Roof Coverings
Roof coverings
Roof covering questions are mostly about slope, underlayment, flashing, and fastening. A roof is a system, and the wrong layer order causes leaks even when the shingles are correct.
Concepts
- Manufacturers set minimum slopes. Asphalt shingles typically need a steeper slope for standard installation; below that, special underlayment is required, and very low slopes need a different material.
- Underlayment is required over the roof deck, with laps and fastening suited to the slope and climate.
- Ice-dam protection is installed at eaves where the code requires it, in addition to underlayment.
- Flashing is required at walls, valleys, penetrations, chimneys, and eaves; valley lining and drip edge have their own details.
- Fasteners must be the specified type and length and must penetrate the deck.
- Attic or roof ventilation must be balanced and unobstructed.
- Re-roofing may require removal of existing layers or a new deck, depending on condition and number of layers.
Traps
- Using shingles below the minimum slope.
- Skipping ice barrier because 'underlayment is enough.'
- Nailing above the exposure line or overdriving fasteners.
- Reusing old flashings or covering weep holes.
Worked example A porch roof is framed at 2:12. Standard shingle installation is not permitted at that slope without the special underlayment the manufacturer requires, and some products are not allowed at all. The correct answer checks the product's minimum slope before approving the covering.
Rule of thumb Water flows down and laps go with it: underlayment laps over the lower course, and flashing laps over the roof covering below it.
Chimneys and Fireplaces
Chimneys and fireplaces
These questions test venting, clearance, and height. A chimney must carry smoke out, keep heat away from combustibles, and terminate high enough to draft and to avoid nearby construction.
Concepts
- The 3-2-10 rule: a chimney must extend at least 3 feet above the highest point where it passes through the roof and at least 2 feet higher than any roof surface within 10 feet horizontally.
- Height is measured from the roof surface at the penetration, not from the ground or the ridge.
- Masonry chimneys need a flue liner, proper wall thickness, a cleanout, and a cap or spark arrestor where required.
- Clearance to combustibles must be maintained; the air space around a chimney is not to be filled with insulation or debris.
- Fireplaces need a firebox, damper, and hearth extension sized to the opening; the extension protects the floor in front of and beside the opening.
- Factory-built fireplaces and stoves must be installed per their listing and manufacturer's instructions, including clearance and vent termination.
- Chimneys need foundation support and anchorage; they cannot simply bear on framing.
Traps
- Measuring chimney height from the ridge instead of the roof penetration.
- Filling the clearance space around a chimney.
- Ignoring the hearth extension when the fireplace opening is enlarged.
- Using single-wall vent connectors where a listed chimney is required.
Worked example A chimney exits the roof 6 feet from the ridge, and the ridge is 4 feet higher than the penetration point. The chimney must be at least 3 feet above the roof at that point and at least 2 feet above the ridge, because the ridge lies within 10 feet horizontally.
Rule of thumb Three feet up, two feet clear, ten feet around-and never fill a clearance.