Lean-To Greenhouse: Cost, Models, What the Wall Adds
A lean-to greenhouse runs $247.99 for a 6x4 Outsunny to $16,499 for a Janssens Arcadia, checked September 20, 2026. Flashing, permits, snow and the wall itself.
Comparison
Quick answer: Checked September 20, 2026, a lean-to greenhouse costs $247.99 for an Outsunny 6x4 kit, $1,325.99 for a Palram Canopia Hybrid 4x8, $2,499 for a Rion Sun Room 8x8, $3,555 for a Solexx Harvester 8x8, $8,965 for a redwood Sturdi-Built Garden Sunroom 8x12, and $10,299 to $16,499 for a Janssens Arcadia in tempered glass. Hartley Botanic and Alitex quote only. The wall changes four things the sticker does not show: the frame must be sealed and often flashed to your siding, and Exaco ships no attachment hardware at all; the ridge has to clear your soffit, so Sturdi-Built needs 8 ft 3 in to 9 ft 4 in of clear wall; snow slides off the house roof onto the greenhouse, which only Vego Garden warns about; and an attached structure loses the 200 square foot detached-shed permit exemption in the model code, so cities like New York file it as a renovation. Every extension service that describes the lean-to calls it the least expensive type to build and heat, and every one lists limited ventilation as the tradeoff.
Best for
Homeowners with a sunny south or east wall who want a small heated growing space close to power and water and need the real list of what attaching to the house costs.
Wrong fit
Growers who want maximum bench space or the best air movement per dollar. A freestanding even-span house does both better.
Tradeoff
The wall gives you cheaper heat, a shorter walk and a lower kit price, and takes back ventilation, light from one side, a permit exemption, and a flashing detail that decides whether your siding rots. The cheap kits do not include the attachment; the expensive ones include a drawing for a wall you build.
Checked September 20, 2026, the cheapest walk-in lean-to greenhouse for sale in the US is a $247.99 Outsunny 6x4 and the most expensive one with a published price is a $16,499 Janssens Arcadia in tempered glass. Both lean on the same idea: use a wall you already own as the fourth side, and borrow the house's warmth, its power and its water tap. The University of Georgia, Clemson and Colorado State extension services all call the lean-to the least expensive greenhouse to build and run, and all three list the same drawback in the same words: limited ventilation and temperature control.
We don't sell greenhouses. We save you from buying the wrong one, and a lean-to is the type where the kit price hides the most. This guide prices every model we could read today, then walks through what the wall adds: sealing and flashing, wall height, roof snow, and the permit you probably lose. For the rest of the project, the real cost of a greenhouse and the foundation guide price the base and site work.
Quick Answer: Every Lean-To by Price
Model
Size
Glazing and frame
Price found September 20, 2026
Stock
What the box leaves out
Outsunny 6x4
6x4
Polycarbonate, aluminum
$247.99 at Aosom
In stock
Base, attachment, thickness not stated
Outsunny 8x4
4x8
4mm twin-wall, aluminum alloy, 2 in base
$317.99 at outsunny.com
Sold out
Foundation, attachment
Palram Canopia Hybrid Lean-To
4x8
4mm twin-wall roof, 0.8mm clear walls, aluminum, steel base
3.5mm twin-wall polyethylene, R 2.1, composite frame
$3,555 at Dive To Garden
In stock, ships 3 to 4 days
Nothing structural; built-in base needs no foundation
Sturdi-Built Garden Sunroom
6x12 to 10x18; 8x12 shown
1/8 in glass walls, tempered roof, redwood
$8,965 for 8x12
Sold out
8 ft 3 in to 9 ft 4 in of clear wall; optional 18 in basewall
Exaco Janssens Arcadia
2x5 m to 4x6 m
4mm tempered glass or 10mm twin-wall, 17-gauge aluminum, 4 in foundation frame
$10,299 to $16,499 at Backyard Oasis
Ships 5 to 9 business days
Attachment hardware and weather stripping, per Exaco
Hartley Botanic Lean-To
7 ft 4 in wide, 7 ft 6 in to 24 ft 7 in long
4mm toughened glass, aluminum
Quote only
Made to order
Foundation, built by you from Hartley's drawing
Alitex
Bespoke
Glass, aluminum
Quote only; the Kew Collection starts at $60,000
Made to order
Everything is designed after a visit
Harbor Freight sells no lean-to model, so the budget floor is Outsunny. Home Depot's search snippet showed the Palram kit far cheaper than the price above, but the page blocked our fetch, so that figure is not in the table.
How These Numbers Were Built, and When
Every price was read from the manufacturer or a named US retailer on September 20, 2026, and the retailer is stated because the same kit differs by hundreds of dollars between dealers. Where dealers disagreed on the Arcadia we used one dealer's full size ladder rather than mixing. Attachment, wall-height and foundation statements come from the manufacturers' own pages and assembly manuals. Permit statements come from the model code, the New York City Department of Buildings and a Colorado county's January 2026 handout. Extension statements come from Georgia, Clemson and Colorado State. We have not built any of these kits.
