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Historic Preservation - Technical Procedures

Spectitle:

Installing A Terne Sheetmetal Roof

Procedure code:

0761007R

Source:

Hspg Prepared For Nps - Sero

Division:

Thermal And Moisture Protection

Section:

Sheet Metal Roofing

Last Modified:

02/24/2012

Details:

Installing A Terne Sheetmetal Roof



INSTALLING A TERNE SHEETMETAL ROOF


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance in the application of
         four different types of seams for a terne sheetmetal
         roof.  For terne-coated stainless steel, see procedure
         07610-13-R.

    B.   In this procedure, it is assumed that the roof deck is
         wood, and that any insulation that may be required is
         installed within an attic space and allows for proper
         ventilation of the underside of the roof.  If conditions
         other than this exist, consult roofing material
         manufacturer.

    C.   For terne roofs, there are typically four types of seams
         used, depending on the appearance of the existing roof:

         1.   Flat seam (also called flat locked seam):  A seam
              between adjacent metal sheets, formed by turning up
              both edges, folding them over, and then flattening.
              In a flat seam roof, and at valleys, all seams are
              soldered.

         2.   Standing seam:  A seam between adjacent metal
              sheets, formed by turning up the edges of two
              adjacent sheets, and then folding them over.

         3.   Batten seam:  A seam that is formed around a wood,
              fiberglass or plastic core.  Typically, nearly
              square in cross-section.

         4.   Cross seam:  Cross seams are perpendicular to the
              above seams and are intended to provide the correct
              length for sheet metal pans.  They should be
              staggered from bay to bay to ensure strength and
              stability of the sheet metal.

    D.   Historic and regional roofing craftsmanship and details
         which are characteristic of the structure are to be
         treated with sensitivity.  Such details are to be
         preserved and copied.

    E.   Replacement roofing work shall be equal to original
         workmanship.  The appearance of the new roof shall match
         the existing roof in exposure, bay size, pattern and
         material.

    F.   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.   There should be no unnecessary walking over roof.
              The roof shall not be used as a storage area for
              other materials.
   
         3.   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.

         4.   Keep the deck clear of waste material as the work
              proceeds.  Sweep the deck clean after all old
              roofing has been removed.

         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
                   manila rope.

              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.
                   Scaffolding legs shall be planked to
                   distribute load to not exceed  # per square
                   foot on roofs.  Ladders shall not be supported
                   on hanging gutters.  They may be distorted
                   which can affect the slope to drain.

    G.   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.   Bay - a unit of sheet covering as laid between seams.  

    B.   Capping - a strip, covering the top of a batten roll,
         welted to the edges of the sheets which are dressed up
         the side of the roll.

    C.   Cleats or Clips - strips, cut to specified length
         according to the type of seam being used, placed at
         intervals directed by roofing manufacturer.  Cleats are
         securely nailed to the roof deck and the ends are welted
         in with the edges of the sheets to hold the roofing
         sheets in position.

    D.   Drip edge - formed metal sheets at roof edges which
         prevent water from dripping down vertical surfaces.  One
         edge is welted to roof sheeting to form weather-tight
         seam.

    E.   Expansion cleats - additional cleats which accommodate
         the thermal movement of the metal covering when a single
         length of metal exceeds 30'.

    F.   Lock joint - a single or double welted joint.

    G.   Saddle End - the completion of a batten roll covering or
         a standing seam against an abutment.

    H.   Solder - metal or metallic alloy of tin and lead used to
         join metallic surfaces.

    I.   Standing Seam - a double welted joint formed between the
         sides of adjacent bays and left standing.

    J.   Welting - joining metal 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 SUBMITTALS

    A.   Shop Drawings:  Before replacing roofing, prepare
         working drawings showing bay width and length between
         seams.  Prepare typical and unusual seam details, valley
         details, and fastening patterns for reroofing guidance.

1.04 PROJECT/SITE CONDITIONS

    A.   Wet weather:  Do not apply new metal roof in misty or
         rainy weather.  Do not apply metal roofing to wet roof
         sheathing.

