The building shown at right is a single-story structure with a BV-CMU cavity wall. This assignment has three parts: (1) a 3-D (axonometric or isometric) view of the detail where the cavity wall supports the roof; (2) a calculation of the width of the (horizontal) sealant joint; and (3) a calculation of heat loss through the building envelope.

Part I, 3-D view.
Draw a cut-away axonometric or isometric (suggested scale is 1-1/2" = 1'-0") showing an overhanging roof supported on a structural cavity wall. The wall consists of 4" brick veneer, 4" total air space (containing 2" rigid insulation), mastic (troweled on) air barrier, 8" CMU back-up/structural wall, 3/4" metal furring strips, and 1/2" drywall interior finish. The total thickness of the wall is therefore 17-1/4 inches. The roof consists of the following elements: 30"-deep open-web steel joists (OWSJ) spaced at 4'-0" on center resting on and welded to a 3/8" x 6" continuous steel plate anchor bolted into the top course of the CMU (which is a bond beam); 2" deep corrugated steel deck supporting tapered rigid insulation and a single-ply roofing membrane.

Three images in the text explain the construction of, and relationship between, the wall and roof. Refer to p. 340, figure 10.2(e) for an image of cavity wall reinforcement-ties and insulation. Refer to p. 354, figure 10.12, for the general configuration and detailing of wall and roof. Note that this latter image must be modified for this assignment in the following respects, as shown in the sketch to the left: you should use brick instead of textured concrete block; the building is only 1-story high; the metal soffit has been replaced by a plywood soffit with a horizontal sealant joint between it and the top course of brick veneer; and you should show insulation and air barrier within the cavity rather than on the inside face of the CMU. Note that furring of drywall is illustrated in the text on p.808, figure 23.6.

Show only the top of the building where roof intersects wall; cut-away layers of wall and roof as necessary to show the following: roof membrane, tapered insulation, corrugated roof deck, OWSJ, metal fascia/wood soffit, gravel stop, pressure-treated built-up 2x6 nailing strip at roof edge, all cavity wall components (brick, air space, insulation, air barrier, CMU, furring strips, drywall ceiling and wall). It is not necessary to label, or dimension, elements in the drawing. Drawing may be reduced, if necessary, to fit on standard sheet size (8-1/2"x11" or 11"x17"); submit drawing flat or folded, but NOT rolled.

Part II, Sealant joint calculation.
Assume that the wall has a horizontal sealant joint at the top of the 16-foot high brick veneer. Calculate the required width of the sealant joint, assuming the following: sealant movement capability of 50%; coefficient of thermal expansion of brick = 0.0000036; temperature range from -10 degrees F to 100 degrees F; installation temperature range from 40 to 65 degrees F; moisture expansion coefficient of brick = 0.0002; shrinkage coefficient of CMU = 0.0002; structural deflection or creep will be neglected; construction tolerance = 1/8 inch. Show calculations in a neat, orderly, and clear format (in other words, do not simply submit your initial worksheet). Consider what happens to sealant joint when brick expands and concrete shrinks at the same time. Round answer to nearest 1/8".

Part III, Heat loss calculation.
Calculate the total (winter) heat loss from the building in BTU/hour units, using an indoor temperature of 70 degrees F and an outdoor temperature of -10 degrees F. Assume the following:

• total window area = 1,000 sq. ft. (U-value for insulated, low-E windows is 0.3)
• total wall area (excluding windows) = 4,760 sq. ft. (R-values for the wall materials are: drywall=0.45; CMU=1.11; insulation=8.0; air space=1.0; brick=0.44; neglect air film contribution)
• total roof area = 7,200 sq. ft. (assume 3"-average thickness of roof insulation with R=12 and drywall ceiling with R=0.45).
• Neglect heat loss through the insulated slab-on-grade.

Academic Integrity:
"Course Assignments. Students are encouraged to discuss the content of a course among themselves and to help each other to master it, but no student should receive help in doing a course assignment that is meant to test what he or she can do without help from others."
--From the "Code of Academic Integrity," Policy Notebook for Cornell Community, Aug. 1998-99, p.78

Graphic Examples:
Examples of student work from ARCH 262 Assign #3, Fall 2003, show cut-away views of cavity wall construction in a different context.