Installing a Transverse Expansion Joint in a Standing Seam Copper Sheetmetal Roof

Procedure code:
761002S
Source:
Hspg Prepared For Nps - Sero
Division:
Thermal and Moisture Protection
Section:
Sheet Metal Roofing
Last Modified:
10/23/2014

PART 1—GENERAL

1.01 SUMMARY

A. This procedure includes guidance on installing an expansion joint in a standing seam copper sheetmetal roof to prevent future sheetmetal cracking. Note: Generally, this work should be accomplished by an experienced roofing contractor.

B. Standing seam copper sheetmetal roofs sometimes crack in long roof slopes (generally exceeding 30 feet). In roof lengths greater than 30 feet, the sheetmetal bays are unable to accommodate the cyclical stresses of expansion and contraction over a long period of time. One way of eliminating this problem is to install an expansion joint across the roof slope to absorb some of the longitudinal movement.

C. Long roof slopes of batten seam copper sheetmetal typically do NOT experience this type of problem, as the upstands in a batten roll system are separated by a wood-roll which allow the individual bays to move independently of one another.

D. Cracks caused by long roof slopes are usually concentrated in the center of the roof area about 1/3 of the way down the slope.

E. Safety Precautions

  1. Wear rubber-soled shoes that have non-slip or grid type tread (preferably sneakers with a high top for good ankle support). Avoid wearing loose clothing.
  2. Wear a safety belt or harness and secure it to a substantial chimney or to a window on the opposite side of the building. Leave only enough slack so you can work comfortably in one area, and adjust the slack as you work on other sections of the roof.
  3. Be sure the roof is clear of debris and water.
  4. Do not work on wet or snow covered roofs. Work on cleated walkboards.
  5. Steep roofs: On roof slopes greater than 4 inches rise per foot, special consideration must be given to both footing and materials handling.
    1. Secure chicken ladders or cleats at the top for adequate footing.
    2. Hang and secure approved safety lines with rope of sufficient strength.
    3. Carry a limited number of materials so that balance and footing are not impaired.
    4. Use scaffolding, ladders, and working platforms as required to execute the work. Ladders shall not be supported on hanging gutters. The gutters may be distorted which can affect the slope to drain.

F. Historic Structure Precautions: Historic and regional roofing craftsmanship examples characteristic of the structure are to be treated with sensitivity, to be preserved and followed.

G. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:

  1. Safety Precautions
  2. Historic Structures Precautions
  3. Submittals
  4. Quality Assurance
  5. Delivery, Storage and Handling
  6. Project/Site Conditions
  7. Sequencing and Scheduling
  8. General Protection (Surface and Surrounding)

These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).

1.02 DEFINITIONS

A. Anneal—the operation of heating and cooling the metal to soften it and make it less brittle.

B. Brazing—to solder with a non-ferrous metal that melts at a lower temperature than that of the metals being joined.

C. Bay—a unit of sheet covering as laid between rolls or standing seams.

D. Cleats or clips—copper strips, cut to lengths to suit roll or seam, placed at intervals and securely fixed to the roof base, the ends being welted in with the edges of the sheets to hold the copper roofing in position.

E. Cross welt or transverse seam—in flexible metal roofing, a seam between sheets; usually parallel to the gutter or to the ridge.

F. Lock joint—a single or double welted joint.

G. Solder—metal or metallic alloy of tin and lead used when melted to join metallic surfaces.

H. Standing seam—a double welted joint formed between the sides of adjacent bays and left standing.

I. Turn up—where the two adjacent edges of metal sheets are brought together vertically and folded over.

J. Welting—joining copper sheets at their edges by folding together. Welting may have single or double folds, such joints being termed single or double welts respectively.

1.03 SYSTEM DESCRIPTION

A. The maximum length of straight standing seam runs should not exceed 30 feet. There should be no sign of strain at the seams, especially at the cross welts.