    B.   Terne metal is likely to deteriorate from chemical action
         by pitting or streaking.  This can be caused by airborne
         pollutants; acid rainwater; acids from lichen or moss;
         uncured alkalis found in lime mortars or portland cement
         fastenings.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Follansbee Steel
         P.O. Box 610
         Follansbee, WV  26037
         800/624-6906 or FAX 304/527-1269

    B.   Metal Sales Mfg. Corp.
         Deer Lake Industrial Park
         P.O. Box 158, Dept. TB
         Orwigsburg, PA  17961
         717/366-2020

2.02 MATERIALS

    A.   Fasteners:

         1.   Nails - 7/8" minimum length, flat head, galvanized
              roofing nails

         2.   Screws - For batten seam roofs, use galvanized
              screws, long enough to securely fasten batten to
              roof deck.

    B.   Terne cleats - 2" wide, length as required by type of
         seam being used.  Consult roofing manufacturer.  Pre-
         formed cleats are often available.

    C.   Terne sheetmetal - to match gauge, or .012 (30 ga.) or
         .015 (28 ga.) as directed by roofing manufacturer based
         on type of application; see 3.02 below.

    D.   Solder - 50% tin, 50% lead

    E.   Rosin soldering flux
   
    F.   Rosin Paper

    G.   Paint - red iron oxide, linseed oil; especially
         formulated to be used on terne metal

    H.   Wood, fiberglass or metal battens - size dictated by
         existing roof.

2.03 EQUIPMENT

    A.   Chicken ladder, safety belt or harness

    B.   Protective gloves and gear

    C.   Straight snips for cutting straight or slightly curved
         lines in sheet metal

    D.   Soldering copper, soldering iron

    E.   Tongs for bending the edges of the solder

    F.   Metal seamer

    G.   The application of sheet-metal roofing requires a full
         range of metal-working tools and shop equipment, plus
         special handling, hoisting equipment, and machinery for
         long lengths.


PART 3---EXECUTION

3.01 PREPARATION

    A.   Surface Preparation:

         1.   Prior to installation, remove all oil, dirt, and
              other debris from the roof deck.  All surfaces
              shall be dry and free from frost.

         1.   Carefully examine, measure, and record existing
              sheetmetal patterns at edges, hips, ridges, and
              other special conditions.

         2.   Be careful not to damage old metal wall and vent
              flashings that may be used as a pattern for cutting
              templates.  If metal cap flashings at the chimney
              and other vertical masonry wall intersections have
              not deteriorated, bend them up out of the way so
              that they may be used again.  Be especially careful
              roofing in these areas to avoid damaging reusable
              base flashing.  

         3.   Inspect the deck to determine whether it is sound.

              a.   Remove loose or protruding nails or hammer
                   them down.  

              b.   Replace rotted, damaged, or warped sheathing
                   or delaminated plywood.  DO NOT USED WOOD
                   TREATMENTS WHICH ARE HYGROSCOPIC OR CHEMICALLY
                   TREATED.  Spacing between boards shall be no
                   more than 2".  Plywood shall have a minimum
                   thickness of 1/2".

         4.   Make whatever repairs are necessary to the existing
              roof framing to strengthen it and to level and true
              the deck.

         5.   Lay rosin paper over the deck.  DO NOT secure to
              deck.  This paper serves as a slip sheet between
              the terne metal and the deck.  DO NOT use roofing
              felt as an underlayment on a terne roof.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   Flat Seam Applications:

         1.   Terne shall be .012 (30 ga.) or .015 (28 ga.).
              Terne is available in 14" x 20" and 20" x 28"
              sheets.  Maximum sheet size is 20" x 28".

         2.   Form sheets on a brake as indicated by roofing
              manufacturer.  

              a.   Mark folds 3/4" from edge on all four edges.
                   Clip corners at 450 angle at intersections of
                   markings.  

              b.   Fold two adjacent edges up and over and the
                   opposite adjacent edges down and under the
                   sheet.

         3.   After all sheets have been prepared in this manner,
              paint one side of each sheet with one coat of
              primer made for terne metal.  THE MILL-APPLIED SHOP
              COAT IS NOT SUFFICIENT.  Allow to fully dry before
              proceeding.  All special pieces such as drip pans
              shall also be painted in this manner.

         4.   Before beginning the first course, be governed by
              proper application at ridge, drip edge, end or side
              wall, gutters, valleys, etc.  Consult roofing
              manufacturer.  All roof perimeters shall have
              appropriate terne metal drip edge.

