with the end of each stone facing outward and built as two faces, some two feet thick at the bottom and narrowing together as the wall increases in height so that a cross-section through the wall is an elongated triangle with the top sliced off. Larger stones are used in the bottom courses.

The centre of the wall is filled with smaller stones known as ‘hearting’ and absolutely never gravel or earth! Halfway up the wall crosswise stones are put in every metre or so to bond the wall. These are called ‘through stones’ and bind the two faces together. The face stones are wedged in place with ‘pinning stones’ which are more small stones. The ‘second lift’ are slightly smaller face stones to build the top half of the wall and then the ‘coping’ finishes off the top. It is essential that the joints between the stones of one course do not lie above the joint of the course below – the stones should overlap to provide strength.

A good drystone wall will last for years but sadly they can become damaged and bulging is usually a sign that the wall is about to fail. Ivy and creepers are often culprits, gardeners sometimes plant the walls to be more decorative but this can allow water to penetrate into the structure and damage to the stones is then caused by frost action. Ivy or creeper growth should be cut or weed-killed first, then left to die back. Then the dead strands should be carefully pulled away, not just ripped out! Foxes, badgers and pets will sometimes decide to use a lower area of wall as a motorway and small paws can, over time, create quite a lot of damage. Recent weather conditions have been extremely severe for these natural components.

There has been some very learned work carried out on drystone walls with scientific studies set up to examine the mechanisms by which walls fail. There is also the phenomenon of ‘stable bulging’, observed where the wall has suffered some movement but will not get any worse.

I suggest you contact a local stone-walling expert – they can be found through the Dry Stone Walling Association which has local branches and ask them to restore your wall. It is well worth doing, not that expensive and the walls are an intrinsic asset and part of the Cotswold vernacular.

PS. Remember to ask a roofer to overhaul your Cotswold stone roofs this season after such a severe winter!

Central Surveying has offices in the Cotswolds and Knightsbridge, specialising in independent professional surveying and property consultancy services for commercial and residential clients in the Cotswolds, South West and London. Robert Hamilton works from Naunton in the heart of the North Cotswolds. To contact Robert, telephone 01285 640 840 or visit www.centralsurveying.co.uk.