Building System Details
Emseal gasket, can expand up to 1" depth. As logs shrink a bit in diameter, gasket seals against any air infiltration.
Eastern white pine is available in my local in lengths up to 24’, while 36’ long logs can be obtained a further distance away. The sawmill where I obtain the timbers that will be incorporated into your log structure is given a set of standards regarding the quality/grade of logs and acceptable sawing methods needed to produce structurally sound timbers for a log structure. Only boxed-heart timbers are used in the construction of your log cabin. This sawing method produces a timber where the pith/heart, or the center of the tree remains in the center of the timber along its entire length, resulting in a much more dimensionally stable wall log. Another benefit in the conversion process from round log to sawn rectangular profile is that most of the weak, rot-prone sapwood is removed from the logs, leaving the dense heartwood which is more resistant to decay and insects. By specifying only boxed-heart timbers when ordering from the sawmill, and not accepting halved or quartered logs (where the heart is far off-center or not present), the undesirable drying characteristics common to these sawing methods is eliminated.
Another material-quality checkpoint is that all wall logs are thoroughly inspected with regards to spiral grain patterns, to ensure their proper placement within the wall. Virtually all logs/timbers, regardless of how straight they may appear, have some varying degrees of left or right-hand spiral grain. This can readily be seen as drying checks (cracks) develop on the log surface. These checks will follow the fiber alignment of the log. Logs with a slight-to-moderate left-hand spiral tend to be more prone to distortions during the drying process and are placed only in the lower 1/3 of the wall, where the weight of the building and/or alignment pins will hold them in place. Logs that slightly spiral to the right can be used anywhere in the wall system, as they have more balanced stresses within and will remain stable.
Although I go to great lengths to ensure quality logs go into your log structure, you may feel more comfortable using logs that have been structurally graded by an accredited log grading agency. Or perhaps your local building inspector will require grade-stamped logs. In either of these instances, I can supply building logs that have been structurally graded according to Log Home Council Grading Standards.
Once your logs arrive at my yard, great care is taken to insure that they maintain that sawmill fresh look. All timbers are stacked and stored in my shop, and during the warm months, multiple box-fans provide sufficient air flow between layers in the stack, to help inhibit any possible fungal growth. White pine is especially susceptible to blue stain, a fungus that attacks only the sapwood, and is present in airborne spores when dew points are high and air temperatures range between 40 and 105 degrees. Structurally, it is of no consequence, but it is visually unappealing (to most) and difficult to eradicate once it takes hold. Keeping timbers dry and with good air-flow are important preventive measures in the fight against blue-stain.
I work with a log building system which allows a wall thickness of 8" and incorporates 8" x 12" wall logs of two different profiles: 1) rectangular-sawn timbers that result in an even, symmetrical horizontal chink-gap between log courses, and, 2) for those interested in a more authentic/traditional look, a log profile where the log is hand-hewn and flattened on 2 faces with the broadaxe, and the chink joint follows the natural contour of each log.
Another measure taken that addresses both wall-alignment and settling issues at window and door openings is the use of angle iron splined jambs. Slotted 2” x 8” window/door jambs are re-enforced with 1½” x 1½” x ¼” angle iron, providing an extremely rigid framework and allowing the window/door assemblies the freedom of vertical movement to settle along with the log walls. In addition, 3" x 6" load-bearing wall support blocks are placed at all window and door openings.
A log cabin was built of round logs, and often disparagingly referred to as a pole-shack, usually as temporary shelter and the first living quarters built as soon as a clearing in the forest permitted. It was hastily erected, sometimes with only the earth as a floor, with little time to be spent on craftsmanship. Oftentimes, slaves’ quarters were constructed of round logs and referred to as cabins. On occasion, in the absence of a chimney, a large opening was left in the roof to allow smoke from cooking fires to escape. By contrast, a log house was built of hewn logs, flattened on two, or occasionally all four sides, with carefully fitted dovetail corner notches, and was of a much higher degree of craftsmanship. It was somewhat of a status symbol for the settler, indicating that he and his family had prospered enough to rise above the crude, round-log cabin of his past. However, many dovetailed log structures were soon sided over, in an effort to emulate the refined, town-dwelling Englishman and his house of timber frame construction covered with sawn clapboards.
