Installing A Terne Sheetmetal Roof

Procedure code:
761007S
Source:
Hspg Prepared For Nps - Sero
Division:
Concrete
Section:
Sheet Metal Roofing
Last Modified:
03/13/2017

PART 1---GENERAL

1.01 SUMMARY

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
      1. Secure chicken ladders or cleats at the top for adequate footing.
      2. Hang and secure approved safety lines with sufficient strength rope.
      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. Scaffolding legs shall be planked to distribute load to not exceed 20# per square foot on roofs. Ladders shall not be supported on hanging gutters. They may be distorted which can affect the slope to drain.
  7. 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

  1. Bay - a unit of sheet covering as laid between seams.
  2. 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.
  3. 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.
  4. 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.
  5. Expansion cleats - additional cleats which accommodate the thermal movement of the metal covering when a single length of metal exceeds 30'.
  6. Lock joint - a single or double welted joint.
  7. Saddle End - the completion of a batten roll covering or a standing seam against an abutment.
  8. Solder - metal or metallic alloy of tin and lead used to join metallic surfaces.
  9. Standing Seam - a double welted joint formed between the sides of adjacent bays and left standing.
  10. 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

  1. 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

  1. Wet weather: Do not apply new metal roof in misty or rainy weather. Do not apply metal roofing to wet roof sheathing.
  2. 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

  1. Revere www.revere.com Follansbee, WV 26037
  2. Metal Sales Mfg. Corp. www.metalsales.us.com

2.02 MATERIALS

  1. 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.
  2. Terne cleats - 2" wide, length as required by type of seam being used. Consult roofing manufacturer. Pre- formed cleats are often available.
  3. 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.
  4. Solder - 50% tin, 50% lead
  5. Rosin soldering flux
  6. Rosin Paper
  7. Paint - red iron oxide, linseed oil; especially formulated to be used on terne metal
  8. Wood, fiberglass or metal battens - size dictated by existing roof.

2.03 EQUIPMENT

  1. Chicken ladder, safety belt or harness
  2. Protective gloves and gear
  3. Straight snips for cutting straight or slightly curved lines in sheet metal
  4. Soldering copper, soldering iron
  5. Tongs for bending the edges of the solder
  6. Metal seamer
  7. 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

  1. 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.
    2. Carefully examine, measure, and record existing sheetmetal patterns at edges, hips, ridges, and other special conditions.
    3. 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.
    4. Inspect the deck to determine whether it is sound.
      1. Remove loose or protruding nails or hammer them down.
      2. 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".
    5. Make whatever repairs are necessary to the existing roof framing to strengthen it and to level and true the deck.
    6. 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

  1. 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.
      1. Mark folds 3/4" from edge on all four edges. Clip corners at 45 degree angle at intersections of markings.
      2. 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.
  2. 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.
      1. Taper pans longitudinally (narrower at the bottom) a minimum 1/16" to fit at the cross seams.
      2. To form on site, fold one long side up 1- 15/32", forming a 90 degree angle. Fold top 15/32" over 90 degrees to create a "C" in section. The folded piece is called an up-stand.
      3. Fold opposite long side up 1-7/8", forming a 90 degree angle. Fold top 7/8" over 90 degrees away from the pan. Fold 3/8" of top edge down so that it is parallel with the 1" up-stand.
      4. To form fold for cross seam at both the top and bottom of the pan make a 3/4" long cut parallel to the up-stand and 1" away from the up-stand. 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 up-stand has only two folds. Nail free end of cleat to deck using two nails. Place nails close to the up-stand 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:
      1. 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 up-stand. Nail as described under A.5. above. Hook next higher pan over fold and cleat of lower pan and carefully mallet seam together.
      2. 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 up-stands. Fold up-stands 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 180 degrees 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 stand up over the shorter ridge. Fold both ridge up-stands 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.
  3. Batten Seam Application for application of 3" per foot minimum pitch (Consult roofing manufacturer if 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.
      1. Taper pans longitudinally (narrower at the bottom) a minimum 1/16" to fit at the cross seams.
      2. 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.
  4. 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 50 degrees 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.
  5. 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 bird droppings and any other debris which can corrode sheet metals.
    8. Inspect the secure-ness of cleats and fasteners and the condition of the sheet metal after particularly heavy storms.
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