Repair Of Star Cracks In Copper Roofs
- Procedure code:
- Hspg Prepared For Nps - Sero
- Thermal and Moisture Protection
- Sheet Metal Roofing
- Last Modified:
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.
- This procedure includes guidance on repairing copper sheetmetal roofing damaged with star cracks. GENERALLY, THIS WORK SHOULD BE ACCOMPLISHED BY AN EXPERIENCED ROOFING CONTRACTOR.
- 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.
- 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.
- 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:
- 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.
- Individual copper bays have a soft temper in order to facilitate hand fabrication.
- Individual copper bays are not profiled, fixed, or bonded in the areas between joints to allow for thermal movement of the sheetmetal.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- anneal--the operation of heating and cooling the metal to soften it and make it less brittle.
- bay--a unit of sheet covering as laid between rolls or standing seams.
- 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
- Packing and Shipping:
- 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.
- 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 piece.
- Storage and Protection:
- Material storage: Keep uninstalled roof materials under cover, dry, free from scratches, condensation, and distortion during delivery, storage, and handling.
- Salvage storage: Historic material to be used as example of original construction shall be stored as directed by the RHPO.
- 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
- Environmental Requirements: Do not begin repair in misty or rainy weather. Do not apply metal roofing to wet roof sheathing.
- Keep the roof clear of debris, and trim all overhanging branches that might cause mechanical damage.
- Inspect for and eliminate bird droppings and other debris that can corrode sheetmetals.
- Inspect the secureness of cleats and fasteners and the condition of the sheetmetal after particularly heavy storms.
- Copper nails with large flat heads and barbed shank
- Copper cleats
- Copper sheets, to match weight and temper of existing
- Rosin paper
- Chicken ladder, safety belt or harness
- Protective gloves and gear
- Straight snips for cutting straight or slightly curved lines in sheetmetal 24 gauge or lighter
- Metal seamer
- The application of sheetmetal roofing requires a full range of metal-working tools and shop equipment, plus special handling, hoisting equipment, and machinery for long lengths
- Fire extinguisher
- 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.
- 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.
- 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.
- At the end of each work day, provide building protection for any exterior roofing element removed for repair or replacement.
- 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
- 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 bays.
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.
- Remove and replace the affected section, or shorten the original bay by at least a third.
- 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.
- Before replacing a bay, cut back worked edges of affected bays to flat unworked metal.
- If worked edges must be retained, flatten edges and anneal before reworking to join replacement bays.
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 THICKNESS.
- 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.