A greenhouse attached to a house is most commonly called a lean-to greenhouse. You’ll also hear it called a conservatory, sunroom, or solarium, depending on how the space is used and where you live. These terms overlap quite a bit in everyday conversation, but each one carries slightly different expectations about design, materials, and purpose.
Lean-To Greenhouse
The most straightforward term is “lean-to greenhouse.” This describes a structure built directly against an existing wall of your house, using that wall as one of its sides. The roof typically slopes away from the house at a pitch of about 27 degrees. Lean-to greenhouses are designed primarily for growing plants, with maximum light transmission and a functional, utilitarian layout. They can be attached to any exterior wall, though a south-facing wall captures the most sunlight in the Northern Hemisphere.
What makes the lean-to distinct from a freestanding greenhouse is shared infrastructure. The house wall provides structural support, insulation on one side, and sometimes access to electricity, water, and heating. That shared wall also creates a unique thermal relationship between the two spaces, which is one of the biggest practical advantages of attaching a greenhouse to your home.
Conservatory, Sunroom, and Solarium
Once a greenhouse-style structure starts doubling as a living space, the terminology shifts. In the UK, a conservatory has a specific legal definition: at least 50% of its side walls must be glazed, and at least 75% of the roof must be transparent glass or polycarbonate. In practice, “conservatory” evokes an ornate, Victorian-style glass room, often used for both plants and relaxation.
The terms sunroom and solarium describe structures that lean more toward living space than plant growing. A sunroom typically has large windows but may have a solid, insulated roof. A solarium usually has a fully glazed roof, closer to a true greenhouse in appearance. The public uses all three terms interchangeably, but the key distinction is intent: if it’s primarily for plants, it’s a greenhouse. If it’s primarily for people (with some plants), it’s a sunroom or conservatory.
A related but distinct term is “orangery,” which historically housed citrus trees in cold climates. An orangery differs from a conservatory by having a more solid roof structure, with less than 75% of the roof surface made from glass.
How an Attached Greenhouse Heats Your Home
One reason people attach greenhouses to their homes is passive solar heating. During the day, sunlight warms the air inside the greenhouse. That warm air can flow into the house through doors, windows, or vents in the shared wall, reducing heating costs in cooler months.
To keep that warmth going after dark, many designs include thermal mass: dense materials that absorb heat during the day and release it slowly at night. Water-filled barrels, stacked concrete blocks, and sand-filled walls all work for this purpose. Concrete block thermal mass can raise nighttime air temperatures inside the greenhouse by up to 18°F above outdoor temperatures. The most effective setups orient the greenhouse east to west, with the thermal mass placed along the north wall to capture the most daytime energy.
Glazing Materials and Insulation
The two main glazing options for an attached greenhouse are glass and polycarbonate panels. Glass offers the classic look and superior clarity, but single-pane glass provides very little insulation, with an R-value of roughly 0.16. Polycarbonate panels, by contrast, have a layered structure with trapped air pockets that slow heat transfer, delivering R-values around 1.54 per inch. That’s nearly ten times the insulating ability per inch.
For an attached structure, insulation matters more than it would for a freestanding greenhouse. Poor insulation means rapid cooling at night, which pulls heat from your house through the shared wall. If you prefer the look of glass, double-pane or triple-pane options with low-emissivity coatings can close the gap with polycarbonate, though at a significantly higher price. Glass roofs with a standard 6:12 pitch also have a practical advantage: condensation runs off the surface cleanly rather than dripping onto plants below.
Humidity and Moisture Control
Attaching a humid, plant-filled space to your home creates a moisture management challenge. Warm, moist greenhouse air migrating into your house can encourage mold growth and damage interior finishes over time. The most effective countermeasure is active ventilation: exhausting humid air and replacing it with drier outside air two or three times per hour, particularly in the evening after sundown and again at sunrise when condensation is heaviest.
Temperature plays a surprisingly large role in humidity. For every 20°F increase in air temperature, the air’s water-holding capacity doubles and relative humidity drops by half. This means that heating the greenhouse air slightly before venting it into the house reduces the moisture load considerably. If you use a fan-based exhaust system alongside a furnace or boiler, you’ll need a relay to prevent the fan from drawing combustion gases back into the greenhouse while the heating system runs.
Foundation and Drainage
Because an attached greenhouse connects to your house, its foundation needs to be compatible with your home’s foundation. A concrete foundation is generally recommended for attached models, since any settling or shifting could damage the connection point with the house. If you live in a climate where the frost line extends deeper than 12 inches, the foundation should reach below that depth, often using concrete sonar tube supports sunk to the required level. Local building codes typically specify exactly how deep.
Drainage is equally important. A concrete floor should slope slightly toward an interior drain, and the exterior grade should slope away from the greenhouse to prevent water from pooling against the foundation. Without proper drainage, standing water underneath or around the structure can undermine the foundation and create moisture problems in both the greenhouse and the house.
Cost and Home Value
Building an attached greenhouse typically costs between $5 and $35 per square foot, depending on the design. Simple hoop-style structures run $5 to $10 per square foot, while permanent A-frame designs cost $25 to $35 per square foot. The national average for a greenhouse project is around $9,640. Custom conservatory-style builds with high-end glazing and climate control systems can exceed these ranges considerably.
As for resale value, a fully enclosed, four-season sunroom or conservatory typically recoups 50 to 70% of its cost when you sell your home. Four-season rooms specifically return about 50 to 60%, while simpler three-season rooms recover 30 to 50%. These additions usually increase your home’s assessed value, which means higher property taxes. A more utilitarian lean-to greenhouse without finished living space will add less to your appraisal but also won’t bump your tax bill as much.