asphalt shingles

Roof Replacement/Installation

Building permits are required for all roofing projects. Submit your application to the Inspections Department at City Hall. Building permits for roofing are generally issued at the time of application.

All contractors engaged in roofing work must have a state contractors license and show proof of the license to obtain a permit. Specific questions regarding contractor licenses should be directed to the Minnesota Department of Commerce.

Code requirements and roofing information

The State of Minnesota has updated the building code effective January 24, 2015. We are in the process of reviewing our website to make sure everything is up to code, but you should always review the State of MN Building Code before beginning any project.

The scope of this page is limited to the installation of four types of roofing materials: asphalt shingles, mineral-surfaced roll roofing, wood shingles, and wood shakes. For information on other roof coverings such as metal paneled roofs, metal shingles, clay and concrete tile, slate shingles, built-up roofs, modified bitumen roofing, single ply membrane roofs, sprayed polyurethane foam roofing, or liquid applied coatings, please contact the Inspections Department.

General Information

All roof covering materials must be delivered in packages bearing the manufacturers identifying marks and approved testing agency labels when required.

All asphalt shingles must be either self-sealing or interlocking.

The code requires that roof decks be solidly sheathed for asphalt shingles or mineral-surfaced roll roofing. Solid sheathing may be plywood, OSB, or 1-inch nominal boards. When using 1-inch nominal boards, the shingle manufacturers instructions should be reviewed to determine if the manufacturer places any limitations on the use of their shingles on a board sheathed roof.

Wood shingles and shakes may be applied over solid or spaced sheathing. When using spaced sheathing, sheathing boards must be not less than 1x4's and must be spaced on centers equal to the weather exposure to coincide with the placement of fasteners. If the center-to-center spacing of 1x4's is 10 inches or more, additional 1x4's must be installed between the sheathing boards. The portion of the roof receiving ice protection must be solidly sheathed.

Flashing is required at all wall and roof intersections, wherever there is a change in roof slope or direction, and around roof openings. When flashing is metal, it must be corrosion resistant metal with a thickness of not less than 0.019 inch (No. 26 galvanized sheet). Kickout flashing/diverters must be installed where the lower portion of a sloped roof stops within the plane of an intersecting wall cladding in order to divert water from the assembly.

Ice & Water Barriers

Ice and water barrier location diagram

An ice and water barrier is required on all roofs.* The barrier may be at least two layers of underlayment cemented together or a self-adhering polymer modified bitumen sheet. There are several manufacturers who make materials specifically for this requirement that are marketed under differing trade names. The ice and water barrier must extend from the edge of the eaves to a point 24 inches inside the exterior wall line of the building.

*Exception: Detached accessory structures without a conditioned floor area.

Roof Edging

Roof edging is not required by the code. There may be some benefit from the use of roof edging as it will help to project runoff further from the edge of the roof and prevent water from backing up under shingles. Application of roof edging should be in accordance with the shingle manufacturers written instructions. Most manufacturers specify the edging to be installed directly to the deck along the eaves and over the underlayment along the rakes.


Asphalt Shingles

Fasteners for asphalt shingles must be galvanized steel, stainless steel, aluminum, or copper roofing nails, minimum 12 gauge shank with a minimum 3/8" diameter head. They must be long enough to penetrate through the roofing materials and a minimum of ¾" into roof sheathing. When roof sheathing is less than ¾" thick, the fastener must penetrate through the sheathing.

Mineral-Surfaced Roll Roofing

Roll roofing must be installed in accordance with the manufacturer's installation instructions.

Wood Shingles

Fasteners for wood shingles must be corrosion-resistant with a minimum penetration of ½" into the sheathing. For sheathing less than ½" thickness, the fastener must extend through the sheathing. A minimum of two fasteners per shingle are required.

Wood Shakes

Fasteners for wood shakes must be corrosion-resistant with a minimum penetration of ½" into the sheathing. For sheathing less than ½" thickness, the fastener must extend through the sheathing. A minimum of two fasteners per shake are required.


The installation of a new roof is an excellent time to install additional ventilation in your attic. Improper ventilation can result in either excessive heat or moisture trapped in the attic. Either of these conditions can spell problems for your home.

Excessive heat in the attic can warm the interior of the home compromising comfort and driving up cooling costs and reduce the life or your roof and in some cases void shingle manufacturers warranties.

Excessive moisture can reduce the effectiveness of insulation and deteriorate framing members.

