Term Description
Shrinkage

A decrease in one or more dimensions of an object or material.
Shrinkage crack

In waterproofing, a separation in a material, such as a concrete substrate, caused by the inability of the material to resist a reduction in size that occurs during its hardening or curing process or both.
SI

An abbreviation for the International System of Units (Le Systeme International d'Unites).
Side lap

The continuous longitudinal overlap of neighboring like materials.
Side-lap fastener

A fastener used to connect adjacent panels together at the side lap.
Siding

The finish covering of an exterior wall of a frame building; the siding may be a cladding material such as wood, aluminum or vinyl (but not masonry).
Sieve

An apparatus with square apertures for separating sizes of material.
Silicone coating

A liquid-applied elastomeric coating; the principal polymer in the dispersion contains more than 95 percent silicone resin.
Single tees

Structural precast prestressed concrete members of a T-shaped cross-section used as precast roof and floor deck systems.
Single-component (coating or foam)

Polyurethane or silicone material that does not require mixing of "A-component" and "B-component."
Single-ply membranes

Roof and waterproofing membranes that are field applied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers.
Single-ply roofing

A roof system in which the principal roof covering is a single-layer flexible thermoset or thermoplastic membrane.
SJI

Steel Joist Institute.
Skin

The dense film portion on the surface of a liquid coating or mastic.
Skinning

Function of the time necessary to form a dense film on the surface of a liquid coating or mastic to the extent that the material is unaffected by a water spray.
Skylight

An opening in a roof that is covered with a transparent or translucent material; used to admit diffuse light to the space below; commonly mounted on a framed curb.
Slab

A layer of reinforced concrete, generally flat and horizontal (or minimally sloped), usually of uniform thickness, placed on prepared earth or supported by beams, columns or walls.
Slag

(1) A hard aggregate that is left as a residue from blast furnaces; may be used as a surfacing material on certain (typically bituminous) roof membrane systems. See "blast furnace slag"; (2) the fused agglomerate which separates in metal smelting and floats on the surface of the molten metal.

Slate

A hard, brittle metamorphic rock consisting mainly of clay minerals used extensively as dimensional stone for steep roofing and in granular form as surfacing on some other roofing materials.

Slip sheet

Sheet material, such as reinforced kraft paper, rosin-size paper, polyester scrim or polyethylene sheeting, placed between two components of a roof assembly (such as between membrane and insulation or deck) to ensure no adhesion occurs between them and to prevent possible damage from chemical incompatibility, wearing or abrasion of the membrane; also called a "separator layer" and "separator sheet."
Slippage

Relative lateral movement of adjacent components of a roof membrane. It occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather.
Slit sample

In spray polyurethane foam roofing, a small cut about 1 inch by 1/2 inch by 1/2 inch in a half-moon shape used to measure coating film thickness.
Slope

The angle of incline, usually expressed as a ratio of rise to run, or as an angle. See "roof slope."
SMACNA

Sheet Metal and Air Conditioning Contractors’ National Association.
Smooth surface texture

In spray polyurethane foam roofing, the condition of the foam in which the surface shows spray undulation and is ideal for receiving a protective coating.

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