Do I Need a Permit for a Greenhouse?

Most small backyard greenhouses in most places do not need a building permit. Many do. Which one you are is decided by a handful of local variables, and the only reliable way to find out is to ask.

The good news is that this is a genuinely easy call to make. Building departments answer this question constantly, the answer is usually immediate, and a ten-minute conversation before you order is the cheapest insurance in the whole project. The expensive version is finding out after a neighbour complains, or when you sell the house and a structure appears on the survey with no permit behind it.

These are the factors jurisdictions commonly key off. Any one of them can require a permit even when the others would not.

• Floor area. Many places exempt accessory structures below a stated size. The threshold varies - figures in the region of 100, 120 and 200 sq ft all appear in different codes - and yours may be different again or may not exist at all. Do not assume a number you read online, including these.
• Permanent foundation. A concrete slab or footing frequently converts a structure from temporary to permanent in the eyes of the code, and permanent structures are far more likely to need a permit. A gravel base often does not have the same effect. Often, not always.
• Electrical supply. Running power to an outbuilding usually requires an electrical permit and inspection in its own right, independent of the structure. This one catches people out constantly.
• Plumbing. A water supply or a drain generally triggers a plumbing permit on the same basis.
• Height. Accessory structures often have a maximum height in the zoning code, separate from any building permit question.
• Setbacks. How close you may build to a property line, an easement, a septic field or another structure. This is zoning rather than building code, it applies whether or not you need a permit, and it is the rule most commonly discovered too late.
• Lot coverage. Some jurisdictions cap the total impervious or built area of a lot. A greenhouse plus a garage plus a shed can push you over.
• Special overlays. Flood zones, coastal high-wind zones, historic districts and wildfire zones all add requirements, and they can be strict.

A homeowners association can be stricter than the city, and its rules are contractual rather than statutory - the building department will not enforce them and will not warn you about them. Common HOA provisions cover where an accessory structure may sit, how tall it may be, what it may be made of, whether it may be visible from the street, and whether an architectural review committee must approve it first.

Read your covenants and, if there is an architectural committee, submit before you order rather than after. Deed restrictions on the property itself can do the same thing even where there is no active association.

1. Say what it is: a prefabricated hobby greenhouse, giving the exact footprint in feet and the peak height.
2. Ask whether a building permit is required at that size, and whether there is an area threshold below which it is exempt.
3. Ask whether the answer changes if the base is compacted gravel rather than concrete.
4. Ask what the setback requirements are from side and rear property lines, and from any easement or septic field.
5. Ask whether there is a height limit for accessory structures.
6. Ask whether an electrical permit is required if you run power to it, and whether it can be a separate application later.
7. Ask what the design snow load and design wind speed are for your address - useful whether or not you need a permit.
8. Ask what documents a permit application would need, and whether a manufacturer specification sheet is acceptable in place of stamped drawings.
9. Write down the name of the person you spoke to and the date.

If a permit is required, the package is normally modest for a structure this size:

• A site plan - your lot, the property lines, existing structures, and the proposed greenhouse with dimensioned distances to each boundary. Hand-drawn to scale is usually acceptable.
• Manufacturer specifications - dimensions, frame material, glazing, and the rated snow and wind loads.
• A foundation or anchoring detail - what the structure sits on and how it is fixed down.
• Sometimes an engineer's stamp, most often in high-wind coastal zones, heavy snow regions or flood overlays.

This is one place published ratings earn their keep. Our frames are 1 in. square hot-dip galvanized steel, rated to shed 5 ft of snow, with wind ratings stated per series - 75 mph on the Arc Series, 65 mph on the Loft Series and 65 mph on the Gable Series. We publish those individually rather than averaging them, which is exactly the form a plans examiner wants to see.

Enforcement is usually complaint-driven, so plenty of unpermitted greenhouses stand for years untroubled. The risk is not that an inspector patrols your yard; it is what happens when something else brings attention.

The realistic consequences, in rough order of likelihood: a neighbour complaint leading to a stop-work or retroactive permit process with fees; a problem at resale when the structure appears on a survey or an appraisal with no permit record; an insurance claim complicated by an unpermitted structure; and, at the far end, an order to remove it. None of these is common. All of them are worse than the phone call.

Many states exempt genuine agricultural structures from parts of the building code, and greenhouses used in commercial production are often included. The definitions are specific - typically tied to the parcel's agricultural classification, its acreage, or documented farm income - and a hobby greenhouse on a residential lot almost never qualifies, whatever is being grown in it.

If you think you may qualify, ask the building department directly and ask what evidence they want. Assuming an exemption you do not have is worse than not having one.