Leviathan Diamond Corner Pergola 3m x 3m | 120mm Posts | Smart Seal Treated | Nationwide Installation Included | Dunster House

Leviathan Diamond Corner Pergola – 3m x 3m | 120mm Posts | Smart Seal Timber Treatment

Make a bold statement in your garden with the Leviathan Diamond Corner Pergola by Dunster House — the premium, heavy-duty corner pergola built for those who refuse to compromise on quality. With massive 120mm x 120mm upright posts, a striking diamond roof design, and a footprint of 3m x 3m, the Leviathan commands attention and delivers an outdoor living space that feels truly architectural.

Crafted from slow-grown, pressure treated spruce and finished with Smart Seal timber sealant, this pergola is engineered to withstand the British climate for a decade and beyond — backed by a 10-year guarantee against rot and insect infestation. Smart Seal provides a superior protective barrier that locks out moisture and UV damage, keeping the timber looking and performing at its best for years to come.

🌟 The price includes professional nationwide installation and Smart Seal timber treatment — both included free of charge. Our experienced fitting teams install across the whole of Mainland UK, handling everything from delivery to final fitting so you can enjoy your Leviathan from day one.

Key Features

• ✅ Imposing 120mm x 120mm upright posts — exceptional structural strength and premium visual impact
• ✅ Distinctive diamond roof design — architectural elegance that elevates any garden
• ✅ Fully pressure treated slow-grown spruce — long-term rot and insect resistance
• ✅ Smart Seal timber treatment included free of charge — superior moisture and UV protection
• ✅ 10-year guarantee against rot and insect infestation
• ✅ Nationwide installation included as standard — anywhere across Mainland UK, free of charge
• ✅ Corner-fitting design — maximises use of garden corners and boundary spaces
• ✅ 7.42m² internal area — generous usable space for dining, entertaining, or relaxing
• ✅ Pre-cut, pre-notched, planed timber — precision engineered for a clean, professional finish
• ✅ All fixings supplied — everything needed is included

Specifications

• Overall External Dimensions: 3.321m x 3.321m (10' 10.75" x 10' 10.75")
• External Width: 3.040m (9' 11.75")
• External Depth: 3.040m (9' 11.75")
• Internal Width: 2.724m (8' 11.25")
• Internal Depth: 2.724m (8' 11.25")
• Internal Area: 7.42m²
• Overall Height: 2.350m (7' 8.25")
• Internal Eaves Height: 2.260m (7' 5")
• Upright Posts: 120mm x 120mm
• Timber: Slow Grown Spruce (Fully Pressure Treated)
• Timber Finish: Smart Seal (included)
• Guarantee: 10 Years against Rot and Insect Infestation
• All sizes quoted are nominal. All fixings supplied. Timber is pre-cut, pre-notched, and planed.

Why Choose Bespoke Oak and Slate?

At Bespoke Oak and Slate, we supply and install premium Dunster House garden structures across the UK. Every Leviathan order includes professional installation and Smart Seal timber treatment as standard — completely free of charge. No hidden costs, no surprises — just a beautifully installed, fully treated pergola ready for you to enjoy.

Frequently Asked Questions

Does the price include installation?

Yes — professional nationwide installation is included in the price, free of charge. Our experienced fitting teams cover the whole of Mainland UK. The price you see is the price you pay — fully installed, no extras.

What is Smart Seal and is it included?

Smart Seal is a premium timber sealant that provides a superior protective barrier against moisture penetration, UV damage, and weathering. It goes beyond standard pressure treatment to keep your pergola looking and performing at its best for longer. Smart Seal application is included free of charge with every Leviathan order — applied by our installation team as part of the fitting process.

Do you install anywhere in the UK?

Yes. We install anywhere across Mainland UK at no extra cost. From Cornwall to Caithness, our professional teams will come to you regardless of your location.

Why does the Leviathan have 120mm posts?

The 120mm x 120mm upright posts are significantly larger than those found on standard pergolas, providing exceptional structural rigidity, a premium heavyweight appearance, and the ability to support additional wall panels, roofing options, and climbing plants without any flex or movement. This is what sets the Leviathan apart as a truly premium structure.

Is the Leviathan Diamond Corner Pergola pressure treated?

Yes. All timber is fully pressure treated slow-grown spruce, providing long-term resistance to rot and insect infestation. It is also finished with Smart Seal for additional moisture and UV protection. The pergola comes with a 10-year guarantee against rot and insect damage.

What is the internal usable space?

The Leviathan offers a generous 7.42m² internal area, with an internal width and depth of 2.724m (8' 11.25") each — plenty of room for outdoor dining furniture, a sofa set, or a hot tub enclosure.

What are the overall dimensions of the Leviathan?

The overall external footprint is 3.321m x 3.321m (10' 10.75" x 10' 10.75"), with an overall height of 2.350m (7' 8.25") and an internal eaves height of 2.260m (7' 5"). All sizes are nominal.

Can I add wall panels, decking, or a roof to the Leviathan?

Yes — the Leviathan is designed to be highly customisable. Optional extras include full-height panels, glazed panels, half-height panels, decking, protective paint, and roof trellis for growing plants and additional shelter. Please contact us to discuss the options available for your project.

Does this pergola need planning permission?

In most cases, a pergola of this size falls within permitted development rights and does not require planning permission, provided it meets standard conditions (e.g. not covering more than 50% of garden area, not positioned forward of the principal elevation). We always recommend checking with your local planning authority if you are unsure.

Is the timber pre-cut and ready to install?

Yes — all timber is pre-cut, pre-notched, and planed for a precise, professional finish. All fixings needed for assembly are supplied. As installation is included as standard, our team handles the entire build for you.

How long does installation take?

Installation is typically completed in a single visit by our professional team. Lead times vary by location and current demand — please contact us directly for an accurate timeline for your area.

What is the guarantee on the Leviathan?

The Leviathan comes with a 10-year guarantee against rot and insect infestation on the pressure treated timber, provided the care instructions supplied by Dunster House are followed.

How does the Leviathan compare to the Utopia Diamond Corner Pergola?

The Leviathan is the premium, heavy-duty version of the diamond corner pergola range. Its key differentiators are the 120mm x 120mm posts (vs 70mm on the Utopia), greater internal height, larger internal area, and the inclusion of Smart Seal timber treatment. It is the choice for those who want the most substantial, impressive structure available.