         5.   Place first sheet, paint side down, into position
              at the lowest point of roof slope.  Top edge must
              be one of the edges which is folded up and over.
              Hook one end of cleat into edge formed on sheet and
              nail free end of cleat to deck.  Place nail close
              to the fold but DO NOT NAIL THROUGH ROOFING SHEET.
              Bend end of cleat up and over nail head.  Attach
              each sheet with two cleats per side.

         6.   Continue laying roofing sheets in this manner.
              Align horizontal joints, stagger all vertical
              joints.  Lay individual sheets so that the fold of
              the sheet higher on the roof hooks onto and is over
              the fold of the lower adjoining pan.

         7.   At valleys, edges of individual roofing sheets will
              require custom fitting to provide proper flat lock
              seam.  Sheet metal used for valleys should be as
              long as possible to reduce the number of cross
              seams.

         8.   All seams must be soldered.  Use solder that is 50%
              tin and 50% lead only.  Use rosin only as a flux.
              Remove excess rosin before painting.  

              NOTE:  FLUX CONTAINING ANY ACID SHALL NOT BE USED.

         9.   Surface must be painted as soon as possible after
              completion of roof.  Paint as directed below in D.

    B.   Standing Seam Application, 3" per foot minimum pitch (for
         lower slopes consult roofing manufacturer):

         1.   If initial sheet width is 20" wide or less, terne
              shall be 30 ga.  If initial sheet width is greater
              than 20" use 28 ga.

         2.   Determine width and length of each pan.  Maximum
              recommended width between seams is 21", with
              maximum length of 20'.  If pan length is between
              20' and 30', pan width between seams should be
              reduced to 17".  Final pan width should match
              original roof.  Individual pans may be either
              preformed by the manufacturer or formed on site.
   
              a.   Taper pans longitudinally (narrower at the
                   bottom) a minimum 1/16" to fit at the cross
                   seams.

              b.   To form on site, fold one long side up 1-
                   15/32", forming a 900 angle.  Fold top 15/32"
                   over 900 to create a "C" in section.  The
                   folded piece is called an upstand.

              c.   Fold opposite long side up 1-7/8", forming a
                   900 angle.  Fold top 7/8" over 900 away from
                   the pan.  Fold 3/8" of top edge down so that
                   it is parallel with the 1" upstand.

              d.   To form fold for cross seam at both the top
                   and bottom of the pan make a 3/4" long cut
                   parallel to the upstand and 1" away from the
                   upstand.  At the top end of the pan, make a
                   fold up and over.  At the bottom of the pan,
                   make the fold up and back behind.

         3.   IF TERNE DOES NOT ALREADY HAVE A MILL-APPLIED SHOP
              COAT, UNDERSIDE OF ALL PANS MUST BE GIVEN ONE COAT
              OF TERNE METAL PRIMER.  Primer should be brush
              applied and allowed to dry thoroughly before
              installation.

         4.   Lay down first pan, paint side down, into position.
              Hook one end of cleat into side of pan whose
              upstand has only two folds.  Nail free end of cleat
              to deck using two nails.  Place nails close to the
              upstand but DO NOT NAIL THROUGH PAN.  Bend end of
              cleat up and over nail heads.  Cleats should be
              spaced approximately 12" on center, the entire
              length of the pan.

         5.   Where cross seams are required:

              a.   on roofs with pitch greater than 6" per foot,
                   slide two cleats onto fold at top of pan.
                   Place each one about 1" away from the upstand.
                   Nail as described under A.5. above.  Hook next
                   higher pan over fold and cleat of lower pan
                   and carefully mallet seam together.

              b.   on roofs with pitch less than 6" per foot,
                   cleats secure lower pan as described above.
                   Approximately 4" below the fold of pan solder
                   a strip of terne, approximately 1-1/2" wide by
                   the full width of the pan.  Use solder that is
                   50% tin and 50% lead only.  Use rosin only as
                   a flux.  Remove excess rosin before painting.
                   Solder only the upper edge of the strip in
                   place.  The bottom fold of the next upper pan
                   hooks onto this strip rather than the fold of
                   the pan which has been folded in with the
                   cleat.  The upper pan will then cover both the
                   fold and cleat of the lower pan, and the
                   strip.

         6.   With first row of pans secure, lay second row next
              to the first row, leaving a 1/16" gap between the
              upstands.  Fold upstands of two pans together and
              down creating a 1" tall standing seam.  Continue in
              this manner until roof is covered.  Stagger cross
              seams in a uniform pattern.

