The Truth About Roof Leaks
The truth is that while many roof leaks are easy to repair, their sources are often difficult to find. Water dripping from a ceiling may not be from a leak directly above, but from a leak many feet away that runs down the rafter or across the ceiling before coming in. It could also be caused by the condensation of moisture rising from a bathroom, collecting on the roof sheathing and then dripping through to the ceiling below. It might just as easily be from a plumbing leak situated in a wall or ceiling and incorrectly attributed to a roof leak.
The best way to start tracking a roof leak is to become familiar with the many possible causes. Then, by carefully examining the roof and using the process of elimination, you should be able to locate its source.
The most frequent causes of roof leaks are:
- Improper flashing, sealing or worn-through flashing around projections through the roof such as plumbing stacks (vent pipes), chimneys, skylights antennas, dormers, etc.
- Missing, broken or pierced shingles, caused by stones, hail, broken branches or walking on the roof.
- Tears in the roof valleys, created by expanding and contracting metal or by someone walking in the valley. Also debris can build up in the valley and block run-off.
- Exposed nails, nails in the wrong places or nails not set flush with the underlying shingles.
- Wind driven rain: through an attic window or louver, into the chimney brick or mortar or under shingles, through the siding, and behind the step flashing where a lower roof joins the vertical side of the main house.
- Ice dams, which prevent proper run-off and force water to back up under the shingles.
- Improperly installed roof or roofing type which is incorrect for the slope involved.
- Cracked and blistering of roof mastic on rolled asphalt or on build-up roofing.
- Ponds of water, created when flat or low sloped roofs begin to sag. Clogged roof drains.
- Cracked or disintegrating chimney caps.
Roof Type Covering
* Not recommended on slopes less than 3/12
** Approximate weight per 100 square foot of coverage
*** Replacement costs vary with degree of difficulty, disposal fees of removed materials, and the amount of preparation of roof deck.
Material
Life expectancy
General Remarks
Asphalt Shingles*
15-20 years in the North
12-15 years in the South
Approximate weight 235#.** Used from the 1920s to present. Asphalt shingles are used on more than 80 percent of all homes today. Usually a 3-tab design with self-sealing strips to protect against blow-off. Replacement costs are about $2.00 to $3.00 per square foot.***
Asphalt Multi-Thickness Shingles*
20-25 years in the North
15-18 years in the South
Approximate weight is 245#-400#.**. Multi-thickness shingles are of heavier weight, are more expensive, have somewhat longer life expectancies, and are usually for architectural effect. Replacement costs are about $2.50 to $4.00 per square foot.***
Asphalt/Fiberglass Shingles*
8-12 years in the North
6-10 years in the South
Approximate weight is 215#.**. Used from the mid 1970s to present. In general usage today as replacement for asphalt shingles. The mat is of a fiberglass material that is impregnated with asphalt and covered with fine granules in various colors. $2.00 to $3.00 per square foot for replacement.***
Asphalt Roll
15-20 years in the North
12-15 years in the South
Approximate weight 90#.** Used from the 1930s to present. Usually used on low-sloped roofs. Each roll covers one square. May be single coverage type (called Selvage) with granules over half the roll. Replacement costs are $2.00 to $3.00 per square foot.***
Built-up Roofing
15-20 years in the North
8-12 years in the South
Approximate weight 400#-650#.** Used on low slope or flat roofs. Usually applied in a minimum of three altering layers of hot tar and 15# felt paper. Covered with hot tar and gravel, slag, or something painted with aluminum coating to repel ultra-violet sun rays. Replacement costs are $5.00 to $7.00 per square foot.***
Wood Shingles/Shakes
15-30 years in the North
10-15 years in the South
Approximate weight is 200#-300#.** Used from 1800s to present. May be redwood, cypress or cedar, with cedar being the most common, and No. 1 handsplit being the best. Requires periodic maintenance and treatment with a preservative. The recommended minimum slope for application is 4/12. Best if installed with hot dipped galvanized or copper nails. Staples are used in cheaper construction. $6.00 to $9.00 per square foot for replacement.***
Clay or Concrete Tile
20-25 years in the North
10-15 years in the South
Approximate weight 900#-1600#.** Used from 1800’s to present. Manufactured in flat, half barrel (mission), or “S” shape (Spanish). May be nailed down or set in mortar with all mortared, may last 50 years or more. Other types are not waterproof, and depend on sub surface roofing (usually 90# rolled) for watertightness. $6.00 to $8.00 per square foot *** for replacement.
Slate Shingles
30-100 years
Approximate weight is 800#-1800#.** Used from the 1800s to present. Buckingham and Vermont slates are the longest lasting. Bangor or Pennsylvania have a shorter life expectancy. Very expensive, heavy, brittle material. Should be installed with hot dipped galvanized or copper nails. Do not walk on surface. $16.00 to $24.00 per square foot *** for replacement.
