“We very very very rarely have any sort of dancers onstage so a dance surface isn't a huge concern.” — a comment heard at many theatre planning meetings.

Stage floors are a common point of controversy in many facilities. The use of the floor can vary greatly, and so the performance characteristics must suit a wide range of needs. There are several key performance parameters that drive most floor designs:

• The Slipperiness / Grip of the floor surface. This affects the safety of both dancers and other performers. It is highly dependent upon the paint or top skin (aka ‘Marley’) of the floor and can change with use and abuse. The application of cleaning agents, rosin, floor wax, blood, sweat, tears, aerosol glitter, hair gel, skin creams / lotions, as well as spilled fluids like fruit juices, sodas, water, and sports hydration drinks can all affect the traction, both real and perceived, by the performers. The traction also varies with humidity, temperature, and the type of shoe or bare foot. There is a way to objectively measure this and it can be found in ANSI Standard E1.34 - 2009 - Entertainment Technology - Measuring and Specifying the Slipperiness of Floors Used in Live Performance Venues.
• The Hardness of the top surface. A cushion-backed vinyl floor may be appropriate for some bare-foot dance routines, where a rock-hard surface is best for tap dancing and rolling pianos around. Various grades of wood materials are better than others for resisting indentations by the tips of cello posts, road case casters, piano legs, chairs, and tables. Pine is a soft wood and should not be used for stage floors as it can be damaged very easily and then present splinters that can stab performers feet, hands, and other parts of their bodies as they move (roll, slide, writhe, twist, bounce) across the floor.
• The ‘Give’ and ‘Springiness’ of the floor. This is actually two different dynamic properties, and it must be fairly uniform both locally and regionally.
  • The ‘Give’ of the floor is the ability to depress and absorb energy from the performer as they impact the floor. The extreme ends of this range are ‘No Give’ – like a solid concrete slab (OUCH!); and a very soft gel or mud where you sink-in until all the energy of your fall is absorbed. Obviously, neither of these conditions are desirable, so the selection of the flooring support materials must be made to provide a reasonable cushioning of the landing.
  • The ‘Springiness’ of the floor is the ability to actually return some of the energy back to the performer. Too little and they floor requires a lot of work on the part of the performer to continually re-launch themselves to their next movement; and too much energy return and the floor gets bouncy like a trampoline. Again, the suspension system under the floor must meet a good compromise.

The Local and Regional aspects have to do with how much the floor flexes within a given area. If a floor gives too much locally, then it will visibly deform under the point-loads imposed by a heavy object like a piano leg or an orchestra shell tower. Therefore, it is important that the floor act monolithic and spread the load to all the supports in the general area of the load. This can keep a tall set piece or an orchestra shell tower from toppling-over due to an uneven support. This is one area where many portable dance floors do not perform well – they give too much at the panel-to-panel joints creating local surface irregularities that can be dangerous.

Most of this aspect of a floor can be quantified by ANSI Standard E1.26 - 2006 - Entertainment Technology - Recommended Testing Methods and Values for Shock Absorption of Floors Used in Live Performance Venues.

• The over-all load bearing capacity of the floor. This determines how heavy of an object can be placed safely on the stage. This can become a significant issue if the stage is constructed without a walk-on service gridiron. In buildings where the grid has been omitted, the only way to access the stage rigging for inspection and service is with a very large man-lift or boom-arm service lift. These are very heavy and can damage or even collapse a floor if it is not properly constructed.
• The Acoustic Response of the floor. This affects musicians, dancers, and most other performers. A symphony hall may desire a floor that resonates musically with the instruments, where most theatrical and dance performers prefer a floor that is acoustically damped so that it doesn’t sound like a herd of buffalos when they cross the stage.

You may have no dancers on your particular stage, but there is still a lot of other 'creative movement' that takes place on a stage - fight scenes, acrobatics, tumbling, etc., so constructing a stage that 'gives' properly is still important to reduce the likelihood of joint injuries. A floor the is too hard and does not properly absorb the shock energy of performer impacts can significantly affect both the joints and the teeth of dancers (dancers clench their teeth while smiling – so each landing on the floor tends to rattle their teeth a bit).

