The Most Common Roofing Mistakes

“The repair of an improperly installed roof can require the total replacement of the roof and cost thousands of dollars,” says Mark Graham, associate executive director of technical services for the National Roofing Contractors Association (NRCA.)

Educating yourself will protect you from having to pay for future repairs that could cost you thousands of dollars.

  1. The number one mistake is hiring the wrong contractor.
  2. Plywood or roof sheathing that is not dimensionally stable or strong enough to hold/not properly repaired or replaced.
  3. Not addressing incorrect or lack of attic and roof ventilation.
  4. Improper Valley Flashing Installation.
  5. Shingle Underlayment.
  6. Shingle Installation.
  7. Misuse of Underlayment.
  8. Flashing.
  9. Other Important Considerations.

1. The number one mistake is hiring the wrong contactor

Did you know?
  • that only 1% of roofing licensed roofing contractors are certified?
  • that only 1% of roofing contractors are members of their trade association?
Mistake

Hiring a contractor without checking his qualifications and references

Problem
  • An incompetent, inexperienced or unqualified contractor may be affordable – at first. However, you pay the price when the same job has to be re-done multiple times to fix his mistakes.
  • What most contactors don’t do is take the time to understand the roofing problem or ask the right questions.
  • Roofers need to become more knowledgeable and take a more holistic approach. Roofers need to understand how the whole house is working as a system. Furthermore, they need to understand how attic moisture can lead to roof decay and mold problems.
Proper application and solution
  • Always ask potential contractors to provide you with complete proof of certification
  • Read an accounting of the issues one homeowner had with contracting an unqualified contractor on more than one occasion for the same roof!

2. Plywood or roof sheathing that is not dimensionally stable or strong enough to hold/not properly repaired or replaced.

Mistake
  • Installing shingles over damaged plywood or dry rotted plywood.
  • Installing shingles over dimensional lumber like 1x8 or 1x10 roof boards.
  • Patching holes or in wood sheathing with sheet metal.
Problem
  • Roof Leaks from an uneven roof surface can cause water to travel across the roof instead of down the slope.
  • Structurally not sound and unsafe for snow loads, or the weight of trades person on the roof.
  • Roof wind damage and shingle blow offs.
  • Voids shingle manufactures warranty.
Proper Application and Solution
  • Repair or replace uneven or warped plywood. Use a minimum of ½’ plywood with H-clips when re sheathing an entire roof slope.
  • Install a dimensionally stable wood (like Plywood) over roof boards that are deemed unacceptable to the Asphalt Roofing Manufacture.

3. Not addressing incorrect or lack of attic and roof ventilation.

Did you know?

Did you know that 80 percent of roofs are incorrectly ventilated or lack proper ventilation? Mistakes
  • Mixing different types of roof vents, and venting them into the same attic space will short circuit the system.
  • Venting a bathroom fan into the attic (instead of out through the roof) or installing the wrong exhaust vent.
  • Insulation that is blocking the air flow from the soffits or other obstructions like wood panels under the vented soffit panels.
  • Not using a ventilation calculation or considering the amount of air the vent provides for intake and exhaust.
Problems
  • Not using a ventilation calculation or considering the amount of net free air the vent provides for intake and exhaust.
  • Moisture laden air is known to cause wood rot, damage insulation and cause dangerous mold.
  • Increased attic temperatures are known to increase energy bills and cause ice damming.
  • On a 90 degree the attic temperature day can reach 140 degrees. This causes super-heating of the shingles which can lead to premature roofing shingle failure.
  • Will void almost every manufacture warranty.
Proper Application and Solutions
  • There are many different roof types and challenges when venting a roof. Start by inspecting the attic if possible and familiarizing yourself with the different types of venting systems, determining what will work best.
  • Make sure the ventilation is balanced with 50 percent at the top of the roof and the other 50 at the eaves edge or under the soffit.
  • The desired application is Ridge to Soffit Ventilation. When ridge is long enough to accommodate Ridge Venting make this your first choice.

4. Improper Valley Flashing Installation.

Did you know?

Did you know most roof leaks go unnoticed for a long time before showing up inside your home?

