Building Energy-Efficient Oak Frame Homes

Sofia Delgado explores how technological advances have helped oak structural systems remain a popular choice for self-builders
by Sofia Delgado
11th May 2018

Oak frames have been popular in construction for centuries. Oak’s sustainability, sturdiness and durability make it an excellent choice for the environmentally conscious and many simply fall in love with the charming character offered by this hardwood as it dries.

What’s more, the method’s inherent benefits continue to be enhanced to suit modern self-builders’ needs. Today’s oak homes offer high insulation standards, impressive airtightness and innovative architecture alongside their innate aesthetic appeal.

High performance

If sourced responsibly, oak can be a sustainable material – look for PEFC and FSC certifications to ensure you’re buying from environmentally managed forests. The embodied energy (the resources consumed by all of the processes associated with the production of the building) is also relatively low compared to some systems – plus oak frame homes can last for hundreds of years.

For entire dwellings you’ll be using green oak, which means it has been felled in the previous 18 months and has a moisture content of around 80%. This is cheaper and easier to cut and shape than air or kiln dried wood.

One of the challenges for oak frame has been achieving a highly insulated, airtight structural shell, while still preserving the character of the timber.

The solution is to combine traditional and modern techniques by wrapping the oak frame in a insulating encapsulation system. This could be done with masonry, timber frame, structural insulated panels (SIPs) or even products such as insulating concrete formwork (ICF) or natural straw bale.

This modern home is the work of Carpenter Oak, who combined steel with oak frame and SIPs for a contemporary look
The house features large expanses of glass and a blue zinc roof. Click the images to read the full self-build story

Browse: More self-build projects from Carpenter Oak 

Combining the method with SIPs has become very popular in recent years. These panels consist of two layers of oriented strandboard (OSB) bonded around an inner core of insulating material. They are manufactured in a factory, cutting down on building time and labour on site, and the controlled environment means they’re finished to excellent specifications.

Some oak frame specialists supply their own proprietary wraparound panels using alternative materials, such as natural insulation. These options can provide equally impressive performance.

“An appropriately designed and manufactured walling and roofing system will ensure the dwelling achieves good airtightness,” says David Grey from Oakwrights, which recently completed the UK’s first oak frame Passivhaus (a standard requiring exceptional levels of insulation and airtightness).

“The oak structural frame will shrink and move during the natural drying process, so allowing the frame to settle independently from the insulated wall and roofing system maintains the performance of the building on an ongoing basis.”

The quality of craftsmanship will play a crucial role when it comes to maximising the energy efficiency of your new home. “Airtightness is achieved through a combination of good design, appropriate materials and excellent construction detailing methods,” says Merry Albright from Border Oak.

“The most important thing is to educate the team on site, as even the most airtight building envelope can be ruined by a misplaced pipe hole or bad taping.”

Modern architecture

A wide range of internal layouts is possible thanks to the sizeable beams – you can specify trusses up to 10m for domestic purposes – as well as the incorporation of steel in some designs. So you can create both small and large open-plan spaces; although very large rooms and zones will need intermediate posts to support the spans.

One of the characteristics of oak frame homes is the shrinking and splitting of the timber as it dries out. These do not constitute a structural issue; however your designer will have to take the wood’s behaviour into account, especially when incorporating glass in the design.

Good architectural detailing at the planning stages, followed by proper execution on site, are key to successfully incorporating glazing into an oak frame scheme.

So make sure you work with a specialist team who understand shrinkage in oak and have a proven track record of success. New techniques exist that mitigate against this issue, as well as accommodating other potential movement as the oak dries, such as twisting and splitting.

Welsh Oak’s Build It Awards-winning house combines concrete insulated formwork (ICF) and a traditional oak frame
A Border Oak bespoke home with an exposed frame that creates the right balance between open-plan and separate, defined zones

Source it: Find the right supplier for your project’s structural system

One of the most popular solutions is to fit sealed units on to the face of the posts and beams, as opposed to installing the glass panels in the frame itself. “The secret to introducing glazing to your design is to have a flexible joint between the structural oak and the glass,” says David. This, coupled with flexible weather seal joints, allows the structure to move independently.

“The appearance of the frame externally is then achieved by using oak capping on the outside of the glass panels,” says Kat Hamilton from Oakmasters. “This way, the glazing and envelope stay watertight.”

Another modern solution that has noticeably updated the look of oak frame dwellings is the incorporation of stainless steel. The pairing of these two elements brings an industrial feel to the home when the metal is left exposed. It also allows for further versatility in the design.

The incorporation of steel joints and beams can help to enable larger spaces and architectural options, such as cantilevers and wider spaces of full-height glazing.

Glulam beams (glue-laminated wood) are a modern alternative to standard oak. The product’s laminated makeup and low moisture content of around 12% mean it won’t shrink or twist as green oak does.

Glulam can span great distances, which opens up new design possibilities. Its stability also means decorative finishes can be applied more easily, as the structure won’t move – or split – over time as much as green oak does.

Speed of construction

Building with oak can be a great deal faster than with other traditional methods. Once you have your design, the frame is fabricated in the workshop while works such as clearing the plot and laying foundations start on site.

Once the oak skeleton is delivered, it can be erected in just a few days thanks to the use of cranes, significantly cutting down overall build time. “And if you are wrapping with SIPs, then you can reach watertight stage even faster,” says Vicci Lewis, designer at Oakmasters.

Is oak frame a fire risk?

  • All houses have to meet Building Regulations standards for fire safety, and oak is no different than other construction methods.
  • In case of fire, the beams will char on the outside but remain structurally safe. More so than steel, which warps when exposed to high temperatures.
  • Insulation materials inside the modern wall panels are self-extinguishing, too, so fires won’t propagate.

Low maintenance

Most self-builders choose a flat-planed finish, making the wood soft to the touch (no splinters) and evening out saw marks from the felling and conversion procedures.

Your oak frame will have to be cleaned after the building is completed, to erase any unwanted marks from the construction process – such as dust, mud etc. This is done with oxalic acid, which will give the timber a clean look, or by sand blasting for a rougher, more rustic feel.

“Oak frames don’t need any form of treatment to keep their structural integrity,” says David. “European oak, which is used the most by manufacturers, is naturally durable. So any finish that is applied is for aesthetic purposes only.”

Unique design

Modern oak frames can be covered in an extensive variety of finishes. “Any cladding can be applied to the outside of the insulated walling and roofing system,” says David.

Which one you choose will come down to your personal preferences, what suits the surroundings and any conditions in your planning permission. A popular trend is to pair up the high-performance frame with materials such as handmade bricks, natural stone or timber cladding.

The overarching style of vernacular architecture in your area may dictate your choice of cladding and roofing materials. For instance, oak homes often feature a stone finish in the Cotswolds, or tile hanging in areas such as Kent.

“Render and weatherboard are very popular for contemporary designs, with most new builds having a mix of materials alongside extensive glazing” adds Merry. “That is the beauty of oak framing. It is versatile and organic and offers a tremendous creative range.”

Top image: The owners of this Oakwrights home mixed traditional and modern, opting for a glazed gable featuring exposed oak left to silver. The structure was also clad in stone to reflect the local vernacular

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