The question that decides a greenhouse budget is not "how big?" but "how cold does it get in January, and what do I want to grow then?" A structure for starting seedlings in March is a modest project. One that grows tomatoes through a northern winter is a small heated building with an energy bill to match.
HomeAdvisor puts the typical greenhouse build at $3,071 to $16,209, with an average of about $9,640.[1] Where you land in that range follows from the season you are planning for.
Key takeaways
- HomeAdvisor reports an average build of about $9,640, or $5 to $35 per square foot.
- Cool-season crops need about 50 to 70°F by day; warm-season crops about 60 to 85°F (Colorado State Extension).
- Growing warm-season crops in winter is not cost-effective without solar collectors or extra heat.
- Budget for power and water to the greenhouse, not just the frame and glazing.
Match the greenhouse to the season
Colorado State University Extension gives these temperature targets for vegetables grown in a hobby greenhouse:[2]
| Crop type | Day | Night |
|---|---|---|
| Cool-season (lettuce, spinach, radish) | 50 to 70°F | 45 to 55°F |
| Warm-season (tomato, pepper, cucumber) | 60 to 85°F | 55 to 65°F |
The same guide says warm-season crops can't be grown cost-effectively in winter without solar heat collectors or supplemental heat, and that winter crops grow slowly because of low light.[2] So an unheated or lightly heated greenhouse that extends spring and fall, and grows greens in winter, gives the best return on a modest budget. Year-round tomatoes in a cold climate is a heating project.
Structure types and what they cost
| Type | Per square foot |
|---|---|
| Hoop house | $5 to $10 |
| Geodesic dome | $10 to $25 |
| A-frame | $25 to $35 |
A hoop house covered in plastic film is the cheapest way to enclose growing space and suits season extension. Rigid glazing and a framed structure cost more and hold heat better. Extension's example hobby greenhouse is about 12 feet long, 4 feet high at the sides and 7 feet at the peak.[2]
Film, polycarbonate or glass
The covering decides how much light gets in, how much heat stays in and how often you will be replacing it. Polyethylene film is the cheapest and goes on quickly, but sun breaks it down, so plan on re-covering every few years. Twin-wall polycarbonate panels cost more, scatter light evenly so plants don’t scorch, and insulate much better than a single layer. Glass gives the clearest view and lasts the longest, but it is heavy, needs a strong frame and loses more heat unless it is double glazed.
For a season-extension greenhouse on a budget, film on a hoop frame is hard to beat. If you plan to heat it in winter, better glazing usually pays for itself in lower heating bills.
Heat without a huge bill
A few low-cost steps help a greenhouse hold heat. Insulate the north wall, which gets little useful sun, and line it with something reflective to bounce light back onto the plants. Add thermal mass, such as dark barrels of water along the north side, which soak up heat by day and release it at night. Small fans that move air around the greenhouse even out cold spots.
If you do add a heater, use a thermostat so it only runs when needed. Any heater that burns fuel must be designed and vented for that use, because combustion in a closed space can produce carbon monoxide and fumes that harm plants and people.
Summer is the harder season
Many new greenhouse owners lose more plants to heat than to cold. On a sunny day the temperature inside can climb well past what crops tolerate within an hour. Plan ventilation from the start: roof vents or an exhaust fan up high, intake louvers down low, and automatic vent openers that work without electricity if you are away during the day. Shade cloth over the roof in midsummer cuts the heat further.
Setting up the inside
Benches at waist height save your back and leave room underneath for storage or crops that like shade. Keep the main aisle wide enough to turn around with a tray of seedlings. A gravel floor drains well and is easy to keep clean. A potting area near the door, a rain barrel or tap within reach, and a shelf for tools make daily chores quick, which matters because a greenhouse needs checking every day in hot weather.
Freestanding or attached to the house?
A lean-to greenhouse built against a south-facing wall of the house borrows some of the home’s warmth, and water and power are only a few feet away. It is also right outside the door, which makes daily checks easy. The trade-offs are less light, since one whole side is a wall, and the need to flash and seal the connection to the house properly so moisture doesn’t get into your siding. A freestanding greenhouse gets light from every side and can go wherever the sun is best, but every utility has to be brought out to it, and it loses heat from all four walls.
What to grow in the first year
Start with jobs a greenhouse does easily. Raising your own vegetable and flower seedlings in late winter and spring is the classic first use, and it can save a good share of what you would spend on transplants. Leafy greens and herbs through fall and into early winter come next. Once you know how warm and cold your greenhouse actually gets, which a cheap thermometer that records highs and lows will tell you, you can decide whether chasing warm-season crops later in the year is worth the extra heat.
Plug your house size, land price and quotes into the free calculator. It uses the same NAHB 2024 averages as this guide.
Frequently asked questions
How much does it cost to build a greenhouse?
HomeAdvisor reports a typical range of $3,071 to $16,209, with an average of about $9,640, or $5 to $35 per square foot.
Can you grow tomatoes in a greenhouse in winter?
Colorado State Extension says warm-season crops cannot be grown cost-effectively in winter without solar heat collectors or supplemental heat, and they need 55 to 65°F at night.
What is the cheapest type of greenhouse?
A plastic-covered hoop house, which HomeAdvisor prices at about $5 to $10 per square foot.
Do I need a permit for a greenhouse?
It depends on your town and the size. Many places exempt small structures below a size threshold, but foundations, electrical work and larger buildings usually need permits. Check setbacks and HOA rules too.
How can I keep a greenhouse warm in winter cheaply?
Insulate the north wall, add thermal mass such as water barrels, use fans to mix the air and run any heater on a thermostat. Better glazing such as twin-wall polycarbonate also holds heat longer.
Is an attached greenhouse better than a freestanding one?
An attached lean-to stays warmer and is closer to water and power, but gets less light and must be sealed carefully against the house. A freestanding greenhouse gets more light but loses more heat.
Sources
- HomeAdvisor, "What Does a Greenhouse Cost to Build?", updated June 19, 2026 Verified
- Colorado State University Extension, "Growing Vegetables in a Hobby Greenhouse" (GardenNotes #723), reviewed August 2024 Verified
Figures last checked October 19, 2026. National averages are a planning guide, not a quote. See our editorial policy and data sources.
