Roofing Code

  • Building construction in Baltimore County shall comply with the 2015 editions of the International Building Code, the International Residential Code, the International Mechanical Code and the International Energy Code as well as local amendments, all as set forth in County Council Bill Number 40-15. (PDF)

    ​Roofing ​

    SECTION R803


    R803.1 Lumber sheathing. Allowable spans for lumber used as roof sheathing shall conform to Table R803.1. Spaced lumber sheathing for wood shingle and shake roofing shallconform to the requirements of Sections R905.7 and R905.8. Spaced lumber sheathing is not allowed in Seismic Design

    Category D2.

    TABLE R803.1

    48a1 ½ T & G
    60b1 ½ T & G
    72c1 ½ T & G


    For SI: 1 inch = 25.4 mm.

    1. Minimum 270 Fb, 340,000 E.
    2. Minimum 420 Fb, 660,000 E.
    3. Minimum 600Fb, 1,150,000 E.

    R903.1 General. Roof decks shall be covered with approved roof coverings secured to the building or structure in accordance with the provisions of this chapter. Roof assemblies shall be designed and installed in accordance with this code and the approved manufacturer’s instructions such that the roof assembly shall serve to protect the building or structure.

    R903.2.1 Locations. Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings. A flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.5 mm) (No. 26 galvanized sheet).

    R903.2.2 Crickets and saddles. A cricket or saddle shall be installed on the ridge side of any chimney or penetration more than 30 inches (762 mm) wide as measured perpendicular to the slope. Cricket or saddle coverings shall be sheet metal or of the same material as the roof covering.

    R905.1.2 Ice barriers. In areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2(1), an ice barrier shall be installed for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. The ice barrier shall consist of not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building. On roofs with slope equal to or greater than 8 units vertical in 12 units horizontal, the ice barrier shall also be applied not less than 36 inches (914 mm) measured along the roof slope from the eave edge of the building.

    R905.2.8.2 Valleys. Valley linings shall be installed in accordance with the manufacturer’s instructions before applying shingles. Valley linings of the following types shall be permitted:

    1. For open valleys (valley lining exposed) lined with metal, the valley lining shall be not less than 24 inches (610 mm) wide and of any of the corrosion-resistant metals in Table R905.2.8.2.
    1. For open valleys, valley lining of two plies of mineral-surfaced roll roofing, complying with ASTM D 3909 or ASTM D 6380 Class M, shall be permitted. The bottom layer shall be 18 inches (457 mm) and the top layer not less than 36 inches (914 mm) wide.
    1. For closed valleys (valley covered with shingles), valley lining of one ply of smooth roll roofing complying with ASTM D 6380 and not less than 36 inches wide (914 mm) or valley lining as described in Item 1 or 2 shall be permitted. Self adhering polymer modified bitumen underlayment complying with ASTM D 1970 shall be permitted in lieu of the lining material.

    R905.2.8.3 Sidewall flashing. Base flashing against a vertical sidewall shall be continuous or step flashing and shall be not less than 4 inches (102 mm) in height and 4 inches (102 mm) in width and shall direct water away from the vertical sidewall onto the roof or into the gutter. Where siding is provided on the vertical sidewall, the vertical leg of the flashing shall be continuous under the siding. Where anchored masonry veneer is provided on the vertical sidewall, the base flashing shall be provided in accordance with this section and counterflashing shall be provided in accordance with

    Section R703.7.2.2. Where exterior plaster or adhered masonry veneer is provided on the vertical sidewall, the base flashing shall be provided in accordance with this section and Section R703.6.3.

    R905.2.8.5 Drip edge. A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section

    R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the underlayment along rake edges.

  •  Why Is The Substrate So Important? 

    A shingle roof substrate is the “foundation” for your roofing system. The substrate provides the smooth structural base on which asphalt shingles are installed. If the substrate is inferior, the integrity of the roofing system may be compromised. 

    What’s Considered A “Standard Deck” For Shingles? 

    Standard decks include: 

    o Plywood or OSB… 3/8” minimum thickness, exterior grade as recommended by APA – The Engineered Wood Association (15/32” minimum thickness for Slateline® shingles) 

    o Wood planking… Nominal 1” thick (min.) x 6” wide (max.) wood planking, with a maximum 1/8” spacing at the ends and sides 

    o Note: For existing older installations, if spacing is > 1/8” ≤ 1/4”, install a double layer of underlayment. If the spacing is greater than 1/4” install a layer of 3/8” minimum thickness APA labeled exterior grade plywood or OSB over the wood planking. 

