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How to Build a Roof

Did you ever wonder how to build a roof? Well, there’s more to it than meets the eye, especially when it is built in compliance with updated building codes that promote energy efficiency. The asphalt shingles you see on the majority of residential roofs in the DMV are only the outermost layer of a precisely engineered roof system consisting of carefully integrated components that meet vital needs.

As Owens Corning puts it, the best roof simultaneously seals, defends and protects. First, it is a waterproof barrier that keeps moisture out. Second, it defends against nature’s fury, including high winds, heavy rain, deep snow, hail and tropical storms. Third, it breathes to facilitate proper attic ventilation.

Before it is possible to build a roof, you need architectural plans that specify a roof system conforming to local codes. Also, construction cannot begin until the permitting process is complete.

Roof Framing

The roof is then framed-in with rafters and joists or trusses. Joists are the horizontal members of a roof’s frame, while the rafters are the angled members that give the roof its pitch. Joists are typically supported in the middle by an interior load-bearing wall. Braces or webs add structural strength. Modern residential roof framing may use either traditional rafters and joists or trusses.

Pre-manufactured trusses were first used on smaller structures like garages and sheds. The top chord of a truss is the pitched segment that supports the roof deck. The bottom chord runs horizontally between supports, often exterior load-bearing walls. These primary sections of the truss are reinforced with angled braces that run between the top and bottom chords.

Trusses are delivered to the construction site where they are usually hoisted into position by a crane and secured by the construction crew.

Carpenters frame in the roof by securing the joists, rafters and trusses to the wall studs and to the ridge board that runs along the very top of the roof. Architectural designs usually call for spacing that is either 16 or 24-in on-center (o.c.).


Next, a layer of code-compliant plywood or oriented strand board (OSB) is nailed to the roof framing. The thickness of the sheathing is determined by building codes as well as the roof’s design (including rafter spacing) and expected loads. For example, a slate roof may require thicker sheathing than a traditional asphalt shingle roof.

When rafters are 24 inches apart, construction-grade CDX plywood is often 15/32-in thick. When OSB sheathing is used, it is often 7/16-in thick. Four-foot-wide sheathing covers two 24-in o.c. spaces, or three 16-in o.c. spaces between rafters.


Traditional felt is also called builder’s paper or tar paper. Code-compliant, asphalt-saturated 15-lb felt underlayment performs essential functions. There are advanced underlayment options that can improve moisture resistance, like durable synthetic underlayments like Deck Defense and ProArmor from Owens Corning.

A good quality underlayment performs several key functions by:

  • Adding another layer of moisture protection
  • Preventing wood resins in the sheathing from reaching the shingles
  • Improving a roof’s fire rating

Ice and water barrier

A self-adhesive waterproof underlayment that may be installed on the most vulnerable areas of the roof, including valleys, areas around roof protrusions and the lower roof edge near the gutter. Sometimes, an ice and water barrier is installed across a lower-pitched roof to provide maximum protection.

Water migration is an ongoing challenge in places like the Mid-Atlantic, where moisture from wind-driven rain, ice and heavy snow can work its way into your home. Waterproof ice and water barriers help ensure that water will successfully drain off the roof. For example, WeatherLock Self-Sealing Ice & Water Barrier from Owens Corning minimizes water migration under asphalt shingle and other roofs. Factory-applied adhesives stick to the roof deck to maintain a watertight seal around nails and other fasteners.


Waterproofing roof protrusions like vents and chimneys, and architectural detail like dormers, is vital to the successful long-term performance of the roof. Flashing in valleys speeds the drainage of water off the roof. To ensure that water won’t work its way under the shingles, a self-sticking underlayment is typically extended several inches up vertical surfaces before the flashing is installed around chimneys, dormers and vents.

Asphalt Shingles

When the bundles of shingles arrive at a residence, they are mechanically hoisted onto the roof. The bundles are carefully distributed across the roof to minimize movement during installation.

A row of starter shingles is typically applied so they extend slightly past the roof drip edge. Installers work their way up the roof, installing one row of shingles after another.

There are a wide variety of heavy-duty architectural shingles to choose from. For example, Owens Corning offers Duration Shingles and Duration Designer Shingles.

TruDefinition Duration Shingles – These architectural shingles are available in a wide range of popular colors. Duration shingles combine pleasing curb appeal and dimensionality in a rugged, durable design that incorporates Owens Corning’s patented SureNail system.

Duration Designer Shingles – These architectural shingles combine enhanced curb appeal with the superb performance of patented SureNail technology. The highly textured look adds an appealing three-dimensional look to your roof. Select from one of the deep, rich colors that will readily coordinate with your exterior architecture, paint and trim.

