Roof Exterior Finishing
BY FRANK GEHR ·
FEBRUARY 21, 2014
The exterior roof covering is an important milestone in the house construction process because it brings the job’s progress to the point of being closed in against the weather, or in the terminology of many builders: under roof.
The reasons for reaching this stage as quickly as possible are to protect the already completed construction from extensive damage due to rain, snow, and exposure, and to provide cover and enclosure so that further construction can proceed despite inclement weather.
ROOFING MATERIAL SELECTION
Good reasons exist as to why you should explore the various types of roofing materials available for your house. Indeed, your selection may be influenced by the following:
1. The desire for fire protection. At one time, the combustibility of a house’s roofing material substantially influenced the fire insurance rate charged. Certainly, if you’re miles away from the nearest hydrant, you might want to think twice about wood shakes or shingles.
2. The effect that weather elements have in the area you live in. Certain roofing materials hold up better in certain climates than others will.
3. The life expectancy of the roofing. The price of the labor needed to replace a roof is high. Therefore, it’s important to pick out a roofing material that will last. Don’t make the mistake of selecting a material that will need replacing in less than 10 years. A quality product should last for 20 to 30 years of normal use.
4. The type of house and how the house is positioned on the lot. If large expanses of sloping roof will be visible from the ground, try to choose a material that will contribute to the overall attractiveness of the home. Too often an owner will select expensive siding materials only to downgrade the building’s appearance with a cheap roof. Instead, give careful attention to your roof; use materials that add color, patterns, or textures as desired.
TYPES OF ROOFING
There are basically six types of roofing that cover about 95 percent of the residential roofs: asphalt shingles, fiberglass shingles, wood shingles and shakes, slate shingles, tile shingles, and metal shingles.
By far, asphalt shingles are the most common roofing material in both warm and cold climates. Sometimes they’re also referred to as composition shingles.
These durable shingles, depending on their weight, have a life expectancy of 15 to 30 years. They’re made of a heavy paper known as felt, which is coated with hot liquid asphalt then covered with fine rock granules.
Asphalt shingles are manufactured in many different colors by many different companies. These shingles vary in weight from about 165 pounds per roofing square (a roofing square equals 100 square feet of roof area) to about 340 pounds per square. The heavier shingles are more expensive and have greater textures and longer life. They also take more time and effort to put up, and most roofers will charge a higher rate for applying them.
There are many different kinds of asphalt shingles. The minimum grades weigh about 165 to 235 pounds per square, the medium grades run about 235 to 250 pounds per square, and the top grades weigh above 250 pounds per roofing unit. If a medium- or heavy weight shingle is selected, the house framing will have to be strengthened enough to support the additional weight. The heavier the shingle, the longer the life expectancy. A 300-pound or heavier asphalt shingle should last between 20 to 30 years. Besides being more durable, premium shingles are offered in better colors, colors that do not fade as quickly as the less-expensive models do. The 250- to 340-pound shingles are also less susceptible to wind damage than the lighter shingles because of their heavier, stiffer construction. But even if you live in a severe windstorm or hurricane area and decide to use the heavier asphalt shingles, they should have self-sealing tabs so curling doesn’t result.
Winds can play havoc with asphalt and other shingles. To prevent such damage from occurring, choose only shingles with self-sealing tabs, plus opt for the interlocking types having tabs and slots used to hook each shingle together with the adjacent ones. Consider that light shingles have a tendency to get blown around in heavy wind.
Last, although asphalt shingles are the most popular selection for roofing materials on new construction, they should be used warily on roofs having pitches of less than 3–12. With very low slopes, water seepage can occur under the shingles, especially during times of high winds.
These shingles are similar in appearance to the asphalt variety, but are more resistant to fire. Ask your insurance agent about the possibility of reduced premiums for your homeowner’s policy if you elect to go with fiberglass shingles. As with the asphalt type, the heavier fiberglass shingles are the more durable. Stick with self-sealing or interlocking shingles for protection against wind and curling. Along with the asphalt shingles, fiberglass ones should not be used with a pitch of less than 3–12 unless a properly installed underlayment is laid first.
Fiberglass is a popular choice due to its favorable combination of appearance, price, and durability.
Wood Shakes and Shingles
Wood shakes and shingles are available in several species of wood, with red and white cedars the most popular, followed by cypress and redwood. The term “shingle” means that the wood has been sawn, whereas “shake” indicates that the wood has been split. The shake is usually thicker and has a more rustic appearance.
