Description: Potential problems with standing seam roofs due to expansion and contraction stem from three conditions:
- Racking of cleats due to cyclical expansion/contraction
- Structural strength of the formed pans
- Seam lock-up
Typically, racking of cleats and subsequent loosening of fasteners is a greater problem, and can result from inappropriate installation of fixed cleats for long runs of copper roofing utilizing a double locked standing seam system. As this system expands and contracts, fixed cleats, locked tightly into the seam, are flexed and can loosen their deck fasteners.
Some of this movement can be accommodated by the copper pans as indicated by the "oil-canning" of the pans. If aesthetically objectionable, "oil-canning" may be minimized by the use of expansion cleats, and by limiting the use of fixed cleats to pans 10 feet maximum in length. Fixed cleats should be installed at the midpoint of the respective pan in the patternindicated. The dimension "E" in the respective details denotes the total amount of expected relative movement of the components in the details.
Historical details and installation procedures have recommended the installation of continuous roof seam lengths up to 30' utilizing fixed cleats. For seam lengths exceeding 30', the recommendation has been to utilize expansion cleats. Although such recommended techniques have proven effective with satisfactory historical roof performance, contemporary building design and construction practices require a more careful approach. Insulated roof systems potentially leading to higher roof temperatures, and light weight roof decks leading to higher differential movement all require careful design.
On reviewing historical and contemporary design and installation conditions, this Handbook has adopted a conservative approach and is referencing all pans and seam lengths greater than 10' as Long Pan construction.
The second issue, structural strength of the formed shape, relates to the ability of roof pans to transfer accumulated expansion stresses to a pre-determined point of release. This ability becomes limited as the roof pan becomes longer and a 45 foot limit should be set for individual roof pans.
The third issue deals with short lengths of pans, under 10 feet, in standing seam installations, locked together so tightly as to prevent free expansion and contraction movement between pans. This "locking" together may result from multiple thicknesses of metal in the seam (seven at the transverse seam) and deformation through malleting and in particular through the use of mechanical seamers.
The end result may lead to expansion being transferred from pan to pan resulting in a long-pan installation in spite of short pan utilization.
This condition can be mitigated by requiring the following:
- Omit any cleats in the transverse seam.
- Review all transverse seam locations carefully to ensure sufficient off-set.
- Use expansion release points for very long seam runs
- Correct use and location of fixed and expansion type cleats.
Note: Expansion release points can be loose locked seams that allow expansion and contraction of adjacent pans relative to each other.
Long Pan construction details are designed to accommodate the cumulative expansion stress which develops over long spans of copper sheets. The points of stress relief are typically accommodated at eaves, transverse joints, and ridge and base conditions by ensuring that the copper sheet is provided with proper clearances and is secured by expansion fastening devices that will not hinder thermal movement.
Long Pan construction requires the use of expansion cleats and installation details substantially different than short pan construction where pans are less than 10 feet in length.
The proper alignment of pans is critical for both appearance and function as is the proper placement of expansion cleats and the design of all associated seams.
Adjacent pans should be layed out symmetrically to a common centerline, to allow for ease of installation of the fixed cleats. See Long Pan Layout on Table 188.8.131.52.
Particular building dynamics should be considered before specific copper details are established. Building expansion joints must be accommodated and properly detailed. Similarly, building orientation should be taken into consideration. A south sloping roof will incur greater heat gain differentials than a north sloping roof.
Under certain conditions, for a southerly sloping roof with clear skies and no wind, it is possible for the copper roof temperature to exceed the ambient air temperature by 75° to 85°F. Seam design should take into consideration the maximum temperature extremes. Under most conditions, the minimum (lowest) temperature will occur approximately 1 hour before sunrise under clear skies and no wind. Depending upon building construction and heat loss, the lowest roof temperature may be somewhat higher than air temperature. Prudent design suggests designing for minimum rather than roof air temperatures.
All roof penetrations should allow for expansion in the same amounts as the roof panels, voids or spaces should be filled with loose insulation or compressible joint filler.
A. Typical Long Pan Roof Section This detail indicates the proper cleat locations for a long pan copper roofing sheet. Expansion cleats are positioned according to the temperature of the panel during the installation and the anticipated temperature extremes. Substantial tolerances should be designed into the installation since a 100°F change in roof temperature in a single day is possible. Most commercially available expansion cleats permit a maximum 3/4" movement in either direction. Therefore, when set at mid-point a total expansion of 3/8" can be accommodated in either direction.
B. Transverse Seam - Low Pitch For a long span roof utilizing multiple seamed pan lengths, transverse seams are required. For roof slopes less than 6" on 12", the upper roof pan is attached to a locking strip soldered to the lower pan. The lower pan is cleated to the roof deck with the indicated clearances determined by expansion calculations. See Example Table 184.108.40.206.
