The roof is the building, its contents and occupants’ primary protection against rain, snow, hail, wind, cold, sun light and sun heat.
Basic terminology:
The roof pitch is the angle at which the roof rises from its lowest support (pitch plate) to its highest point (Example: the ridge).
A roof hip is a sloped ridge formed by the meeting of two roof planes like a pyramid which has four hips. The hip sits at the exterior corner of a house and usually rises to the ridge. Hip roofs are ideal in hurricane regions.
A roof valley sits on an internal corner of a building and joins two sloping roof planes and rises to the ridge to form the opposite shape to a hip.
The soffit is the underside ceiling of a roof (horizontal or sloped) from the exterior wall to the eave or exterior roofline.
The Fascia caps the end of the roof at the roofline and support the rain gutter.
The roof overhang is the roof projection beyond the perimeter bearing exterior wall.
For log homes and exposed timber or log construction, large overhangs over 4’ to 5’ wide minimum are a must to protect the wood from rain, sun weathering and damage.
In passive solar building design; to maximize energy savings, roof overhangs are designed to block the high summer sun light and heat from entering the house thru windows, doors and perimeter walls. In winter the overhangs are designed to let the sun light and heat flow through the window and door openings as the sun is much lower in the sky to reduce heating costs especially in temperate to colder climates.
Different roof designs and roofing materials are used around the world depending on the local climate, material availability and cost, local traditional architectural practices, building codes and bylaws.
Choosing the right roofing material for your home:
Homeowners want an inexpensive roof that last forever and requires minimum maintenance.
With the skyrocketing cost of energy we also need a roof that minimize cooling cost in summer
Over 90% of roof in the world uses dark color roofing materials like asphalt, ceramic & stone tiles, or wood shakes for examples.
Those dark roofing materials absorb vast amount of sun heat and thus dramatically increase the need for cooling which is not energy efficient.
The cool roof:
A cool roof can reflect part of the infrared, ultraviolet and visible wavelength of the sun and thus reduce the transfer of sun heat to the home:
The cool roof is also able to release much of the absorbed solar heat that was not reflected back to the sky. Add large attic ventilation to maximize energy savings.
Solar reflectance is a percentage of the amount of heat reflected back to space.
Asphalt, tar and gravel roofs have a solar reflectance from 3% to 18%.
Ceramic tiles vary from 10% to 35% depending of lightness of the tile color.
Highly reflective light color metal roofs do much better with a solar reflectance from 60% to 70%.
White paint roofing finish can reach up to 90% solar reflectance.
To evaluate roof coolness a simple value (SRI) called solar reflectance index is used, combining solar reflectance and emittance.
Black roofs have a very low SRI value and can reach temperatures over 180 degrees F or 85 degrees C.
This means higher cooling cost and shorter roofing material life span. This translates in higher roof maintenance cost and more roof waste to the landfill.
Cool roofs are a must in hot and temperate climate to save energy.
A light color roof with significant roof ventilation also works well for cold climates. In winter snow tends to stay on the roof adding more insulation to the existing heavy insulating material dictated by local building codes.
Thermoplastic white vinyl roofing reflects about 80% of sun radiation and emits 70% of the heat absorbed by the house making it one of the best cool roofing materials available on the market.
White paint coated on an existing black roof significantly drops cooling energy consumption.
Green roofs also qualify as a cool roof that can last up to 50 years in right climate conditions.
They provide great insulation especially against heat and noise.
They absorb large amount of rain as they behave like a sponge.
However they cost 5 to 10 times more than conventional roofs and require stronger structural support due to the added weight of soil, plants and water.
Green roofs are not suitable to all climates and have high maintenance costs and expensive repair cost to find and repair leaks.
Common roofing materials:
Roof finish, ventilation and roof insulation must be designed to work together to control interior ambient air moisture content to a minimum and as well control inside temperature with minimum energy consumption.
Fiberglass roofing is available in sheets, shingles and corrugated panels. They are light weight, durable (25 to 30 years) and less than half the cost compared to most roofing materials.
The most popular fiberglass roofing is opaque white.
Asphalt shingles or composite shingles are popular because of its low cost with a life expectancy from 15 to 25 years depending on thickness.
Metal cladding or metal tile is light, fire resistant and has good reflective quality. In snow areas it is used to shed snow as it is a sliding roof material. It may be dangerous to let the snow slide and most ski resorts have bylaws requiring installation of snow clip to hold the snow on the roof. Golf course communities do not allow reflective roofs for obvious reason.
It is an affordable roof that last 30 to 50 years and is the number one choice for many home owners.
Ceramic and concrete tiles are expensive but have a great traditional aesthetic look. This roofing is very popular in hot climate and last up to 100 years. They are fire proof and are the most used roofing material in the world.
Slate is good for up to 200 years but will cost about the same as the house itself. Roof structure needs to be robust to support the weight.
Red cedar shakes are attractive giving a rustic look to your home. They last about 25 years.
They can be installed over asphalt roof but they are much more expensive and far less fire resistant unless impregnated by fire retardant.
Rubber tiles use recycled material like tires… This roof is best for areas where hail is an issue. Cost is similar to metal roofing.
Rubber tiles are thick with R3 insulation and are great sound insulators. This is a new exiting eco friendly material but there is little information on its life expectancy at this time.
Roof ventilation is often underestimated. Most homes are under ventilated and thus roofs have a reduced life because of moisture damage to roof framing, sheathing…
A house produce about 5 pounds of water a day and that moisture must be vented out thru the roof by using air intake at the soffits along the length of the lower roof and exhaust using attic vents and vented ridge caps.
Log homes design calls for vaulted ceilings. If a traditional frame roof is used a minimum of 2 1/2” airspace is required above the insulation to move the moist warm air from soffits to vented ridge cap. Venting must be allowed at roof valleys to flow freely up the inside of the roof to ridge.
Roof maintenance is crucial to a long life roof.
Leaks happen mainly at protrusions like chimneys, vents and at roof valleys. Roofs should be checked twice a year. Clean debris with air blower, check old caulking, and hammer back sticking nails. Replace broken tiles and missing shingles. Clean gutters and downspouts to allow good drainage.