Attics should be provided with ventilation as follows:

  • For attics without ceiling vapor barriers, 1 square foot of net free ventilating area should be provided for each 150 square feet of attic area.
  • For attics with vapor barriers or without ceiling vapor barriers and having at least 50% but not more than 80% of the ventilating area provided by ventilators located in the upper portion of the space to be ventilated and at least 3 feet above the eave vents and the balance of the ventilation provided in the eave vents, ventilation may be 1 square foot of net free ventilating area for each 300 square feet of attic area.

Asphalt Shingles

Asphalt shingles may only be used on roof slopes of two units vertical in 12 units horizontal (2:12) or greater. For roof slopes from 2:12 to 4:12, double underlayment is required.

Underlayment must conform with ASTM D 226 Type I, ASTM D 4869 Type I, or ASTM 6757. For roof slopes of less than 4:12, two layers of underlayment are required and must be applied in the following manner. A 19-inch strip of underlayment is applied parallel with and starting at the eaves. Also starting at the eaves, a 36-inch wide sheet is applied over the first. Each successive course is lapped 19 inches.

For slopes of 4:12 and greater, underlayment must be applied shingle fashion. Laps must be a minimum of 2-inches. End laps must be offset by at least 6 feet.

For normal application, strip shingles must be fastened with a minimum of four nails. For interlocking shingles, two nails are required.

Valleys must be lined in accordance with the shingle manufacturers written instructions. In addition, valleys may be of any of the following:

  • For open valleys lined with metal, the valley lining must be at least 24 inches wide and of galvanized steel of at least 26 gage or other approved materials.
  • For open valleys, two plies of roll roofing may be permitted. The bottom layer must be at least 18 inches wide and the top layer at least 36 inches wide.
  • For closed valleys (valleys covered with shingles), valley lining of one ply of smooth roll roofing complying with ASTM D 6380 Class S Type III, Class M Type II, or ASTM D 3909. and at least 36 inches wide or one of the two methods previously listed may be used.

Crickets or saddles are required on the ridge side of any chimney or penetration greater than 30 inches wide. Cricket or saddle coverings must be of sheet metal or of the same material as the roof covering.

Flashing against a vertical sidewall must be by the step-flashing method.

Flashing against vertical front walls, soil stacks, vent pipes, and chimney flashing must be in accordance with the asphalt shingle manufacturer's printed instructions.

Mineral Surface Roll Roofing

Mineral surfaced roll roofing may only be applied on roofs with a slope of 1:12 or greater. Mineral surface roll roofing must conform to ASTM D 3909 or ASTM D 6380, Class M. Mineral surface roll roofing must be installed in accordance with the manufacturers installation instructions. Underlayment must comply with ASTM D 226 Type I or ASTM 4869 Type I or II. The ice barrier requirements also apply.

Wood Shingles

Wood shingles must be installed on slopes that are at least 3:12 or greater. They must be made of a naturally durable wood of grades 1, 2, or 3 approved by the Cedar Shake and Shingle Bureau. A label of an approved grading or inspection bureau or agency must identify each bundle of shingles.

Wood shingles must be installed in accordance with the manufacturers instructions and the following. Wood shingles must be laid with a side lap of not less than 1 ½" between joints in courses and no two joints in any three adjacent courses shall be in direct alignment. Spacing between shingles may not be less than ¼" nor more than 3/8". Weather exposure may not exceed what is specified in the accompanying table.

Wood shingles must be attached to the roof with two fasteners per shingle. Fasteners should be not more than ¾" from the edge of the shingle and not more than 1" above the exposure line.

Weather Exposure and Roof Slope

Roofing Material Length (inches) Grade Exposure (inches)
3:12 pitch to < 4:12 4:12 pitch or steeper
Shingles of naturally durable wood 16 No. 1 3 ¾ 5
No. 2 3 ½ 4
No. 3 3 3 ½
18 No. 1 4 ¼ 5 ½
No. 2 4 4 ½
No. 3 3 ½ 4
24 No. 1 5 ¾ 7 ½
No. 2 5 ½ 6 ½
No. 3 5 5 ½

Wood Shakes

Wood shakes must be installed on roof slopes of 3:12 or greater and must be installed in accordance with the manufacturers installation instructions and the code. Wood shakes must be laid with a side lap of not less than 1½ inches between joints in adjacent courses. Spacing between shakes in the same course must be between 1/8 inch and 5/8 inch for shakes and taper sawn shakes of naturally durable wood and ¼ inch and 3/8 inch for preservative taper sawn shakes. Fasteners for wood shakes must be corrosion resistant. Shakes must be attached with two fasteners per shake. Fasteners must be positioned not more than 1 inch from each edge and not more than 2 inches above the exposure line.