1.04 QUALITY ASSURANCE

A. Qualifications: Copper roofing should be applied by qualified sheet metal mechanics using methods devised or approved by the manufacturer. Details may vary depending on the properties of the metal, local custom, and architectural effect required.

1.05 DELIVERY, STORAGE, AND HANDLING

A. Storage and Protection:

  1. Keep uninstalled roof materials under cover, dry, free from scratches, condensation, and distortion during delivery, storage, and handling.
  2. Salvage storage: Historic material to be used as example of original construction shall be stored as directed by the RHPO. Often original roof metal scrap pieces with exposed weather can be found in attic spaces.
  3. Care must be taken to prevent damage to corners and edges of metal roofing during handling and storage.
  4. Manufacturer’s delivery or job markings on metal, and adhesives for manufacturer’s labels shall be either a neutral or slightly acidic material. In no case shall such material be alkaline; any staining of the metal by alkaline materials will cause for the rejection of the piece.

PART 2—PRODUCTS

2.01 MATERIALS

A. Copper nails

B. Copper cleats

C. Copper sheet metal, weight to match existing (minimum 16 oz.)

D. Solder and flux

E. Cleaners

F. Rosin Paper

G. Lumber for cant strip

2.02 EQUIPMENT

A. Chicken ladder, safety belt or harness

B. Protective gloves and gear

C. Straight snips for cutting straight or slightly curved lines in sheet metal 24 gauge or lighter

D. Soldering copper

E. Handy tongs for bending the edges of the solder

F. Metal seamer

G. The application of sheet-metal roofing requires a full range of metal-working tools and shop equipment, plus special handling, hoisting equipment, and machinery for long lengths.

PART 3—EXECUTION

3.01 EXAMINATION

A. Whenever possible, make inspection from ground or from above if possible.

B. Inspect for cracks near the cross seam of a long slope.

C. Inspect the underside of the roof deck from the attic to detect leaks.

3.02 PREPARATION

A. Surface Preparation

  1. Carefully examine, measure, and record existing metal shingle or sheet metal patterns at edges, hips, ridges, and other special conditions.
  2. Be careful not to damage old metal wall and vent flashings that may be used as a pattern for cutting templates. If metal cap flashings at the chimney and other vertical masonry wall intersections have not deteriorated, bend them up out of the way so that they may be used again.
  3. For safety of the personnel, keep the deck clear of waste material as the work proceeds.
  4. For installation of new material, verify the type, thickness, weight/gauge prior to installation.

3.03 ERECTION, INSTALLATION, APPLICATION

A. For a temporary repair where the number of cracks are minimal, small copper patches may be soft-soldered over cracks. For patching procedures, see 07610-05-R. Though the patches will last for several years, it will eventually be necessary to install an expansion joint across the full slope of the roof to permanently reduce thermal stresses.

B. Introducing a transverse expansion joint

Note: For a detail of this procedure, see the book Practical Building Conservation by John & Nicola Ashurst, English Heritage Technical Handbook. Vol. 4: Metals. New York: Halsted Press, 1988, p. 63.; check for latest edition of this book.

  1. Make two cuts across the slope of the roof and remove a section of roofing of sufficient width to allow a wood cant strip to be nailed to the roof deck.
  2. The vertical height of the front of the cant strip should be minimum of 1-3/8" with a gentle taper on the uphill side of the slope of the roof.
  3. Replace rosin paper as required where copper roofing has been cut and the new copper will be inserted.
  4. Turn up the ends of the existing copper roofing below the cant strip so that an upstand may be formed to go against the front of the cant strip.
  5. Anneal the seams on the existing copper roofing above the cant strip for a distance of about one foot, and carefully unfold the seams.
  6. Along the full length of the new expansion joint cut back alternate bays by 6" in order to create a stagger in the final cross welts.
  7. After a further anneal, fasten additional cleats or clips into position as required.
  8. Join new copper to the existing sheets with double-lock cross welts.
  9. Complete the standing seams and drip-edge welt.

3.04 PROTECTION

A. At the end of each work day, provide building protection for any exterior roofing element removed for repair.

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