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Oak Frame Extensions: Everything You Need to Know

Oak and glass extension
(Image credit: Welsh Oak Frame)

Oak is a popular choice for new build homes, and offers many of the same benefits for those looking to extend their home.

A big part of oak frame’s appeal is its flexibility — from barn-like additions to Tudor-style extensions and oak frame sunrooms, this construction system can be used to create a wealth of different styles.

On this note, oak frame extensions also suit a range of properties — from period cottages to post-war homes.

Another huge draw is the texture and character oak brings to a new extension.

Oak frame extensions can be quick to build. (Unlike on-site methods of construction like masonry, the majority of the oak frame structure is prefabricated off-site).

Oak frame provides the opportunity to create architectural features, such as vaulted ceilings and glazed gable ends, with relative ease.

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oak frame extension to a listed building

Oak frame extensions can suit a wide variety properties — as this sympathetic extension, by Living Oak, to a listed property, goes to show (Image credit: Living Oak)

Designing an Oak Frame Extension

Approaching an oak frame company who can provide an in-house design service, or an architectural practice with experience designing timber extensions, is typically the most cost-effective route. They will have working knowledge of the possibilities, challenges and limitations of this construction system — meaning you will not need to rework your design at a later date to accommodate the oak frame.

As with any new extension, the connection to and impact on the existing house requires thought. Extensions which are subservient but draw their cue, in terms of design and materials, from existing house, tend to work best.

Finally, one clever way of making a new extension feel instantly at home is introduce oak to the main house.

“We recommend that you include some other oak frame elements to the house if possible – such as an oak porch or an internal glazed oak screen – which would help to visually tie the extension to the existing house," explains architect Mike Hope of Roderick James Architects; a practice well versed in designing oak home buildings.

oak frame kitchen diner extension with glazed gable

Oak frame can be used to create very different aesthetics, as these kitchen diner extensions go to show: the oak has been pared-back in this modern extension by Greenrooms by Oakwrights (Image credit: Oakwrights)

Is Planning Permission Required for an Oak Frame Extension?

traditional style oak frame extension for a kitchen diner

Exposing the rafters and including curved oak members in this Roderick James Architects project provides a more traditional look (Image credit: Roderick James)

As with any extension, regardless of construction system, an oak extension must comply with planning rules. Fortunately some extensions do not need planning permission — the work could fall under Permitted Development.

“It is very important to speak to the planning authority regarding size, style and specific requirements and policy restrictions — some extensions may not actually need planning approval but some houses will have lots of conditions and restrictions,” recommends Border Oak’s Merry Albright.

How to Build an Oak Frame Extension

Most homeowners will work with a specialist oak frame company to build their extension. This company may design and supply the frame; they may also provide the 'encapsulation' system.

Traditionally, the frame would have been infilled with wattle and daub, or brick. Today, the oak frame is encased within a system such as SIPs (structural insulated panels) or timber panels. This allows extensions to meet Building Regulations standards for thermal efficiency.

This encapsulation system also means that extensions can be clad in a variety of materials. So an oak frame extension can still be an option in a stone belt region where the planners may insist on a local stone cladding, for example.

traditional style oak frame extension for a kitchen diner

Oak frame extensions can be clad in a variety of materials. This single-storey extension by Welsh Oak Frame has been clad in stone (Image credit: Welsh Oak Frame)

Render and timber cladding are also options, so is brick (although heavier claddings such as brick and stone often have to be built off their own foundations).

When it comes to the build, most oak frame companies will require the homeowner to commission a builder or groundworking company to complete the foundations, before delivering and erecting the oak frame on site.

Once the oak frame is constructed, the homeowner will typically have option to project manage individual trades to finish of the extension, or commission a builder to manage this process for them.

Linking to the Existing House

Oak frame extensions are typically built to be structurally independent. In other words, the house and extension sit next to one another – with a weathertight seal created between – so that the extension does not require structural support from the main house.

“This means that we don’t need to mess around with the main building (often this is an old building and you never know what you may find). This route can offer more control over the whole project and the costs involved,” says Merry Albright of Border Oak.

Another option is to create a glazed link between the two — this device visually separates old from new and helps draw light into the house.

oak frame extension with glazed link to main house

A glazed link can be a good means of connecting a new oak frame extension to an existing house. (The oak frame extension is by Border Oak) (Image credit: Border Oak)

How Much Will an Oak Frame Extension Cost?

Oak frame is considered a premium building material. “Building with oak is a little more expensive but not hugely. We advise a project cost of £2,500/m² (including groundworks through to finishing)” says Charlie Mills of GreenRooms by Oakwrights.

“There are several factors that could impact on cost, such as the amount of oak used. For instance, using oak roof rafters rather than softwood would inevitably cost more," adds Charlie Mills.

The amount of glazing specified will also impact (i.e. introducing large sets of bi-fold doors, as opposed to a simple set of French doors, will add to the price). So too will factors such as the complexity of the extension and the location of the build.

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What to Consider

Good communication between the homeowner and/or their builder, and the oak frame company is key to keeping the build on track, and ensuring that there are no long delays between the groundworks being completed and the oak frame being delivered to site and erected.

Access to the site of the extension is beneficial, as a crane is commonly used to erect both the frame and the SIPs (if used). However, where access is limited, there are solutions. "Difficult sites often involve specialist lifting equipment — occasionally the oak frame has been craned over the house, and there is lifting equipment available that can fit through the space of a garden gate," says Paul Brierley of Paragon Oak.

barn style oak frame kitchen diner extension

Exposing oak rafters as well as the principal members will add to the cost of an oak frame extension. The oak frame for this striking, double-height, barn-style kitchen diner extension is by Westwind Oak (Image credit: Westwind Oak)

“Oak is a natural material and even with offers of ‘dry’ oak, the timber will still crack and move slightly — it’s not a structural weakness, simply a feature,” says Charles Mills of GreenRooms by Oakwrights.

Due to the shrinkage of the oak, glazing between the oak frame is an area that requires particular attention. A method called face or direct-applied glazing can be used to overcome this issue.

“Oak is very versatile but has some limitations with regards to spans before you need a post before you start using massive timbers," says Charlie Mills of GreenRooms by Oakwrights. "Therefore, if someone is looking for a huge span completely open with minimal posts, oak frame may not suit."