Front of a massive Janssens Gigant Greenhouse

Features

Feature image with the front of a Gigant showing the large footprint of the Janssens Gigant Greenhouse

Feature image with an interior shot of the Janssens Gigant Greenhouse showing the height options

Feature image showing the roof options for the Janssens Gigant Greenhouse

Janssens Gigant Greenhouse

Name: Janssens Gigant Greenhouse
Brand: Janssens
SKU: 580
Availability: InStock

Price range: $43,999.00 through $50,500.00

Roof Glazing

Size

Clear

Features

Massive, walk-in glasshouse: up to 600 sq ft in in-stock models (and customizable beyond)
Extra-strong oversized aluminum profiles for long-term rigidity and stability (17-gauge)
Tall, open interior: up to 10'10" peak height (in-stock models)
Glass or hybrid roof option: 4mm tempered glass or 10mm heat-block polycarbonate roof (helps with sun/heat control)
Most customizable model in the Janssens lineup: stock models available now, plus built-to-order configurations
Double hinged door included for easy entry and day-to-day use
Built-in airflow package: roof windows + side windows for fast heat release and steady fresh-air intake

What's Included

Frame + glazing + hardware
Portal frames (qty varies by size)
Roof vents with automatic openers and manual openers (qty varies by size)
Push-out side windows (qty varies by size)
Double hinged door(s)
Victorian ridge cresting
Gutters + downpipe

Dimensions

In-stock sizes:

15' x 25': 15’ W x 24’8" D x 9′10" H
20' x 30': 19’11" W x 29’6" D x 10′10" H

Other custom sizes available

Shipping

Ships via LTL freight (curbside): Liftgate + pallet jack delivery; plan 2–3 people to move boxes off the pallet and into place.
Lead time: 5–7 business days (in stock). Up to 12-14 weeks (if not in stock).

Assembly & Warranty

Average assembly time: approx. 2-3 days with 3-4 people
Assembly Manual: Download here
15-year warranty limited

Secure Checkout

Nationwide Delivery

Veteran-Owned

Real Greenhouse Owners

Personalized Planning Help

Description

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The Janssens Gigant is the answer when standard greenhouse kits feel too small, too short, or too limiting. It’s a massive, elegant glasshouse—taller, roomier, and highly customizable — designed to become a true focal point in your backyard.

The Gigant is ideal when you want a glass space that supports your plan—whether that’s a botanical garden room, a walk-in greenhouse for serious growing, or a protected entertaining area like a dining space or bar-style retreat. We keep two proven models in stock, and custom configurations are still available if you want different dimensions, doors, ventilation, glazing, or color.

Maximize Space with Grand Height

The Gigant’s soaring peak—up to 10’10″—gives you the feeling of a true architectural room, not just a greenhouse.

Whether you want tall tropical plants, hanging gardens, or an airy dining setup, the vertical space allows for more creativity and comfort.

Engineered for Stability & Strength

The Gigant uses oversized 17-gauge aluminum profiles for long-term rigidity.

Inside, portal frames—thicker support beams placed every 3-4 panels —add significant structural reinforcement, ensuring stability even in large spans. These frames help the greenhouse stand firm in challenging weather, offering peace of mind for both growing and living spaces.

Classic Glass Beauty, Better Sun Control

If you want maximum clarity and a true “glass room” feel, go all-glass—it delivers full light and that seamless indoor/outdoor look people buy the Gigant for.

For hotter, sun-heavy regions, the hybrid roof is often the better choice. The 10mm milky twin-wall polycarbonate softens harsh sunlight, drops roof light transmission to 58%, and helps block the heat so the space feels more manageable on bright days.

Note: Polycarbonate is lighter than glass, which makes assembly easier. It also offers better insulation and reduces the weight on the roof which could be especially helpful in winter conditions.

Easy Access, Flexible Entry

The Gigant includes a double hinged door for comfortable, wide access—great for moving large plants, benches, or furniture in and out without feeling tight. And because door placement is flexible, you can position the entry where it fits your yard layout best.

If you want multiple access points, you can also add additional doors for extra entries and easier flow.

Ventilate with Ease

The Gigant uses a mixed vent setup on purpose: some roof vents have automatic openers for hands-free heat release, and some are manual so you can control airflow when you want to.

The auto openers are great peace of mind on sunny days, while manual vents are especially useful if you’re running an exhaust fan system and prefer to manage vent positions more precisely.

To support balanced airflow, the Gigant also includes push-out side windows to bring fresh air in at plant level while heat escapes out the top.

Available Customizations For the Janssens Gigant

Choose Your Footprint

Build it to fit your plan—not just the space you have. The Gigant can be configured from 15′–20′ wide and 15′–59′ long, so you’re not forced into a “close enough” layout.

Set the Height You Want

Need more vertical presence or a more open interior feel? Sidewall heights can be ordered from 7′–10′, with peak height options up to 13′9″ depending on the configuration.