Asphalt shingles with highly reflective granules keep home interiors cooler by sending more solar energy back into the atmosphere. Products like Energy Star-rated Duration® Premium COOL Shingles from Owens Corning can reduce home cooling costs. They can also reduce long-term, heat-related wear-and-tear on roof components.

Streaking is the bane of traditional asphalt shingle roofs. It is typically caused by the growth of blue-green algae that too often leads to distracting black marks on your roof. StreakGuard from Owens Corning uses triple-layered granules to attack the problem. A middle layer of copper prevents algae formation while an outer ceramic layer offers excellent protection from the elements.

Shingle adhesives

Factory-applied sealants bond each course of shingles to the next. When an installation is performed to the manufacturer’s specifications, the shingles are bound together into a unified system. Tru-Bond sealant from Owens Corning is a proprietary formulation that ensures a firm, long-lasting seal that handles the tough weather conditions we face in the Mid-Atlantic region.

Since adhesives that bond shingles to one another are somewhat temperature sensitive, installation should occur when ambient temperatures are well above freezing. Warmer temperatures and the sun’s UV rays both help activate the sealants. Also, in very windy conditions, wind uplift may weaken the bond as the sealant sets. It is also ideal to watch the weather forecast so the shingles are not immediately subjected to heavy rain or snow.

Advanced sealants and patented SureNail technology from Owens Corning ensure excellent wind-resistance and a tight seal around the nails.  In fact, SureNail technology allows Owens Corning to offer a 130 mph wind guarantee in its warranty. Lab tests demonstrate the product’s superior wind resistance.

Once all the shingle courses are in place, roofers “cap the ridge” by positioning ridge caps along the very top of the roof. These specially shaped components often feature a double thickness of shingles for strength and durability. It is ideal to install them so the overlaps face away from prevailing winds. Similarly, specially curved shingles finish off the roof hips.

Even with SureNail technology, care and professionalism is required to drive nails in accordance with the manufacturer’s specifications. Proper nailing is essential to maximize performance. Improper nailing is a major cause of roof leaks, so the need for qualified, experienced installers cannot be overstated.


The proper inflow and outflow of air in the space beneath the roof deck accomplishes a number of things. Proper ventilation:

  • Reduces attic temperatures, reducing the load on your cooling system
  • Allows attic insulation to dry out, maintaining R-values, reducing the potential for mold buildup
  • Increases the longevity of your roof by reducing long-term deterioration caused by excess heat and condensation
  • Makes your roof complaint with modern building codes that require ventilation

There are a variety of products that promote proper ventilation, such as ridge vents, soffit vents and back vents.

Since long, narrow ridge vents run the entire length of the roof, they provide for uniform cooling throughout the attic. They combine with soffit vents to promote proper airflow through the enclosed space beneath the roof deck. Ridge and soffit vents lack moving parts, so they are not dependent on weather conditions for proper performance.

Back vents also have no moving parts. They are simply a weather-resistant opening through which hot air and moisture escape. Since hot air rises, they are frequently positioned near the roof ridge. There are more detailed options as well. Wind turbines feature spinning blades that draw air and moisture up and out of the attic. Electric power attic vents include thermostats programmed to activate the unit when air temperatures reach a certain level. These vents are either hard-wired or solar-powered.

Effective roof venting requires proper sealing of gaps and cracks where conditioned air in the living space could otherwise escape.


Once a complete roof system is in place, homeowners want the peace of mind that comes with superior warranty coverage. Manufacturers typically offer the best warranties to homeowners who use roofing contractors specially certified to install their products. For example, the highest certification level available from Owens Corning is Platinum Preferred. Such contractors are authorized to offer the best manufacturer warranties available.

A Total Roof System

When a modern roof is built right, it will be highly water-resistant and very durable. With the right air/moisture barrier applied between the sheathing and the shingles, a modern roof ensures the comfort of the home’s occupants.

The proper use of venting and insulation enhance the performance of a complete roof system. Temperatures are modified in a way that can reduce cooling costs. Attic moisture evaporates so it does not condense in the roofing itself or in the insulation. This maintains R-values and extends the life of the shingles and other roof components.

Owens Corning carefully integrates a variety of roofing components into its Total Protection System. The end result is a state-of-the-art roof that successfully serves the homeowner on a number of levels. Above all else, it provides essential peace of mind when severe thunderstorms, tropical systems and blizzards are in the forecast.

Contact Us Today

BRAX Roofing serves homeowners in Maryland, Washington D.C. and Virginia with a full range of roofing services, including roof replacements, re-roofing, emergency repairs, roof inspections and routine maintenance.

We’d welcome the opportunity to schedule a complimentary roof inspection for you. We’ll carefully review the results as we help you sort through your options for repairing or updating your roof.

BRAX Roofing is proud to be an Owens Corning Platinum Preferred Contractor. For more information about the Total Protection Roof System, please contact us today.

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    • Meet to discuss your project and free estimate.
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