Mistake
  • Incorrect Fastening.
  • The wrong Valley system for the shingles being installed.
  • When metal is being used the Valley Flashing should be installed with a “W” shape metal.
  • Not Cutting the points and sealing each side of the valley.
  • No waterproofing underlayment installed under the valley as a liner.
Problem
  • Flashings and penetration areas are some of the most vulnerable areas of the roof.
  • Water snow or ice can become trapped and travel under the roofing system and leak.
  • When insufficient caulking or fasteners are used when securing roofs, this can cause the valley flashing to buckle, eventually causing a leak.
  • Heavy rainfall flowing down the roof valley will catch the points of the asphalt shingles and run horizontally long the top edge and under the shingles. When the water finds a hole in the underlayment it will run into the attic and then into the house.
  • Roof Leaks will void almost every manufacture warranty.
Proper Application and Solution
  • Most valleys require a closed valley system.
  • Metal Valley Flashing should be installed with a “W” shape metal rather than a v shape.
  • Check with the manufacturer’s application instructions to see what the required or preferred valley is; taking the roofing slope and the shingle type being installed into consideration.
  • Cutting the points. This shingle and all others that end with a point in the valley should be trimmed back from the waterline. Simply cut the shingle at a 45-90 degree angle a minimum of 2 inches back from the point.

5. Shingle Underlayment.

Did you know?

Did you know that the Ontario Building Code does not require underlayment under the entire roof?

Mistake
  • No underlayment under the shingles.
  • No underlayment far enough up from the eaves even to meet building code.
  • No waterproofing underlayment used under the most vulnerable area’s where snow ice and water is most likely to build up.
Problem
  • May void manufacture warranty.
  • Limited roof protection during extreme weather conditions.
  • Roof leaks.
Proper Application and Solution
  • Application of underlayment provides benefits to the roof system at the deck and shingle components. These benefits add to the long-term weatherproofing success of the roof system. Another primary reason for their use is that most building codes require the application of underlayments on steep-slope roofs. Underlayments are also required on lower slope (2:12 to 4:12) shingle applications. It is imperative that contractors familiarize themselves with the codes in their work areas. Installations that are not completed in accordance with codes can be very costly to remedy, particularly in this case where the remedy would include the removal of the steep-slope covering.
  • Underlayment’s serve as a weatherproofing barrier, protecting the deck from moisture prior to shingle application, and they can be applied to dry in the roof in advance of the shingle installation. This is of particular importance on new construction projects where there can be a lengthy lapse between deck installation and shingle application. Moisture absorption in the deck could lead to delamination or warping of the deck surface, providing an unsuitable long-term substrate.
  • In the completed system, the underlayment provides secondary protection against moisture infiltration. It prevents moisture from entering into the interior spaces if the shingles are lifted, displaced or torn. The underlayment also provides added protection to the applied shingles by separating the contact of wood resins and the shingles. Some wood resins can have an adverse effect on the shingles, contributing to deterioration over time. Underlayments also serve in leveling the deck by bridging over any slight irregularities and creating a flat and even surface for the shingle application.

