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Historic Preservation - Technical Procedures

Spectitle:

Repairing Holes In A Sheetmetal Roof

Procedure code:

0761005R

Source:

Hspg Prepared For Nps - Sero

Division:

Thermal And Moisture Protection

Section:

Sheet Metal Roofing

Last Modified:

10/23/2014

Details:

Repairing Holes In A Sheetmetal Roof



REPAIRING HOLES IN A SHEETMETAL ROOF


PART 1---GENERAL

1.01 SUMMARY

    A.   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.

    B.   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.

    C.   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.

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

              b.   Hang and secure approved safety lines with
                   rope of sufficient strength

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

              d.   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.

    D.   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).

1.02 DEFINITIONS

    A.   anneal--the operation of heating and cooling the metal to
         soften it and make it less brittle.

    B.   brazing--to solder with a non-ferrous metal that melts at
         a lower temperature than that of the metals being joined.

    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 roofing in position, made from
         same material as roofing.

    D.   solder--metal or metallic alloy of tin and lead used when
         melted to join metallic surfaces.

    E.   standing seam--a double welted joint formed between the
         sides of adjacent bays and left standing.

    F.   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.

1.03 QUALITY ASSURANCE

    A.   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.

1.04 MAINTENANCE

    A.   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.

    B.   Keep the roof clear of debris, and trim all overhanging
         branches that might cause mechanical damage.

    C.   In addition to scheduled inspections, inspect after each
         exposure to unusually severe weather conditions such as
         strong winds, hail, or long continuous rains.

    D.   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.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.  Revere Copper 
         www.revere.com         

    B.  Zappone
         www.zappone.com
         
    C.  Metal Sales Mfg. Corp.
         www.metalsales.us.com
         

   D.  Vulcan Supply Corporation
         www.paradigmshingles.com
         

   E. Fine Metal Roof Tech
        www.finemetalrooftech.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 (*).

    A.   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

    B.   Cleats, same material as roof

    C.   Sheetmetal to match remainder of roof

    D.   Solder

    E.   Soldering flux

    F.   Rosin Paper

    G.   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, CORROSIVE TO FLESH;
              CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS,
              FLAMMABLE.

         4.   Available from chemical supply house, drugstore or
              pharmaceutical supply distributor, or hardware
              store.

    H.   Clean, soft cloths

2.03 EQUIPMENT

    A.   Chicken ladder, safety belt or harness

    B.   Snips for cutting sheet metal

    C.   Soldering copper, soldering iron

    D.   Handy tongs for bending the edges of the solder

    E.   Metal seamer

    F.   Stiff bristle brushes


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Whenever possible, make inspection from ground, or from
         above if possible.

    B.   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.

    C.   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.

3.02 PREPARATION

    A.   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 shall
              be dry and free from frost.

3.03 EXECUTION, INSTALLATION, APPLICATION

    A.   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
              hold it firmly to the metal.  If the patch is on a
              steep slope or vertical surface, clamp or tack-
              solder it in place.

         4.   Soft solder the patch over the defect.  For
              guidance on soldering, see 05010-07-R "Procedures
              for Soldering Metal".

    B.   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.

              a.   Carefully remove the damaged piece of metal
                   sheeting.

              b.   Level the indentation in the decking with a
                   suitable wood filler.

              c.   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:

              a.   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.

              b.   Replace rosin paper underlayment as required.


              c.   Seal the welt by flowing soft solder under the
                   final fold and into the mitered corners using
                   a large copper bit.

              d.   Pre-tin the edges of the new and existing
                   metal and dress the welt tight to create a
                   capillary soldered joint for maximum strength.

    C.   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.

3.04 PROTECTION

    A.   At the end of each work day, provide building protection
         for any exterior roofing element removed for repair or
         replacement.

    B.   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.

                             END OF SECTION
 


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