TIMBER FRAME CONSTRUCTION

The aim of the article is to determine the advantages of wood frame construction and reveal the most suitable roof truss type for the climate of Russia.

A timber frame construction technology has come to Russia from Canada. As the climate there is similar to ours, that technology has become so popular in Russia.

A wood frame construction uses posts and beams with traditional mortise and tenon joinery to create the framework of the structure. Massive posts support equally substantial horizontal beams which carry joists and rafters. This method requires a high level of craftsmanship of the builders to create the skeleton that holds structural insulated panels or the shell that encloses your house.

Advantages of using timber

Timber frame houses are often thought of as a lightweight form of construction, but it is not always true. It is a custom-made structure, which is strong and durable. There are many advantages of wood frame construction, but its best-known quality is its environmental excellence.

• Ecology and sustainability

People have been building with timber for thousands of years. Timber is ecological and sustainable and a renewable building material. Wood is grown quicker than it is used.

• Low in production energy

It takes very little energy to transform the wood in trees to the lumber used in building. This means that the embodied energy in timber is low. In fact, it is one of the lowest of almost all common building materials.

• Easy to work

Timber is multifunctional and can be used in a wide variety of ways. Due to its light weight, it is easy to install and can be worked with simple equipment, which reduces the energy required for construction. Different species of tree produce timber of differing colors, textures and qualities.

• Quick build time

The speed of building is quicker with timber. A wood frame can be partly pre-cut, modulated, and built to precision making build time much quicker than for a brick build. Time is also saved since less building debris is around to clear. Wood frame buildings are far quicker to erect than stone, brick or concrete buildings. A less build time saves money for both domestic and commercial property owners.

Advantages of wood-frame construction

Timber frame construction can combine dimension lumber, engineered wood products and structural wood panel sheathing into wall, floor and roof assemblies that are robust, economical and fast to build. Current timber frame technology is the result of many years of expansion and improvement and extensive research.

When well-designed and constructed, wood-frame construction is:

• fast and easy to build;
• fast and easy to renovate;
• lasting;
• built from a renewable resource;
• a natural insulator that is easy to insulate to minimize heating and cooling costs;
• easily reinforced to withstand extreme wind and earthquake loads;
• suitable for different climates ranging from hot and humid to extremely cold;

Fire safety

Recently there have been lots of fire accidents and it may seem, that timber is not fire resistant, but it is not always true. Timber-frame technology is considered to provide an acceptable level of fire safety dependent on gypsum board finishes properties, that provide essential fire protection of structural elements for a certain period of time. Also, occupants are considered to be familiar with hazards and safety features of such buildings and to know how to safely exit the house. Fire safety is a combination of many factors, some of which can be minimized by building requirements, and others that can only be controlled by the occupants.

Insulation

The effectiveness of a building assembly such as a wall or ceiling in resisting the flow of heat is measured as its thermal resistance or RSI-value in metric units (R-value in imperial units). Although materials used for structure, cladding and finishes have some resistance to the flow of heat, insulation materials are required to provide sufficient levels of thermal resistance. Insulating materials have nominal thermal resistance values determined by laboratory testing. Construction assemblies have effective thermal resistance values, which usually are lower than nominal values because they take into account thermal bridging through materials caused by framing members and fasteners that have less insulating value than the insulation material itself. . Insulation is manufactured from a variety of materials and in various forms. The most common types of insulation used in wood-frame housing are described below.

Batt Insulation

Batt insulation is made from fibers of glass, mineral or steel-mill slag spun together with a binding agent. The product comes in lengths and widths to fit standard framing spaces and in a range of thicknesses that provide different RSI-values (R-values).

Loose-Fill Insulation

Loose-fill insulation is made of materials such as cellulose fiber and mineral wool fiber and is installed by pouring or blowing it into spaces between the framing. In attics, the loose fill extends above the top of the ceiling joists to raise the insulating level and reduce thermal bridging caused by the framing members. Loose fill insulation in walls must be installed behind a membrane that permits visual inspection to ensure there are no gaps or voids before the interior finish is applied.

