A roof is much more than a cap that you put on the log walls of your home. Just as you wouldn't pick a car by looking at a plan of it, to design your home solely from the floor plan is to ignore the potential a roof has not only to enclose your home, but to define the look and feel of your home. Yet often, many homes look like the roof was an afterthought.The pitch, or slope, and the shape of your roof will greatly affect the exterior appearance and the feel spaces within. It can also be a reflection of the local area in which you are building. For example, if you are building in a ski resort, you may want to use a steep pitch, not only to help with shedding snow, but to echo the surrounding terrain. On the other hand, roofs in flat land often look more appropriate if they have a gentle pitch. Of course, being harmonious with neighbouring properties is often a good idea, although certainly a personal choice.As ceilings are usually direct reflections of the roof overhead, rooms feel very different under different roofs. Compare the sense of space inside a rancher with a low open ceiling, a chalet with a huge vaulted ceiling, a home flat ceilings. In addition to roof shape, different construction systems and roofing materials reflect very different looks, and influence cost and performance.Let's look first at roof pitch--the slope of the roof or how steep it is. A shallow pitch is less dramatic than a steep pitch and, therefore, the structure below it tends to have more emphasis. However, it is less easy to incorporate usable space within the roof structure. To do so, you will need to increase the pitch of the roof, probably to a ratio of at least 8:12 (vertical rise:horizontal distance) or more. To increase light, headroom and usable space you will likely need to add dormers. A dormer can have a peaked roof or gable (sometimes called a doghouse dormer) or have a single slope, called a shed dormer.The direction of the ridge will also have a strong impact on the look of your home. A roof with the ridge running parallel to the front of your home looks very different from one with the ridge running perpendicular to it. Ridges running perpendicular to each other create a combination of roof face and gable end on the same elevation. The resulting valley creates a definitive appearance both on the interior and exterior and has structural implications.Log homes need generous overhangs to protect your logs from the elements. I generally use 4' overhangs on the low end of the roof pitch and more on gable ends. The International Log Builders' Association Standards recommend an overhang of at least one foot beyond the furthest log extension per eight foot of rise. With steeper roof pitches, large overhangs lower the height of the fascia--the trim board at the low end of the roof. This may mean having to raise the roof in order to keep the fascia above the windows. However, by doing this, you can create additional headroom on the second floor.Your roof can be constructed using one or more structural systems. Like any building system they influence your finished home in a variety of ways, including aesthetic and economic. You can generally use any type of interior ceiling finish or exterior roofing material with any structural system, although different materials may require different backing. Wood frame trusses, the most common roof system in the conventional housing industry, are not used so extensively within the log home industry. Wood frame trusses are inexpensive and easy to install and vent. However, they limit the use of logs in your roof system, the extent of vaulted ceilings and usable space within your roof system. One type of truss called a scissor truss can give you some vaulting.When extensive ceiling vaults, lofts, or dormers are desired, dimensional rafters are commonly used. The depth of the rafters has to be sufficient to achieve desired insulation levels and allow an air space for venting over the insulation. You may combine a log roof system with dimensional rafters or other non-truss systems. It may include several components:Ridge: a structural member supporting two parallel intersecting roof planes.Purlins: a horizontal roof member supporting the roof deck or rafters.Rafters: roof members sloping from the ridge to the outside wall.Valleys: roof members at the internal intersection of two sloped roof planes.Hips: roof members at the external intersection of two sloped roof planes.Other than supporting conventional rafters, log roof systems may support other roof systems such as roof panels. Sometimes referred to as stress skin panels, they are large pre-manufactured panels consisting of rigid insulation sandwiched between rigid sheets of a nailable building surface, usually OSB (oriented strand board). They generally run from the ridge to the overhang and can accommodate almost any interior and exterior finish material. Although they can be more expensive than conventional roof systems, they are becoming more common with log roof systems. They work well when log or timber rafters or purlins are desirable, or if you have a crane already on site for the log assembly, as the panels can be flown into place at the same time. This greatly reduces the amount of time your log structure is exposed to the weather. They are less practical to use when you have multiple hips and valleys or if you have a limited number of structural logs in the roof system.Structural roof decking applied over the log rafters or purlins is a common way of finishing log roof systems. The log roof members need to be close enough together to support the limited spans of the decking (typically 4'-5'), although thicker decking can be used for increased spans. In this method, your interior finish is accomplished at the same time as your structural roof deck. The decking is then insulated on the exterior with rigid insulation. An additional nailing surface will need to be provided for the roofing material or substrate, or typically, an air space for ventilation.Ventilation is critical to most roof systems. An air space between your roof insulation and the underside of your roofing material reduces the possibility of condensation and inherent moisture problems. It also reduces thermal stresses on the roofing materials themselves, critical with the use of asphalt shingles.I often get asked what is the ideal roofing material to use on a log home. The answer is that there is no ideal material. All materials have their pros and cons. Weigh the aesthetic considerations against cost and performance. Here are just a few of the materials to consider.Asphalt Shingles are the primary roofing material used in North America. They can have either a fiberglass, or an 'organic', usually cellulose based, core. Nowadays, they are primarily designated by their life expectancy or warranty, such as 20 years or 30 years. While the use of fiberglass in the composition is becoming the standard, make sure they meet the American Society for Testing and Materials Standard D 3462, in order to avoid potential problems with buckling or cracking. If you live in a warm climate, lighter colors will yield greater energy efficiency in your home due to their reflective capacities. Asphalt shingles come with a variety of fire resistance ratings.Wood shingles or shakes are often a favorite for log homes because of their natural construction and appearance. Shingles are machine split and shakes are hand split. They are more expensive and, unless treated with fire retardant, are less fire resistant and are even prohibited in some regions. Their life expectancy is generally similar to the cheaper asphalt shingles, although they can be treated with preservative or other wood finish.Other shingles are made from a variety of materials. In addition to metal and fiberglass shingles, there are a variety of composites on the market.Tiles are another choice for roofing. Generally, they are made of clay or concrete. They are heavier than other materials and may require additional structural support. Slate tiles are the most expensive and, although they require very skilled labor to install, will generally last a very long time.In addition to a host of metal shingles on the market, sheet metal roofing is often a choice for log homes, due to its relatively low cost and durability. While standing seam roofs are commonly used on commercial structures, overlapping sheets are more common in residential construction. Use a heavy gauge metal and make sure corrosion resistant fasteners, such as stainless steel, are used.While extremely rare on log homes, bitumen products are usually used on extremely low-sloped roofs or on roof decks. There is a wide range of bitumen products on the market. In a similar vein, it is becoming more common to use high-density polyethylene membranes underneath some shingle products as an added layer of protection against the elements.
