Eco Timber Frames Styles/Trusses
In the world of timber framing there are many different styles. For the sake of this discussion we are concerned with two basic styles of timber frame construction that have more to do with the way the roof is framed than any other aspect of the structure. These two styles of timber frame construction are Bent systems and Common Rafter systems. We'll discuss each, and then explain the system that Mill Creek uses and why.
Timber Frame Terms
French King Post
King Post with Hammer Beam
King Post with Crossframe
Bent framing is what many people think of when they hear the words "timber frame". In a Bent system, a complete "bent," consisting of two posts connected to two rafters tied with some type of collar tie and other connecting timbers, is built flat on the floor deck of the building, braced and secured, then raised up into a standing position. Perhaps you have seen old pictures of a "barn raising," where many people with long pike poles are pushing a large bent up into position. This would be continued down the length of the building, perhaps every 10-12 feet. These "bents" would then be connected together by beams running between each bent. At the roof, horizontal members called "purlins" would connect the bents, and support the roof load. For simple floor plans laid out in a grid structure, this type of framing works well.
The other method of timber framing, and the one that Mill Creek employees prefer, is that of the Common Rafter system. Instead of large "bents," the supporting structure for the roof system is built, at its simplest, from horizontal beams supported by vertical posts. This system of posts and plates is constructed, then the roof system of "Common Rafters" is built on top. In its simplest form, the rafters run up from the horizontal plate, joined at the peak, and connected with a collar tie. These rafter pairs are then spaced no more than four feet apart for the length of the building. This is very similar to the way that conventionally framed homes are built, except that we are using very large timbers in place of 2x4 lumber. This system also allows a crew of three people along with a mechanical lift to assemble a complete timber frame home.
A major benefit of this style of framing is that it allows for a great deal of flexibility in the design of the floor plan. The timbers still define the spaces in the design, but the grid is more forgiving than that of the Bent system. Posts can move to accommodate a door, and rafter centers can vary over the length of a building depending on the size of the spaces below that they help define. This flexibility in design, along with the ease of construction, is why Mill Creek uses this system of timber framing almost exclusively.
Mill Creek's style of timber framing also allows for a variety of different rafter systems based on the width of the frame, the style of the design, and the client's desires. We have already touched on the simplest style of roof framing, the collar tie system. In its most basic form, the individual rafter pairs in a collar tie system look like the letter 'A'. Two rafters connected at the peak, and tied together with a horizontal collar tie. There are a few variations on this basic form: the king post truss, the queen post truss, and the hammer beam truss.
The king post truss adds a vertical post from the collar tie to the peak, usually with angled struts running from the king post to the rafters. The queen post truss is similar, but has two vertical members equidistant from the center of the collar tie that connect into the rafters. Again, there may be angled struts running from queen post to rafter. Both of these styles may be used anywhere that a collar tie frame is used. Typically they are used as a design element, such as every other rafter or so, to add visual appeal, a consideration to be decided during the design process.
A hammer beam truss is actually a form of "Bent" framing. Typically, Mill Creek uses hammer beam trusses in a great room as a way of adding visual interest and as a way to delineate space. A hammer beam, as Mill Creek uses in our timber frame system, typically includes two large posts at each rafter, two larger than normal rafters, a larger than normal collar tie, and a series of braces and horizontal and vertical beams. The larger size of the timbers used in the hammer beam trusses make them stand out from the other collar tie trusses, and provide for impressive visual appeal. Your Mill Creek Representative will help you decide if this is something that would suit your project, and the best way to implement it into your design.
Eco Timber Frames Co.
1970 Holbert Cove Road ·
Saluda, NC 28773 · Phone: 828.749.8000 · Fax: 828.749.8001 · E-Mail: email@example.com
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