Making Repairs To Sheetmetal Flashing

Procedure code:
762004S
Source:
Maintenance, Repair & Alteration Of Hstrc Bldgs - Gsa/Pbs
Division:
Concrete
Section:
Sheet Metal Flashing And Trim
Last Modified:
04/20/2015

PART 1---GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on repairing various types of problems found in sheetmetal flashing work. Typical causes of the problems are also listed.
    GENERALLY, THIS WORK SHOULD BE PERFORMED BY AN EXPERIENCED CONTRACTOR.
  2. Flashing is an integral part of a roofing system and protects against water infiltration at roof hips and valleys; penetrations such as chimneys; where roofing meets a vertical surface such as a parapet or at a porch roof; or at drip edges.
  3. Copper, with copper nails, galvanized sheet metal with hot-dipped galvanized nails, or terne-coated stainless steel with stainless steel nails are the primary materials used for flashing.
    CAUTION: THE DIFFERENT METALS SHOULD NOT BE MIXED. RAINWATER RUN-OFF FROM COPPER FLASHING WILL CORRODE BOTH GALVANIZED SHEET METAL AND STAINLESS STEEL THROUGH GALVANIC ACTION. GREAT CARE SHOULD BE TAKEN TO USE A FLASHING MATERIAL COMPATIBLE WITH THE REST OF THE ROOF SYSTEM.
  4. Safety Precautions:
    1. Wear rubber-soled shoes that have non-slip or grid type tread (preferably high top sneakers for good ankle support. Avoid wearing loose clothing.
    2. Wear a safety belt or harness secured to a substantial chimney or to a window on the opposite side of the building. Leave only enough slack to work comfortably in one area, and adjust the slack as work proceeds 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, or on a brittle roof surface. Work on cleated walkboards.
    5. On steep roofs:
      1. Secure chicken ladders or cleats at the top for adequate footing.
      2. Safety lines should be tied and secured with rope of sufficient strength.
      3. Carry a limited amount of materials so that balance and footing are not impaired.
  5. Flashing may deteriorate for a number of reasons. Some common problems are listed below:
    1. Cracks: Common at bends in sheetmetal work; often caused by metal fatigue and erosion.
    2. Buckling: Occur in running lengths of sheetmetal; often caused by inadequate provision for expansion and contraction, inadequate gauge of metal, adhesion of asphalt building felt to back of metal, or movement in wood backing of metal.
    3. Splitting of solder at the seam: Often caused by using too soft a solder, not pre-tinning the seams, movement in metal on either side of the seam, cracked, deteriorated or improper sealant.
    4. Cracked sealant: Often caused by deteriorated or improper sealant, or loss of cohesion due to movement of metal.
    5. Crumbling and powdering of the metal: Often caused by galvanic action from two incompatible metals, atmospheric corrosion, erosion, or deterioration of the galvanic coating.
    6. Pitting and corrosion: Pitting is often caused by the settling of chemical particles from the environment; corrosion is often caused by galvanic action from two incompatible metals or the decomposition of atmospheric chemicals on the surface.
    7. Blister-like mounds: Most common in running copper work; often caused by insufficient number of expansion joints for the length, or the gauge of metal is too light.
    8. Fastener deterioration: Often caused by incompatibility of fastener with base metal.
  6. 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).
  7. See 07620-03-R and 07631-03-R for guidance on patching sheetmetal. For more extensive flashing repairs, see 07620-02-R.

1.02 SYSTEM DESCRIPTION

  1. Flashing is performing as it was intended when there are no cracks, splits or torn areas. It should not show any signs of corrosion. Where flashing meets a vertical surface, all cap flashing should be secure and the flashing itself should be soundly anchored.

1.03 MAINTENANCE

  1. Check flashings as a part of the annual roof inspection (preferably in late autumn). Repair defects immediately because flashing is a critical part of the roof fabric. Small leaks in the flashing which are neglected may lead to major faults in the roof system. See also Section 3.01 Examination below.

PART 2---PRODUCTS

2.01 MANUFACTURERS

  1. Dow Corning Corporation www.dowcorning.com
  2. General Electric Silicone Products Div., www.ge.com
  3. 3M Consumer Products Group wwwshop3m.com

2.02 MATERIALS

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. Sheetmetal flashing, of gauge and type of metal to match or be compatible with existing.
  2. Metal fasteners, compatible with existing and/or new metal.
  3. Solder
  4. Rosin soldering flux
  5. Bituminous felt backing or wood backing
  6. Metal primer such as Rust-Oleum, or approved equal
  7. Mineral Spirits:
    1. A petroleum distillate that is used especially as a paint or varnish thinner.
    2. Other chemical or common names include Benzine* (not Benzene); Naphtha*; Petroleum spirits*; Solvent naphtha*.
    3. Potential Hazards: TOXIC AND FLAMMABLE.
    4. Safety Precautions:
      1. AVOID REPEATED OR PROLONGED SKIN CONTACT
      2. ALWAYS wear rubber gloves when handling mineral spirits.
      3. If any chemical is splashed onto the skin, wash immediately with soap and water.
    5. Available from construction specialties distributor, hardware store, paint store, or printer's supply distributor.
  8. Backing Rod - closed cell polyethylene foam or butyl rod stock (diameter of rod should be 25% greater than width of joint).
  9. Sealant such as (Dow Corning, General Electric, 3M) or approved equal.
  10. Clean, soft cloths