Supply and labor costs to install wood shakes or shingles can be four to five times that of installing standard asphalt or fiberglass shingles. Homeowners, though, consider wood shakes and shingles a step up in quality and beauty.
“Hand-split” wood shakes and wood shingles have been popular for quite a while in the western United States, but did not reach the Midwest and East in appreciable numbers until the late 1960s. Their increasing popularity is attributed to their textures, deep shadow tones, longevity, weather resistance, and compatibility with Colonial, Modern, and Contemporary house styles. The main drawback to wood shakes and shingles is their flammable nature.
Slate is one of the finest roofing materials available, and one of the most expensive. Certainly it’s one of the most durable shingles you can cover a roof with. But it also can weigh over 3,000 pounds per square (compared with 165 to 350 pounds for asphalt and fiberglass, and 200 to 450 pounds for wood), so a slate roof frame must be designed strong enough to support such an ambitious load. Roofs made of slate shingles can add considerably to the value of a house. Pieces of slate are available in smooth commercial grades or rough quarry runs, in different colors and variegated shades depending on where they come from. They make a beautiful roof and, if cut from a good mineral bed, will last 100 years and more.
It’s unfortunate that slate has been given a bad name from older homes where tree-damaged roofs or roofs undermined by rotting wood supports caused by a lack of proper ventilation result in loose and fallen slate roofing. People have heard horror stories about the high costs of repairing old slate roofs and have unjustly grown overly wary of the slate shingles.
Clay or cement tile shingles are especially popular in the sunbelt areas. They come in all kinds of decorator shapes and colors and textures. They’re simple to install but physically taxing because of their incredible weight—from 800 to 2,600 pounds per square. As with slate shingles, a tile roof needs to be well braced to support its own weight. The tiles are apt to be expensive, especially in areas where they aren’t frequently used (outside of warm-climate locations), but they are durable and have a long life expectancy. They should be used sparingly for flat-sloped roofs, and should generally be applied where the pitch is steep enough for water to run down quickly to avoid water backup and leaking roofs.
Metal roofs, especially ones made of high-quality copper, terne (tin/lead alloy), or aluminum are very durable. At the same time, they’re relatively expensive and can be noisy to the point of aggravation in a rainstorm.
Aluminum shingles are lightweight when compared with other roofing materials (about 40 to 60 pounds per square) and come in many modern colors, shades, and styles, mostly in a shake-type texture. They’ll last a long time if fastened securely with aluminum nails.
If your roof is a complex one, with many dormers, valleys, and varying planes, medium to dark roofing shingles will tend to pull it all together in a nice way.
Check other houses that are already completed in the area or on the street you’re planning to build. If several or many of them are using similar colors, it might be wise for you to select something different so your home doesn’t “blend in” with the rest of them, to break the monotony. Be aware that a light-colored roof reflects heat and is more desirable in areas where air-conditioning is the greatest energy user. Whites and light grays are the most effective shades and when it comes to keeping roofing and attics cool under strong sun rays. Other colors and darker shades convert more of the sun’s rays to heat. In humid locations and places where tree leaves and debris tends to fall on roofs, algae and mildew growth may be a problem. This can be seen as dark areas or streaks on light-colored roofs. If your site has these conditions, select algae-resistant shingles. They have a slight amount of copper in the surface granules. Copper ions retard the growth of algae.
If you live in a warm climate and still decide to select a dark-colored roof, make sure you have sufficient ventilation, insulation, and air cooling to negate the additional warmth absorbed by the shingles.
VENTILATION AND SOFFITS
The roof and attic should be assured of adequate ventilation to allow for the escape of heat and humidity. All ventilation units installed on the roof or in gable ends should be designed to shed rain and snow and not permit any moisture penetration. In addition, the free opening vent areas must be screened to protect against entry by insects, bats, rodents, squirrels, and similar invaders Soffits, the flat painted surfaces under a roof or overhang, should be constructed of prepainted or vinyl-coated sheets that are maintenance free.
They’re available with either a smooth unbroken surface, but also with perforated or slotted surfaces that will encourage ventilation of the attic or roof space. You need a steady pattern of perforated soffits to ensure effective air flows for circulation. Eave soffit vents work by allowing circulation of air through an attic to prevent moisture condensation and its consequential damage to roof structure and insulation. When installing the soffit vents, insulation must not plug the spaces between the rafters just above exterior walls. To prevent this from happening, consider the installation of baffles that will allow air to move past the insulation. Also remember that venting the eaves alone is insufficient. Because warm air circulates upward, roof or gable vents mentioned earlier should be used in addition. There must also be enough free opening areas near the top of the attic to match the collective opening space of the eave soffits.
