Design Standards, Roofing/Waterproofing

 

Building Codes

  • International Building Code (IBC 2006) (For projects in which Predesign began after September 30, 2009, use IBC 2009.)
  • International Plumbing Code (IPC 2006) (For projects in which Predesign began after September 30, 2009, use IPC 2009.)
  • ASCE 7 (American Society of Civil Engineers) Minimum Design Loads for Buildings and Other Structures
 

Directives, Standards, and NPS Guidelines

  • National Roofing Contractors Association - Roofing and Waterproofing Manual
  • Factory Mutual Global
  • Underwriters Laboratories
  • Architectural Sheet Metal Manual, 2003 by Sheet Metal and Air Conditioning Contractors National Association, Inc. (SMACNA)
  • Design Handbook (Section 4 - Architectural Detail) and (Section 5 - Architectural Specifications), by Copper Development Association
  • Copper in Architecture - Handbook (publication 4050) by Copper Development Association
  • Wind load as calculated using ASCE 7
  • Determination of fire rated roof Classification.
  • Roof drainage as calculated using IPC or other established sources.
  • Determine dew point location in roof assembly and vapor barrier needs.
 

Professional Guidance

Asphalt Shingles Roofs

  • Specify a 2-ply laminated shingle, conforming to ASTM D3462, with a minimum 50-year material warranty and a minimum 15-year non-prorated labor and material watertightness warranty (i.e. Certainteed-Sure Start Plus 5 Star, GAF-Golden Pledge, Malarkey-steep slope system, etc.).
  • In humid and wet climates, specify algae resistant shingles.
  • In hailstorm areas, specify impact resistance shingles passing an UL 2218 test for Class 3 or 4.
  • In high wind areas, (greater than 90 mph) specify wind resistant shingles rating to wind speed determined by ASCE 7, and require a 10-year wind warranty.
  • In snow/ice climates, specify fully adhered moisture protection underlayment extending from the eave to 3 feet from the inside face of the exterior wall, at valleys, ridges and along dormer or other walls. Use cold roof design technology if possible.
  • Fasten shingles with minimum 12 gauge corrosion resistant nails only. Minimum nail head diameter shall be 3/8". Shank shall penetrate minimum of 3/4" in wood decking or completely through plywood decking.
  • Asphalt-saturated felt underlayment shall meet ASTM D 226 and/or D 4869. Use double layers on roof slopes less than 4:12.
  • Specify roof perimeter edge metal and step flashing at walls and chimneys.
  • Minimum slope 3:12.
  • Specify open, closed, or woven valleys.

Clay and Concrete Tile Roofs

  • Specify clay tile manufacturers who offer a 20-year labor and material warranty, for the installed cost of roof, to replace defective tiles resulting from defects in materials or workmanship.
  • Clay Tile shall meet or exceed ASTM C1167 Grade 1 requirements for durability and ASTM C1167 Type I, for appearance.
  • Concrete tile shall meet or exceed ASTM C1492 requirements.
  • In freeze/thaw climates specify clay tile manufacturers who have tiles with a moisture absorption rate of less than 1% per ASTM C67. Concrete tile shall have a minimum compressive strength of 7500 psi, shall not have more than 1% loss in dry weight per ASTM C67 and not absorb more than 8% of the dry weight in ASTM C140 immersion test.
  • Specify 2 layers of 30# asphalt-saturated felt underlayment meeting ASTM D 226 and/or D 4869.
  • In snow/ice climates or as required for warranty, specify fully adhered moisture protection underlayment extending from the eave to 3 feet from the inside face of the exterior wall, at valleys, ridges and along dormer or other walls. Use cold roof design technology if possible.
  • In hailstorm areas, specify manufacturers who provide a minimum 10-year hail warranty covering material replacement of damaged tiles.

Green Roof Systems

  • Reference Green Roof Systems Manual (2007 Edition) by National Roofing Contractors Association (NRCA).
  • Reference LEED Certification (DSC Sustainability Standards).
  • Green Roof System Components
    • Fully adhered waterproofing membrane, protection course
    • Root barrier
    • Drainage layer
    • Moisture-resistant insulation
    • Aeration layer
    • Moisture-retention layer
    • Reservoir layer
    • Filter fabric layer
    • Engineered soil-based growth medium with plantings
      • Permanent installations (annual maintenance required)
      • Tray systems (flexibility, seasonal use, enhanced drainage)
  • Green Roof Assemblies
    • Structural deck
    • Waterproofing membrane
    • Associated green roof components
    • Engineered overburden (soil based growth medium and plantings)
  • Design Considerations
    • Internally drained roof surfaces preferred.
    • Choose shallow, moderate depth or deep roof system based on initial cost, structural considerations, roof pitch, maintenance requirements, sustainability (LEED) objectives and aesthetic goals.
    • XPS rigid insulation (minimum compressive strength of 40 psi) (R-value of 5.0 per inch thickness).
    • EPS rigid insulation (minimum 2-pound density) to be used as filler material to reduce weight and attain slope contour.
    • Install moisture-resistant insulation above the membrane to protect the membrane against thermal gradients and contact wear/damage.
    • Restrict moderate and deep roof systems to roofs with 2:12 pitch or less. Use extensive shallow roof systems where roof pitch is greater than 2:12.
    • Employ edge retainers and erosion-control devices to grid landscape layout and stabilize overburden on steeper roof slopes. Controlling soil slippage and retention/distribution of water important to landscape health.