Before you read too much further, I would like to clarify some potential misconceptions that may pop up regarding what some may define as a log-builder. First, I am not contracted with nor am I a representative of any log home company, nor am I simply a kit-builder, who in reality is one whose only role in the process is basically that of an assembler; a contractor who assembles the highly processed, pre-fabricated log home “kits” that have been produced by others. Those individuals and the companies they represent differ greatly from what I do and how I approach the craft of building with logs, and as you read on I hope that you will agree.
2) Dovetail Corner Notching - Most log structures are defined by the distinct and prominent style of corner notching they display, and the "Appalachian dovetail" is the log corner profile most commonly used in the log dwellings found in the mountain regions of Appalachia. It is a self-draining (slope of dovetail drains rain-water to exterior), self-locking timber joint that draws the corners of the building tighter as the weight of the upper logs is applied. Inherent in dovetailed log construction is the fact that the corner notches are designed to bear 70-80% of the weight of the building, resulting in constant compression on the notches while ensuring that the joinery remains tight. Notch extensions are additional amounts of wood left on the log ends and aid in the protection of the dovetail notches from end grain deterioration. I allow for a 1” overhang, although this extension varied a bit depending on the preference of the builder and geographic region.
Exterior Design Recommendations - Some exterior design features that may be common and appropriate in stud-frame construction should not be employed when building a log structure. In my opinion, the two biggest design flaws in log construction are foundations that permit the base course logs to be too close to the ground, and uncovered decks that are attached to the house. Both of these errors in design allow rain splash-back to hit the lower course logs, and/or melting snow to pile up against those bottom logs, creating a situation where mold, and then eventually rot become a certainty. Water is the enemy of log homes. Dry logs do not deteriorate. Initially, splash-back will present itself as a maintenance issue, causing black mold stains on the lower 2-3 courses. This continued exposure eventually results in the base course log or logs rotting and needing to be replaced. Needless to say, this is a much different scenario than with a simple clapboard-sided building, where replacing a few pieces of siding would remedy the situation.
Another very important aspect in a properly designed log structure in terms of its longevity is sufficient roof overhang. A wrap-around porch would be the ideal design feature, as it offers full protection against sun and rain for wall logs and corner notches. A down-side to the wrap-around is that it does tend to limit the amount natural light entering the home, resulting in a somewhat darker interior. A well-designed log structure that features effective preventive-maintenance strategies incorporated within its exterior design are: foundations that place the base course log at least 16” above grade (20” is better), wide (24”minimum, 36” is better) roof overhangs at the gable and eave ends, and/or covered or wrap-around porches.
Keep all shrubbery at least 3’ from log walls, as all ground plantings are prone to holding moisture-laden air, especially on the north side of buildings, and tend to cause mold and contribute to the decay process.
Avoid the tendency to stockpile firewood against log walls. The combination of wind-blown rain and leaves that will get lodged in between the pile and log wall is a recipe for mold and also offers a convenient pathway for insects to enter your home.
Not to be ignored when addressing the topic of water and log structures is the potential damage that water from inside the house can do. High-moisture areas like kitchens and baths generate water vapor that can seep into loft-joist pockets in the wall logs. What happens over time is the loft joist ends will shrink a bit in diameter, while the wall log (and the mortise the joist sits in) will show virtually no shrinkage (longitudinal) along its length. This shrinkage differential will result in small gaps appearing at the joist end and wall log interface. In the winter, the loft-joist ends, being notched in and located closer to the colder exterior surface of the wall log, will attract warm, moist air through these gaps that will seek to condense on the colder joist ends. Hidden frost can form on these joist end notches, which will eventually melt. Repeated wet/dry cycles over the years create conditions for decay, not only on the joists, but also in the wall logs. Any shrinkage gaps around joist-ends where moist interior air can get to should be filled with backer rod and caulked.
