Roofing Systems

roof structureYour roof needs to perform three main functions.  First and formost it is a waterproof "lid" for the housing structure. Secondly it needs to 'shed' water effectively away from the building foundation, and lastly it needs to retain heat in the winter and cooling air in the summer.

There is a wide variety of  roof coverings available in many styles and different materials to perform the waterproofing function. Regardless of the material or style their effectiveness will rely both on their quality and installation.  

Shedding water is the domain of the roof drainage sytem and is comprised first of the drip edge shown in the illustration and of the gutter-downspout installation which is not shown but an important aspect of the home inspection process.  All roofs require a drainage system, else the rain water diverted by the roof would be deposited adjacent to the foundation on either side of the structure or pool on flat roofs and overload the structure.  We don't want this.

The conventional rafter design illustrated, composed of a ridge board and diagonal rafters needs to support the weight of the roofing materials and whatever added load nature might impose in the way of snow. This is true as well of more common engineered trusses and these are all examined during your home inspection.

Any of us who have stored things in the attic are well aware of how hot they become in the summer. The sun places a tremendous load on roofing materials which may cause as much wear and deterioration as seasonal precipitation.  This heat needs to be ventilated in some way to prevent this process.  The common rule is that 1 square foot of ventillation is required for every 300 square feet of attic floor space. Ideally we want the attic air to be the same temperature as the outside air, to stabilize the roofing materials and prevent unwanted condensation and the resultant mold and material degradation that will accompany it.

Ideals are just that, and we rarely achieve them.  We now have, however, an attic that is still hot in the summer sun and cold in the winter.  Older homes seldom had enough insulation in the attic.  With the advent of air conditioning and the ever increasing need of energy conservation we simply can not afford to lose heat or cooling to the attic space.  Attic space needs to be sealed from the building structure, ventilated and insulated.

Minimum attic insulation in Maryland should be R38 and cathedral ceilings should be R30.

Roofing Vocabulary

Rafter: Structural wood, usually slanted, to which sheathing is attached.

Rake: The slanting edge of a gable roof at the end wall of the house.

Ridge: The horizontal line at the top edge of two sloping roof planes.

Sheathing: Boards or sheet material that are nailed to the rafters to which shingles or other outside roofing materials are secured.

Shingle Flashing: Flashing that is laid in strips under each shingle and bent up at the edge of a chimney or wall.

Pitch (Slope): The number of inches of vertical rise in a roof per 12-inches of horizontal distance.

Soffit: The area that encloses the underside of that portion of the roof that extends out beyond the sidewalls of the house.

Square: One hundred square feet of roof or the amount of roofing material needed to cover 100 square feet when properly applied.

Underlayment: The material (usually roofing felt) laid on top of sheathing before shingles are applied.

Valley: Where two sloping roof sections come together.

Valley Flashing: The metal or fabric in valleys, extending in under the shingles on both sides.

Built-Up Roof :A low-slope or flat roof covered with alternating layers of roofing felt and hot-mopped asphalt and topped off with a layer of gravel.

Cornice :The wood or metal finishing at ends or edges of buildings including a fascia, frieze, or rake.

Counter Flashing: The flashing that is embedded, or attached, and sealed at its top in a wall or other vertical structure and is lapped down over base flashing.

Courses : Horizontal rows of shingles or tiles.

Drip: The strip of metal extending out beyond the eaves or rakes to prevent rainwater from curling around the shingles back into the wooden portion of the house.

Eaves: The lower edge of a roof (often overhanging beyond the edge of the house).

Eave, Ice, and Snow Guard: A 3-foot wide rubber membrane adhered to the sheathing at the roofs edge that attempts to stop migrating water from entering your home during severe ice dams.

Felt: The bituminous paper used by roofers, usually made of a combination of asphalt and either paper or rags.

Fascia: A decorative board extending down from the roof edge either at the eave or at the rake.

Flashing: Sheet metal or other material used at various planes on a roof to prevent water leakage.

Frieze Board: A board at the top of the house's finished wall, forming a corner with the soffit.

Independent Home Inspection of Maryland