Oak frame extensions bring a warm, timber-led look to Somerset's stone and cob cottages, but they sit at the pricier end of the extension market. Here's a realistic breakdown of what drives the cost and what you might expect to pay, based on the kind of projects we see across Somerset.
Oak frame extensions cost more than a standard brick-and-block build because you're paying for a structural timber frame, skilled joinery, and usually a fair amount of glazing. The frame itself, whether it's green oak cut and jointed by hand with traditional mortice, tenon and oak pegs, or a hybrid design using oak posts with structural insulated panels for the walls and roof, is the single biggest factor in the price. A fully exposed green oak frame costs more than one using engineered beams or blockwork infill, but it's also what gives the honest, exposed-timber look most people want when they choose oak in the first place.
Size and shape matter just as much as the frame type. A simple rectangular single storey extension is cheaper per square metre than a vaulted garden room with exposed trusses, a glazed gable end or a curved roof. Bi-fold doors, roof lanterns, underfloor heating and a fitted kitchen inside the new space all add cost on top of the frame and shell.
As a rough guide for Somerset, most oak frame extensions fall somewhere between £2,200 and £4,000 per square metre once the frame, roof, glazing, insulation and a reasonable standard of finish are included. A small 15 to 20 square metre garden room or snug extension with a modest frame might land between £45,000 and £75,000.
A more typical 25 to 35 square metre kitchen or dining extension, the most common request we get, generally runs from £75,000 to £130,000 depending on how much glazing you want and whether the frame is fully exposed inside or partly boxed in behind plasterboard. Larger or two storey oak additions, or ones with a vaulted ceiling and a full glazed gable, can push past £150,000. These figures cover the build itself, not a high-spec kitchen or bathroom fit-out, or landscaping afterwards.
Ground conditions vary a lot across the county and they affect your foundation costs, which feed into the overall price. Homes on the Somerset Levels or near rivers such as the Parrett and Brue often sit on clay or peat, meaning you may need reinforced or piled foundations to carry the weight of a timber frame, which can add several thousand pounds compared with a site on firmer ground around the Blackdown or Mendip Hills.
Planning is handled by Somerset Council since the 2023 unitary reorganisation. Most single storey rear extensions within permitted development limits won't need full planning permission, though a lawful development certificate is worth having for peace of mind. If your home is listed, which is common in villages around Wells, Bruton, Castle Cary and across the Levels, or it sits within a conservation area, you'll need listed building consent or conservation area approval, and the design will need to respect the character of the original building. Done well, an oak frame extension usually sits more comfortably against older Somerset stone or cob than a modern render-and-glass box would, which can help when discussing a design with planning officers.
Because so much depends on the specific design, ground conditions and finish level, any figure you read online is only a starting point. The most reliable way to budget is a site visit and a detailed quote that breaks the frame, foundations, roof, glazing, insulation and internal finishes out separately, so you can see where the money goes and where there's room to adjust if the first number comes in higher than you hoped.
Most oak frame extensions in Somerset cost between £2,200 and £4,000 per square metre, depending on how much of the frame is exposed, how much glazing you want, and the finish level inside. A simple single storey design sits at the lower end, while vaulted ceilings and large glazed gables push the price up.
Many single storey rear extensions fall within permitted development and don't need full planning permission, though it's worth getting a lawful development certificate from Somerset Council to confirm this. Listed buildings and homes in conservation areas, common in villages like Wells and Castle Cary, will need additional consent.
A typical oak frame extension takes around four to six months from groundworks to completion, though the oak frame itself may be cut and jointed off-site in advance to reduce time on site. Larger or more complex designs with extensive glazing or difficult ground conditions can take longer.