Leviathan Wooden Pergola 5m x 3m | 120mm Posts | Smart Seal Treated | Nationwide Installation Included

Leviathan Wooden Pergola – 5m x 3m | 120mm Posts | Smart Seal Timber Treatment

This is the one that stops people in their tracks. The Leviathan Wooden Pergola 5m x 3m by Dunster House is the flagship of the entire Leviathan freestanding range — a full five metres wide, three metres deep, and built with the same commanding 120mm x 120mm upright posts that define the Leviathan name. When it’s installed in your garden, it doesn’t just add a feature. It becomes the garden.

Five metres is a different proposition entirely. It’s the length of a full outdoor dining table with room to spare at both ends. It’s a hot tub at one end, a bar at the other, and a seating area in between. It’s a covered walkway along the back of the house, a sheltered outdoor kitchen, a garden room without walls. The 5m x 3m Leviathan gives you the canvas — what you create beneath it is entirely up to you.

Built by Dunster House from slow-grown, pressure treated spruce — not cheap pine — with every rafter pre-cut, pre-notched, and planed to precision. All timber is fully pressure treated (not merely dip treated) and finished with Smart Seal timber sealant as standard, delivering a superior protective barrier against moisture, UV damage, and the relentless British weather. Backed by a 10-year guarantee against rot and insect infestation.

🌟 Professional nationwide installation and Smart Seal timber treatment are both included in the price, free of charge. Our experienced fitting teams cover the whole of Mainland UK — handling everything from delivery to final fitting so you can simply step outside and enjoy the most impressive pergola in your neighbourhood.

Key Features

• ✅ Flagship 5m x 3m footprint — the largest Leviathan freestanding pergola, unmatched outdoor living space
• ✅ Imposing 120mm x 120mm upright posts — heavyweight structural strength and architectural presence
• ✅ Slow-grown spruce, not cheap pine — denser grain, superior long-term durability
• ✅ Fully pressure treated (not dip treated) — long-term rot and insect resistance
• ✅ Smart Seal timber treatment included as standard — superior moisture and UV protection
• ✅ 10-year guarantee against rot and insect infestation
• ✅ Pre-notched, pre-cut, planed rafters — precision engineered for a clean, professional finish
• ✅ All fixings included — no hidden extras
• ✅ Spectacular for climbing plants — 5m of rafter span creates a breathtaking natural canopy
• ✅ Nationwide installation included as standard — anywhere across Mainland UK, free of charge

Specifications

• Approximate Size: W5m x D3m (W16'5" x D10')
• Upright Posts: 120mm x 120mm
• Timber: Slow Grown Spruce (Fully Pressure Treated)
• Timber Finish: Smart Seal (included as standard)
• Guarantee: 10 Years against Rot and Insect Infestation
• All sizes quoted are nominal. All fixings supplied. Rafters are 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 sealed 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 — going beyond standard pressure treatment to keep your pergola looking and performing at its best for longer. Smart Seal is applied as standard with every order, free of charge, 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. Whether you’re in the South West, the Midlands, Scotland, or anywhere in between — our teams will come to you.

Is this the largest Leviathan pergola available?

Yes — the Leviathan 5m x 3m is the largest freestanding pergola in the Leviathan range. It offers the greatest internal space, the longest span, and the most flexibility for outdoor living, entertaining, and landscaping. If you want the very best, this is it.

Why choose the 5m x 3m over the 4m x 3m?

The extra metre of width makes a transformative difference. The 5m x 3m allows you to genuinely zone your outdoor space — a dining area, a lounge, and a bar or hot tub, all beneath the same structure. It also works beautifully as a covered walkway or veranda along the rear of a house. If you have the garden space and want the most impressive result, the 5m x 3m is the clear choice.

Can this pergola be used as a covered walkway or veranda?

Yes — the 5m width makes the Leviathan 5m x 3m particularly well-suited for use as a covered walkway along the back of a house, a veranda-style structure, or a sheltered outdoor corridor connecting different areas of your garden or property.

What makes the Leviathan different from cheaper pergolas?

The Leviathan is a Dunster House product built from slow-grown spruce, not cheap pine. Slow-grown timber has a denser grain structure, making it significantly stronger and more durable. Combined with full pressure treatment, Smart Seal finishing, 120mm x 120mm posts, and precision pre-notched rafters, the Leviathan is in a different class to budget pergolas.

What is the difference between pressure treated and dip treated timber?

Pressure treatment forces preservative deep into the timber fibres under pressure, providing long-lasting protection from the inside out. Dip treatment only coats the surface and offers far less protection over time. The Leviathan uses full pressure treatment plus Smart Seal as an additional protective layer — which is why it comes with a 10-year guarantee against rot and insect infestation.

Can I grow climbing plants on this pergola?

Absolutely — and the 5m span makes this the most spectacular pergola in the range for climbing plants. Wisteria, roses, jasmine, clematis, and ivy can spread across the full five metres of rafter, creating a breathtaking living canopy that transforms the entire feel of your garden.

Does this pergola need planning permission?

Given its size, we strongly recommend checking with your local planning authority before installation. At 5m x 3m, this structure may exceed permitted development thresholds depending on your garden size and property type. Our team is happy to advise, but formal planning confirmation should come from your local council.

Are all fixings included?

Yes — all fixings needed for assembly are included at no extra cost. As installation is included as standard, our professional team handles the entire build for you.

What is the guarantee?

The Leviathan Wooden Pergola 5m x 3m 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.