Repairing Holes In A Sheetmetal Roof

Procedure code:
Hspg Prepared For Nps - Sero
Thermal and Moisture Protection
Sheet Metal Roofing
Last Modified:


  1. This procedure includes guidance on patching holes in a sheet metal roof by brazing and welting. Generally, this work should be accomplished by a experienced roofing contractor.
    NOTE: do not use asphalt roofing compound or cheap aluminum-based roof coatings to make the patches. These repairs seldom last, and are hard to undo, and are potentially damaging to the existing roof.
  2. Falling masonry, scaffold poles, and other objects are responsible for inflicting damage to many roofs at some time during their life. Damage is mostly of a minor and localized nature, and in the case of a fully supported, traditional metal roof is usually no more than a shallow indentation in the metal and supporting boards, with perhaps a small rupture in the covering at the base of the depression.
  3. 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 house. 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. They may be distorted which can affect the slope to drain.
  4. 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. Anneal--the operation of heating and cooling the metal to soften it and make it less brittle.
  2. Brazing--to solder with a non-ferrous metal that melts at a lower temperature than that of the metals being joined.
  3. 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 roofing in position, made from same material as roofing.
  4. solder--metal or metallic alloy of tin and lead used when melted to join metallic surfaces.
  5. standing seam--a double welted joint formed between the sides of adjacent bays and left standing.
  6. welting--joining copper sheets at their edges by folding together. Welting may by single or double folds, such joints being termed single or double welts respectively.


  1. Qualifications: Metal roof systems and their accessories should be applied by qualified sheet metal mechanics using methods devised or approved by the manufacturer of the metal. Details may vary depending on the properties of the metal, local custom, and architectural effect required.


  1. The amount of maintenance required will depend on the kind of roofing used and the exposure hazards. It will also depend on the degree of waterproofing quality and exterior appearance that is acceptable.
    1. Small pieces of metal with exposed fasteners and simple laps may require more maintenance than full-length zipped panels.
    2. Factory enamel coatings and concealed fasteners add immeasurably to the appearance and life of a metal roof, and reduce the maintenance cost to the minimum.
  2. Keep the roof clear of debris, and trim all overhanging branches that might cause mechanical damage.
  3. In addition to scheduled inspections, inspect after each exposure to unusually severe weather conditions such as strong winds, hail, or long continuous rains.
  4. Never use any black goop (asphaltic roofing compound) or caulk to seal joints on a metal roof. Asphalt attacks metal roofing, and no caulk lasts long enough for this application.


  1. Revere Copper
    Revere Copper Products, Inc.
    One Revere Park
    Rome, NY 13440-5561
    (800) 448-1776

  2. Zappone
    2928 North Pittsburg St.
    Spokane, WA 99207
    (800) 285-2677

  3. Metal Sales Mfg. Corp
    545 South 3rd Street, Suite 200
    Louisville, KY 40202
    (800) 406-7387

  4. Vulcan Supply
    No. 29 Coppersmiths, Inc
    PO Box 100
    38 Stewart Road
    Westford, VT 05494
    (802) 878-6415

  5. Fine Metal Roof Tech
    79 West 4500 South, Suite 6
    Murray, UT 84107
    (801) 462-5264

NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).

  1. Nails of metal appropriate for metal used:
    1. For terne or terne-coated stainless steel: Use galvanized nails
    2. For copper: Use copper nails or brass screws
  2. Cleats, same material as roof
  3. Sheet metal to match remainder of roof
  4. Solder
  5. Soldering flux
  6. Rosin Paper
  7. Muriatic acid*: (generally available in 18 degree and 20 degree Baume solutions)
    1. A strong corrosive irritating acid.
    2. Other chemical or common names include Chlorhydric acid; Hydrochloric Acid; Hydrogen chloride; Marine acid*; Spirit of salt*; Spirit of sea salt*.
    3. Potential Hazards: toxic, caustic to flesh; corrosive to concrete, steel, wood or glass, flammable.
    4. Available from chemical supply house, drugstore or pharmaceutical supply distributor, or hardware store.
  8. Clean, soft cloths


  1. Chicken ladder, safety belt or harness
  2. Snips for cutting sheet metal
  3. Soldering copper, soldering iron
  4. Handy tongs for bending the edges of the solder
  5. Metal seamer
  6. Stiff bristle brushes


  1. Whenever possible, make inspection from ground, or from above if possible.
  2. Inspect roof parts for signs of warped, cracked, split, or out of place sheets, pulled fastenings, broken joints and seams, excessive weathering, or metal punctures.
  3. Inspect the underside of the roof deck from the attic to detect leaks. Flashings are the most vulnerable points. Therefore, inspect the underside carefully at all flashing points for evidence of leakage such as water stains.


  1. Surface Preparation:
    1. Carefully examine, measure, and record existing sheetmetal patterns at edges, hips, ridges, and other special conditions.
    2. For safety of the personnel, keep the deck clear of waste material as the work proceeds.
    3. For installation of new material, verify the type, thickness, weight/gauge prior to installation.
    4. Prior to installation, remove all oil, dirt, and other debris from the surface. All surfaces shallbe dry and free from frost.


  1. For Small Repairs:
    1. Thoroughly clean the area to be patched of all rust and/or roofing cement. When finished, the metal should be bare and shiny.
    2. Cut a metal patch, using the same material as the roof, to the required size and shape. Fold the edges under 1/2 inch and snip off the corners (this makes the patch stronger and takes off easily damaged sharp corners).
    3. Place a weight, such as a brick, over the patch to Nhold it firmly to the metal. If the patch is on a steep slope or vertical surface, clamp or tack-solder it in place.Soft solder the patch over the defect. For guidance on soldering, see 05010-07-R "Procedures for Soldering Metal".
  2. For Medium-Sized Repairs:
    1. Brazing:
      NOTE: Silver brazing requires extremely high temperatures, so the method can only be used where the metal can be raised from the decking allowing a fire-resistant insulation sheet or pad to be placed between the two. This will require a nearby seam to be unfolded.
      1. Carefully remove the damaged piece of metal sheeting.
      2. Level the indentation in the decking with a suitable wood filler.
      3. Silver braze the new metal to the existing bay using a "dog tooth" joint to hold the edges together and prevent undue distortion.
    2. Welting: If fire precautions make it impractical to use brazing, try welting:
      1. Welt a new square of sheet metal into the existing damaged bay. Make sure the metal patch is the same material as the existing roof.
      2. Replace rosin paper underlayment as required.
      3. Seal the welt by flowing soft solder under the final fold and into the mitered corners using a large copper bit.
      4. Pre-tin the edges of the new and existing metal and dress the welt tight to create a capillary soldered joint for maximum strength.
  3. For Large Repairs:
    1. Remove the damaged sheets carefully.
    2. Repair the decking.
    3. Replace the rosin paper underlayment.
    4. Close the covering with new metal, matching original seam type, pan size, metal type, etc. Install new clips or cleats as required.


  1. At the end of each work day, provide building protection for any exterior roofing element removed for repair or replacement.
  2. Work only on a quantity of roofing which may be repaired 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.


Last Reviewed 2016-07-22