Typical floor construction is built-up with several layers:

• Skin / Dance Surface: Varies by brand, and is usually a vinyl sheet that has a micro-textured surface to provide specific traction / friction characteristics and/or color.
• TOP - Sacrificial layer that can be replaced every few years as it gets torn-up. Sometimes it is called 'Masonite' which is a misnomer as Masonite Corporation no longer makes tempered pressboard products. They used to make a product called Duron WR that was great for stage floors, but alas, it is no more. Other common products are luan, plywood, Simpson Plyron (which is a plywood layer that is pressure laminated to a tempered pressboard sheet), or generic 'masonite', aka "tempered pressboard". The key to a successful material selection is using a product that has high moisture resistance (garden variety 'masonite' from the local hardware store usually does not have this feature, so when it gets wet it swells, puffs-up, then flakes apart). The high density water resistant material is very hard, too, so it doesn't dent under heavy wheeled traffic. Good (green) products are manufactured formaldehyde free, so they are safer to cut (the saw dust doesn't poison you). Sierra Pine makes a good product called Medite. The Medite II version is slightly denser, and the Medite FR version is pretreated with Fire Retardant. This layer is typically about 1/4" thick. Being very hard and dense means that you have to pre-drill screw holes in it. The face of the sacrificial stage should be painted with an intumescent (fire-proof) paint, which is available in the favorite theatre color of black. There is another product made by RenewResources called PolyBoard that is plastic based. One concern with this product is the amount of smoke and toxic gasses that it might produce if it were to catch fire, and the flamespread rate for it seems to be much higher than Medite. However, it has been used on some high profile theatre projects recently.
• Structural Layers: The next two layers are typically the decking that provides the structural support for the monolithic strength. They are typically fire resistant 3/4" plywood. The key to a good monolithic stage (one that doesn't sag locally under point loads) is staggering the joints by 12" on both axis layer-to-layer. It is common to lay-down the sheets in a pattern that prevents adjacent layers from having common joints (except at the perimeter edges where it can't be avoided). Each layer is screwed-down to the layer before it at about 12-18" o.c. Plan your screw pattern dimensions carefully and you won't find yourself trying to screw into the top of a screw head two layers down.
  • 1st Layer: Begin at the downstage center of the apron and lay a 2'x8' lengthwise (long axis across the stage), offset 24" to the left. Build-out that row left and right, trim ends as needed. The next row upstage is 4'x8' laid-down with the joint at the centerlines of the previous row of panels, then built-out to the left and right, the successive rows alternate that pattern using 4'x 8' panels, with the last row upstage trimmed to whatever space remains.
  • 2nd Layer: Begin at the downstage center of the apron and lay a 3'x8' lengthwise (long axis across the stage), offset 12" to the left. Build-out that row left and right, trim ends as needed. The next row upstage is 4'x8' laid-down with the joint at the centerline of the previous panels, then built-out to the left and right, the successive rows alternate that pattern using 4'x 8' panels, with the last row upstage trimmed to whatever space remains.
  • 3rd Layer (sacrificial layer described above): Beginning at the downstage center of the apron and lay a 4'x8' lengthwise (long axis across the stage), no offset. Build-out that row left and right, trim ends as needed. The next row upstage is 4'x8' laid-down with the joint at the centerline of the previous panels, then built-out to the left and right, the successive rows alternate that pattern using 4'x 8' panels, with the last row upstage trimmed to whatever space remains.
• Stringer and Cushion Layer: This is where the 'sprung' part of the floor happens. It is done two ways:
  • Rubber Blocks / Pads (generic reference, actual material varies by manufacturer) are spaced about every 12-18" o.c. on both axis and 2x4 stringers are laid flat on top of them. The softness and the thickness of the 'rubber blocks’ determines how much 'give' and ‘springiness’ the floor has. This is the more common modern floor construction. Hardwood basketball floors are also built like this. It is VERY IMPORTANT that the screws from layers above this do not penetrate through and come in contact with the concrete floor below the pads.
  • A Basket-Weave suspension is a multi-layer crisscrossed pattern of ~1x4's laid flat with alternating orthogonal layers positioned at the midpoints of the span between the previous layers. 4-6 layers are common. The exact spacing, thickness, and type of wood determines how much ‘give’ and ‘springiness’ the floor has. This is the 'old-school' way of doing it, and is much more difficult to predict performance. Another down-side to this is that it is very labor-intensive to construct and the wood basket-weave will begin to sag over time and loose its resiliency.
• Infill: Between the stringer / basket weave components the floor void is usually filled with mold-resistant acoustical damping to keep the 'hollowness' or 'boomy' sound from being a problem.
• Vapor Barrier (bottom-most layer): A plastic sheet usually laid on top of the concrete floor to keep moisture from collecting under the floor. This can also be achieved by using a concrete sealant.

In short, this is a general guide to the floor construction. A specific floor should be designed by a Theatre Consultant or Architect that has some good background experience in this area. There are many very important details that make this system work, way too many to mention herein. This is why so many cafetoriums and high school theatres end-up with tile, concrete, carpet, or hardwood “basketball” floors - they know not what they are doing, nor do they understand why they should do it correctly. You wouldn't want your sound system designed by Joe's Guitar Emporium, so don't get your floor from Bob's Discount Wood Flooring.