Wood Finishes for Logs & Interior Timbers - Assuming that you have taken the proper steps involving the exterior design of your log cabin, you will still have log walls that will be exposed to a variety of destructive natural elements. Log walls will need periodic maintenance for the life of the structure, an undeniable fact with not just log structures, but with all exposed exterior wood. But by choosing a high-quality exterior stain and applying it according to manufacturer’s specs, you can lengthen the time span between applications. Log structures need a superior product that has been specifically developed and tested for its unique requirements, and one of the most important decisions you will make once construction is completed is the quality of the finish/stain you will apply to the exterior of the logs. Don’t be tempted to purchase a stain/preservative from the big-box stores. There are many companies that manufacture excellent wood finishes that cater exclusively to the log home industry, with www.permachink.com, www.sashco.com, www.sansin.com, and www.sikkens.com among those that have been around awhile and have informative web sites and produce high-quality products. Permachink was one of the first companies on the scene over 20 years ago that offered maintenance products aimed at the log home industry. Their web site offers valuable tips on the do’s & don’ts concerning exterior maintenance of log walls, as well as a vast array of products that will keep your log structure looking great for many years. Take your time and research the different companies out there and the quality of their product.
slowly re-radiate that heat (a time-lag of around 8 to 12 hours) when the surrounding air temperature falls below that of the material. A concrete driveway on a sunny, hot summer day is an example of thermal mass because it absorbs, holds, and re-radiates heat well. Walking barefoot at noon on that driveway may be intolerable, but take that same barefoot stroll after dark and you will still feel the warmth under your feet. Log walls perform in this same manner. They act as a thermal storage system and delay the impact of outside air on inside air. In the winter, the log walls retain heat that is internally generated and re-radiate that heat, allowing the interior surface of your log walls to remain warm to the touch. Conversely, in the summer, they also absorb and deflect the heat of the outdoors, resulting in an interior that retains cool air and a wall that will feel cool to the touch.
Scale model. 18' x 24' with 12'x18' loft. 8x12 wall logs. Includes timber frame roof, porch, and loft. All chink materials, window/door jambs, alignment pins, site-install, and much more. Call or write for further pricing details. $38,746
I’ve found it interesting to note the historical difference in terminology as it relates to log building, past and present. I’m referring to the distinction between a house and a cabin. In the past, it seems that there has long-been a negative connotation attached to the word cabin as it pertained to a log dwelling, with that negative implication being all but erased with the passage of time. In the pioneer landscape of early America, as opposed to modern-day vocabulary, apparently the size of a log structure was of little relevance as to how it was termed.
Handcrafted Traditional Timber Frames & Dovetail Log Cabins
Building with logs that were hewn with the broadaxe to have flat interior and exterior surfaces was a technique developed by and brought to this country by immigrants from Sweden and Finland. The log house was an unknown in America until about 1638, when the first and only purely Scandinavian settlement, called New Sweden, was founded along the Delaware River, at what is now Wilmington. While the Swedish brought their log-building techniques to Delaware and Maryland, the early 1700’s saw Germans and Scotch-Irish begin to settle in Pennsylvania. While these ethnic groups had a long-standing cultural background in log construction in Europe, and were comfortable in its continuation here in pioneer America, it seems that only the English had no experience building with logs and instead clung to their own familiar building practice of timber framed houses sided with sawn clapboards. The ensuing years produced a melting pot of log construction methods, as ethnic groups migrated from previously settled areas and contributed building techniques that were unique to their European heritage. Generally, historians seem to agree that the hewn, dovetailed log structure as we know it today evolved from the cultural building patterns of the Germans, Scandinavians, and Scotch-Irish. This particular style of hewn log walls with dovetail corner notches became the dominant form of log construction in the Appalachian Mountains, resulting in it commonly being referred to as the “Appalachian Dovetail.”
1) Wall Logs - A superior-quality log structure begins with superior-quality material, which, when combined with appropriate and knowledgeable sawing techniques, are the initial requirements that will have the most impact on the integrity of your log building. I use only full-length eastern white pine logs (with no mid-wall splices) in the structures that I build. Partnered along with material handling issues and my local mills saw-length capacity, these factors will dictate the size of the log cabins.
The Dovetailed Log House in Early America
Each dovetailed corner notch, and all wooden joinery is laid out (framing square, chalk-line, level & protractor) and handcrafted (mallet, chisel, slick, hand saws, axes) with the traditional hand-tools of the past. The handcrafting of your log cabin demands great care, time, and patience. As a famous log builder once said, “Mistakes in wood are damn permanent, so take your time and do it right”, and I work under the guidance of that quote.
