Log Home Engineering and Design Criteria1

by: Log Home Living Modern log homes aren't the same simple structures our ancestors built a century or two ago. Today's log homes can be even more complex in design than conventionally framed wood homes. Therefore, the likelihood of your log home performing up to your expectations is directly proportional to the amount of professional engineering and design work the producer has invested in the development of its design and construction system. In this section, we intend to review the importance of engineering and design, how they relate to building codes, the importance of building codes to the home owner and the various methods log home producers use to meet these building codes.

Engineering and Design

A log home is a complex structure to design and build. However, the engineering principles involved in designing these structures are not always apparent to the untrained eye. There are many ways to design and build log walls and roof systems, but to do so properly requires knowledge of many factors. As an example, the seemingly simple placement of fasteners in a log wall involves calculations that consider snow loads, wind loads and even seismic activity where the log home is to be built. Designing a roof system involves complex structural calculations, a knowledge of wood technology and even heat loss calculations, since the roof system affects energy efficiency and energy efficiency is a requirement of many building codes.

Structural Stresses

Snow loads. A log home roof system must be designed to carry the weight of the heaviest snow load likely to occur in a two-month period in the area where the home is built. For instance, most roof systems are designed to carry a dead load of 20 pounds per square foot. This figure includes the weight of the roof rafters, decking and shingles. However, in localized areas of some snow-belt regions, such as Colorado, the Great Lakes and New England, snow loads of 150 pounds per square foot are not uncommon. Therefore, the design of the roof system must take snow loads into account in order to produce a safe and sound structure and to meet building code requirements.

Wind Loads

The wind is perhaps the most important force affecting the structural integrity of a house. In a strong wind, a home acts like a sail. If not properly designed to resist these forces effectively, the home will bend and flex. Over years, this bending and flexing can weaken the connections between walls and the roof system and even cause doors and windows to stick. In the worst case, the home can literally be blown down. In most parts of the United States, homes are designed to resist a wind load of about 15 pounds per square foot, which is equivalent to a wind gust velocity of about 80 miles an hour. However, along the Gulf and Atlantic coasts, especially in Florida, winds of up to 150 miles an hour can be experienced with a hurricane. As a result, homes in these areas must be built to withstand such forces.

Seismic Loads

Earthquakes are not as severe a problem for log homes as they are for brick, block and masonry homes. Wood is not as brittle as masonry and tends to bend and absorb seismic pressures more readily. Nonetheless, the design of all homes must take seismic loads into account in order to meet building codes. In the United States, in Zone 0, no earthquake risk exists. However, the damage from earthquakes doubles from Zone 1 to 2 and doubles again from Zone 2 to 3.

Building Codes

In spite of protection provided by the various building codes, in many parts of the country, especially rural areas, it is still possible to build a home without first obtaining a building permit. These areas have no building officials to review plans, issue permits or inspect construction work in progress. This situation is very unfortunate for home owners, for while there are some building officials who can be difficult to deal with, they do provide valuable protection, both for home owners and builders. Building codes are standards of construction designed to protect the health and safety of a home's occupants. There are three building code associations in the United States and one in Canada. Each of these organizations has developed a model set of building codes and standards, which essentially describe in detail exactly how a home should be built. States, provinces and most local municipalities generally adopt one of these model building codes as their official building code. Once a building code is adopted, local building officials enforce the code by requiring builders to submit plans and specifications to them for review before they issue a building permit. If the plans meet the requirements of the code, the building official issues a building permit, and construction can begin. After a permit has been issued and construction begins, these same officials inspect the work at four or five specific times during construction to ensure that the builder is building the home in accordance with the plans they approved. If there is a variance between the way the home is being constructed and the approved plans, the building official can require that work stop until the variance is corrected or new plans are approved. In the unlikely event construction starts before a building permit is issued, building officials can legally require that work stop and that all construction be removed.

Code Compliance

When considering the purchase of a log home package, the buyer needs to know if the home will meet building code requirements. There are a number of ways log home producers handle building codes. Since there can be considerable costs associated with this service, buyers should pay particular attention to the method producers use to comply with building codes. 

Non-Compliance

Some producers address the issue by not providing design services. Buyers must have their plans drawn elsewhere. The log home producer then acts as a building materials supplier and provides the necessary number of logs needed to build the home. This arrangement transfers the risks, responsibility and cost of complying with building codes to the buyer and the designer of the log home.

Company Certification

Other producers, generally those who sell in a small local area, have designed their homes to meet local building codes and provide their company's assurance that the homes they design will meet building codes in their local area. When they sell out of their local area, they may need to have their plans reviewed by a professional engineer or architect in order to get a building permit. This review and certification may result in additional cost to the buyer.

Professional Assurance

Other producers, especially those who sell in one or more states, generally have had their plans and specifications developed by professional engineers or architects. These professionals then provide their assurance that the homes meet or exceed building code requirements, generally by affixing their seal on copies of plans before submitting them to building officials. The cost of providing th is additional assurance is generally included in the cost of the producer's package.

Code Certification

Those producers who sell nationally or in a half-dozen or more states generally find it beneficial to their buyers to offer certification by one or more of the model building code organizations. This certification requires a considerable effort on the part of the log home producer. The building code agency requires producers to submit technical documentation on their building system. The technical staff of the code agency then reviews this material and, if acceptable, issues a document, known as a "Research Report on Compliance." This compliance report certifies that all homes designed in accordance with the system meet the requirements of its model building code. Once producers have a Research Report, they need only refer to their report number to satisfy the need for technical documentation required for a local building permit. The cost associated with this level of assurance is included in the cost of the producer's material package, but it is a cost home owners should be willing to pay because of the resulting protection and peace of mind.