Metal Roofs

  • Specify metal roof manufacturers who offer Full System Manufacturer's Roofing Warranty for 20-year labor and material warranty, for the installed cost of roof, to repair leaks in the roof panels, flashing and trim resulting from defects in materials or workmanship. Roof manufacturers shall be required to inspect the work during construction (i.e. AEPS span-weather tightness, Berridge-Total Single Source, MBCJ-single source III, etc.).
  • Verify with manufacturer their underlayment requirement for the 20-year warranty.
  • Steep roof (hydrokinetic) roofs shall pass air and water infiltration tests per ASTM E1646 and E1680. Low slope (hydrostatic) roofs shall pass water infiltration tests per ASTM E2140. Submit test report.
  • Specify Kynar 500 or Hylar 5000 paint finish on metal panels which require paint.
  • Specify 22 gauge galvalume/zincalume and/or galvanized metal roofs. For structures located in coast regions use 0.040" aluminum or 20 oz copper. For high profile structures, use any of the above 3 materials.
  • For architectural panel roofs, specify snap type standing or batten seam with continuous length panels. Panel should be kept off substrate by manufacturer's clips. Double lock standing seams should only be used in high snow areas where snow will accumulate on the roof over the winter.
  • For structural or structural/architectural panel roofs, specify concealed fasteners and clips for panel attachment. No fasteners shall be located in the pan of the panel except at the ridge.
  • Panels and trim shall be rolled formed at the manufacturer's prime manufacturing plant.
  • Specify manufactured prepared shop drawing on a minimum 24" by 36" sheet.
  • Metal shingles and shingle panels to be used on steep slope (3:12 or greater). Investigate the bottom, top and side of each shingle to determine the interlocking mechanism and watertightness of the lap, joint and seam. Examine ridge, valley, hip and perimeter flashings profiles for watertightness. These products maybe problematic on roofs that retain snow for long periods of time.
  • Specify rosin paper slip sheet under all architectural metal roofs.
  • In snow/ice climates or as required for warranty, specify fully adhered moisture protection underlayment extending from the eave to 3 feet from the inside face of the exterior wall, at valleys, ridges and along dormer or other walls. Use cold roof design technology when possible.
  • Specify self-adhered high temperature underlayment.

SBS Modified Bitumen Roofs

  • Specify 2-ply system where roofing products, including each type of sheet, are all manufactured in the United States, supplied by a single manufacturer which has been successfully producing the specified types of primary products with the same materials without making adjustments, modifications or alterations to the chemical or physical composition of the products for not less than the specified warranty period.
  • Specify a 20 year system and require a 15-year System Roofing Manufacturer's Warranty for labor and material, without monetary limitation, to correct defects in materials or workmanship. Warranty shall contain no exclusions for random occurrences of ponding water.
  • APA systems are not permitted.
  • Specify SBS roof systems where high puncture resistance, exposure to abuse or frequent access is needed on the roof to maintain mechanical equipment.
  • Specify torch down and adhesive systems, avoid hot mop asphalt.
  • Specify a dense, fire and water resistance cover board made from gypsum or other man made materials to be placed over the deck or insulation board. Use adhesive to attach cover board to insulation.
  • Specify cant strips and curbs to be pressure treated wood unless metal curbs are used. Fiber products are not permitted.
  • Specify a pre-manufactured 2-piece counterflashing; coping system; roof edge/fascia system; and mechanical equipment curbs.
  • Minimum roof pitch of 1/4"/ft and 1/8"/ft along valleys.
  • Install stepping stone pavers with shims on low slope roof surfaces along a path from the roof hatch to mechanical equipment requiring cyclic maintenance, installed with a sufficient area to limit damage to finished roof system from foot traffic and service tools/equipment.

