How To Read Expansion Joint Cover Specifications: The 3 Key Numbers

An expansion joint is a structural gap for absorbing movement. Left open, it's dangerous and unsightly. A joint cover bridges it safely, moving with the building while optionally handling loads, finishes, or water.

When you open a MEISHUO expansion joint cover product page or data sheet, the first three numbers you see are always the same: joint width, exposed surface, and movement capacity — all in millimeters. These three dimensions define how the cover fits, how it looks, and how it performs. Yet across the industry, different manufacturers and standards use different terms for the same concepts, and movement is sometimes expressed as a percentage rather than an absolute value. This article cuts through the confusion and strips things back to the essentials — what each of the three core parameters actually means for your selection, illustrated with MEISHUO's classic MSDG model.

1. Joint Width (W)

Joint width is the structural gap between two building sections, measured at the median expected temperature. It is the opening the cover must span. At installation, the actual gap may differ. If the building is unusually hot or cold at the time of installation, the joint opening will have temporarily expanded or contracted. This normally does not prevent cover installation, but it is worth measuring and communicating to your supplier.

W determines the cover size. Generally, a cover sized for a 100 mm joint won't fit a 120 mm gap, but it may suit an 80 mm one — just ask our engineering team to confirm. 

For the MSDG model, the following sections take a 50 mm joint width as an example.

2. Exposed Surface (ES)

The exposed surface, also called the visual surface, is the visible portion of the expansion joint cover once installed. It is the metal, rubber, or infill surface that pedestrians see and walk across.

In reality, the cover almost always extends beyond the gap on both sides to anchor securely, so ES is typically larger than W.

For the MSDG model with a 50 mm joint width, the exposed surface (ES) is 150 mm.

A practical reality is making an expansion joint disappear entirely is rarely achievable, and we generally don't recommend trying to hide it. In many finished spaces, exposed joint covers don't look out of place or unsightly at all.

Our design goal is usually a clean, well-finished surface that integrates naturally into the floor or wall, becoming a considered part of the overall design rather than something that needs to be disguised.

That said, for clients who do prioritize a more "invisible" look, we typically suggest either choosing a narrower joint cover profile to reduce visual impact and keep things unobtrusive, or simply laying carpet over the area.

3. Movement Capacity

Movement capacity, also known as movement rating, describes how much the joint cover can expand and contract as the building moves. It is the single most performance-critical parameter.

Movement capacity is sometimes expressed as a percentage of the nominal joint width — for example, ±50% — and other times as an absolute value in millimeters. Both represent the same physical capability. At MEISHUO, we use millimeters because it gives an immediate, calculation-free number on site. A movement rating of ±50 mm means the cover handles 50 mm of compression and 50 mm of expansion.

For certain models, we break the movement figure into two separate values: + (extension) and - (compression) , with the total representing the full movement range. For example, a model specified as +30 mm / -20 mm tells you it can extend by 30 mm and compress by 20 mm, giving a total movement capacity of 50 mm. This split format is particularly useful when the joint is expected to behave asymmetrically.

 Typical movement ranges depend on what the joint is designed for:

Thermal movement (temperature changes): typically ±10% to ±25% of nominal joint width.

Seismic movement (earthquake loads): typically ±50% to ±100%.

Wind-induced movement (high winds causing sway): normally rated similarly to seismic, though the direction is typically horizontal or shear.

On a MEISHUO specification, movement capacity is the third number — so the complete basic spec for this MSDG reads W = 50 mm, ES = 150 mm, Movement = +100 mm / -25 mm, total 125 mm, indicating 100 mm of extension and 25 mm of compression.

For floor applications specifically, there is a fourth critical parameter: load capacity.

For floor applications, standard MEISHUO expansion joint covers are designed to handle normal pedestrian traffic, trolleys, and wheelchairs without issue. For heavier demands — warehouses with forklift crossings, parking garages with constant vehicle loading, or industrial facilities — heavy-duty models are available and should be specified from the outset.

Every expansion joint cover selection starts with these three key numbers. From there, secondary requirements — load capacity, surface finish, water resistance, fire rating — are layered on as the project demands.

Have a project and need help selecting the right expansion joint cover? Contact our engineering team — we'll work with whatever project details you have and provide a tailored recommendation.