Asbestos-Cement Shingles
30-60 years
Approximate weight is 300#-600#.** Used from the 1940s to the late 1960s. Durable and brittle. Repairs may not be feasible. Replacement material is not readily available. This material is currently considered hazardous waste.***
Metal Roofing
15-40 years
Approximate weight is 150#-250#.** May be standing, flat or batten seam type and either galvanized, painted steel or copper. Aluminum is less common but is growing in popularity. Metal roofing can be found as individual shingles or sheets stamped to resemble individual shingles. Can be used successfully on low pitches, and may be used on flat roofs as flat metal soldered joints. Steel must be kept painted or coated to prevent rust. If coated with tar, expect early replacement, as the real condition of the metal cannot be detected. $8.00 to $12.00 per square foot *** for replacement.
Single Ply Membranes
15-25 years
Approximate weight 150#-300#.** May be sealed down with adhesive and/or heat, or laid loose and covered with stones for ballast. Replacement costs $4.00 to $6.00 per square foot.***
Exterior Surfaces & Sidings
Aluminum Siding
Aluminum siding has been commonly used since the 1950s. It may be installed horizontally or vertically, and may be produced in smooth or textured wood grain finishes. It is durable, especially in salt air climates. Aluminum siding is vulnerable to dents and can be damaged in hail storms. Most manufacturers claim that the siding never required paining, but siding more than 20 years old may require repainting.
Vinyl Siding
Vinyl siding came into existence in the 1970s. They may be installed vertically or horizontally, in smooth or textured finishes. These products have the color all the way through the material and may never require paining. Vinyl siding tends to be very brittle in cold weather and may crack or break if struck.
Steel Siding
Steel siding is durable and long-lasting if properly maintained. Scratches and corrosion should be repaired. This material should be grounded at each corner of the building.
Wood Siding
Wood siding may be in the form of individual boards, plywood panels, hardboard or shingles. Wood is available in many varieties and is generally reasonably priced, which has led to its widespread usage. If properly maintained, wood siding will generally last the lifetime of the building.
Good building practices require that wood products have a minimum of 6″ clearance from the soil.
Most wood products require regular maintenance in the form of paint, stain or varnish. Some woods, such as redwood and cedar, have a natural resistance to decay and rot while others may be pressure treated to resist rot and insects.
Plywood
Some of the early technology “Texture 1-11” type plywood siding had a tendency to delaminate. This may be most obvious on the exterior face where signs of peeling may be evident. These panels were typically made in 4′ x 8′ or 4′ x 10′ sheets. When this condition is present, the siding may have to be replaced. However, generally the structural integrity of the plywood is not affected, but the siding is cosmetically damaged.
Hard Board
Hard board is a popular siding material made of wood fibers that are combined under pressure and heat. They are frequently treated with moisture and fire retardant chemicals. These products seem to be especially vulnerable to rot and decay and must be kept sealed and painted.
Stone
Stone is occasionally used as a structural component of the building, but more commonly used as a veneer. Look for signs of moisture penetration or deterioration in the mortar joints. Again (like brick), many man-made products are on the market and have been used, so take a careful look.
Stucco
Stucco can be applied to any clear masonry or concrete surface, and is used over metal lath in frame construction. Stucco is portland cement plaster that is very durable and withstands repeated freeze/thaw cycles.
Stucco applied over metal lath in frame construction will tend to crack and telegraph the joints in plywood sheathing, due to the normal expansion and construction of the wood. These cracks should be sealed to prevent moisture penetration and damage to the wood framing members and the interior wall surface.
Even hairline cracks in stucco can allow moisture to penetrate to the interior wall surface and cause damage.
Asbestos Cement Siding
Asbestos siding was used extensively from the late 1940s to the mid 1970s. It is durable and long-lasting, but brittle and therefore broken easily. Replacement material is scarce and hard to find. When remodeling is undertaken to the building, this product must be removed according to the Environmental Protection Agency (EPA) standards. The cost can be significant. Removal and disposal should be done by qualified contractors.
Brick
Brick has long been the most noble of siding materials. Prior to the 1930s or so, many buildings were constructed of solid brick. Most construction today uses brick as a veneer.
Look for any signs of crumbling or weakening mortar joints. Old mortar joints should be properly cleaned out and repointed, to seal out the elements and maintain the structural integrity of the brick. Look for signs of efflorescence, moisture penetration or spalling bricks, and repair as necessary. Spalling bricks usually occur due to moisture penetration in the brick or freezing weather. The source of any moisture penetration should be located.
In some regions of the country, a colored stucco coat of material is applied over masonry or frame construction and mortar type joints are struck in the material. The result is a simulated brick that is difficult to distinguish from real brick.
Another product is manufactured wherein ½ inch thick bricks are mounted on an asphalt impregnated fiber sheathing and nailed in place. The joints are then grouted and the effect is a brick sided building.