Table 220.127.116.11 Example Expansion Joint Calculation
A long pan standing seam roof is being installed in 80 degree weather, in an area where the maximum temperature range is from -20° to 100° Farenheit. The roof pitch is 5" per foot. The ridge and eave details are designed for movement. The total run of the roof is 50 feet. This exceeds the maximum recommended length (30 feet) for each long pan. Locate and design the expansion joint between pans.
The expansion joint could be located in the middle of the roof run, with the length of each pan at 25 feet. For the purposes of this example, unequal length pans are used, to demonstrate how to accommodate such differences. The lower pan is 30 feet long, the upper pan is 20 feet long.
Since the ridge and eave conditions are detailed for expansion and contraction, fixed cleats are used at the mid-point of each pan, see Detail A.
Min. design temperature = -20°F
Max. design temperature = 100°F + 75°F (superheat) = 175°F
Contraction temperature difference = 80 - (-20) = 100 degrees
Expansion temperature difference = 175 - 80 = 95 degrees
Dimension A is based on expansion and contraction of the lower pan (#1) only, see Detail A, Plate 4.2.11.
Amount of contraction,
dLc = 15' x .0000098 x 100 = 0.0147' = 0.18", say 3/16"
Amount of expansion,
dLe = 15' x .0000098 x 95 = 0.00140' = 0.17", say 3/16"
Allowing 1/8" clearance with pan #1 contracted,
Min. A = 1/8"
Clearance at installation,
A = 1/8" + 3/16" = 5/16"
Clearance when pan #1 is expanded,
Max. A = 5/16" + 3/16" = 1/2"
Dimensions B, C, and D are based on the total expansion and contraction of both the lower (#1) and the upper pan (#2).
Amount of contraction,
dLc = contraction of pan #1 + contraction of pan #2
= (15' + 10') x .0000098 x 100
= 0.0245' + 0.29", say 5/16"
Amount of expansion,
dLe = expansion of pan #1 + expansion of pan #2
= (15' + 10') x .0000098 x 95
= 0.0233' = 0.28", say 5/16"
Allowing 1/8" clearance with pans contracted,
Min. D = 1/8"
Clearance at installation,
D = 1/8" + 5/16" = 7/16"
Clearance when pans are expanded,
Max. D = 7/16" + 5/16" = 3/4"
Total relative movement of pans = dLc + dLe
= 5/16" + 5/16" = 5/8"
Allowing 1/4" overlap (B) between pans #1 and #2, dimension D (pan #2 fold and locking strip leg),
C = Min. B + Max. D = 1/4" + 3/4" = 1"
C. Transverse Seam - High Pitch For slopes greater than 4" per foot, the lower pan is folded under the upper pan. The lower pan is installed, before the second pan is installed. The detail shows the completed seam.
D. Eave Detail This detail indicates a method for terminating a copper roof at the eave. The fascia trim is bent to extend onto the roof deck to become an integral flashing apron nailed to the roof. The copper pan is secured to the apron lip in order to achieve vertical restraint. Horizontal movement of the copper roof sheet is accommodated by the loose-lock fold of the pan over the fascia lip.
E. Eave with Gutter This is an alternate eave detail and is recommended in snow areas when using a gutter. The gutter is extended to the roof to form a flashing apron fastened to the roof with cleats at 12" O.C. A 20 oz. copper locking strip is soldered to the apron and engages the end of the copper roof pan. The locking strip prevents vertical wind up-lift of the roof pan, but allows horizontal expansion and contraction. Proper clearances must be maintained as outlined in the above example.
F. Gable Rake Edge Compensation for expansion and contraction at a rake edge is shown using a double lock seam detail. A continuous edge strip is fastened to the fascia board followed by the installation of an expansion cleat.. The moveable tabs of the cleat hook onto the edge of the roof pan, as shown in the detail.
The detail on the right shows the completed joint. The fascia rake edge is engaged into the edge strip and all 3 components are formed into a double lock seam. The lower end of the rake edge is formed into a loose lock around the edge strip to accommodate unrestrained movement.
G. Non-Venting Ridge For the installation of a non-vented ridge, a blocking framework is formed as indicated. The copper roofing is formed into a "bread pan" with the required expansion space as indicated.
H. Venting Ridge This detail shows the installation of a ridge cap where venting is a requirement. A sub-frame of plywood and blocking is formed to follow the slope of the roof. This frame is covered with copper which is allowed to float freely from the copper roof pan. The pan is terminated in a folded "bread-pan" with the required expansion space as indicated.
For Additional Information:
- Roofing Systems - Introduction, for general roofing systems descriptions and requirements.
- Flashing and Copings, under the appropriate sections for flashing details.
- Roofing Systems - Standing Seam or Batten Seam, for additional information on the respective roofing types.