Coming back to earth
Being a builder specialising in conservation work, Robin Dukes was keen to exchange his modern two-up two-down house in Aylesbury for a period property with potential for renovation. His wife Kate agreed.
Eventually they found what they were looking for in a village 10 miles away. The Grade 11 late 18th Century listed cottage has external walls of wychert (the word means 'white earth'), a sticky white subsoil found widely in historic buildings in the Vale of Aylesbury. Many old houses in the area have walls that were constructed simply by piling up this material in layers and letting it dry.
"Earth houses are fun: there are thousands in this country, but sometimes people living in them do not know!" says Robin. "They are warm in winter and cool in summer. They provide a lovely atmosphere to live in."
In recent years, the cottage hadn't been well cared for. It had been in the same family for three generations, and in the three years before the Dukes bought it, it had been occupied by an elderly lady who was confined to the downstairs rooms. It smelt damp and musty, there were patches of damp at low level, and sections of the exterior wall were falling away at the front.
"The main problem was fairly obvious, but it needed a pretty radical cure," Robin explains. "Sometime in the 1960s the house had been covered with a very hard, thick cement-based pebble dash render. In addition, some of the internal lath and plaster and wattle and daub walls had been plastered with modern gypsum-based materials."
All these hard, modern materials were incompatible with the flexible, porous walls, which in a building like this both absorb and then readily permit the evaporation of moisture. This is often known as the ability of the building fabric to 'breathe'. A more technical phrase is 'vapour permeability'.
Robin explains that hard, cementitious renders such as the pebble dash applied to the exterior of old houses are designed to keep the weather out. But when the render cracks, usually because it is incompatible with the softer historic fabric, water from driving rain can get in and run behind the pebble dash, forming channels that, in the worst cases, can lead to collapse. The result was all the cement-based renders and plasters had to be removed.
Outside, after stripping off all the pebble dash, they had some remedial work to do where there had been a collapse in the front wall at the north corner. They used unfired clay bricks from a local brickworks to fill this. This technique meant minimal shrinkage. Where repairs were needed in smaller, more localised areas of the external walls, they made their own wychert using clay from the garden mixed with straw and a little water. They then covered the outside with a lime render. Inside Robin and Kate were keen to take a fairly contemporary approach to the furnishing to avoid clutter, a frequent problem in old cottages with small rooms. Nevertheless, they found the house was getting very full, so as their two children, now aged 12 and seven, were growing rapidly, they decided to extend.
Kate explains: "Originally, it was two farmworkers' cottages. In the 19th Century, a utility room and staircase had been added at the rear of the property with a staircase and the downstairs bathroom and WC added in the one-storey extension.
"We saw a second, two-storey extension as a means of getting the bathroom and WC upstairs. Apart from the added convenience, we knew this would make the property far more saleable should we decide to move at any stage."
Upstairs it was still necessary to go through one room to get to another - a situation often found in old cottages - which made it especially inconvenient getting to the far bedroom.
By adding a fourth bedroom, they were able to release the first one to make an upstairs bathroom, then create a corridor by adapting the ends of the remaining two bedrooms. The new master bedroom is above the new sitting room. It has all worked very well.
After a lot of heart-searching, Robin and Kate decided to use lightweight dual skin blockwork for the extension, rather than building in wychert.
"It would have been perfectly possible to use wychert, but it would have been very labour-intensive and taken for ever," Robin says. "I could have used the team from my own company to build the walls, but they would have been available only at weekends, and this would have caused no end of problems."
Robin and Kate used a lime mortar between the blockwork in the extension, and finished the inside walls with a rough-textured lime putty-based plaster. "Lime putty is softer than hydraulic lime, which comes dry in bags. In putty form, the lime is better for accommodating any movement," Robin explains the choice.
"On the outside of the blockwork however, I believe hydraulic lime is better because it sets more readily on blockwork than lime putty.
"A lot of people do not realise that it is perfectly possible to use traditional lime mortars with modern blocks. You can do a reasonably good disguising job, while at the same time being reasonably 'eco' in the materials you use. We avoided using Portland cement altogether, as it would never have been used in a building of this age."
The Dukes used handmade clay tiles for both the roof of the extension and the
front elevation. Inside, they used reed laths for the new ceilings. "With a lime plaster, this gives a more 'homely' feel to a traditional cottage than the finish that results from plasterboard, which we avoided," Robin says. "Reed lath is cheaper than riven oak or chestnut."
Their crowning glory was the large inglenook fireplace they rediscovered in the living room, which had been completely filled in. "We knew it would be here, but restoring it was still a pretty big job," Kate says. "The material we took out filled two skips!"
