Adding a Mezzanine Game Loft to a Steel Building

A customer in Ohio bought a 40 by 60 steel building from us three years ago as a workshop and vehicle store. Last year he asked about adding a mezzanine at one end, a raised floor about ten feet up, to use as a game loft. He wanted a pool table, a card table, a couple of couches and a screen for football, all up above the workshop floor where his trucks and tools lived.

A mezzanine is one of the best ways to add usable space to a steel building without making the footprint bigger. It is also one of the easiest additions to get wrong, because it changes how loads move through the whole structure.

Why a mezzanine works well in steel buildings

Clear span steel buildings often have more height than the ground floor needs. A 14 or 16 foot eave height leaves a lot of empty air above a workshop. A mezzanine turns some of that volume into floor space.

• No new foundation for the building shell, although the mezzanine columns need their own footings.
• Keeps the ground floor clear for vehicles, machinery or storage.
• Separates noisy or dirty work below from a cleaner space above.
• Costs much less per square foot than extending the building.

The customer's loft covered 20 by 40 feet, adding 800 square feet of floor space for a fraction of what an extension would have cost.

Loads are the whole question

A game loft carries heavy loads, and they are not evenly spread. A slate pool table can weigh 800 pounds or more, concentrated on four legs. Add eight people for a big match night, a couple of couches, a fridge and a large screen, and the floor needs to be designed for far more than a storage mezzanine.

His loft is busy most weekends. A few friends play pool and cards, the football runs on the screen, and at least one of them usually has a phone out checking his pool picks on ankertoto between frames. That means people crowded around one table for hours, often exactly where the pool table already sits. The engineer designed for that worst case.

These figures are general guidance only. Your local building code and a licensed engineer set the actual numbers for your project.

The advice I disagree with: hang it off the main frame

A common suggestion, especially from general contractors used to timber buildings, is to save money by attaching the mezzanine directly to the building's main frame columns rather than giving it its own columns.

In most pre engineered steel buildings, this is a mistake unless the building was designed for it from the start. The main frames are engineered for the specific loads of the original design: roof, snow, wind and the building's own weight. Adding a heavy floor to them can overstress members that were never meant to carry it. The failure may not be immediate. It may show up years later during a heavy snow load.

The safer approach is a freestanding mezzanine with its own columns and footings, designed to stand independently, or a building ordered from the start with mezzanine loads included. Our customer went freestanding. It added about 3,000 dollars to the cost and removed the risk entirely. How snow and wind loads affect a building is covered in snow load and wind zone numbers you cannot skip.

Stairs, rails and fire safety

An occupied mezzanine is a floor, and building codes treat it like one.

1. Stairs must meet code for rise, run and width. Ship ladders are usually not acceptable for occupied spaces.
2. Guardrails are needed along every open edge, typically at least 42 inches high with gaps small enough to stop a child falling through.
3. A second exit may be required depending on the area and occupancy.
4. Fire separation between a workshop with fuels and solvents and an occupied loft above is often required.

Check with your local building department early. Mezzanines often need a permit even when the original building did not.

Comfort in a steel loft

Warm air rises, and a mezzanine sits right in it. Without insulation and ventilation, a loft under a steel roof becomes very hot in summer. Good roof insulation matters more for a mezzanine than for any other part of the building. Insulation choices that matter more than the steel itself covers the options.

The customer's finished loft cost about 26,000 dollars including engineering, steel, decking, stairs, rails, insulation and electrical work. He tells me it is now the most used part of the building. More ideas for making steel buildings work beyond storage are in our Uses section.