Once all dovetail corner joinery and related shoulder cuts are finished, a slotted vertical groove is cut on the inside face of each notch for placement of an Emseal gasket, (explained further on down), followed by a paraffin-based wax coating end-grain sealer that is applied to the freshly exposed ends to control end-grain checking (splits). This end-grain sealing process forces moisture to leave the timber through the long-grain surfaces (sides) and at a much slower rate than if allowed to exit the timber from its preferred and faster path of travel, which is via end-grain evaporation.
3) Chink Joint - Dovetailed log construction is not only characterized by the distinctively joined dovetail corners, but also the horizontal gap between each log course known as the chink space, one of the prominent characteristics in American log building. Historically, this chink space was filled all sorts of materials ranging from moss to wood chips, to cow manure, and plastered over with various mixtures of clay, lime, straw or horse hair. Materials and solutions evolved over the years to include wire lath nailed to the logs and coated with a cement/clay mix. Today, there are many synthetic, flexible chinking compounds (that have the look and feel of mortar) on the market designed specifically for log homes to accommodate log movement. Some well known companies with excellent product lines and informative catalogs that have been around a while include www.sashco.com, www.permachink.com, and www.sansin.com.
The chink joint in the dovetail log system averages about 2” to more closely resemble log cabins of the past. When chinking rectangular-sawn wall logs, the underside of each log is grooved (¾”x ¾”) along both edges to accept a 3/8” strip of rigid spline board. The top of the log has a beveled edge onto which the bottom of the spline is nailed. This spline board is angled out and down, allowing the chink joint to effectively shed rain. Synthetic chinking compound is then applied over the spline board to complete the exterior chinking process. This forms a weather-tight seal, while still being flexible enough to stretch to accommodate the expansion/contraction cycles common to heavy timber structures. When chinking hand-hewn logs with an irregular chink gap, Grip-Strip from Perma-Chink is applied inside and out, followed up by synthetic chink compound.
Before the interior chinking is applied, the chink joint insulation is installed from inside your cabin. There are a variety of insulation materials for this particular application, some more suitable than others. I recommend the use of natural sheep wool for the chink joint insulation from www.goodshepherdwool.com. According to their product literature, their wool batts are made from 100% pure virgin wool, with no acrylic fillers, and no artificial materials such as recycled carpet fibers that contain plastics and/or petrochemicals. Sheep wool has natural insulating properties with millions of tiny air pockets, has a rated R-value of approx. 3.5 per inch of material thickness, and is also flame retardant. In addition to these naturally occurring characteristics, the wool used in your log structure has been infused with natural borax for increased rot and insect resistance, with no harsh chemicals like boric acid or other boron compounds mixed in. Due to its crimped structural nature, sheep wool will retain its original shape within the chink joint and not be prone to settling or breaking down like other insulating materials can. In the unlikely event that moisture does penetrate the chink joint, sheep wool has the unique ability to absorb up to 30%-40% of its own weight in moisture without becoming wet to the touch. This inherent characteristic does not compromise wools’ natural insulating qualities, as is common to both fiberglass and cellulose. And unlike fiberglass, natural sheep wool handles nicely on-site as there are no respiratory or skin related irritations associated with its use. Strips of wool 3" x 8" x 8' are placed in the 2" chink joint, allowing for a snug top/bottom and side-to-side fit with very little compression.
All chinking material can be supplied by Square Peg Timber Joinery (or you can purchase it yourself) and is to be installed as part of the finish work by the owner or general contractor. Visit www.permachink.com for an excellent write-up on the proper methods of chink material application. An interesting side-note is Perma-Chink advises using no insulation in the chink space.
4) Air & Water Infiltration-The sealant system used in the chink space between log courses that was detailed previously is just one feature addressing potential air and water infiltration. Unlike timberframe construction where the layers of exterior skin protect against the elements, a log wall acts as both the structural frame and the first/last line of defense against air and water intrusion. Therefore, key elements in this regard begin with a quality building system, followed by a sound and effective plan to prevent air and water infiltration.
