Roof Anatomy

roof anatomy

1. rafter10. down spout
2. collar beam11. splash block
3. ridge board12. rake
4. solid decking13. lookout
5. felt underlayment14. fascia
6. shingles15. ridge board
7. vent pipe flashing16. valley underlayment
8. chimney flashing17. valley flashing
9. gutter18. spaced sheathing


What do I need to know when purchasing a new roof?
Major roofing components
  • Decking
    • The boards or sheet material that are fastened to the roof rafters to cover the house.
  • Roof Covering
    • Shingles, tiles, or panels which protect decking from the weather.
  • Roof Structure
    • The rafters and trusses constructed to support the decking.
  • Drainage
    • The features of the roof’s design, such as shape, slope, layout, etc., which affect its ability to shed water.
  • Flashing
    • Sheet metal or other material laid into the various joints and valleys of the roof to prevent water seepage.

Who are the enemies?
  • Sun
    • Heat and ultraviolet rays cause roofing materials to deteriorate over time.
  • Rain
    • When water gets underneath the shingles, shakes or other roofing materials, it can work its way to the deck and cause the roof structure to rot. And, the extra moisture encourages mildew and rot elsewhere in the house, including damaged walls, ceilings, insulation and even the electrical system.
  • Wind
    • High winds can lift the edges of shingles (or other roofing materials) and force water-and debris underneath them. Very high winds can do extensive damage.
  • Snow and Ice
    • Melting snow often refreezes at the roof’s overhang (where the surface is cooler), forming an ice dam and blocking proper drainage into the gutter. Instead, the water backs up under the shingles and seeps into the interior. In the early melt stages, gutters and downspouts can be the first to fill with ice and be damaged beyond repair or torn off the house.
  • Moss and Algae
    • Moss can grow on wood shingles and shakes if they are kept moist by poor sunlight conditions or bad drainage. Once it grows, moss holds even more moisture to the roof surface, causing rot, and its roots actually work their way into the wood. Algae also grows in damp, shaded areas on asphalt shingle roofs. Besides creating an ugly black-green stain, it can retain moisture, causing rot and deterioration. Trees and bushes should be trimmed away from the house to eliminate damp, shaded areas, and gutters should be kept clean to ensure good drainage.
  • Tree and Leaves
    • Tree branches touching the roof will scratch and gouge the roof material as they are blown back and forth by the wind. Falling branches from overhanging trees can damage-or even puncture-shingles and other roof materials. Leaves on the roof surface retain moisture and cause rot, and leaves in the gutters block drainage.
  • Missing or torn Shingles
    • The key to a roof’s effectiveness is complete protection. When shingles are missing or torn off, the roof structure and the interior of the home are vulnerable to water damage and rot. And, the problem is likely to spread-nearby shingles are easily ripped or blown away. Missing or torn shingles should be replaced as soon as possible.
  • Shingles Deterioration
    • When shingles get old and worn out, they curl, split and lose their waterproofing effectiveness. And, weakened shingles are easily blown off, torn or lifted by wind gusts. The end result is structural rot and interior damage. A deteriorated roof only gets worse with time and it should be replaced as soon as possible.
  • Flashing Deterioration
    • Many apparent roof leaks are really flashing leaks. Without good, tight flashings around chimneys, vents, skylights and wall/roof junctions, water can sneak into the insulation and cause damage to walls, ceilings, insulation and even the electrical system.
  • Condensation
    • Condensation can result from the build-up of relatively warm moisture-laden air. Moisture in a poorly ventilated attic promotes decay of the wood decking and rafters, possibly destroying the roof structure. The solution may be to increase attic ventilation through the use of larger or additional vents, so that the attic air temperature will be closer to the outside air temperature.
  • The importance of ventilation
    • When a house has been properly ventilated, a positive airflow is created which allows the house to breathe and helps prevent moisture build-up. That’s why proper attic ventilation is a serious issue that should always be considered when re-roofing your home.
    • Normal household activities can wreak havoc on an attic and ultimately, a roof. Showers, laundry, dishwashing and cooking all generate moisture that can damage insulation, rafters, wood deck, underlayment and shingles during winter. Summer heat buildup in the attic promotes premature aging and cracking of wood and roofing materials. All of which could shorten roof life. For maximum roof protection, a well-ventilated attic is the key.
    • In warm weather, proper ventilation prevents the attic from becoming a hot box that spills unwanted heat down through the attic floor into the living area (even if the attic is insulated).
