Interiors and Circulation

BIM for Architecture, Engineering, and Construction Curriculum


Creating Simple Stairs and Ramps

How does changing the riser height affect the number of risers required and as the number of risers changes, what happens to the overall length of the stair?

Increasing the riser height decreases the total number of risers needed since each step provides a larger gain in elevation. If we assume a constant tread depth, the total length of the stair decreases. This method essentially increases the slope of the stair.

If you need to shorten (or lengthen) the total run of a stair, which properties can you change to accomplish this?

To shorten a stair, increase the riser height and decrease the tread depth. To lengthen a stair, decrease the riser height and increase the tread depth.

What are the required properties of a wheelchair-accessible ramp as specified by the Americans with Disabilities Act?

The ADA defines regulations for ramps in section 4.7 and 4.8 of their Standards for Accessible Design. In general, the maximum slope for a ramp in new construction is 1:12 with a clear width of 36 inches.

Modeling Custom Stair Shapes

What is the typical relationship between tread length and riser height in a single family residence? For an exterior stair? Explain the difference.

Interior stairs in a typical residence typically have a riser height of about 7.25-inches tall with a tread length of about 11 inches. For comfortable and safe use, the riser height and tread length should maintain the relationship: 2*Riser Height + 1*Tread Length = 25". Building codes in the United States limit the riser height to no more than 8 inches.

Exterior stairs are typically designed with a shorter riser height and a longer tread length to create a shallower slope. This reduction is appropriate for exterior conditions which are often slippery or wet.

What is the maximum riser height and minimum stair width allowed by today\u2019s building codes?

Except for spiral stairs and winders, risers may not exceed 8 inches in height measured vertically from tread to tread. Treads shall be at least 9-inches wide measured horizontally from nosing to nosing.

Modeling Floor and Ceiling Openings and Railings

How much clearance is required between the treads of a stair and the floor above (so users do not bump their heads)?

The required clearance between the treads of a stair and the floor above varies slightly based on the building code used. Typical values are 76 to 80 inches.

What can you do to a floor opening to increase the clearance provided?

You can enlarge a floor opening to increase the clearance between the floor and the treads of the stair below.

What are the key differences between a handrail and a guardrail?

Handrails are generally defined as being used for guidance and support while the purpose of guardrails is to resist accidental falls. Handrail heights are commonly between 34" and 38", while guardrails are 42" in height. There is often a requirement that a guardrail have a handrail included as well.

Handrails are required on stairs, and guardrails are required on balconies and around floor openings.

Modeling Elevators and Shafts

What are the advantages and disadvantages of creating floor openings with shaft opening elements versus editing the floor boundary?

By using the shaft opening tool, Revit automatically creates an opening extending through multiple surfaces. This is convenient when multiple boundaries must be edited because it eliminates the need to do each one separately.

The shaft tool creates problems when different shapes need to be created or when a different floor must extend into the shaft region. If part of a new floor or roof passes through a shaft region, it will not be displayed.

Why are stairs and elevators typically located very close to each other?

Both stairs and elevators are essential circulation elements and they must be easily located. If the elevators are nonoperational and in cases of emergency, the stairs should be easy to access from the elevator location.

It is also common to place elevators next to stairways since they both require continuous vertical shafts.