Despite the most diligent of efforts, there still remains the ever-slight possibility that wind-driven rain may penetrate the corner joinery at some time in the life of your log cabin, as the constant expansion/contraction cycles common to wooden structures may create small openings in even the most well-crafted and tight dovetail corner notches. A vital element in addressing this issue is the employment of an open-cell foam gasket by Emseal Log Home Tape. This high performance sealant has been impregnated with acrylic-modified asphalt, and is placed in a shallow, slotted groove (in which it can expand) at the vertical interfaces of all dovetail corner joinery. Combined with the use of high-quality caulk (designed exclusively for log structures and applied by homeowner or GC) around the entire self-draining dovetail notch perimeter, both air and water infiltration will be eliminated.
5) Wall Alignment- To ensure lateral wall stability at window and door openings, and to keep logs from twisting, hardwood alignment dowels (1¼” x 20”) are placed on either side of openings and in long wall-length runs. These beefy drift pins are octagonal in shape, sawn from air-dried oak, and wax-coated to reduce friction. They assist in keeping the walls in a proper vertical plane and increase the rigidity of the log wall, while the octagonal shape ensures that the logs can shrink around the pin and settle with no vertical impediment, as only the corners of the octagonal pins will be "biting" into the sides of the holes.
6) Allowances for Log Settling - Settling, as applied to a log structure, refers to the vertical reduction in height of horizontally laid logs in a wall system due to the combination of cross-grain shrinkage in a log and the compaction of the logs from the weight of the wall and roof system. Green logs will shrink, and will do so more in cross-section than along their length, although eastern white pine is one of the most dimensionally stable of the softwoods and has some of the lowest shrinkage rates. ILBA Log Building Standards state that green logs (in chinked dovetail) must be allowed to settle approx. 4% of total wall height. That doesn’t mean the log walls will settle that much, but those accommodations must be accounted for. A variety of factors affect the total amount of settlement in a log wall, including moisture content of the logs, wood species, density of the wood, and roof loads. This height reduction usually occurs slowly and over a 5 year period in a heated building. Effective methods to counter any potential problems with logs settling include cut outs in header logs above door and window openings, Nortek settling jacks (which can be hidden by finish trim) under all vertical members, and not spiking window and door jambs at log end openings. To properly allow window and door units to settle along with the log walls, slotted and angle iron-splined window and door jambs are employed, as opposed to simply nailing the jambs in place. The consequence of nailing the jambs directly to the log ends is that as the logs gradually settle downward, the fixed-in-place jambs (and the attached windows) do not move with the logs, creating many problems. Also addressed (in the structural drawings) with regards to settling are interior partition walls, gable stud framing, staircases, and generally any area where the natural settling of horizontal logs can be impeded by fixed vertical members.
7) Electrical Wiring - All wall logs are vertically pre-drilled with 1¼” holes at various points to run the wires. The open 2” chink space in the dovetail system is an ideal location for wire and box placement. Other options include a built-up baseboard that provides an electrical chase behind the baseboard, and conventionally framed interior partition walls and floor system. Wiring up to loft areas can be laid in a pre-routed channel in the top surface of a rafter or beam and before the decking is nailed on. Be sure to check with local building codes for acceptable installation details concerning the wiring of your log structure.
