Historic Preservation - Technical Procedures
- Repair Of Star Cracks In Copper Roofs
- Procedure code:
- Hspg Prepared For Nps - Sero
- Thermal And Moisture Protection
- Sheet Metal Roofing
- Last Modified:
- Repair Of Star Cracks In Copper Roofs
- Last Modified:
REPAIR OF STAR CRACKS IN COPPER ROOFS
THIS PROCEDURE HAS THE POTENTIAL TO ALTER THE HISTORIC APPEARANCE
OR CHARACTER OF A BUILDING. IT SHOULD ONLY BE PERFORMED BY AN
EXPERIENCED PROFESSIONAL AND ONLY UPON APPROVAL FROM THE REGIONAL
HISTORIC PRESERVATION OFFICER (RHPO) OR DESIGNATED REPRESENTATIVE.
THIS PROCEDURE SHOULD BE PERFORMED UNDER THE DIRECTION OF AN
HISTORICAL ARCHITECT OR ENGINEER TO DECIDE THE MOST EFFICIENT AND
LEAST DESTRUCTIVE MANNER FOR EXECUTING THE WORK.
A. This procedure includes guidance on repairing copper
sheetmetal roofing damaged with star cracks. GENERALLY,
THIS WORK SHOULD BE ACCOMPLISHED BY AN EXPERIENCED
1. Star cracks are star shaped cracks which occur
because of repeated flexing or bending of the
sheetmetal due to wind loads or thermal stresses.
As the sheets are flexed up they tend to fold in a
diagonal pattern. Stresses are created where these
lines cross and "star cracks" develop.
2. If left unrepaired, star cracks will get larger and
eventually allow rain and wind to penetrate the
covering. The combined wind loading above and
below the sheet can cause large areas of the
covering to become detached from the decking, and
torn from the roof by a high gust of wind.
B. Bay size in copper roofing is extremely important, as it
can limit the potential for damage to bays by windlift.
Copper roofing is more susceptible to damage by windlift
than other materials for several reasons:
1. Copper roofing is relatively light weight and,
therefore, lacks some of the inherent stability of
heavier materials whose shear weight allow them to
resist negative wind loading.
2. Individual copper bays have a soft temper in order
to facilitate hand fabrication.
3. Individual copper bays are not profiled, fixed, or
bonded in the areas between joints to allow for
thermal movement of the sheetmetal.
C. 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
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).
A. anneal--the operation of heating and cooling the metal to
soften it and make it less brittle.
B. bay--a unit of sheet covering as laid between rolls or
C. cleats or clips--metal 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 sheetmetal roofing in position.
1.03 DELIVERY, STORAGE AND HANDLING
A. Packing and Shipping:
1. Hoisting equipment and procedures will depend on
the design of the panels, weight, and length.
Lengths of approximately 35 feet are generally the
maximum for rail or truck shipment, but expansion-
type truck trailers are used to handle lengths up
to 60 feet.
2. Manufacturer's delivery or job markings on metal,
and adhesives for manufacturer's labels shall be a
neutral material. In no case shall such material
be alkaline; any staining of the metal by alkaline
materials will cause for the rejection of the
B. Storage and Protection:
1. Material storage: 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.
3. Heavy bundles of nested panels require suitable
mechanical equipment and reasonable care must be
taken to prevent damage to corners and edges.
1.04 PROJECT/SITE CONDITIONS
A. Environmental Requirements: Do not begin repair in misty
or rainy weather. Do not apply metal roofing to wet roof
A. Keep the roof clear of debris, and trim all overhanging
branches that might cause mechanical damage.
B. Inspect for and eliminate bird droppings and other debris
that can corrode sheetmetals.
C. Inspect the secureness of cleats and fasteners and the
condition of the sheetmetal after particularly heavy
A. Copper nails with large flat heads and barbed shank
B. Copper cleats
C. Copper sheets, to match weight and temper of existing
D. Rosin paper
A. Chicken ladder, safety belt or harness
B. Protective gloves and gear
C. Straight snips for cutting straight or slightly curved
lines in sheetmetal 24 gauge or lighter
D. Metal seamer
E. The application of sheetmetal roofing requires a full
range of metal-working tools and shop equipment, plus
special handling, hoisting equipment, and machinery for
F. Fire extinguisher
A. Detect for early signs of wind displacement: Listen for
a drumming noise during windy conditions caused by the
vibration of the sheets striking the roof deck.
B. Look for poorly designed roof edges or improperly spaced
or decayed decking which permits wind penetration. Check
the underside of the roof deck from the attic to detect
leaks. Make repairs as necessary.
C. In addition to scheduled inspections, inspect after each
exposure to unusually severe weather conditions
especially strong winds. Look for visual cracking as
described in Section 1.01 A. 1. above.
1. At the end of each work day, provide building
protection for any exterior roofing element removed
for repair or replacement.
2. Remove only a quantity of roofing which may be
replaced on that same day. At the end of the day,
use 15 pound roofing felt or polyethylene sheeting
to drape over missing roofing and insert under roof
unit laps or temporarily secure areas of existing
roofing and roof as required to make roof
watertight and windproof.
3.03 ERECTION, INSTALLATION, APPLICATION
A. For localized damage such as at the verge, ridge or eaves
of a roof, replace damaged sheets with narrower and
possibly shorter verge bays and shorter ridge and eave
NOTE: AT THE VERGE BAYS, DO NOT EXCEED A NET WIDTH OF
1'-3" WITH DOUBLE LOCK CROSS WELTS SPACED NOT MORE THAN
3'-0" ON CENTER.
1. Remove and replace the affected section, or shorten
the original bay by at least a third.
2. If cracks are widely distributed across a bay,
replace the entire bay with two new bays.
NOTE: EACH NEW BAY SECTION SHOULD BE APPROXIMATELY
HALF THE LENGTH OF THE ORIGINAL.
a. Before replacing a bay, cut back worked edges
of affected bays to flat unworked metal.
b. If worked edges must be retained, flatten
edges and anneal before reworking to join
NOTE: WHEN ANNEALING, TAKE PRECAUTIONS
AGAINST FIRE. INSERT FIRE-RESISTANT
INSULATION PADS OR SHEETING BETWEEN COPPER AND
ANY COMBUSTIBLE MATERIAL DURING ANNEALING AND
LEAVE IN PLACE UNTIL THE COPPER HAS COOLED.
NOTE: DO NOT ANNEAL LATER THAN TWO HOURS
BEFORE WORK IS FINISHED FOR THE DAY.
NOTE: DO NOT RE-USE FASTENERS OF ANY KIND.
COPPER CLIPS, FIXING STRIPS, NAILS AND SCREWS
SHOULD BE NEW AND OF THE APPROVED SIZE AND/OR
B. If cracks are widely distributed throughout the entire
roof, the roof will need to be replaced using narrower
and shorter bays. Selective replacement is not
appropriate, because it is likely that remaining
undamaged bays will eventually become damaged.
END OF SECTION