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Design free

Build it, then keep it growing.

Start with the step-by-step guide to building a greenhouse, then size the heat and the air for your climate. Every number comes from the greenhouse designer and the extension guides behind it, so the guides and your plan agree.

  • 2 guides
  • 13 questions answered
  • 13 sources from 12 publishers
  • Updated Oct 14, 2026

Six numbers worth knowing before you build

For the 8x12 gable greenhouse in 8 mm twin-wall, as the designer draws it. Our default: the number the greenhouse designer builds to. Source rule: an extension guide, the model code or the sheet maker's table. Depends: your town or your site changes it. Your building department has the last word.

Then the parts that decide the season.

Price it before you order, then plan the winter heat and the summer air. Every drawing is the 8x12 gable greenhouse from the free plans, as the designer draws it.

  1. Step 1

    Size it and price it

    Pick the size and price every line of the materials list before anything is ordered.

  2. Step 2

    Heat it and air it

    Keep it above the coldest night you plan for, and let the heat out on a sunny day.

The questions people ask first.

Each links straight to its answer, with the sources beside it. The guides answer 13 in all.

  1. Do I need a permit to build a greenhouse on my property?How to build
  2. How do the Amish heat their greenhouses?Winter heat

Start from a design

Work it out for your own greenhouse.

How the guides are checked.

Extension guides and makers first

University extension guides, the model code and the polycarbonate and fan makers' own tables come first. A seller's guide is marked secondary and used only where no extension source or maker gives a number.

Numbers from the designer

Vent areas, sheet counts, heat loss and prices come from the greenhouse designer's plan for a real size, the same engine that draws the free plans.

Dated store prices

Every price names its store and the day we read it, and a line with no price stays empty. How the checks work

Design it, then build it

Grow longer, in a greenhouse that fits your yard.

Change the size, the roof, the glazing, the vents and the benches. The roof supports, the vents and the materials list follow every change. Free, no account.

Design my greenhouse, free
Designing
Free
Builder's plan
$29 once
Account
Not needed
Inside a wooden greenhouse: slatted benches of seedlings on both sides of a gravel aisleIllustration