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Heavy Cedar Shake Roof Staggered Concrete Tile Roof Z Bar Wall Flashing Concrete Tile and Primary Wall Flashing Slate Roof Rake Wall Z Bar Flashing

Building Code Conflicts

Below are some examples of conflicts, pertaining to roofing, between the International Building Code (IBC) (for commercial buildings), the International Residential Code (IRC) (for residential buildings), the International Code Council (ICC) Evaluation Services Current and Legacy ICC-ES Reports or other Approved Material Testing Agencies, and Manufacturer's Installation Specifications/Instructions, or Manufacturer Association Manuals.

Whichever is more restrictive is used in writing our RFP/Guidelines and performing our Mid-Roof Inspections and Final Roof Inspection because weather conditions cannot tell the difference between a roof on a residential building or on a commercial building.  And there are weather conditions that do occur here in Colorado that affect the performance of roofing materials and accessories and their installation.


Examples of Building Code Conflicts

  1. Hail Damage Prone Areas:  The 2006 and 2009 IRC recognizes that most of the Front Range and the Eastern Plains of Colorado including the Metro Denver area are located in a Moderate Hail Exposure Area.  An example of one of the Building Code requirements for areas located in a Moderate Hail Exposure Area is the removal of all roof coverings to the deck when installing Asphalt Shingles.  Only one layer of Asphalt Shingles is permitted because a single layer is more resistant to damage from hail than two layers of asphalt shingles.  The 2006 and 2009 IBC for the roof coverings on commercial buildings does not recognize hail damage prone areas.  Impact damage to asphalt shingle roof coverings from hail is the same whether the roof coverings are on a commercial building or residential building.   This requirement was dropped in the 2012 IRC Revision and forward.  Why this criteria was dropped from the Building Codes, I do not know, but it does not make any sense.  So we will be using the 2006 and 2009 IRC requirement and write a correction notice for more than one layer of Asphalt Shingles.

  2. Wind Driven Snow Areas:  For decades the ICC Evaluation Service's legacy reports have recognized areas with wind driven snow which require vertical battens to be installed under all horizontal battens or horizontal battens with risers for all Tile roofs.  Low sloped roofs require 2 plies of base felts applied in shingle fashion since water easily penetrates through the tile and soaks the underlayment.  Since wind driven snow frequently blows up under the tiles and also soaks the underlayment, the underlayment should be treated the same on all slopes.  Tile roofs require both vertical and horizontal battens and Code approved ASTM numbered underlayments of either 2 plies of Type II underlayment (30 pound base felt) or a single ply of an approved ASTM numbered 90 lbs. rolled roofing or Ice and Water Membrane.

    1. This same requirement is stated again in the Concrete and Clay Tile Roof Design Criteria Manual for Cold and Snow Regions :  "Felt underlayments are intended to protect the building from wind driven snow or rain.  They are required by code.  Even a good tile may allow a dry light snow to blow in under it and onto the felt where melting will eventually occur.  On a well designed tile roof, the underlayment generally wears out before the tile.  Two layers of ASTM D226, Type II, No. 30 asphaltic felt overlaid in shingle fashion is the recommended minimum."

    2. So we, like a few other City/County Building Departments, also recognize that this is a Wind Driven Snow Area and will write a correction notice for missing vertical battens or risers and/or the approved above listed underlayments as listed in our Roofing Guidelines Examples web page.  Any approved alternate underlayment equal to ASTM D226 Type II underlayment (30 pound base felt) must also be applied in the same shingle fashion with 2-ply coverage.

  3. Eave Ice and Water Membrane:  The 2006 IBC and IRC was changed to better define when the use of an ice and water membrane is required.  The current definition all through Chapter 15 of the IBC and Chapter 9 of the IRC is:  "In areas where there has been a history of ice forming along the eaves causing a backup of water a membrane that consists of at least two layers of underlayment cemented together or of a self-adhering polymer modified bitumen sheet shall be used in lieu of normal underlayment..."  In other words, if your area has ice forming along the eaves which by the very nature of ice damming backs up water, you must use an ice and water membrane.  The entire Colorado Front Range as well as most of the rest of Colorado has ice forming at the eaves to various degrees every year from 2" to as much as 18" as occurred in January - February of 2007.  Some Building Departments are unaware of the damage ice damming has caused their citizens because Building Permits are generally not obtained to make the necessary repairs.  So, like some Cities and Counties, we recognize there is ice forming along the eaves and will write a correction notice for missing ice and water membranes at the eaves.

  4. Weather Blocking Material (approved flashing):  The ICC Evaluation Legacy Reports and the Tile Manufacturer's Installation Manuals require weather-blocking material (approved flashing) to be installed.  From the 2015 Tile Manufacturer's Manual  "Openings at the hips, ridges, and headwalls including chimneys, skylights, solar panels, and down slope horizontal abutments shall be fitted with weather blocking material to keep water on the surface of the field tile".  It is also required for flashing at jacks and vents.  Flashing on the surface of a tile roof is needed in areas where debris can accumulate as also stated in the manufacturer's manual and is common sense.  Debris will accumulate just from trees in all areas.  All other types of roofing material have always required flashing to be placed so that the water is kept on the surface of the field roofing material for obvious reasons.  Therefore we will write a correction notice for missing primary flashing (flashing on surface of tiles) as well as secondary flashing (flashing over the underlayment but under the tile) at all Jacks, Vents, Head Walls, Rake Walls, Chimneys, Skylights, Curbs, Swamp Cooler Ducts, Hips, Ridges and any Other Protrusions through the tile roof to help keep as much water as possible on the surface of the tile and limit the access for debris and critters to get in under the tile.  (See our Roofing Guidelines Examples web page for Clay and Concrete Tile under Primary Flashing and/or Weather Blocking Material for more information.


Visit our Roof Inspection Services web page and the many other web pages throughout this website to find
answers to your roofing questions and solutions to your roofing problems.


Page Revised/Updated 2/27/2023