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ARCH 2614/5614 Lecture notes

Jonathan Ochshorn

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Movement, joints, and flashing

Building joints and movement


tolerances example with cladding vs frame
This detail section shows a potential conflict between a cladding panel and a structural concrete slab.

Tolerances: Difference between rough and finished construction. "Rough" construction, in general, refers to the structural frame, which may deviate from it's "ideal" position. "Finished" construction, in general, must be able to be positioned in its exact location, as it is manufactured or constructed with a higher degree of precision. To accommodate the discrepancies between rough and finished construction, details must account for the tolerances of rough construction. The following sketch shows the difference in the dimensions of a clip angle designed for (1) a perfect world; and (2) reality. We assume that the concrete frame has a horizontal tolerance of plus or minus one inch.

abstract tolerance example with concrete frame and cladding
Tolerance example assumptions: (1) concrete tolerance is + 1" laterally; (2) bolt spacing is 2" from girder edge and 3/4" from clip angle edge.

misalignment of steel column and concrete pier
Apparent misalignment of concrete foundation pier and steel column, Collegetown Crossing, Ithaca, NY (photo by J. Ochshorn, Oct., 2015)

Constructability: In addition to installation clearances to account for constructability and tolerances, it is useful to have connecting strategies or details with 3-way alignment opportunities:
3-way adjustment in clip angle
In the sketch above, the clip angle can be adjusted in three orthogonal directions using shims for the vertical direction, and slotted holes in the angle for the two "lateral" or horizontal directions.

Sources for tolerance information

  1. American Concrete Institute (ACI) 117-06 Specifications for Tolerances for Concrete Construction and Materials

  2. Precast/Prestressed Concrete Institute (PCI) Tolerance Manual for Precast and Prestressed Concrete Construction

  3. American Institute of Steel Construction (AISC) 303-05 Code of Standard Practice for Steel Buildings and Bridges

  4. Architectural Woodwork Institute (AWI) Architectural Woodwork Quality Standards

  5. David Ballast The Handbook of Construction Tolerances (latest edition)

Trim strategies:

Sources of movement:

Note increased tendency for movement issues to surface in modern construction because of:

building movement joints
Movement joints in buildings (adapted from Architectural Graphic Standards

building separation joints
Building separation joints ("expansion" joints): from (a) Architectural Graphic Standards; (b) using pre-cured silicone sealant with metal cover plates; and (c) within a floor slab.

building separation joints - Milstein Hall, Cornell
Building separation joint in Milstein Hall, Cornell University (photo by J. Ochshorn)

Strategies for dealing with movement:

Structural movement relative to cladding:
structural movement

Examples of accommodation:
accommodation of movement

Types of movement joints:

Flashing: Examples given of flashing (metal or "fabric," i.e., rubberized membranes), often used where two materials intersect and water needs to be excluded from the joint. The classic instance is at the intersection of roof and parapet, where flashing traditionally is constructed in two parts that interlock to allow movement.

flashing at parapet
Flashing at parapet from Architectural Graphic Standards

flashing at parapet
Flashing strategies at parapet: bad, better, and best.

flashing at dissimilar material intersections
Flashing at dissimilar material intersections.

Flashing must accommodate movement:

flashing at parapet to accommodate movement
Flashing and coping at parapet to accomodate differential expansion and contraction.

strategy to accommodate movement
Strategy to accomodate movement.

flashing at parapet to accommodate movement
Flashing at parapet to accomodate movement.

control joints
Control joints for materials that shrink (portland cement based).

control joints
Control joints to support architectural expression (photos by J. Ochshorn).