At Parthenon, we not only care about providing you with the most quality roof - we also care about showing you what puts it together. When considering replacing or purchasing a new roof, it is helpful to know what main components make up the roof over your head and what functions they serve.

Being knowledgeable about these components will help you better identify any problem areas that need to be fixed in the future. 


Here's a breakdown of what goes into a residential roof:

Image by GAF via Madison WI LeafGuard

Image by GAF via Madison WI LeafGuard


1. underlayment

Underlayment, also known as “felt paper”, is installed onto the decking. Today, the best felt products are synthetic and provide better moisture resistance than felt paper. Proper underlayment creates an additional barrier against rain and wind along with the shingle layer by providing extra protection in case of broken or torn shingles. 


2. ice and water shield

Ice and water shield is an underlayment placed in valleys and around problem areas like chimneys. It is a reinforced fiberglass mat backed with a strong adhesive that secures it to the decking. The mat is self-sealing making it much more leak resistant than valley metal. In warmer climates, ice and water shield has replaced valley metal due to its moisture resistance.



Decking is the foundation of your roofing system and ties all of the structural parts of your roof together. The most commonly used decking materials for homes are oriented strand board (OSB) or plywood. The decking is attached with nails to the truss/rafters (the wooden structural framework that supports the outer layers of the roof). 


4. ridge vent

The ridge vent is installed at the peak of a sloped roof, and allows warm air to escape from the attic. It acts in concert with the soffit vents to create a flow of air under the decking, prolonging the life of the shingles and the underlayments and increasing energy efficiency.


5. shingles 

Shingles are the outer shell of your roofing system. Shingle materials vary – the five main types are asphalt, wood, slate, metal, and tile. The most commonly used shingle material is a combination of fiberglass coated with asphalt and mineral granules, either in a one layer three-tab style or a laminated multi-layered architectural-style.



Flashing (not pictured) refers to thin pieces of material such as aluminum or galvanized steel, strategically placed over joints in the roof and at areas where wall construction meets the roof plane. Its purpose is to help water flow off the roof reducing saturation of the roof decking.