What the Wall Changes
The attachment nobody ships
A freestanding kit has four walls in the box. A lean-to has three, and the fourth is your siding. Exaco says plainly that the Arcadia's attachment hardware and weather stripping for the building connection are not included. The Wisconsin Greenhouse Company's attached-greenhouse guide, one of the few manufacturer documents that describes the joint, says it supplies sealants to seal the greenhouse to the existing wall and that "in some situations it may be beneficial to provide a flashing detail." A Reddit buyer asked the question every first-time lean-to owner asks: "Do you have to remove the siding when building a greenhouse like this, or do you just attach the walls but keep the siding in place?" The manufacturers do not answer it. A flashing detail that sheds water over the siding rather than behind it is carpentry, not assembly, and it is a line to price before the kit.
The wall has to be tall enough
The ridge lands against the house, and the house has a soffit. Wisconsin's guide says the ridge is designed "to fit snugly underneath your soffit" or the end walls jog around the eave. Sturdi-Built publishes the numbers: a 6-foot-wide Garden Sunroom needs 8 ft 3 in of clear wall, an 8-foot needs 8 ft 7 in, and a 10-foot needs 9 ft 4 in. The Arcadia peaks at 110 to 114 inches. A standard 74-inch door needs a raised sidewall on the Wisconsin design. Measure from grade to the underside of the soffit before you pick a width.
Heat you borrow, and heat you lose
Georgia's Bulletin 910 says a lean-to is "usually close to available electricity, water and heat" and can be heated "with an extension from the home heating unit or through a window or open door with a fan." Colorado State calls it "less expensive to operate and construct." Wisconsin frames the wall the other way, as solar gain that helps heat the home in winter. What no primary source publishes is a percentage saving from the shared wall; the "30 to 40 percent" figure that circulates online exists only in search snippets, so it is not on this page. What the same three extension sources do say, all of them, is that the lean-to has limited ventilation. Clemson: "the even-span has a better shape than a lean-to for air circulation." One roof vent on a Rion, two on an Arcadia, and a louver plus a heat-activated opener on the Solexx is what you get; the ventilation guide explains why a lean-to on a south wall cooks in July without a fan.
Snow comes off your roof
A lean-to sits under the eave of a pitched house roof. When the roof sheds, the greenhouse catches it. Vego Garden is the only manufacturer on this list that says so: "If your greenhouse is installed beneath a sloped house roof, watch for sliding snow or ice from above and clear it promptly." Nobody publishes a snow rating for a lean-to that accounts for a roof dump. The snow load guide covers what published ratings mean and do not mean.
The permit exemption you lose
The 2021 International Residential Code exempts "one-story detached accessory structures, provided that the floor area does not exceed 200 square feet" from a building permit. Detached. A lean-to is attached, so the exemption most shed and greenhouse buyers rely on does not apply, and Wisconsin's page says a lean-to is "considered an addition to your home." New York City files an attached greenhouse as a renovation, caps it at one story or 15 feet, and lists footings and possibly a soil test in the scope. Larimer County, Colorado, requires a permit for any greenhouse with utilities or glass over 200 square feet, applies setbacks to all structures, and wants engineer-stamped wind and snow calculations. Georgia's bulletin puts it simply: "Usually a building permit is required to erect a greenhouse." The permit guide walks through the call to make.
The Base Under a Lean-To
Palram's assembly manual for the 4x8 says the kit "must be positioned and fixed on a flat level surface" and recommends concrete, pressure-treated wood, a wood deck or paver blocks; it ships no floor or base. Wisconsin recommends a concrete foundation, level and square. Hartley requires a foundation and sends a fully specified drawing on order. Exaco includes a 4-inch foundation frame. Sturdi-Built offers an 18-inch redwood basewall or a masonry base. Solexx is the outlier, with a built-in base it says needs no foundation. A Reddit owner asked whether to drill into the house slab: "Could it crack the foundation or compromise waterproofing? Are there alternatives to attach it securely for wind without penetrating the concrete?" Anchoring into a slab edge is a question for a contractor, and the wind anchoring guide covers the alternatives.
Model by Model
Outsunny 6x4 and 8x4, $247.99 and $317.99. Aluminum alloy, 4mm twin-wall on the 8x4, a sliding door, a roof vent and a 2-inch base. The 8x4 was sold out. This is the kit for a protected wall in a mild climate and a buyer who will seal every seam.
Palram Canopia Hybrid Lean-To 4x8, $1,325.99. 4mm twin-wall roof over 0.8mm clear polycarbonate walls, aluminum frame, galvanized base, a warranty Palram states as "at least 5 years". Sold out with a late-September restock date. Palram's own page says it comes with no floor or base. The Palram review covers what its warranty ladder actually pays.
Rion Sun Room 2, $1,752 to $4,325. The resin-frame lean-to in four lengths from 6x6 to 8x20, with a 4mm twin-wall roof, 3mm acrylic walls, a hinged reversible door and one roof vent. The 8x8 at $2,499 is the size most buyers land on. The Rion review sets its sheltered-site cutoff.