Picture 1. Loose-fill insulation

Semi-rigid Insulation

Semi-rigid insulation boards are made of glass or mineral fibers and usually applied to flat surfaces such as walls. They are more flexible than rigid insulation products and not as easily damaged by impact or bending. Some semi-rigid insulation has good drainage properties and can be used on below-grade walls.

Picture 2. Semi-rigid insulation

Foamed-in-place Insulation

Specially formulated polyurethane and isocyanurate insulations can be installed by spraying or injecting under pressure. The liquid sets into a rigid mass within minutes of installation.

Picture 3. Foamed-in-place Insulation

Basic types of trusses

Prefabricated Roof Trusses

Prefabricated roof trusses offer many advantages. They are designed to handle snow loads that the trusses will be subjected to, are manufactured with a high level of quality control, reduce lumber waste and speed up the process of enclosing the house. They provide a surface for the roof sheathing, a surface for the ceiling finish material and a space for insulation. Ventilation of the attic space is easily provided through the eaves and at the ridge. Usually, trusses are designed to span from exterior wall to exterior wall without any intermediate load-bearing walls to support the roof loads. This gives flexibility to interior planning because the partitions can be placed without any regards to structural requirements.

King post truss

A king post roof truss is a cost-effective design and is very attractive when modified with curved braces and webs. The post, dividing the gabled space is called a king post; it represents a bold and intriguing design that is commonly used in conjunction with other truss styles. Then it often incorporates two struts on either side that not only add strength but also character.

Picture 4. King-Post truss

Queen post truss

The queen post roof truss is similar to the king post truss in that it uses a bottom tie beam, but it also adds the two posts dividing the gabled space that are known as the queen posts. This works well for highlighting the windows in great rooms and adds strength and character as well.

Picture 5. Queen post truss

Scissor truss

Scissor trusses do not have a horizontal chord. This cathedral-ceiling look has inclined chords, which support the rafters, and tie the members into place. The scissor truss has two beams that run from the lower part of the rafter to the other opposing rafter crisscrossing each other. While it can sometimes be difficult to figure out the best way to join the timbers in the middle from an engineering standpoint, they do add character to the frame.

Picture 6. Scissor truss

Hammer beam truss The last truss is the hammer beam truss. This design is the most complex and deserves an engineer’s touch to make sure it holds up over time, but the results are well worth any effort you put into it. It brings a sense of old architecture to the interior, and the style has a heavier feel than other truss styles. One advantage of hammer beam trusses is the use of shorter lumbers. It does require more components, but you are not paying a premium for long lengths of timber.

Due to our climate, it is reasonable to use gable and hip roofs. Because of the large amount of precipitations, a certain roof slope is required. The weight of the snow rapidly increases the load that is carried out by the roof trusses, wall framing and foundation. To reduce the volume of the snow, which stays on the roof, it is suggested using gable roofs and hip roofs.

Conclusion. As we have seen, timber frame construction is not only cheaper than concrete construction, but it also has acceptable fire-resistant properties, it reduces the costs of insulation. The use of prefabricated roof trusses accelerates the construction process, reduces construction waste and provides high quality of the structure. Timber frame building can be easily insulated by a wide variety of ways. So, wood frame construction is suitable for our climate, it is eco-friendly, it is fast to build, it is well insulated, durable and cheap to build. As for the roof, the most suitable and most common are hip and gable roofs, using the king post trusses and queen post trusses.

References:

1. Brice Cochran. Creating a Timber Frame House A Step by Step Guide. Timber Frame HQ, 2014. 76с.
2. Theodore J.; Lio, Michael Kesik. Canadian wood-frame house construction. Canadian Mortgage & Housing Corporation (C.M.H.C), 2013. 315с.