11 supports are level. Sorry to sound like a broken record, but you will be thrilled when you install your greenhouse that it goes up according to plan! Suggested Guidelines for Wood Foundation * 4 x 4 timbers Up to 100 square feet or any greenhouse no wider than 10 feet. * 6 x 6 timbers Necessary with any greenhouse with a truss (a truss typically requires a 5 inch sill to attach); any greenhouse 12" x 16" and over. For additional strength, we recommend that the 4 x 4’s are connected with galvanized or deck screws or galvanized connectors with alternating stackable joints. For larger greenhouses, two rows of alternating stackable joints will be required. If you live in a high wind area, you should consider tying down your wood foundation. One option would be to incorporate a concrete pier block that has a galvanized bracket to anchor the wood. Others will simply drive a steel rebar into the ground and pin it to the wood. construction tip For larger green- houses (20 feet or longer), place a pier block or sona tube at the 6 to 8 foot mark and/or at truss location mark on each of the sidewalls for the best support. Generally speaking, the more the merrier. construction tip