Recent wildfire losses across the country has raised awareness among log home owners about fire protection measures for their buildings. Firefighters must have sufficient manpower and equipment available in order to put out flames effectively, otherwise these structures become vulnerable and are at risk.
Design professionals, building departments and insurance underwriters all recognize four principles of fire control as essential: prevention, detection, evacuation and containment.
Endurance Ratings
Log wall construction differs significantly from post and beam walls in that there is often no cavity space within them, making these solid log walls highly resistant to fire. Furthermore, their lack of cavities reduces how fast logs respond to flame and smoke during a fire and further contributes to their endurance rating. According to credible tests conducted on solid wood log walls of 6″ thickness or thicker can sometimes keep its integrity for over two hours and allow occupants plenty of time to escape and contact 911 before collapsing completely.
Laminated logs are designed to be as strong and sturdy as possible, with each log lamination securely glued into place to help preserve dimensional integrity of walls while avoiding movement such as twisting, splitting and cracking. In addition, laminated logs are kiln dried for increased durability by decreasing moisture content that may lead to mold growth or decay; additionally kiln drying helps lower humidity in log homes thus decreasing risk of warping or shrinkage.
Chinking can further decrease the risk of damage to log homes in case of fire by applying products meeting Underwriters Laboratories requirements, like those listed here. Chinking should be applied along the top and sides of a log wall assembly for maximum impact resistance against fire, while its insulation benefits also help ensure minimum energy code requirements are met.
While there is no single answer for determining the R-value of a log wall assembly, AF&PA research and experience have revealed an effective methodology that engineers or builders with knowledge of log homes can quickly use to calculate its R-value. This technique, included in the ICC 400 Standard on Design & Construction of Log Structures as well as in the ANSI/AWC National Design Specification for Wood Construction (NDS), allows them to calculate fire rating according to wall thickness – with at least six-inch wide walls required as per narrowest dimension.
Fasteners
Log homes built using traditional techniques – using dowels and metal bolts between log layers – often pass one-hour fire ratings without losing structural integrity, due to the insulation provided by charred wood and the lack of concealed cavities through which flame can travel (ultimate fireblocking). Chinking products designed specifically to seal gaps or reduce fastener penetrations into log walls further boost this performance.
Before construction begins, it is vitally important that manufacturers’ recommendations regarding fastener selection and installation/spacing are observed in order to achieve a desired endurance rating. In most instances, this requires selecting fasteners with low thread profiles suitable for fitting into log walls as well as corrosion-resistant coatings that meet code requirements; some manufacturers offer specially formulated coatings designed specifically for log wall systems.
Use of kiln-dried, stress graded lumber and regular inspection of gluelines during application and curing are keys to creating successful log building. They ensure the fasteners used have low enough thread profiles that penetrate logs without pulling out from forceful driving of them into place; this reduces chances of loosening or fastener failure under excessive loads or vibration, potentially leading to moisture or insect issues.
To achieve optimal energy and weather protection performance, it is essential that attention be given to the layout of log framing, use of high efficiency mechanical equipment, and use of reduced cross-section method in log wall building. While this may require greater care in terms of detail than with traditional stud or concrete-frame structures, the results will speak for themselves.
Air infiltration control can have a profound impact on both durability and fire resistance of log houses, so using energy-efficient HVAC equipment with an AFUE 90 rating or greater as well as designing log frames with enough insulation and sealant can help ensure minimal air leakage, thus decreasing utility bills, indoor pollution risks and helping regulate internal humidity levels.
Sealants
Fire resistance of log walls depends both on the quality of wood used and on any sealants applied. A good chinking system will offer some air infiltration protection; however, this won’t protect logs against fire or heat impacts or moisture penetration into their interior surfaces – which is why LTHC suggests our builders use fire-resistant caulking exclusively when sealing logs.
Most residential building codes do not mandate fireproof walls on log houses, though if one of the log walls separates a garage or other structure from your home it should have at least an one hour fire-resistance rating.
Log buildings used in other occupancies often face the question of fire-resistant construction; rather, the question should focus on how long it will take for fire to spread before occupants can safely evacuate the building. A 1-hour fire resistance rating is often specified and this goal can often be attained with proper selection of wood species and log size.
Many LTHC Members have successfully designed and constructed log buildings with 1-hour fire resistance ratings using relatively large log sizes, yet acceptance by code officials remains difficult due to costly fire suppression systems that need to be installed and maintained.
Key to achieving higher fire resistance ratings when using smaller logs is creating a uniform and dense structure, using larger diameter logs in the main frame construction known as the buck of your building. Furthermore, adding headers over window or door openings further strengthens their fire resistance ratings.
Attention to detail in the design and construction of log walls can help prevent air-leakage, which is one of the biggest sources of energy waste, indoor pollution and moisture damage. A blower door test should be run during framing stages to detect and correct any gaps or leaks before final inspection and insulation is installed.
Joints
Log homes are built upon logs, and laminated log houses utilize this fundamental aspect as its cornerstone. When using laminated construction methods like glulam construction, logs are cut to size and treated with special fire retardants before being stacked together and secured using heat-activated glue – creating strong yet long-lasting logs which also resist fires.
Kuusamo Log House wood is carefully selected from forests and sorted at sawmills to ensure only top-grade logs are utilized for its manufacture. Following that step, logs are then kiln-dried until their moisture content meets optimum levels before fabrication into wall sections – the whole manufacturing process being carefully monitored to meet exacting quality standards.
Research on timber elements’ fireproofing capabilities has been extensive; however, few tests have been conducted on log columns due to difficulties obtaining solid, flawless rectangular sections for testing purposes. Still, test data exists which can be used to calculate a fire rating for columns containing logs.
Fire ratings in the United States can either be determined using actual tests or calculations derived from these tests. Since it would be nearly impossible to physically inspect every specific building, existing studies and laboratory tests can be used as evidence that it will achieve an acceptable fire rating.
American Wood Council (AWC) published Technical Note Y245 which details how wood fasteners or metal screws can be hidden, treated and concealed for fire-resistance of log walls. Another option may be using a chinking system consisting of sealants placed between logs – these must first be tested to see if their performance affects that performance negatively.
At openings in log walls, it is often customary to install a wood frame (buck) to support windows or doors. This not only adds visual appeal but can help improve fire resistance as the buck helps protect both ends of header log(s) as well as bottom of door/window frames from direct exposure during a 1-hour fire endurance test.