The Importance of Grading Structural Oak Beams – And Why We Choose Air-Dried or Green Oak
At Oakfield Beams & Framing in Horsham, West Sussex, we’ve been supplying and working with oak for over 30 years. One of the most common questions we get from customers is: “What do the grades actually mean, and should I use green oak or air-dried?”
Getting this right is critical — especially for structural work. The wrong choice can affect safety, building regulations, long-term stability, and how beautiful your project looks in 10 or 20 years’ time.
What Is Oak Beam Grading?
Oak beams used for structural purposes (oak framing, load-bearing beams, trusses, extensions, garages, etc.) must be visually graded according to British Standard BS 5756.
This grading process looks at:
Size and position of knots
Slope of grain
Splits and fissures
Wane (bark edge)
Distortion and straightness
From this, beams are graded as:
TH1 / THa → Higher quality (can achieve D40 strength class)
TH2 / THb → Good structural grade (usually D30)
D40 is the highest structural grade possible for European oak in the UK. We only supply properly graded beams so your project complies with Building Regulations.
Why does grading matter so much? A properly graded beam gives structural engineers confidence in load-bearing calculations. Poorly graded timber can lead to excessive movement, weakness, or even rejection by building control.
Green Oak vs Air-Dried Oak – Which Should You Use?
FeatureGreen OakAir-Dried OakMoisture ContentHigh (50%+)Lower (20–30%)Best ForTraditional oak framing & new buildsFireplace beams, visible beams, renovationsWorkabilitySofter and easier to cut & jointHarder but more stableShrinkageShrinks as it dries in the buildingMost shrinkage has already happenedSpeed of ProjectCan be used immediatelyReady to install with minimal movementCostGenerally lowerHigher (due to years of seasoning)AppearanceDevelops characterful shakes over timeCleaner, more stable look
When we recommend Green Oak:
Traditional oak framed buildings, garages, extensions, and porches.
It’s strong, flexible, and cost-effective.
As it dries naturally in the frame, the joints actually tighten up over time — a beautiful feature of traditional oak framing.
When we recommend Air-Dried Oak:
Fireplace mantels and beams
Visible internal beams
Projects where minimal movement is essential (e.g. near glass, in heated homes)
Renovation work where you need stability straight away
At Oakfield Beams we keep large stocks of both — properly graded and often sourced locally in Sussex and surrounding counties.
Our Approach at Oakfield Beams
We don’t just sell oak — we help you choose the right material for your specific project.
All our structural beams are graded in line with BS 5756 standards.
We offer both green and air-dried options.
We specialise in hollowed beams and beam casings (especially popular with air-dried oak).
Every load is hand-selected for quality.
Whether you’re an architect, builder, or homeowner planning an oak frame or a striking fireplace, we’ll guide you on the best grade and seasoning for your needs.
Ready to source properly graded oak beams?
📍 Visit our yard in Lower Beeding, near Horsham, West Sussex 📞 Call us on 01403 892599 🛒 Browse our full range of oak beams online
We offer UK-wide delivery and are always happy to advise on your project — no obligation.
Have a question about grading or green vs air-dried for your build? Drop us a message or comment below!
Oakfield Beams & Framing Quality Oak Beams | Oak Framing | Fireplace Beams Horsham, West Sussex