The starter course at the eaves must be doubled and the bottom layer may be 15-inch, 18-inch, or 24-inch wood shakes or shingles. Fifteen-inch or 18-inch wood shakes may be used for the final course at the ridge. Shakes must be interlaid with 18-inch-wide strips of No. 30 felt shingled between each course in such a manner that no felt is exposed to the weather by positioning the lower edge of each felt strip above the butt end of the shake it covers a distance equal to twice the weather exposure. Underlayment must comply with ASTM D 226, Type I.

Wood Shakes Weather Exposure & Roof Slope

Roofing Material Length (inches) Grade Exposure (inches)
4:12 pitch or steeper

Shakes of naturally durable wood
18 No. 1 7 ½
24 No. 1 10
Preservative-treated taper sawn shakes of naturally durable wood
18 No. 1 7 ½
24 No. 1 10
18 No. 2 5 ½
24 No. 2 7 ½
Taper-sawn shakes of naturally durable southern yellow pine 18 No. 1 7 ½
24 No. 1 10
18 No. 2 5 ½
24 No. 2 7 ½

Gutters & Drainage

Gutters are not required by the code. Gutters may be useful in directing water away from buildings reducing erosion, settlement, and wet basements. Lead-outs on downspouts should extend far enough from the building to effect positive drainage.

Removal of Existing Roofing

No new roof coverings may be applied without removing the existing roof.

Disposal of Debris

The removal of existing roofing materials often results in debris moving about the neighborhood on windy days. Shingle wrappers and other construction debris also end up in neighbors' yards. As you install a new roof on your dwelling, regularly police your yard and adjoining areas for debris that may blow around.

Dumpsters must be kept on private property unless a dumpster permit is obtained from the Public Works Department to place them on the street. Proper positioning of warning signs and markers are important to insure the safety of motorists.


Architectural Shingles: (See Laminated Shingles)

Asphalt: A bituminous waterproofing agent applied to roofing materials during manufacture.

Deck: The structural surface to which the roofing or waterproofing system (including insulation) is applied.

Felt: A flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat. Felts are manufactured principally from vegetable fibers (organic felts), glass fibers (glass fiber felts), or polyester fibers (polyester felts); other fibers may be present in each type.

Fiberglass Mat: An asphalt roofing base material manufactured from glass fibers.

Flashing: Pieces of metal or roll roofing used to prevent seepage of water into a building around any intersection or projection in a roof, such as vent pipes, chimneys, adjoining walls, dormers and valleys.

Granules: Ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.

Hip: The inclined external angle formed by the intersection of two sloping roof planes. Runs from the ridge to the eaves.

Incline: The slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal unit of run. Also referred to as slope.

Interlocking Shingles: Individual shingles that fasten together mechanically and provide greater wind resistance.

Laminated Shingles: These shingles have more than one layer of tabs to create extra thickness. They are often referred to as three-dimensional or architectural shingles because they create visual depth on a roof and impart a custom look.

Membrane: A roof covering or waterproofing layer whose primary function is the exclusion of water.

Organic Felt: An asphalt roofing base material manufactured from cellulose fibers.

Re-covering: The process of covering an existing roofing system with a new roofing system.

Re-roofing: The practice of removing an existing roofing system and replacing it with a new roofing system.

Roll Roofing: Asphalt roofing products manufactured in roll form, either smooth- or mineral-surfaced.

Saturated Felt: An asphalt-impregnated felt used as an underlayment between the deck and the roofing material.

Strip Shingles: Manufactured in both standard and metric dimensions, these asphalt shingles are approximately three times as long as they are wide, and are distinguished by the number of cutouts or tabs that they have. The most common are three tab.

Square: A unit of roof measure covering 100 square feet.

Three-Dimensional Shingles: (See Laminated Shingles)

Underlayment: Asphalt saturated felt used beneath roofing to provide additional protection for the deck.

Valley: The internal angle formed by the intersection of two sloping roof planes.


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Two inspections are generally required for typical roof installations. You will be given an inspection record card with your permit that includes the type of inspections you need to call for and a phone number.

  • The first inspection is the roof deck and ice and water barrier inspection. Your inspector will determine that the condition and type of deck is appropriate for the roofing material you are using and that the ice and water barrier is being installed.
  • The second inspection is a final inspection when all work is complete.