2.03 EQUIPMENT

  1. Soldering copper, soldering iron
  2. Safety belt or harness; protective gloves and gear.
  3. Chicken ladder; ladders and scaffolding.
  4. Straight snips for cutting straight or slightly curved lines in sheet metal 24 gauge or lighter.
  5. Tongs for bending the edges of the solder
  6. Wire brush or steel wool
  7. Stiff bristle brushes

PART 3---EXECUTION

3.01 EXAMINATION

  1. Flashing is usually a weak part of the roofing system and, therefore, should be inspected regularly for damage or deterioration.
    1. Outside, inspect flashing for splits, holes or corrosion.
    2. Inside, inspect the underside of the roof deck for evidence such as water stains or damp wood; inspect the ceiling and walls around fireplaces and chimney flues for stained or spalling plaster or wallpaper, or peeling paint.
    3. Look for daubs of roofing cement on the flashing - this is an indication of previous leaks. This type of repair is not recommended and may not have completely stopped the leak.
    4. Look for uncaulked openings at the tops of flashing where water may enter.

3.02 ERECTION, INSTALLATION, APPLICATION

NOTE: WHEN REPLACING SHEETMETAL FLASHING, USE GAUGE OF METAL SUITABLE FOR STRENGTH AND REQUIRED PERFORMANCE. INSTALL ACCORDING TO METAL MANUFACTURER. CAUTION: BE SURE REPLACEMENT METALS ARE CHEMICALLY COMPATIBLE OR CORROSION BY GALVANIC ACTION IS LIKELY TO OCCUR.

  1. For Cracks:
    1. Remove entire section of cracked flashing; cut out damaged area the full width of the piece.
    2. Replace piece with similar metal; join the new piece using a lock seam, loose, sealant filled seam or by lapping, riveting and soldering. NOTE: THE METHOD OF JOINING WILL DEPEND ON THE TYPE OF METAL SELECTED AND THE SURROUNDING CONDITIONS.
  2. For Outward Buckling:
    1. Examine flashing to determine cause of buckling. Lack of expansion joints for length of sheetmetal may have lead to the problem.
    2. Remove entire length of affected flashing.
    3. Inspect condition of backing material:
      1. For wood, remove and replace damaged material as required.
      2. For bituminous felt, remove felt and replace with heavy weight rosin-sized sheathing paper.
    4. Clean bituminous felt with a solvent such as mineral spirits.
    5. Reinstall the sheetmetal flashing; add expansion joints as needed.
  3. For Splitting of Solder at the Seam:
    1. If damage is localized, remove entire length of flashing and replace it to match existing.
    2. If damage is widespread, replace all affected metal with new metal to match existing or substitute compatible metal.
  4. For Cracked Sealant:
    1. Remove sealant.
    2. Clean metal using a solvent such as mineral spirits.
    3. Check width of joint to make sure it is at least 1/4 inch wide. If is less than 1/4 inch, carefully move the metal edges to allow a 1/4 inch gap.
    4. Prime surfaces of joint following manufacturer's instructions.
    5. Check depth of joint. If joint is at deeper than 5/8 inches and there is no backing material, insert a continuous backing rod. NOTE: DISTANCE BETWEEN FACE OF BACK-UP MATERIAL AND FACE OF JOINT SHOULD BE BETWEEN 1/4 TO 3/8 INCH.
    6. Fill the joint with sealant following manufacturer's instructions.
    7. Immediately remove excess sealant from the face of the metal.
  5. For Crumbling and Powdering Metal:
    1. If damage is localized, remove entire length of flashing and replace it to match existing.
    2. If damage is widespread, replace all affected metal with new metal to match existing or substitute compatible metal.
  6. For Pitting and Corrosion:
    1. If damage is localized, remove entire length of flashing and replace it to match existing.
    2. If damage is widespread, replace all affected metal with new metal to match existing or substitute compatible metal.
  7. For Blisters:
    1. Carefully inspect the affected metal; examine expansion joints to see that they are properly formed or do not exceed the recommended spacing.
    2. Cut out existing expansion joints; fabricate and install new joints with matching metal.
    3. Cut out other problem areas the full width of the metal; replace with new metal, compatible with existing and of same gauge.
    4. Fasten edges by soldering and riveting.
  8. For Fastener Deterioration:
    1. Remove all fasteners from sheetmetal.
    2. Remove residue from around the holes by cleaning with a light abrasive material such as steel wool, emery cloth or other.
    3. Replace fasteners with new ones made of compatible metal and neoprene washers to make a weathertight connection. NOTE: For aluminum and stainless steel metal, use stainless steel fasteners; for copper, lead-coated copper or brass metal work, use brass or copper fasteners; for copper-clad stainless steel metal, use stainless steel, brass, or bronze fasteners; for zinc, lead and galvanized steel metal, use galvanized steel or coated steel fasteners.
    4. If the metal around the fastener connections is too deteriorated to prevent leakage and enable a weathertight connection, remove entire length of flashing and replace it to match existing or substitute compatible metal.
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