19 Engineered Shop Draw- ings for Foundations For larger greenhouses, engineered shop draw- ings that are available to customers can include the foundation and ensuring the foundation and greenhouse meets the specifications of the local building codes. The rules for the permit process depends on your municipality but generally speaking, a structure less than 100 or 120 square feet that is not considered permanent does not require a permit. Depending on the building department code, sometimes non-engineered foundation sketches suffice for a permit, so re- member to ask about that when the time comes. In terms of the footing, minimum thickness is really important when building a greenhouse. For a greenhouse with a regular support truss, a 6 inch concrete footing is fine. A more sub- stantial greenhouse structure (16 foot wide Cape Cod or Cottage models or 18 feet and over for the Traditional and Pacific mod- els), should have a footing that is at least 8 inches wide as the interior supports require a wider surface for attachment. Dimensions and rebar are for reference only. Actual dimensions to be determined by local building code.