Timber Frame Elements - Standard in all Log Structures
Timber Frame Loft - The 18’ x 24’ model cabin shown on this page features an upstairs sleeping loft that covers half the width of the structure, and is designed to provide 6’ of headroom while standing 3’ from an exterior wall. When a larger structure is desired and has an interior width that is wider than 16’, the loft is framed using massive posts and beams with pegged, wood-to-wood joinery and with an 8”x12” tie beam spanning the necessary distance and joined to the eave wall logs with a housed dovetail joint. This tie beam is supported at mid-span
Timber Frame Roof System - The roof system most commonly seen in Appalachian dovetailed log structures and elsewhere was the common rafter roof. In small, one-level structures with no knee-wall, the 6”x 8” rafter pairs are secured at the peak by a pegged tongue & fork joint and joined at roughly mid-span (or lower) by 6”x 8” collar ties. These collar ties feature half-lapped, dovetailed joinery and are fastened to their rafter mates with white oak pegs. A stepped-lapped rafter seat, traditionally a favorite among joiners, locates and seats the rafters on the plate logs. These plate logs and their attachment are a critical structural component, as they must be up to the task of countering the roof thrust that is inherent in rafter framing, which is generated by roof loads that push down and out on the eave plates and (in story-and-a-half structures) the knee-wall logs below. One part of the solution is a 12/12 roof pitch, which provides maximum loft headroom while not looking too “peaky”. Other strategies employed include compound dovetail notches on the plates, the load bearing and structurally superior stepped-lapped rafter seat, and the vertical pinning of the knee-wall logs at 4 feet intervals with 1¼” hardwood dowels. These alignment pins penetrate the top several courses of logs, and provide the required lateral wall stability to the loft knee-wall. Yet without a doubt, the most viable solution to negating the roof thrust imparted onto the knee-wall involves a posted structural ridge beam, in which the rafters are “hung” from the ridge beam, thus eliminating plate spread entirely. In the end though, engineering specs will have the final say in determining the appropriate roof framing system for your particular situation.
GRK’s structural screws are used in the attachment of the rafters to the top plate. Where in the past it was quite common in log and timber frame structures to find a square peg securing the rafters to the top plate (and you may still use this traditional method of attachment if building code allows), I find it less of a compliance issue to use a fastener whose hold-down characteristics can be quantified to building officials.
Timber Frame Porch System - Another optional feature that is available and one that I feel compliments the rustic nature of a structure such as a log cabin, is a full timber frame front porch. Porch posts @ 6”x 6” feature mortise & tenon wood joinery, with pre-drilled “weep-holes” in the brace mortise bottoms to help facilitate rain water drainage that can collect in the brace pockets in the posts. Pegged braces rise to meet the 6”x10” porch plate, which is mortised with step-lapped rafter seats to accept the 4”x 8” rafters. Allowances for settling are provided in the form of adjustable Nortek screw-jacks under all porch posts.
Optional Features to Consider
1) Borate Treatment- Chemically inhibiting fungal growth in timbers with a borate-based wood preservative is an effective method that is available to help control decay-causing fungi. Borate-based wood preservatives are derived from naturally occurring, water-soluble mineral salts that are mined in California. They are highly effective as a wood preservative in preventing fungal decay and are deadly to most wood-boring insects (termites, old house borers, carpenter ants, etc.), but are non-toxic to people, pets, and the environment. Some of you may be familiar with the old-time laundry detergent still found on grocery store shelves, 20 Mule Team Borax, in which borates are a primary ingredient. Borate salts are odorless, have no effect on the color of the wood, are compatible with most exterior stains (check with manufacturer), will not interfere with chink-joint adhesion, and are non-corrosive to metal fasteners. When applied to freshly sawn wood, the water-soluble borate solution uses the woods’ own high moisture content as a transport medium to naturally penetrate and diffuse deep within the log or timber. But, the water-soluble characteristic of borates can also work in reverse order unless some precautions are taken. It has been shown that the borate solution in timbers will tend to leach out of the wood once it has been exposed to rain, unless a high-quality stain/sealer is applied to logs soon after installation, usually within a few days.
2) Through-bolt Fastening System - By this time you are surely well attuned to my affinity for building in a traditional manner, and I suppose that if you have continued reading to this point that you too also share an interest in traditional log structures. And traditional log structures from our American pioneer past did not employ any mechanical fasteners in their log wall systems. The settlers who built these early log cabins relied on the vertical compression of simple gravity in the hope that log corners would remain tight and came to expect the occasional intrusion of wind and a bit of rainwater. Living standards have increased significantly since that long ago time and the log home industry began searching for ways to help prevent air and water infiltration at corner notches. This brings us to the use of modern log-fastening systems which have evolved from simply spiking log courses together (which, unfortunately, many log builders still do), to the latest in self-tightening, compression-spring, through-bolt technology designed to keep your log structure sealed tight against the elements. Although I do have a strong aversion to visible metal fasteners, I do support their use if they are hidden from view and if they make the structure better for it.