Single-Ply Membrane Roofs

  • Specify roofing products, all manufactured in the United States, supplied by a single manufacturer which has been successfully producing the specified types of primary products with the same materials without making adjustments, modifications or alterations to the chemical or physical composition of the products for not less than the warranty period.
  • Specify a 20 year system and require a 15-year System Roofing Manufacturer's Warranty for labor and material, without monetary limitation, to correct defects in materials or workmanship. Warranty shall contain no exclusions for random occurrences of ponding water.
  • Specify PVC (60 mil minimum thickness) and EIP (45 mil minimum thickness) systems to be mechanically attached. Roof membrane is visible from ground shall be fully adhered.
  • EPDM systems shall be fully adhered 60 mil thickness, using 7" wide tape seams, and be warranted for 20 years.
  • TPO membranes shall not be specified.
  • Specify single-ply roof system when foot traffic is minimal, roof shape is complex or when numerous roof penetrations are present.
  • Specify a dense, fire and water resistance cover board made from gypsum or other man made materials to be placed over the deck or insulation board. Use adhesive to attach cover board to insulation.
  • Specify a pre-manufactured 2-piece counterflashing; coping system; roof edge/fascia system; and mechanical equipment curbs.
  • Minimum roof pitch of 1/4"/ft and 1/8"/ft along valleys.
  • Install stepping stone pavers with shims on low slope roof surfaces along a path from the roof hatch to mechanical equipment requiring cyclic maintenance, installed with a sufficient area to limit damage to finished roof system from foot traffic and service tools/equipment.

Slate Roofs

  • Specify slate tile manufacturers who provide a 75-year material warranty. The installer shall provide a 5-year leak proof warranty for the installed cost of the roof, to replace defective flashings and tiles resulting from defects in materials or workmanship.
  • Specify slate manufacturers whose products meet ASTM C406 and can certify their slate to a Grade S1 classification by providing test results which are not more than 3 years old.
  • Specify 3/8" minimum thick slate in freeze/thaw, high wind or heavy hail areas, 1/4" minimum thick slate in other areas. Avoid slate from Pennsylvania.
  • Specify two layers of 30# asphalt-saturated felt underlayment meeting ASTM D 226 and/or D 4869 or one layer of fully adhered moisture protection 40 mil minimum butyl-adhesive based underlayment. Use a 3" minimum headlap for roof slopes between 4:12 to 8:12.
  • In snow/ice climates, specify fully adhered moisture protection 40 mil minimum butyl-adhesive based underlayment extending from the eave to 3 feet from the inside face of the exterior wall, at valleys, ridges and along dormer or other walls. Use cold roof design technology if possible.
  • Specify 10 gauge copper slating nails, stainless steel, bronze or cut-brace roof nails and fasten with 2 nails per slate. In high wind areas or when 3/4" or thicker slate is used, fasten with 4 nails per slate.
  • Provide eave cant for starter course.
  • Flashings shall be fabricated from 20 oz copper or 24 gage stainless steel. Open valley pan shall be formed with a "W" or "V" shaped splash diverter.

Specialty Roofs

  • Evaluated on a case-by-case basis.

Wood Shakes and Shingle Roofs

  • National Parks are slowly transitioning away from wood products as a result of increased fire danger throughout the west, the limited availability of domestic supplied material, and the reduce life expectancy of the product in many parts of the country. However, in some cases historic preservation standards may dictate the use of these products.
  • Specify No. 1 premium official blue label western red cedar shingle; premium grade western red cedar shake; or pressure treated No. 1 vertical grain, all clear yellow pine shingle.
  • Specify one layer (for shingles) or two layers (for shakes) of 15# asphalt-saturated felt underlayment meeting ASTM D 226 and/or D 4869 or one layer of fully adhered ice and water protection 40 mil minimum butyl-adhesive based underlayment. The second layer of felt is interlaced between courses when installing shakes.
  • In snow/ice climates, specify fully adhered moisture protection 40 mil minimum butyl-adhesive based underlayment extending from the eave to 3 feet from the inside face of the exterior wall, at valleys, ridges and along dormers or other walls. Use cold roof design technology if possible.
  • Use a 3 layer starter course for roofs with each course hanging over the lower one by 1/4".
  • Specify a minimum 4:12 pitch roof, prefer a 5:12 minimum pitch and shingle widths between 3 and 9 inches.
  • Specify copper or zinc sheets at ridge in humid climates to reduce moss growth.
  • Hand nail shakes and shingles. Nail guns and staples are not allowed.

Waterproofing Systems

  • Specify waterproofing products, all manufactured in the United States, supplied by a single manufacturer which has been successfully producing the specified types of primary products with the same materials without making adjustments, modifications or alterations to the chemical or physical composition of the products for not less than the warranty period.
  • Specify a minimum 10-year Manufacturer's Warranty for labor and material, without monetary limitation, to correct defects in materials or workmanship. Warranty shall contain no exclusions for random occurrences of ponding water.
  • Specify the use of certified contractors to apply the waterproofing system and that the work be inspected by the manufacturer at a minimum of once a week during installation.
  • Waterproofing below the water table may limit the selection of the waterproofing membrane.
  • Select waterproofing systems that are typically used on substrates as stated in the manufacturer's literature.
 

Last updated: March 27, 2013