Because ventilation is so important, a ventilation system may include soffit vents with a combination of roof ridge vents, louver vents, metal dome vents, gable vents, and turbine vents, any combination of which will:
– Allow outside air to flow naturally upward and out of the attic.
– Promote a cooler, drier attic.
– Prevent moisture from becoming trapped within insulation, structural wood, shingles, and roof deck.
– Help prevent rotting, mildew, drywall damage, peeling paint, and warped siding.
– Provide year-round performance for consistent ventilation, lowering the overall energy consumption.
Protecting framing and insulation from rain, snowmelt and moisture is critical. All can cause great amounts of damage and inconvenience. At the very least, uninvited moisture in its many forms can reduce the insulating value (reducing energy efficiency) and damage your ceilings and walls.
Flashing is sheet metal or other material used to prevent the leakage or driving in of rainwater and general moisture infiltration at joints near openings or where different materials or planes meet, such as around chimneys, vents, roof valleys, and stacks. If a material projects horizontally from the surface of the house, as at window and door trims, or at the insulation around a foundation, flashing is required. It’s also needed wherever roofs and walls join, as with a split-level house or a two-story having an attached garage. Flashing is important at the juncture of a dormer’s siding with a main roof, to prevent water from leaking through.
Aluminum is the most common flashing material. It’s produced in long rolls in several widths and is inexpensive, lightweight, and resistant to corrosion except in industrial areas and near the seacoasts. It has one drawback—a shiny appearance that must be painted. And aluminum does not paint well.
Galvanized steel and terne are also employed as flashing; but they must also be painted. Stainless steel, zinc alloy, and even lead have all been used in similar fashion.
An excellent, though expensive, choice for flashing is copper. It seems to last forever and requires almost no maintenance. One advantage it has is that its corners can be soldered for a watertight connection.
Asphalt roofing material is sometimes used for valley flashing on roofs, and plumbing stacks are frequently flashed with special neoprene plastic collars. Vinyl materials in various colors are also on the market. Vinyl is an excellent choice and costs substantially less than copper.
Because the chimney’s exterior can be a frequent source of unwanted water intrusion, a few words on its flashing will perhaps save considerable trouble in the future. For sure, water seepage around the chimney can enter the attic or spaces beneath the roof and ruin the insulation there, do damage to the roof sheathing and framing, and eventually ruin the ceiling below. When there is such a leak, the problem is usually with the chimney flashing. The sheet-metal flashing around the chimney is supposed to keep the intersection between the chimney and roof watertight.
An effective way to seal a chimney is with two flashing layers: flashing and counter-flashing. The first layer is called step flashing, where sections of L-shaped sheet metal are “woven” into the surrounding shingle courses and lapped snug up against the chimney sides.
This flashing is installed in a stair-step fashion starting at the bottom or lower side of the chimney, working toward the upper part, fastened to the roof only, not to the chimney. Next, a small lip of the counter-flashing metal is embedded in the chimney mortar joints, and folded down to cover the tops of the step flashing. Then when the roof moves with winds or from shrinkage, the two pieces of metal flashing move or slide against each other to prevent bending or damage while maintaining protection from water. The corners of this arrangement are especially vulnerable, and an effective installation will leave only a small spot that must be sealed with high-quality caulk.
A cricket also prevents leaves, twigs, and other debris, snow, and ice from collecting behind the chimney—which can cause rain or snow melt to back up beneath the shingles and leak through the roof. If the cricket is large and exposed to view, it should be framed, sheathed, and finished with the same shingles and flashing used on the rest of the roof. Smaller crickets unexposed to view, can be covered with metal, but must still be flashed at all joints with the roof and chimney.
No matter how good a roof’s materials are, the roof won’t be able to do what it’s supposed to do if the installation is shoddy. Here are some things to watch out for:
– The ice and water guard or similar underlayment, which is needed to protect your roof deck from ice damming and windblown rain, should be flexible, self-adhesive, and waterproof.
– A 3-inch galvanized metal drip edge eave should be installed nailed at least 10 inches on center. Roofing ice and water guard or a similar underlayment should go beneath this drip edge.