    • In cold weather, proper ventilation helps prevent moisture from condensing on the insulation, structural wood, shingles or roof deck. Moisture-soaked insulation becomes ineffective, thereby causing excess energy usage. Condensation on wood leads to rotting and expensive repairs. While those are the most important reasons for proper ventilation, they aren’t the only ones.
    • Excess attic heat causes premature shingle failure and can invalidate the shingle warranty. Excess moisture in the home causes mildew and drywall damage. Moisture problems can cause paint to peel and siding to warp.
    • Balanced airflow keeps attic temperatures from reaching extremes. Vents allow outside air to move through the attic. The result is a cooler, drier attic, which means a longer lasting roof
    • What’s the solution to gain proper ventilation?
    • Ridge vents, when used with proper undereave vents, are the most efficient form of roof ventilation because they allow uniform escape of warm, moist air from attic space.
Frequently Asked Questions
Q. How do I know when my roof has a problem or needs replaced?
A. Roofing problems are usually discovered after minor leaking or some damage occurs. Periodic inspections can uncover damaged or missing shingles, loose seams and deteriorated flashings, excessive surface granules accumulation in the gutters or downspouts and other visible signs of roof problems. If your roof is damaged, look for cracked paint on your ceilings, discolored plasterboard and peeling wallpaper as signs.
Q. My roof leaks. Do I need to have it replaced?
A. Possibly but not necessarily. Leaking can result because some flashings have come loose, or because a section of the roof has been damaged. A roof failure is generally irreversible and results from improper installation or choice of materials. Have an inspection to ensure that you do not need your roof fully replaced.
Q. What causes my shingles to blow off with every high wind?
A. Most of the time it is because of improper nail application, they are usually nailed too high or too deep into the asphalt. There is a nailing line on the shingle that need to be hit with every nail.
Q. How long should my current roof last?
A. The lifespan of your roof will depend mostly on the type of roof you have, the effects of your local environment and the maintenance which the roof has received. Generally asphalt shingles last 15-30 years; wood shingle/shakes 10-30 years; clay/concrete tiles 20+ years; slate 30-100 years; metal roofing 15-40+ years.I know what you are thinking, the warranty for asphalt shingles is usually stated to be 25 to 50 years, but from my experience and observation, most last 15-30 years and are usually replaced because of hail storms in this central part of the U.S.
Q. How do I get an inspection and estimate.?
A. So glad you asked, call RSI or use the request estimate form on this site.Thank you for your interest, Gary Nasalroad/RSI
Roofing Vocabulary
Deck/decking: The surface-usually plywood or oriented-strand board (OSB)-to which roofing materials are applied. Also, the boards or sheet materials which are fastened to the roof rafters to cover the house.
Dormer: A small structure projecting from a sloped roof, usually with a window.
Drip edge: An L-shaped strip (usually metal) installed along the edges of the roof to allow water run-off to drip clear of the deck, eaves and siding.
Eave: The horizontal lower edge of sloped roof.
Fascia: A flat board, band or face located at the outer edge of the cornice.
Felt/underlayment: A sheet of asphalt-saturated material (often called “tar paper”) used as a secondary layer of protection for the roof deck.
Fire rating: The Underwriters Laboratories (UL) system for classifying the fire-resistance of various materials. Roofing materials are “Class A,” “B” or “C,” with “A” materials having the highest resistance to fire originating outside the structure.
Flashing: Pieces of metal used to prevent the seepage of water around any intersection or projection in a roof, such as vent pipes, chimneys, valleys, and the joints at vertical walls.
Louvers: Slatted devices installed in the gable or soffit (the underside of the eaves) to ventilate the space below the roof deck and equalize air temperature and moisture.
Oriented-strand board/OSB: Roof deck panels (4’ x 8’) made of narrow bits of wood, laid down lengthwise and crosswise in layers, held together with a resin “glue.” Often used as a substitute for plywood sheets.
Penetrations: Vents, pipes, stacks, chimneys-anything that sticks up through the roof deck.
Rafters: The supporting framing to which the roof deck is attached.
Rake: The inclined edge of a roof over a wall.
Ridge: The top edge of two intersecting sloping roof surfaces.
Slope: Measured by rise in inches for each 12 inches of horizontal run: A roof with a 4-in-12 slope rises 4 inches for every foot.
Square: The common measurement for roof area-100 square feet (10’ x 10’)
Truss: The engineered components which have supplemented rafters in many newer houses. They are designed for specific
applications and cannot be cut or altered in any way.
Valley: The angle formed at the intersection of two sloping roof surfaces.
Vapor Retarder: A material designed to restrict the passage of water vapor through a roof or wall.

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