         7.   At valleys, drip edges and other special
              conditions, sides of pans will require custom
              fitting to provide proper seams.  Consult
              manufacturer for difficult situations.  Sheet metal
              used for valleys should be as long as possible to
              reduce the number of cross seams.

         8.   To form the ridge, the top of last pan on one slope
              should extend beyond the ridge the desired height
              of the ridge seam, plus 1/2".  The last pan on the
              other slope should extend the desired height of the
              ridge seam plus 3/4".  Make a 1800 fold in each pan
              so that the folds on both slopes butt against each
              other.  Approximately 3" before the ridge, fold all
              standing seams flat, facing in the same direction.
              Fold the top 1/4" of the higher of the ridge
              upstands over the shorter ridge upstand.  Fold both
              ridge upstands over a minimum of 1/2" and press
              together.

         9.   Standing seams and cross seams need NOT be
              soldered.  Seams at valleys, however, MUST be
              soldered.  Use solder that is 50% tin and 50% lead
              only.  Use rosin only as a flux.  Remove excess
              rosin before painting.  

              NOTE:  FLUX CONTAINING ANY ACID SHALL NOT BE USED.

         10.  Surface must be painted as soon as possible after
              completion of roof as directed in section D. below.

    C.   Batten Seam Application for application of 3" per foot
         minimum pitch  (Consult roofing manufacturer is roof
         pitch is less than 3" per foot):

         1.   If initial sheet width is 20" wide or less, terne
              shall be 30 ga.  If initial sheet width is greater
              than 20" use 28 ga.

         2.   Determine width and length of each pan.  Maximum
              recommended width between seams is 21".  Final pan
              width should match original roof.  Maximum length
              of each pan in 10'.  Individual pans to be formed
              on site.  

              a.   Taper pans longitudinally (narrower at the
                   bottom) a minimum 1/16" to fit at the cross
                   seams.

              b.   Folds required for this type of seam are
                   complicated.  Form sheets on a brake as
                   indicated by roofing manufacturer.

         3.   IF TERNE DOES NOT ALREADY HAVE A MILL-APPLIED SHOP
              COAT, UNDERSIDE OF ALL PANS MUST BE GIVEN ONE COAT
              OF TERNE METAL PRIMER.  Primer should be brush
              applied and allowed to dry thoroughly before
              installation.

         4.   Lay down battens which have been sized to match
              original roof.  Screw battens to roof deck,
              matching center lines of original battens.

         5.   Nail cleats to vertical sides of battens, two nails
              per cleat.  Space cleats 12" on center the length
              of each batten, placing cleats opposite on another.
              Cleats shall extend 1" above the top of each
              batten.

         6.   At valleys, drip edges and other special
              conditions, sides of pans will require custom
              fitting to provide proper seams.  Consult
              manufacturer for difficult situations.  Sheet metal
              used for valleys should be as long as possible to
              reduce the number of cross seams.

         7.   Lay individual pans as directed by manufacturer.
              Allow 1/16" space between vertical side of pan and
              the batten.  Fold seams as directed.

         8.   Form cross seams as directed above in 3.02.B.5.

         9.   Surface must be painted as soon as possible after
              completion of roof as directed in section D. below.

    D.   Painting terne roof after completion of installation.

         1.   All surfaces must be clean and dry.  DO NOT PAINT
              OVER CONDENSATION.

         2.   Painting shall be done on a warm, dry day, when
              both the roof surface and air temperature is
              approximately 500 F.

         3.   Apply one coat of primer made especially for terne.
              MILL APPLIED SHOP-COAT SHALL NOT BE CONSIDERED A
              SUBSTITUTE FOR PRIME COAT.  Paint shall be brushed
              on to allow oil to adequately penetrate and adhere
              to metal.  Allow to dry before applying finish
              coat.

         4.   Apply one top coat, using finish paint which has
              been made to be used with selected primer.  Top
              coat shall be brush applied.

    E.   Roof Maintenance:

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

         2.   Inspect ridge details and eaves for metal
              punctures, and broken joints or seams.  Inspect for
              rust, excessive weathering or exposure, erosion, or
              staining indicating overall deterioration.

         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.

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

         5.   Rinse dirt with water annually.

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

         7.   Inspect for and eliminate ant hills and/or bird
              droppings which can corrode sheet metals.

         8.   Inspect the secureness of cleats and fasteners and
              the condition of the sheet metal after particularly
              heavy storms.

                             END OF SECTION