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Historic Preservation - Technical Procedures

Spectitle:

Making Repairs To Sheetmetal Flashing

Procedure code:

0762004R

Source:

Maintenance, Repair & Alteration Of Hstrc Bldgs - Gsa/Pbs

Division:

Thermal And Moisture Protection

Section:

Sheet Metal Flashing And Trim

Last Modified:

02/24/2012

Details:

Making Repairs To Sheetmetal Flashing



MAKING REPAIRS TO SHEETMETAL FLASHING


PART 1---GENERAL

1.01 SUMMARY

    A.   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.

    B.   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.  

    C.   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.

    D.   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:

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

              b.   Safety lines should be tied and secured with
                   manila rope.

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

    E.   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.

    F.   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).

    G.   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

    A.   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

    A.   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

    A.   Dow Corning Corporation
         1225 Northmeadow Parkway, Ste. 104
         Roswell, GA  30076
         404/751-7979
         -OR-
         P.O. Box 994
         Midland, MI  48686-0994
         517/496-4000

    B.   General Electric Silicone Products Div.,
         Waterford, NY  12188
         518/237-3330

    C.   3M Consumer Products Group
         Box 33053
         St. Paul, MN  55133-3053
         612/737-6501 or 800/364-3577

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 (*).

    A.   Sheetmetal flashing, of gauge and type of metal to match
         or be compatible with existing.

    B.   Metal fasteners, compatible with existing and/or new
         metal.

    C.   Solder

    D.   Rosin soldering flux

    E.   Bituminous felt backing or wood backing

    F.   Metal primer such as Rust-Oleum, or approved equal

    G.   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:

              a.   AVOID REPEATED OR PROLONGED SKIN CONTACT.

              b.   ALWAYS wear rubber gloves when handling
                   mineral spirits.

              c.   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.

    H.   Backing Rod - closed cell polyethylene foam or butyl rod
         stock (diameter of rod should be 25% greater than width
         of joint).

    I.   Sealant such as (Dow Corning, General Electric, 3M) or
         approved equal.

    J.   Clean, soft cloths

2.03 EQUIPMENT

    A.   Soldering copper, soldering iron

    B.   Safety belt or harness; protective gloves and gear.

    C.   Chicken ladder; ladders and scaffolding.

    D.   Straight snips for cutting straight or slightly curved
         lines in sheet metal 24 gauge or lighter.

    E.   Tongs for bending the edges of the solder

    F.   Wire brush or steel wool

    G.   Stiff bristle brushes


PART 3---EXECUTION

3.01 EXAMINATION

    A.   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.

    A.   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.

    B.   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:

              a.   For wood, remove and replace damaged material
                   as required.

              b.   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.

    C.   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.

    D.   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.

    E.   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.

    F.   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.

    G.   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.

    H.   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.

                         END OF SECTION