Clear Height in a Warehouse: What It Means

An article in STRUCTURE magazine defines clear height as the height from the finished floor to the bottom of the lowest roof framing member, and describes it as the maximum height racking can extend. Others take a more practical view: one warehouse operator's glossary measures to the lowest thing in the way, including a beam, duct, light fixture or sprinkler head.

That difference is the first thing to pin down when you read a listing. A figure measured to the roof steel may not account for what hangs below it, such as ductwork, unit heaters, lights and sprinkler lines. Ask how the number was measured. Then measure it yourself.

A single height on a brochure describes a building. What you need is the lowest point above each rack run you plan to install.

Height often varies within a building because of roof slope, beams and systems. Bring a laser measure and your rack layout, even a rough one.

1. Mark where your rack rows will go on a floor plan before you arrive.
2. Measure from the floor to the lowest obstruction at several points along each planned row, not just in the center of the room.
3. Record what the obstruction is: joist, beam, duct, light, heater or sprinkler.
4. Note what can move. Lights and some ducts may be relocated, with the landlord's approval and at a cost. Roof structure generally cannot, and a lender's explainer describes raising clear height as practically the same as rebuilding.
5. Check the areas under any mezzanine or office, and around the docks, where equipment may hang lower.
6. Compare your lowest number with the rack height your design requires, including the clearance described below.

Clear height is not the same as stacking height, since material cannot go all the way up to the sprinklers. OSHA's sprinkler rule states that the minimum vertical clearance between sprinklers and material below is 18 inches. An OSHA interpretation letter explains that this works as a horizontal plane across the storage area, so all material should be stored below it, and not just the items directly under a sprinkler head. The same letter notes that specific sprinkler designs for high-challenge fires, such as high rack storage, may need more than 18 inches.

The practical point: 18 inches is the general minimum in that rule and not an answer for your building. High-piled storage adds its own review in many places. The City of Madison's high-piled storage permit, for example, asks for the maximum permitted storage height for each area and the clearance between the top of storage and the ceiling or sprinkler deflector. Your fire protection engineer, insurer and local fire official decide what applies, and it may depend on what you store and how it is packaged.

Rack levels come from clear height and pallet height. The STRUCTURE article notes common US pallet heights of 56, 64 and 72 inches, and allows the pallet height plus 8 inches of clearance per level. The following example uses those inputs, is hypothetical, for illustration, and leaves out details such as beam depth that a rack designer would include.

• Building A has 28 feet of clear height. Subtracting 18 inches leaves 26.5 feet, or 318 inches, for storage.
• With 64-inch pallets, each level takes 72 inches. 318 divided by 72 is about 4.4, so 4 levels fit.
• With 72-inch pallets, each level takes 80 inches. 318 divided by 80 is about 3.98, so 3 full levels fit, just short of a fourth.
• Building B has 24 feet of clear height, leaving 22.5 feet, or 270 inches. With 64-inch pallets, 270 divided by 72 is 3.75, so 3 levels fit.

In this example, 4 feet less height costs one level out of 4, or a quarter of the pallet positions on the same floor. To hold the same inventory, Building B would need more floor area. That is why comparing rent per square foot alone can mislead. A lower rate on a shorter building may buy less storage per dollar.

More height is not automatically better. It helps only if you can use it: your forklifts must reach it, your floor must carry it, and your fire protection must suit it. A lender's explainer puts today's newly built Class A distribution centers at 32 to 36 feet and doubts that many smaller tenants need 40 feet. Do not pay for height your product and equipment will not use.

• ✓Can our forklifts safely reach the top beam with our loads, and do they fit the aisle width we plan?
• ✓Can the floor carry the rack post loads at the proposed height? Ask a structural engineer.
• ✓Does the sprinkler system suit the commodity and the proposed storage height? Ask your fire protection engineer and insurer.
• ✓Does the height trigger a high-piled storage permit, and what would the fire official require?
• ✓Are the lights placed to work with the aisles, and will the racks block them?
• ✓Does the lease allow us to install the racking and anchor it to the floor?
• ✓Do we need a permit for the racks in this municipality?

If your plan depends on height, a marketing sheet is no protection. LeasePilot, a lease software company whose CEO is a former commercial real estate attorney, gives the example of a lease saying "approximately 30 feet" while columns and HVAC reduce the usable height, and suggests specific clear height measurements at defined points, with tolerances and remedies. If you agree to relocate lights or ducts, include who does the work, who pays, and when.

Tenant Advisory Group represents tenants and buyers. On a tour, we focus on whether a building works for your layout, and then coordinate your rack designer, engineer and attorney so the height you need is the height the lease describes.