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Roofing Guidelines for Commercial and Residential Projects

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If you are planning to do a roofing project, the information below will be helpful as you work through your project.  If you need additional information or have other questions about your specific project, please contact the Building Inspection Department at 303-651-8332 or


  • Repair of less than 10x10 (100 sq. ft.) is okay and no permit needed.
  • The City of Longmont has a “1 square” rule. If more than 100 square feet of roofing requires repair or   replacement,  then the entire roof must be replaced not just the affected roof area or plane. See Amendment 16.06.440 section R908.
  • Re-installation of existing materials - Any existing flashings, edgings, outlets, vents, or similar devices that are a part of the assembly shall be replaced where rusted, damaged, or deteriorated.  Aggregate surfacing materials shall not be reinstalled.  (R908.5)
  • Materials and methods of application used for re-covering or replacing an existing roof covering shall comply with Chapter 9.  (R908.1)
  • Roof Coverings and assemblies shall be applied in accordance with the applicable provisions of the IRC Chapter 9 and the manufacturer's installation instructions.  (905.1 and R908.1)
  • It is the Roofing Contractors responsibility to meet all requirements of the manufacturer's installation instructions.  (904.1)
  • The homeowner may pull a roof permit without obtaining a contractor's license; provided the house is the primary residence, and no contractor will perform the work.
  • Ladders and mid-roof inspections are not required unless flat roof.
  • Drip edge is required both eaves and rakes.
  • Over-lay is not allowed over existing roof.
  • All roofing must have a sustained wind warranty of 110 mph and no 3-tab unless it’s laminated. Nearly all manufacturer’s 3-Tab shingles will not meet this code. The only exception is for detached non-habitable structures.
  • For asphalt shingle roofs with multiple layers of roofing, all existing layers of roofing must be removed.
  • Asphalt shingles shall be classified for 110 mph sustained wind.
  • Roof ventilation is required unless a closed cavity roof system with condensation control is used in compliance with IRC table R806.5 climate zone 5 (R20) or IBC table 1203.3 climate zone 5 (R20). Ventilate the roof as per IRC code section 806.2 or per shingle MFG.  Take the footprint of the attic space and divide that area by 300 (1 square foot per 300 square feet rule), then divide that number by 2 (required ventilators half up high, half down low). Now multiply that number by 144 (to get to square inches).  Divide this last number by the square inches that each ventilator is going to provide and that will give you the number of ventilators required up high.  Lower ventilators are generally not within the scope of work for a re-roof unless required by manufacturers specifications.
  • Roof slopes between 1”12 and 2”12, above non-habitable space, shall be permissible to apply a bituminous membrane (ice and water guard) then asphalt shingles.
  • The City of Longmont does not require Ice & Water Shield or comparable unless required by the manufacturer or on an application with a slope less than 2:12. Manufacturer’s installation instructions and code must be followed; where in conflict the more restrictive applies.
  • Can inspect without homeowner as long as no dogs in yard and access granted. Have permit card taped to front door or window.

For additional information please refer to the Residential Re-roof handout:  Handout


  • All commercial roofs (including apartments/condos) require a Class D-2 licensee (no test is required) to perform the work.
  • Only 1 overlay is allowed over an existing built-up roof covering and insulation requirements would not apply.
  • A mid-roof inspection is required, including a ladder, on a built-up roof inspection. In such case the ladder must be sound, secured, and extend safely above the eave.
  • Mid-roof is required before dry in and when above deck insulation or roof sheathing is installed.
  • Manufacture installation instructions must be provided on-site for each material that will be installed.
  • Commercial roofs must comply with the 2018 International Building Code (IBC) and International Energy Conservation Code (IECC).A minimum R-25 is required above deck, with no point less than R11 in tapered systems – OR - R38 attic insulation (beneath decking).
  • Maximum number of layers is two for roof slopes of one-fourth unit vertical in 12 units horizontal or less.  Amendment section 1511.3.1 of the International Building Code (IBC)
  • Over 100 sq ft requires a full roof replacement.  Amendment section 1511.3.1 of the International Building Code (IBC) is amended by replacing the first sentence with the following: When a building of any size is subjected to cumulative roof membrane damage of one hundred sq. ft. or greater, the roof shall be replaced in its entirety. Materials and methods of application used for re-covering or replacing an existing roof covering shall comply with the requirements of Chapter 15 of the IBC.

View our commercial amendments here.

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