There are a few different mechanical fastening methods common in the log home industry, with each one having its own merits and applicable to the many different log building systems out there. In the event it may be required by building code mandate, or simply for extra peace-of-mind on your part, a self-tightening, spring-loaded through-bolt system can be incorporated within the log walls. First let me say that without a well-constructed log wall assembly to begin with, no mechanical fastener will save it from its own shortcomings. Through-bolts are designed as a supplement to quality log building methods, not transform a poorly constructed log structure into a good one.
That being said, the through-bolt system that I offer consists of 3’ lengths of ¾” diameter threaded rod connected with couplers that runs through the full height of the log wall from the top plate log all the way down to the foundation, where it is anchored to j-bolts imbedded in the concrete. It is augmented at the top plate log by a corrosion-resistant zinc nut and washers, beneath which sits a heavy-duty 6½” compression spring rated at 1000# of pressure that provides constant vertical compression within the log wall stack. With the constant downward force generated by the compression spring, solid wood-to-wood contact is maintained at the horizontal interfaces of dovetail corner notches and wall openings, locking the logs in place, and when combined with the octagonal alignment pins, will resist the logs tendency to twist and/or bow as they dry and shrink.
Many “spring-less” through-bolt systems require frequent adjustments on the homeowner’s part, so that when the logs shrink and settle, manual tightening of the nuts will be necessary to maintain the constant compression and to take up the “slack” on threaded rod. In order to ensure maximum effectiveness while at the same time making this system as maintenance-free as possible, ThruLoc self-tightening lock nuts are employed within the assembly. The compression of the log wall stack then follows this path: The top nut is manually tightened down which compresses the spring. The spring comes into contact with theThruLoc self-tightening nut, forcing it to ratchet down the threaded rod and apply constant force where necessary. This system allows the logs to function as a solid unit and settle uniformly with no vertical hindrance as is common in log-on-log nailing systems.
Now that you’ve read all the positives concerning through-bolts, I’d like to point out some difference of opinion regarding their necessity from those “in-the-know” within the world of log building. As I have not used this through-bolt arrangement as of yet, I cannot vouch for the integrity of the system. In theory, the through-bolt assembly and all its parts make complete functional sense. In the real world practice of log construction however, I have heard varying scenarios regarding the effectiveness of the assembly and whether through-bolts are even needed in log structures other than in earthquake prone areas. Some log builders I have heard from believe in a through-bolt system so much that they will not build without their inclusion, while others feel that they are rather unnecessary and their addition tends to place a structure in the overbuilt/overpriced category. As of now, I will be offering a through-bolt system as an optional feature, my intent being to not obligate you to pay for a structural element that may or may not make your log home better for it. I feel that the final decision should be left up to each individual. You, in conjunction with your designer, building code official and engineer, can decide for yourself if a through-bolt system is right for your situation.
Items of Interest
Thermal Performance of Log Walls - When comparing the insulation qualities of a log wall vs. standard frame construction, the common R-value used to measure energy-efficiency cannot and should not be applied here. Eastern white pine, the species most commonly used in log construction, has one of the highest rated R-values at R-1.3 per inch of thickness. This yields an R-value of a little over R-10 for the 8” thick wall. Not too bad in itself, but compare this to the standard 6” stick framed wall packed with fiberglass which carries an R-19 rating, and the log wall lags a bit behind when using that standard of measure. But log walls march to a different drummer and draw their energy-efficiency not so much from an insulation standpoint but from the thermal mass of the logs themselves. Thermal mass refers to the ability of a material to store heat and then
Gasket groove on inside of notch, 3/4" wide x 3/8" deep. Unseen in finished home.
Housed dovetail tenon on loft tie beam & dovetail mortise in wall log.
by a braced and pegged 8”x 8” post. An 8”x12” “summer beam” (girder) runs perpendicular to the tie beam and carries 4”x 8” loft joists to the eave walls. It also features housed dovetail joinery on either end. Cabins with interior widths of 16’ or less can employ a simpler framing method of 6”x 9” loft joists covering this span between eave walls.
1-1/4" x 20" pins are drilled to go thru one 12" log, the 2" chink gap, and then penetrate the log below to its midpoint, tying the log courses together in a very sturdy manner.