About

A greenhouse planned to your size

Most greenhouse plans come in one size, and kits leave you guessing about vents, snow and what to buy. The Greenhouse Planner starts from the size you want: it frames the walls and roof, lays out every polycarbonate sheet, sizes the vents, and shows each check in green, amber or red.

How it works

1
You set the size
Width, length and wall height, a gable or lean-to roof, and the snow load and wind where you build.
2
You pick the parts
6, 8 or 10 mm twin-wall or corrugated polycarbonate, a timber, block or knee-wall base, the door, vents and benches.
3
It checks the design
Roof and side vent area, roof support spacing for your snow load and the bench layout, each shown in green, amber or red.
4
It counts the materials
Lumber packed onto standard boards, sheets laid out face by face, profiles, fasteners and vent openers, with prices.

The method

The checks in the planner come from US university extension publications (UConn, Alabama, Clemson, Oklahoma State, UGA, Wyoming and the NRAES-33 Greenhouse Engineering handbook), from the polycarbonate maker's published guides and load tables, and from the International Residential Code where it applies. Those sources did not review or endorse this site; we read them and apply what they publish.

Each check has a default and a minimum. Green meets our default. Amber sits between the smallest figure a source accepts and our default. Red is below every source we read, or outside the maker's tables, and the designer tells you what to change.

Where the sources give a range or say nothing, we chose a value and call it our default, and the check says so. The roof support spacing for each glazing comes from the maker's tables for the snow load you pick; the vent areas come from the extension guides.

What it is not

The Greenhouse Planner is a planning aid, not an engineered design. Snow or wind loads beyond the maker's tables, exposed sites, a lean-to fixed to a ledger on a house wall, and permits go to your local building department or a licensed engineer. Check the plan against your local rules before you build.

How the site is paid for

The designer, its summary PDF and the free designs cost nothing and need no account. What pays for them is the builder's plan: a PDF for the exact greenhouse you design, with framing per wall, the rafter cut, the sheet layout and cuts face by face, the cut list, a priced shopping list and the build steps, for $29 once. If our plan has an error, we fix it or refund you. The site carries no advertising, and no item is in a plan because someone pays us for it.

Who runs it

The Greenhouse Planner is an independent project operated by Westernmost LLC, 30 N Gould St Ste R, Sheridan, WY 82801, USA. If you find a mistake in a check or a number, please tell us: a fix to the engine fixes every greenhouse at once.

Sources

Last read on October 13, 2026.

Shown for comparison only, never as proof:

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