    Can Other Substrates Be Used Without Prior Approval? 

    When properly installed using the fasteners and construction design recommended by the deck manufacturer, the following substrates may be used: 

    1. Loadmaster Shingle Deck 
    2. Tech Shield or equivalent Radiant Barrier Decking systems with vapor permeable, perforated foil backing 
    3. Ainsworth’s Thermastrand Radiant Barrier 
    4. 2” Minimum Homasote or Thermasote (Homasote Co.) 
    5. 2” Minimum Span Rock Gypsum Plank (USG) – fasteners must have a minimum 40 lbs. of pullout 
    6. Vent-Top Thermacal (Cornell) 
    7. Vented-R (Atlas) 
    8. Vented Nail-Line (Apache) 
    9. Hunter Vented Nail Base 
    10. Foam-Control Nail Base (AFM Corp. Licensed Mfr.) 
    11. Tectum III, Tectum E and Tectum NS (Tectum, Inc.) 
    12. Huber Zip Deck System – A waterproof underlayment such as StormGuard® leak barrier must be used at eaves as required by code or for certain warranty considerations and additional underlayment may be needed on slopes less than 4:12 or on re-roofing projects. 

    Note: GAF shingles are not approved for applications directly over any insulation or fiberboard. 

    What About Structural Insulated Panels (SIP)? 

    SIP may be use when: 

    approved/rated by UL for use as a shingle roof deck 

    with the minimum thickness of plywood or OSB as recommended above 

    installed in accordance with the SIP panel manufacturers recommendations for use as a shingle roof deck 

    What About Codes? 

    Roof decks must meet local codes… and approval from the local building department should be obtained to confirm the deck construction and ventilation meets local code requirements. 

    Is The Substrate Or Workmanship Covered Under GAF Warranties? 

    No. The substrate must be installed in accordance with the deck manufacturer’s specifications. Roof deck installation instructions, including the need for a vapor retarder, for specific deck types must be obtained from the respective manufacturer. GAF does not warrant the installation method, the performance of the decking or problems with the shingles caused by the deck or substrate, including but not limited to: physical movement, thermal bridging and/or moisture migration at the joints. 

    Where Can I Get More Information? 

    GAF Technical Services can assist you… with these and other questions you may have regarding your new roof installation. GAF Technical Services can be contacted at 800-ROOF-411 (800-766-3411). Also, the GAF website is a great resource for just about any question you may have or for additional information you may require. That site is at: 

  •  What Is The Normal Air Temperature Range For Installing StormGuard® 

    And WeatherWatch® Leak Barrier? 

    40°F to 120°F… In keeping with good roofing practice, StormGuard® and WeatherWatch® Leak Barriers should be applied when the deck is DRY and air temperature is between 40°F and 120°F (4.4°C and 48.9°C). 

    Can StormGuard® And WeatherWatch® Be Installed When The Temperature Is Below 40°F? 

    Yes… If necessary and certain precautions are taken. These include: 

    The substrate must be clean and dry… There must be no ice, frost, dew, moisture, dust or dirt present. 

    Store materials in heated area… All membrane rolls and adhesives must be stored for at least overnight at a minimum temperature of 55°F (12.8°C) prior to application. 

    Keep the StormGuard® and Weather Watch® Leak Barriers warm… Remove rolls from the heated storage only as they are being installed. Install membrane rolls immediately after removal from storage to avoid membrane cooling. When the air temperature is below 40°F (4.4°C) leak barrier membranes must be at least 45°F (7.2°C) at time of application. 

    Pre-cut membrane… Pre-cut the leak barrier roll into 10-20′ (3.05m -6.1m) lengths. 

    Immediately back nail… Immediately back nail every 18″(457 mm) in the top selvage 

    edge of the sheet to prevent slippage before the sheet adheres to the deck. 

    Press and hand roll… Press the membrane firmly onto the substrate and hand roll the laps to ensure adhesion. If necessary, a hot air gun can be used at the laps to promote adhesion. 

    Discontinue installation if membrane is not adhering… If the membrane is not sticking to the deck or the laps are not adhering, discontinue installation. 

