Nation RoofingRoofing Terms, in Plain Language
Roofing quotes are full of words nobody explains. Here is what they mean, so you can read your scope and compare two quotes properly.
The layers of your roof
Decking or sheathing is the structural wood surface, usually plywood or OSB, fastened across the rafters or trusses. Underlayment is the waterproof layer laid over the decking, and on a tile roof it is the actual waterproofing. The surface, whether tile, shingle or membrane, protects the underlayment from sun and weather. Understanding this order is most of what you need to read a quote.
Measuring and pricing
A square is 100 square feet of roof area and it is the standard roofing unit, so a 2,000 square foot roof is 20 squares. Pitch is the slope, written as rise over run, so 4:12 rises 4 inches for every 12 horizontal inches. Low slope generally means under 3:12, and it needs a different waterproofing approach from a steeper roof.
Where water is managed
Flashing is the sheet metal that seals transitions: where the roof meets a wall, a chimney, a skylight or a vent. A valley is where two roof planes meet and channel water, and it carries more water than anywhere else on the roof. Drip edge is the metal at the roof edge that directs water off the fascia instead of behind it.
Flat roof terms you will see in Las Vegas
Modified bitumen is an asphalt based sheet membrane applied in rolls, common on valley low slope roofs. Single ply, such as TPO, is a sheet membrane mechanically fastened or adhered. SPF, spray polyurethane foam, is sprayed on to form a seamless insulating layer and needs a UV coating to survive desert sun. A scupper is an opening through a parapet wall that lets water leave the roof. Ponding is standing water that has not drained, and it is the enemy of every flat roof.
Ventilation terms
Soffit vents are the intake at the eaves. Ridge vents run along the peak as the exhaust. Together they move air through the attic, and they have to be balanced: exhaust without intake moves almost no air, which is the single most common ventilation fault we find.
Tile specific terms
Battens are the strips that tile is fastened to, and they create an air gap above the underlayment. Ridge and hip tile are the shaped pieces capping the peaks and the diagonals, and they are the first pieces to slip in wind. Profile is the tile shape, such as flat, low or high barrel, and matching it on a repair matters for both appearance and HOA approval.
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Frequently asked questions
What is the difference between underlayment and decking?
Decking is the structural wood surface fastened to the framing. Underlayment is the waterproof membrane laid on top of the decking. On a tile roof the underlayment is what keeps water out, and it is what wears out first in this climate.
What does a roofing square mean on my quote?
One square is 100 square feet of roof area. It is the standard unit for pricing material and labor, so a quote for 22 squares is describing roughly 2,200 square feet of roof.
Why does pitch matter?
Pitch determines which waterproofing systems are appropriate. Steeper roofs shed water fast and suit tile and shingle. Low slope roofs under about 3:12 hold water longer and need a membrane or foam system rather than shingle.
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