Pick Your Favorite Color

Standard (most popular) frame colors are black, dark green, and white—but any RAL color is possible if you want an exact match or a custom architectural look.

Victorian Detail or Modern Lines

Pane width changes the entire style. Choose 14″ narrow panes for a more traditional Victorian look—or 28″ panes for a cleaner, more modern appearance. You can alsoadd or skip the roof ridge décor to finish the style the way you want.

Elevated Base + Solid Panels

Some buyers choose a stem wall primarily for the finished look—matching existing hardscape, garden walls, or a more permanent “garden room” aesthetic. You can also add solid aluminum panels (half or full) in plain or decorative styles to create more privacy or a more enclosed feel where you want it.

Reinforce for Your Weather

If you’re planning for higher wind or snow conditions, the Gigant can be additionally strengthened with portal frames and reinforcement planning.

Tip: Make sure the truck can access your driveway and you have a clear staging area ready.

Plan Your Gigant With Us

Gallery

Quick Size Guide

Sidewall height: 6’8″

Roof pitch: 22°

Dimensions	Peak Height
15′ x 25′	9’10”
20′ x 30′	10’10”

Every Janssens Gigant Greenhouse kit includes:

Ridge Decoration

Vent Type	Roof Window + Auto Opener	Roof Window + Spindle Openener	Side Windows + Manual Opener	Portal Frames	Double Hinged Door
15′ x 25′	3	3	4	4	1
20′ x 30′	6	2	6	3	2

Specifications

Brand	Janssens
Distributed by	Exaco
Made in	Belgium
Width	25', 30'
Length	15', 20'
Floorspace	375 sq ft, 600 sq ft
Peak Height	9'10", 10'10"
Side Wall Height	6'8"
Framing Material	Aluminum
Frame Color	Black
Roof Glazing	10mm twin-wall polycarbonate, 4mm tempered glass
Wall Glazing	4mm Tempered Glass
Roof Pitch	22°
Roof Vent Opener Type	Automatic (wax)
Roof Vent Dimensions	29″ x 33″
Door Type	Double, Hinged
Door Dimensions	56.75″ x 70.5″
Rainwater Collection	Gutter with downspouts on both sides
Stem Wall Compatibility	Yes
Expandable	No
Warranty	15 years limited

Q&As

Still have a question?

Send us your question

What foundation do I need?

All Janssens greenhouses require a proper foundation despite the strong base frame because glass greenhouse is heavy. A concrete slab or a concrete footing will provide the most solid, long-lasting base. The key is that your foundation is level, square, and well-draining—even small twists can affect door operation and panel fit.

You have to cement the foundation into the footer for the perfect stability. Do not set concrete in the corners until the entire greenhouse frame is complete, level, and square! Please, have a look at the manual or this assembly video for the Royal Victorians. They illustrate how it’s done correctly.

Helpful guides:

Can I assemble it myself (DIY)?

It is recommended to get help from an experienced contractor to assemble this large greenhouse kit.

Do the roof vent openers require electricity?

No. They are wax-cylinder openers, which expand and contract with temperature to open/close the vent—so there’s no wiring and no power required.

Where does this ship from?

Austin, Texas

How Does Curbside Delivery Work?

Freight delivery drops your crate at the curb/end of driveway. Typically, you’ll unload the contents with the driver and the crate remains on the truck. If you have a forklift or tractor with long forks, you may be able to lower the whole crate using the liftgate. Plan for 2–3 people to help.

Tip: Make sure the truck can access your driveway and you have a clear staging area ready.

Made by

Janssens: 75+ years of craftsmanship

Janssens Greenhouses has built premium European glass greenhouses in Belgium for decades, known for elegant design, precise aluminum framing, and a fit-and-finish that’s made to last.

Explore Janssens Greenhouses

Distributed by

Exaco

Exaco is the authorized North American distributor for Alton, known for importing a curated lineup of high-quality European garden products—and for support that goes the extra mile.

More About Exaco

Additional information

Distributed by	Exaco
Door Dimensions	56.75″ x 70.5″
Door Type	Double, Hinged
Expandable	No
Floorspace	375 sq ft, 600 sq ft
Framing Material	Aluminum
Frame Color	Black
Length	15', 20'
Made in	Belgium
Peak Height	9'10", 10'10"
Rainwater Collection	Gutter with downspouts on both sides
Roof Glazing	10mm twin-wall polycarbonate, 4mm tempered glass
Roof Pitch	22°
Roof Vent Dimensions	29″ x 33″
Roof Vent Opener Type	Automatic (wax)
Side Wall Height	6'8"
Stem Wall Compatibility	Yes
Style	Conventional, Modern, Victorian
Wall Glazing	4mm Tempered Glass
Warranty	15 years limited
Width	25', 30'

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