Kiln Dried Oak Boards - Custom Sizes Cut to Order - Window Sills, Furniture, Doors etc (Under 500mm wide)

• For Oak Boards 500mm wide and over, click here
• Looking for Custom Size Oak Shelves with Brackets and Oils?
• Kiln-dried/joinery grade oak boards.
• Depending on the width chosen and our stock availability, these boards may contain joins
• Deliveries within Pembrokeshire: Free shipping! We are unable to provide a day or time as it will depend on order volume and when a driver is in your area but will deliver within 5 working days of the order being completed.
• Deliveries outside of Pembrokeshire: We ship nationwide using 3rd party companies, please continue to checkout and cost will be calculated after entering your postcode. For smaller, more manageable orders we will ship using a courier. Please allow up to a week for delivery upon completion. For larger orders we will ship a palletized delivery via haulier, in this case Multiple people would need to be on hand at time of delivery to handball off vehicle, if this is not possible, we will need to cancel the order. We will contact you prior to despatch to confirm this/discuss delivery timescale.

Current lead-time: Approx. 2-3 weeks. 

Our kiln-dried oak boards are Joinery Grade (QB2). This means that they contain fewer knots and blemishes than character grade oak. This makes them perfect for oak shelves, window sills, furniture, doors, window frames, signs and much more.

For wider boards, it is important to make sure that the weight is properly supported and the boards are fixed correctly to ensure that they do not bend or twist.

Our oak boards are either just Planed, so that they are square and flat or Planed and Sanded, ready for installation and with the edges slightly rounded to remove their sharpness. They are available with or without the tree's natural waney edge.

Important please note the following before purchasing;

As our Oak Planks are a natural product, each piece may be different in appearance and vary slightly in colour.

As this product is planed it can lose some of its size, please state if you require an exact size. If you are looking for a custom size board, please order the size above what you require and specify your chosen size in the 'Order Notes' section of the checkout. We will ensure that it is planed to your specific required dimensions.

Delivery & Lead Time 
Current lead time: Approximately 2–3 weeks
We ship Nationwide across the UK using trusted courier networks, delivery is only available on weekdays.

Installation Guidance
Solid oak is a natural, structural timber and should be installed correctly to ensure long-term stability and performance.

Acclimatisation
Before installation, we recommend allowing your oak window sill to acclimatise in the room where it will be fitted for several days. This allows the timber to adjust to the ambient temperature and humidity levels.

• Store flat
• Keep away from direct heat sources
• Do not lean upright against a wall

Supporting the Weight
Oak window sills are solid and heavy. Proper support is essential.

• Ensure the sill is fully supported across its width
• Use appropriate brackets or battens where required
• Avoid leaving large unsupported spans

For installations above radiators, allow airflow to prevent excessive heat build-up beneath the timber.

Fixing Advice

• Secure using suitable fixings into masonry or framing
• Avoid over-tightening screws
• Always allow for natural expansion and contraction

We recommend fixing the sill close to the delivery date to minimise movement prior to installation.

If you are unsure, consult a qualified carpenter or joiner.If you are unsure, consult a qualified carpenter or joiner.

Timber Variation & Natural Characteristics

Oak is a natural material, and every board is unique. No two window sills will ever look identical — and that’s part of the beauty.

Colour variation
Solid oak can vary in tone from light golden hues to deeper honey shades. Over time, exposure to light will naturally mellow and deepen the colour. This is not a defect — it is a natural characteristic of genuine solid oak.

Grain and knots
You may see natural knots, grain variation, small checks or character markings, and subtle colour shifts. These features add authenticity and character to your window sill.

Joined boards (for wider widths)
For widths generally over 150mm+, boards may be professionally joined to achieve the required depth. We carefully match grain and tone to ensure a seamless, natural appearance. All joints are structurally secure and finished to the same high standard.

Natural movement
As a natural timber product, oak may expand or contract slightly depending on environmental conditions. Correct installation and acclimatisation will minimise movement.

Frequently Asked Questions

Are your window sills solid oak?
Yes. All of our window sills are manufactured from solid kiln-dried European oak. We do not use veneer or MDF-wrapped products.

Can you make them to my exact size?
Yes. Every window sill is cut precisely to the millimetre to match your measurements.

What thickness should I choose?
This depends on the look you want and the size of the opening. Thicker boards provide a more substantial, architectural feel and are ideal for larger windows.

Can I install an oak window sill above a radiator?
Yes, provided adequate airflow is maintained and the sill is properly supported. Oak is durable, but excessive heat build-up should be avoided.

Do the boards come pre-finished?
Boards are supplied planed and sanded to a fine finish, ready for oiling, staining or sealing to suit your interior.

How long is the lead time?
Current lead time is approximately 2–3 weeks from order completion.

Will my board look exactly like the photos?
Each board is unique due to natural grain and colour variation. While the quality and finish are consistent, no two pieces will be identical.

At Celtic Timber, sustainability is at the heart of everything we do. We source our timber from sustainably sourced certified forests, ensuring responsible management and protection of natural resources.

We also actively contribute to reforestation and rewilding projects across the UK, planting over 12,000 trees on our own land. By choosing our products, you’re supporting a company dedicated to reducing environmental impact and preserving the planet for future generations.

Learn more about how we ensure sustainability, here.

Returns & Peace of Mind

We stand by the quality of our products and want you to order with confidence.

We offer a 30-day returns policy on all non-bespoke items. If for any reason you’re not completely satisfied, please contact us within 30 days of receiving your order and we’ll be happy to assist.

If your item arrives damaged or incorrect, let us know as soon as possible and we’ll arrange a replacement or agree an appropriate resolution quickly and fairly.

To qualify for a refund, items must be returned unused and in their original packaging.

Return shipping costs are the responsibility of the customer, except where the return is due to damage in transit or an error on our part.

For bespoke or made-to-measure items, please note that these are manufactured specifically to your dimensions and are therefore non-returnable unless faulty.

Read our full returns and refunds policy here.