Solexx Harvester 8x8x8, $3,555. Twin-wall polyethylene at R 2.1, a composite frame, a louver, a 12x12 vent with a heat-activated opener, in stock and shipping in days, and the only kit here designed "to hug the side of your house, garage, deck, or stand-alone" on a built-in base. Diffused light rather than clear.
Vego Garden, $2,299.95 to $4,299.95. Three sizes from 4.5x8.5 to 8.5x12.5. We could not capture its glazing or frame specification today, so it stays in the table on price only, with credit for being the one maker that tells you to clear roof snow.
Sturdi-Built Garden Sunroom, $8,965 for 8x12. Redwood, glass walls and a tempered roof, solar-powered roof vents, sizes from 6x12 to 10x18, sold out when checked. The wall-height requirements are the useful published number on this whole page.
Exaco Janssens Arcadia, $10,299 to $16,499. Tempered glass or 10mm twin-wall in 17-gauge aluminum with stainless hardware, two roof vents and a 4-inch foundation frame, in five metric sizes from 2x5 to 4x6 meters. Ships in five to nine business days. Bring your own attachment hardware and weather stripping. The Janssens review covers freight and assembly.
Hartley Botanic and Alitex. Quote only. The Hartley Lean-To is 7 ft 4 in wide and 7 ft 2 in high in 3 to 10 pane lengths, in 4mm toughened glass, with a foundation drawing supplied after ordering. Alitex builds to order after a designer visit. The Hartley cost guide and the Alitex cost guide assemble what is public.
Which Buyer Should Get Which
A south or east wall, a mild climate, under $500: Outsunny, sealed, on pavers, with a fan.
A real structure under $4,000 that ships this week: Solexx if you accept diffused light and want a base in the box; Rion 8x8 if you want clear walls and a resin frame.
Glass against the house, $10,000 to $17,000: Arcadia, with a carpenter for the flashing.
Designed, drawn and installed: Hartley or Alitex, and budget the wall and foundation work their drawings specify.
Whatever you pick, get the flashing, the wall attachment, the permit responsibility and the base as written lines with the quote checklist before you pay a deposit.
What We Could Not Verify
Home Depot's Palram 4x8 price; the page blocked our fetch. Lowe's and Walmart Outsunny pages likewise.
Palram's manual text on wall attachment, sealing, wind and snow; only the foundation pages could be read.
Arcadia prices at other dealers, which disagree with each other; one dealer's ladder is used.
Solexx's 5mm price, Vego's glazing and frame, the Outsunny 6x4 panel thickness.
Any percentage heating saving from the shared wall.
Hartley and Alitex lean-to prices; neither is published.
We have not built any of these kits.
Frequently Asked Questions
Do you have to remove the siding when building a greenhouse like this, or do you just attach the walls but keep the siding in place?
The manufacturers on this list do not say, and Exaco ships no attachment parts at all. The one manufacturer document that describes the joint supplies sealants and says a flashing detail is sometimes needed. Flashing that sheds water over the siding, not behind it, generally means working the top edge under the siding or the soffit, which is carpentry. Get it quoted.
Could it crack the foundation or compromise waterproofing? Are there alternatives to attach it securely for wind without penetrating the concrete?
Drilling into a slab edge near a basement wall is a contractor question. The alternatives kits themselves use are a treated-lumber or paver base anchored to the ground beside the slab, with the frame fixed to that base, which is what Palram's manual describes and what the wind anchoring guide compares.
It feels like PC is still the way to go but also seems a bit strange to use PC on something that is attached to house, or can you even?
You can, and most lean-to kits under $5,000 are polycarbonate or acrylic. Glass against the house is what Sturdi-Built, Arcadia, Hartley and Alitex sell, at $9,000 and up. The tradeoffs are the same as freestanding, covered in glass vs polycarbonate, plus one more: a polycarbonate roof under an eave that dumps snow is easier to replace than a glass one.
Lean-to greenhouse against stained cedar siding? Has anyone done this long term without issues?
The risk is trapped moisture at the joint, which is why flashing and sealant matter more than the kit. No manufacturer on this list publishes a siding compatibility statement. Ventilation is the other half: a lean-to on a hot wall with one vent holds humidity against the siding all summer.
I'm thinking about building a lean-to greenhouse on the East side of my house, which gets full sun from sunrise until about midday. Has anyone else done something similar? Is this a stupid idea?
Colorado State's extension says "an eastern or southern exposure is the best." East gives morning light and a cooler afternoon, which for a lean-to with limited ventilation is often a better summer than a south wall.
Has anyone built a lean-to style greenhouse against a 6ft privacy fence? Any words of advice?
A fence is not a wall. Sturdi-Built needs more than 8 feet of clear height and the Arcadia peaks over 9 feet, so most rigid lean-to kits will stand taller than the fence and need their own back wall or a freestanding design. The small Outsunny kits are the exception, and they still need a base and anchoring, not a fence, to hold them in wind.
These guides are built from manufacturer documentation, public specifications, primary research where health claims matter, and repeated buyer questions that show up in real ownership and installation decisions.
Manufacturer responses can clarify pricing bands, warranty terms, support footprint, or common mistakes. They do not move a page up the shortlist on their own.