– All roofing felt should have at least a 6-inch vertical overlap.
– Ice and water guard, a water-resistant underlayment, provides superior roof deck protection and helps prevent damage caused by freeze/thaw cycles, pooled water, wind-driven rains, and normal water flow that occurs around roof valleys, vents, skylights, and chimneys. It should also be installed under shingled roofing eaves to protect against water backup from ice dams and hard rains.
– When anchoring the underlayment and topping materials, power staple guns are the most economical way to go, but they don’t do as sturdy a job as nails do. If your roofing is self-sealing asphalt shingles (shingles with glue underneath each tab that will stick to the shingle below it when baked in the sun), consider that it takes at least one and preferably two hot summers for them to “melt” together to form a strong bond. Up until that time, staples will not provide the holding power of wide-headed nails. High winds are more likely to blow stapled shingles from a roof.
– Roofing nails must meet the shingle manufacturer’s specifications to protect the shingle warranty requirements. At the very least, roofing nails will have very sharp points, flat head diameters, and length long enough for full penetration of the roof sheathing.
– All roofing nails should be nailed flush with shingles.
– When wood shakes and shingles are applied, the manufacturer’s installation instructions must be followed exactly, especially regarding spacing and fastening.
– Because of the high asphalt content in asphalt and fiberglass shingles, it is recommended that temperatures be over 50° Fahrenheit when installed, as they are susceptible to cracking in cold weather.
– Make sure masonry and metal chimneys, skylights, and other obstructions are in place before the roofing begins. Otherwise, the roofers will have to make an extra trip to complete the remaining shingles and flashing, at extra expense.
– All materials should conform to or exceed requirements of the local building code.
Gutters and downspouts work together to collect runoff water from the roof and divert it away from the house so foundation seepage can be prevented. They can divert water away from foundations, plantings, decorative details, basements, siding, sidewalks, driveways, and roof edges, while increasing the width of roof overhangs and helping to prevent snow and ice slides during winter. They’re vital necessities in most cases, but can be troublesome to maintain—tree leaves, seeds, and twigs tend to collect in them and clog the downspouts, squirrels and chipmunks use them as freeways and store winter food in them, plus they can be damaged by ice that collects and hangs from their not-too-strong edges. Here are some important points to consider when planning gutters and downspouts:
4. Metals used in gutters and downspouts vary in thicknesses; 26-gauge galvanized steel is quite strong and common, but 24- gauge is stronger.
5. Cleaning gutters and preventing downspouts from getting clogged can be easily done if you specify removable caps or screens. Then you can just pop off the caps or screens when necessary and flush the small accumulation of silt from the gutters with a garden hose.
6. Gutters should be mounted on the fascia boards (especially when the fascia is not made of or coated with vinyl) so the gutter backs are offset slightly, with an airspace between the fascia so the fascia surface will not deteriorate from lack of ventilation.
7. Large houses with great expanses of roof require that both the gutters and the downspouts have sufficient capacity to handle expected volumes of rainwater. While 5-inch gutters are common, 6-inch gutters may be required to handle roofs having very long spans.
8. A roof plane will collect water during any rainfall, especially if there is wind. The higher the roof ridge, the more true roof area there is and the faster water will race into the gutters. If you plan a steep roof, try to be generous with gutter sizes regardless of the roof area size.
9. Gutter troughs are to be sloped toward downspouts approximately 1 inch for every 12 lineal feet.
10. Your downspouts may be rectangular or round, and plain or corrugated. In cold-climate locations when there is a possibility of standing water freezing in the downspouts, the corrugated type is preferable because it can expand without damage.
11. Downspouts are to be fastened to the wall every 5 to 6 vertical feet.
12. The water discharge can flow from the downspouts into drainpipes that run to storm sewers or to a natural runoff area, perhaps to the street or a storage cistern or rain barrel—as long as it meets building code requirements and does not run into the foundation or form a swamp on adjacent ground.
Depending on the construction of your house, unsupported roof overhangs can protrude from the house a considerable distance. But beyond a certain point they must be supported around the outer edges by columns. Although wood columns, except in very small sizes, are hollow, they still have the strength to bear a substantial load. Trouble is, they’re so intricately made that they cost a fortune.
Factory-painted aluminum columns are the answer. They cost considerably less, are maintenance-free, and because they’re hollow made only of thin metal—they can be installed around a weight-bearing wood or steel post.
POINTS TO PONDER