6. Shingle Installation

Mistake #1
  • Leaving out the starter strip.
  • Turning the starter shingle upside down.
Problem:
  • Does not provide proper base for shingle application.
  • First Roof Shingle is not properly sealed, resulting in blow-offs or animal damage.
Proper application:
  • Starter shingles should be applied at the rake and continue along the eaves.
  • The starter course shingles should be cut to match the exposure of the existing first course.
  • Trim approximately 6 inches off the length of the first shingle to offset or stagger the shingles from the first full course.
  • The sealant strip should be at the lower bottom edge to properly 'SEAL' the first course of shingles.
  • Application should be in accordance with the shingle manufacturer’s latest printed specifications.
Mistake #2:
  • Shingles do not overhang at the eaves.
Problem:
  • Could contribute to roof blow-off.
  • Leaks between the eavestroughs or gutters rotting the fascia.
Proper application:
  • The shingles should overhang the eaves and the rakes by a minimum of 1/2 inch. There should be a 1/16-inch spacing between the shingles.
  • Nailing should be completed 3 inches above the eaves using the proper amount of nails for the geographic wind zone.
Mistake #3:
  • Improper shingle alignment.
Problem:
  • Not aesthetically pleasing.
Proper application:
  • Shingle alignment — both vertical and horizontal — is required.
  • The best way to ensure that the shingles are horizontally aligned in new applications is by the use of a chalk line.
  • On recover applications, the new shingles should be aligned and butted with the existing shingles.
  • Set horizontal chalk lines every 10 inches from the bottom of the first course up the ridge.
  • Set vertical chalk lines every 36 inches from the roof ridge to an end of every shingle along the first course.
Mistake #4:
  • Improper shingle nailing.
Problem:
  • Potential for roof blow-off.
Proper application:
  • Install the proper amount of shingles required by the manufacturer in the specific geographic wind zone.
  • Most three-tab shingles require four nails in typical applications and six nails in high-velocity wind zones.
  • The placement of the nails is as important as the number of nails. Place nails in the manufacturer’s required placement areas. Most dimensional shingle manufacturers now provide shingle placement zones.
  • Nails should be driven straight into the deck.
  • Nailing from an angle should be avoided, and nails should penetrate through the deck a minimum of 3/4 of an inch. Standard roofing nails have barbed shanks and are typically 11-gauge or 12-gauge nails with heads from 3/8 to 7/16 of an inch in diameter.
Mistake #5:
  • Use of asphalt-based cements for shingle repairs.
Problem:
  • Incompatible materials will contribute to further shingle delaminating.
Proper application:
  • Asphalt-based cements should only be applied at the underside of shingles.
  • Deteriorated shingles that show evidence of curling, cracking, splitting or openings should be replaced with new shingles.

7. Misuse of Underlayment.

Mistake:
  • No underlayment application.
Problem:
  • Roof leaks.
Proper application:
  • Application of underlayment provides benefits to the roof system at the deck and shingle components. These benefits add to the long-term weatherproofing success of the roof system.
  • Another primary reason for their use is that most building codes require the application of underlayments on steep-slope roofs. Underlayment’s are also required on lower slope (2:12 to 4:12) shingle applications.
  • It is imperative that contractors familiarize themselves with the codes in their work areas. Installations that are not completed in accordance with codes can be very costly to remedy, particularly in this case where the remedy would include the removal of the steep-slope covering.
  • Underlayment’s serve as a weatherproofing barrier, protecting the deck from moisture prior to shingle application, and they can be applied to dry in the roof in advance of the shingle installation. This is of particular importance on new construction projects where there can be a lengthy lapse between deck installation and shingle application. Moisture absorption in the deck could lead to delamination or warping of the deck surface, providing an unsuitable long-term substrate.
  • In the completed system, the underlayment provides secondary protection against moisture infiltration. It prevents moisture from entering into the interior spaces if the shingles are lifted, displaced or torn.
  • The underlayment also provides added protection to the applied shingles by separating the contact of wood resins and the shingles. Some wood resins can have an adverse effect on the shingles, contributing to deterioration over time. Underlayments also serve in leveling the deck by bridging over any slight irregularities and creating a flat and even surface for the shingle application.

8. Flashing

Mistake:
  • Improper termination of penetrations.
Problem:
  • Roof leaks.
Proper application:
  • Most residential roofs have soil stacks that require proper terminations. Apply shingles up to the vent pipe and cut an opening in the shingle that is set over the pipe. Set the shingle in an approved asphalt cement.
  • Set the vent flange over the pipe — flat on the roof — in asphalt cement that has been evenly applied over the bottom shingle.
  • Resume shingle application and set the successive courses around the pipe. Upper and side shingles that overlap the vent should be set in asphalt cement.
  • The asphalt cement should be applied in an even application in moderation.
  • Do not apply asphalt-based cement over the top of the shingle. Excessive asphalt cement application may cause blistering.

9. Other Important Considerations

  • Avoid warranty pitfalls by ensuring that all materials and products are installed according to the manufacturer’s exact specifications.
  • Avoid using the wrong materials on the roof slope. Different materials demand different specifications

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