    What Are Some Of The Possible Problems That May Result From Improper Cool Weather Installation? 

    o Sheet movement and falls… If the leak barrier is not firmly adhered to the deck, it can move under foot and cause a worker to slip and fall. This is why the cold weather recommendations include back nailing on 18” centers. 

    o Leaks… If the laps are not sealed they can allow water and dirt to enter. If dirt enters the lap area, the lap may never seal. It is critical to always start at the low point on the roof to avoid any backwater laps. 

    o Wrinkles… If the membrane is too cold at time of installation it may wrinkle (develop “mole runs”) that could be visible through the shingles when the roof warms up. In severe cases, the wrinkles or “mole runs” can compromise the watertightness of laps and can result in leaks. 

    Where Can I Get More Information? 

    GAF Technical Services can assist you… with these and other questions you may have regarding your new roof installation. GAF Technical Services can be reached at 800 ROOF-411 (800-766-3411). Also, the GAF website is a great resource for just about any question you may have or for additional information you may require. Visit: 



    What Are Some Causes For “Storm Damage” To Shingles?

    Damage to shingles caused by extraordinary weather conditions such as hurricanes, hail, tornadoes, lightning, winds higher than warranted, or cold-weather related damages such as ice-damming.


    Does The GAF Shingle Limited Warranty Cover This Type Of Damage?

    Extraordinary weather related damages as described above are specifically excluded from coverage*. This damage may be immediately noticeable, or can be latent damage in which case evidence of any damage may not be immediately apparent. This latent damage caused by severe weather or flying debris may cause the shingles to deteriorate prematurely.

    *Some GAF shingles are warranted to withstand winds up to 130 mph following when using GAF WeatherBlocker™ or Pro-Start™ starter strips and 6 (or more) nails.


    What Are Some Examples Of Latent Damage That I Could Expect To See?

    Latent damage may take on many forms such as:

     Granule loss at points of impact of debris or caused by stresses the shingles endure

     Cracks in the granule-asphalt surfacing – especially if high winds blew the shingles back

     Exposed fiberglass mat – which may or may not be immediately visible

     Loosening of the self-seal integrity creating the potential for future shingle blow-off


    What If I Have Granule Loss Concerns?

    Loss of mineral granules as an immediate or gradual consequence of storm damage exposes the asphalt coating directly to the environment. This granule loss may result in the accelerated aging and the premature deterioration of the shingles.

    Any shingle failures caused by storm damage, immediate or as a result of latent damage, is beyond the scope of the GAF Shingle Limited Warranty, and is not be the responsibility of GAF.

    Note: Granule loss is NOT just cosmetic damage and “sugaring,” the process of adding loose granules to damaged shingle with asphalt cement, is not a permanent repair.

    Is There Anything Else To Be Aware Of?

    “Blue Tarped Roofs”: As immediately effective as tarping a damaged roof is to protect the building, securing the tarp by nailing through the shingles damages the shingles. Shingles that were nailed through must be replaced; caulking these nail holes is not a permanent repair and creates a maintenance item that is not a “material defect” covered by a manufacturer’s warranty.


    Can Several Individual Shingles Be Replaced Or Should The Entire Roof Be Replaced?

    While individual damaged shingles on a roof can be replaced, it generally is not recommended if there are more than 2 or 3 damaged shingles on a roof or a plane (section) of the roof because the process of replacing individual shingles requires breaking the self seal of the surrounding shingles, removing their nails, and bending them to remove the damaged shingles and then re-fastening them … all of which can damage the shingles if not done properly. In addition, the color of new shingles inserted will not match the color of the shingles that have weathered for even a few years.

    For long term performance as well as aesthetic reasons, complete replacement is recommended for roofs that have a significant number of shingles that need to be replaced due to storm damage. An additional benefit to complete replacement is the ability of the roofing professional to check for latent damage – something that is difficult to do if just a few shingles are replaced. If the damage is confined to one plane of the roof, replacement of the just the damaged roof plane may be possible.


    Where Can I Get More Information? 

    GAF Technical Services can assist you… with these and other questions you may have regarding your roof installation. GAF Technical Services can be contacted at 800-ROOF-411 (800-766-3411). Also, the GAF website is a great resource for just about any question you may have or for additional information you may require. That site is at: .