Oak Frame Kitchen Extension

Start with the posts

In a brick extension you design the kitchen and the builder puts walls round it. With oak it works the other way. Posts stand at regular centres, usually every 2.5 to 3.5 m, and each one is 150 to 200 mm square. A run of base units has to stop at a post or pass in front of it, and a tall larder cupboard cannot sit under a brace.

So bring the kitchen designer in before the frame drawings are finished. Moving a post by 300 mm on paper costs nothing. Finding out after the raising that the range cooker is 100 mm too wide for its bay is a different matter.

The wall against the house is the natural place for tall units, ovens and the fridge, because it is solid and has no oak in the way. Glazed sides suit the sink, the table and seating.

Wiring, pipes and extraction

Nobody should cut a channel in a structural oak post to hide a cable. Services run instead in the insulated wall panels outside the frame, in the floor screed, or in a shallow service zone behind the plasterboard. Sockets land on the infill between posts, not on the oak.

Pendant lights over an island hang from the tie beam or from a discreet track fixed to it, with the cable brought across the top of the beam where it cannot be seen from below. Decide this early, because the cable route may need a groove cut on the top face in the workshop.

Extraction needs a route to outside. A ducted hood on the house wall is simplest. Over an island, a downdraught extractor ducted under the floor avoids a bulky hood hanging between the trusses.

Opening up the old wall

Most kitchen extensions involve taking out part or all of the back wall of the house. The masonry above then needs a steel or concrete beam, sized by a structural engineer and approved under the Building Regulations. In an old house with soft brick or rubble stone, the padstones that carry the beam ends need as much thought as the beam.

If you share a wall with a neighbour, or dig foundations within 3 m of their building and deeper than theirs, the Party Wall etc. Act requires you to serve notice before work starts. If they do not simply consent, one surveyor agreed by both sides typically costs £700 to £1,500 per neighbour; if your neighbour appoints their own, you pay for both.

Oak, steam and grease

A kitchen is harder on oak than a sitting room, though not by much. Steam does no harm; the frame is already full of water when it arrives. Grease is the nuisance. Bare oak within a metre or so of the hob will darken and mark, so a clear hardwax oil on the nearest post and brace is sensible once the surface has dried.

Keep wire wool and steel pan scourers away from the timber. Tiny fragments of steel react with the tannin in oak and leave blue-black spots that are tedious to remove.

Expect movement in the first two winters. Gaps of a few millimetres will open where oak meets plaster or a worktop upstand. A flexible sealant in a matching colour deals with them, and a good builder will return to do it.

Planning and listed buildings

The planning limits are the same as for any rear extension: in England, 3 m deep on an attached house and 4 m on a detached one under permitted development, single storey, no more than 4 m high. Most kitchen extensions want more depth than that, and a full application at £548 is normal. See the Planning Portal for the complete list of conditions.

For a listed house, listed building consent covers not only the new room but the opening into the old wall, which is often the part a conservation officer cares about most. Keeping a section of the original wall as piers, or linking the new room through an existing doorway, can make the difference between approval and refusal. In Scotland, Historic Environment Scotland publishes the equivalent guidance and a building warrant is needed.