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Historic Preservation - Technical Procedures

Spectitle:

Installing A Transverse Expansion Joint In A Standing Seam Copper Sheetmetal Roof

Procedure code:

0761002R

Source:

Hspg Prepared For Nps - Sero

Division:

Thermal And Moisture Protection

Section:

Sheet Metal Roofing

Last Modified:

10/23/2014

Details:

Installing A Transverse Expansion Joint In A Standing Seam Copper Sheetmetal Roof



INSTALLING A TRANSVERSE EXPANSION JOINT IN A STANDING SEAM COPPER
SHEETMETAL ROOF


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.  GENERALLY, THIS
         WORK SHOULD BE ACCOMPLISHED BY A 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.

              a.   Secure chicken ladders or cleats at the top
                   for adequate footing.

              b.   Hang and secure approved safety lines with
                   rope of sufficient strength.

              c.   Carry a limited number of materials so that
                   balance and footing are not impaired.

              d.   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.

                             END OF SECTION
 


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