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   • Renaissance Project House  
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Think of your roof as a Three-layered Weather Protection System, made of Decking, Felt & Shingles or Tile.

Layer #1 - Decking – Sheets of wood are placed over the roof rafters. Rafters are the parallel beams that support the three-part roof system. The most common types of decking are Plywood or Oriented Strand Board (OSB). We used sheets with a radiant barrier on the Project House. OSB is an engineered wood product made of narrow strands of wood fiber. These strands are oriented lengthwise and crosswise to form a strong sheet of support for the upper layers of the roof.

Radiant Barrier Defined –
We used a radiant barrier OSB Decking. It is a normal piece of Oriented Strand Board with a laminated layer of shiny material on one side. This acts as a low-e (for low emissivity) & high reflectivity system. The shiny side goes down because in summer’s heat, the low-E capability prevails (it does not emit heat radiating from the outside world). In winter, the high reflectivity capability prevails (it reflects back into the house the warmer air from the heated portions of the house). There are three types of heat transfer – radiant, conductive & convective. Radiant heat is the biggest culprit in a house in the summer – heat radiating from the roof system above as it takes a beating from the summer Sun. In general, attic insulation acts as a barrier between the attic & the living space of the house.

Layer #2 - Felt paper – This used to be called “tar paper”. It’s organic felt saturated with asphalt. It serves as a barrier so any water that penetrates the shingle or tile layer runs straight off the roof and does not soak into the wood decking material. Felt paper also makes sure shingles don’t stick to decking under the heat of the Sun, and it prevents a reaction between the chemicals in asphalt and the wood material in the decking.

Layer #3 - Shingles –the top layer of protection against sun, rain and wind. Shingles come in a wide variety of materials (composition, or asphalt-saturated paper; wood; metal; slate or imitation slate made of cement fiber; clay; concrete; etc.).

Weight is Important - Make sure you keep in mind the shingle material you plan to use when you design a roof on a new house. The roof must be built strong enough to bear the weight of the shingles that will sit on top of it. Clay or concrete will weigh four or five times as much as composition shingle, and so a roof design may not be strong enough to support heavier shingle materials unless it’s designed to bear such a load. On the Project House roof, the roofing crew “loaded” the roof with the full set of concrete tiles. This lets the roof adjust to the weight of those tiles. If the roof sags anywhere under the weight of these tiles, you have time to reinforce or brace the roof before they’re permanently installed.

Shingles are measured and sold in Squares. A square will cover a 10’x10’area, or 100 square feet. Shingles are packaged in Bundles.

Shingle Materials:
Concrete Tile – Our Project House roof is covered with concrete mission tiles. The concrete weighs 900 or 1000 lbs. per square.Clay weighs 600 or 700 lbs. Clay does not withstand impact as well as concrete does – that’s important if you live in areas prone to hailstorms.

Composition Shingles – These are asphalt-impregnated fiberglass or paper covered on one side with colored stone granules. This is the lightest, the least expensive and easily the most common shingle. 85% to 90% of homes in the US have composition shingles.

Three-Tab is the simplest and cheapest composition shingle. Weight varies from 220 to 350 lbs. per square. A shingle is a row of (3) pieces called tabs; each individual tab is not a shingle as most people might assume.

Asphalt Shingles are overlapped during installation to provide a double layer of protection against the elements. The composition shingles have a self-adhesive strip that seals two overlapping shingles together once the sun heats them.

Slate – real slate comes mostly from Vermont, and it’s very expensive. Some manufacturers make imitation slate made of cement fiber and sand. Imitation slate generally weighs about 350 lbs. per square. Real slate can weigh 500 lbs. or more.

Metal or Steel – Very resistant to hail damage; these shingle materials can often be installed directly over existing asphalt shingles. Metal & steel are completely fireproof. Different manufacturers make metal or steel shingles that imitate the look of composition, slate, Spanish tile & cedar.

Wood Shingles or Shakes – Wood shingles or shakes are a very traditional roofing material, but these days they’re illegal in many areas because of the potential fire hazard. Some manufacturers build metal & concrete shingles or tiles designed to look like traditional cedar shakes.