The Tandem

Each vehicle or trailer gets its own bay, with about 3' on each side to open doors and walk past, 3' inside the door and 2' behind. A workbench area adds 8' along the back wall and shelving adds 3'. Each bay gets a roll-up door a little wider and taller than what parks there, and the legs are tall enough for the doors to roll up. Then everything rounds up to the next standard size.

Sizes are typical. If yours is longer or taller (a lifted truck, a roof rack, a long tongue), pick the next size up or tell us in your quote request.

Width is the end with the peak, where the big doors usually go. Length runs from that end to the back. Leg height is how tall the walls are, from the ground to where the roof starts; the peak is higher. A roll-up door needs legs at least 1' taller than the door, or 2' for doors 12' and up, so it has room to roll up.

Gable only closes just the triangle at the top of an open end, which keeps sun and blowing rain off the front of what's parked. A top 3' panel does the same along an open side. Enclosed walls go all the way to the ground. Doors and windows go on enclosed walls only.

A good rule is at least 2½' wider and 1' taller than what drives through. Typical picks: 9' × 8' for cars and SUVs, 10' × 8' for pickups, 10' × 10' for tractors, 12' × 12' for boats and campers, 14' × 14' for motorhomes. Walk-in doors are 36" × 80", like a house door. The "What fits" step picks these for you.

Gauge is the thickness of the steel frame tubing: a lower number is thicker. 14-gauge is standard; 12-gauge is heavier and is often used for wide or tall buildings and higher wind or snow ratings.

Certified means the building comes with drawings from the manufacturer's engineer, rated for the wind and snow loads where you live. Many counties want them for a permit. Certification is issued by the manufacturer's engineer, and your local building department gives final approval.

Insulation: steel can "sweat" when warm, damp air meets a cool roof. Double bubble foil under the panels cuts most of that. 2" fiberglass also holds heat in and quiets rain noise; pick it if you'll heat or cool the building.

What it sits on: concrete is the strongest base and keeps floors dry. Asphalt and compacted gravel work well for carports and covers. On dirt or grass the building is held down with long earth anchors, and the floor stays damp.