Flooring for Architects

Section 303 of the 2010 ADA Standards sets three thresholds. A change in level of ¼ inch or less may be vertical. A change between ¼ inch and ½ inch must be beveled at a slope no steeper than 1:2. Anything above ½ inch must be ramped and comply with Section 405 or 406. In practice this is what decides whether two adjacent materials can meet flush, need a reducer, or need their build-ups reconciled — which is a drawing-stage decision, not a field one.

Whichever one matches the attachment method, and the specification should state both. NWFA calls for 3/16 inch in 6 feet or ¼ inch in 10 feet where mechanical fasteners of 1½ inches or longer are used, and 1/8 inch in 6 feet or 3/16 inch in 10 feet for glue-down, floating, or shorter fasteners. It is also worth writing in the distinction NWFA draws explicitly: the floor does not need to be level, it needs to be flat.

ASTM F2170 for in-situ relative humidity, which is the recognised method and is valid for lightweight concrete, together with ASTM F710 for surface cleanliness and contaminants. Avoid relying on ASTM F1869 alone: ASTM has specifically disallowed it for lightweight concrete. Electronic surface meters under ASTM F2659 are appropriate for quickly locating where to test, but the guidelines are explicit that they are not to be used for a go/no-go determination.

Yes, and the constraints are specific enough to design around. The finished wood surface must never exceed 80°F unless the flooring manufacturer specifies otherwise; ASHRAE puts the comfortable range for a heated floor surface at 70–80°F; and NWFA states that setback or programmable thermostats varying a room by more than 5°F per day should not be used over a wood floor. Those limits affect the heat-loss calculation and the floor build-up, so they are worth resolving with the mechanical engineer before the assembly is fixed.