A building control case study of an extensionOn September 6, 2019 by Raul Dinwiddie
In the next clip we’re going to look at a case study of an extension. This was a very typical 1930 semi-detached house. It had a tiny kitchen extension which had been added on years ago which was cold and dark and damp and opened off a small lobby with lots of odd nooks and crannies. And an old chimney breast which made it difficult to use the space. The owners wanted a light bright eat-in kitchen with plenty of room for their family and friends. And their first step was to choose a builder. They used one which had been recommended by friends and neighbours and they checked their reputation out with Building Control. The builder then put them in touch with a local architect that he was used to working with. The architect visited and discussed their requirements, aspirations and budget. The property faces south so they didn’t want a conservatory roof which can actually let the house overheat in summer. They wanted a shower room to ease congestion in the bathroom on busy mornings. They wanted a big cooker and an island and lots of storage and they wanted concealed appliances and a tiled floor and big doors onto the patio and space for a big table and chairs for entertaining and it was important that the extension was low maintenance. So the architect drafted up a couple of options based on their requirements and then he discussed them with the builder to establish what they could afford to spend. The architect then applied to the local council for Building Regulations approval. It didn’t need planning permission but they obtained a certificate of lawfulness in case they ever sell the property. After about five weeks the plans had been checked and amended, the calculations have been checked and the council issued the approval notice. And then it was time for the builders to start work on site. In the first few days he arranged a site visit from Building Control to talk about the project and to agree the other stages that would need inspecting. And the first was the foundations. These had to be a metre deep. Sometimes if there are trees or deep drains on the site they actually have to be much deeper. The drains have to be protected from the load of the new extension to stop them cracking and sometimes they may be shared drains or public sewers and will be owned by the water company and you might need a build-over agreement. The next stage was the floor slab. This could be a solid slab resting on the ground or it can be a timber or concrete floor that sits on the walls and is suspended over the ground below. Sometimes the floor has to be designed to stop gases like methane or radon passing into the building. The floor also has to stop water from the ground rising up into the floor of the extension and so do the walls, so damp courses are used. Sometimes if the walls are partly below ground the builder will need to use a tanking system to keep the water out. The roof is another important structural element and Building Control will want to check the sizes of the joists and the rafters and how they’re all tied together. Insulation is also important throughout the whole structure including the roof, the floor, the walls and making sure that you use the right windows and heating. Heating has to be installed by gas safe or off tech engineers and electrics have to be carried out by competent people. The surveyor came out five times for this particular project. There are a few minor issues but he issued the completion certificate. This service is well worth the fee for the peace of mind that you get. Very few people choose to pay their architect to oversee their work so having an extra pair of eyes on site is really important. You mustn’t lose the completion certificate that the local authority give you because you’ll need this if you ever try to sell your house. So speak to your local Building Control team about your extension.