Hammer Beam Truss
Often referred to as the crown jewel of the timber frame industry, and for a good reason. It is very esthetically pleasing. It has a well established and rich history. And you can create lofty living space and yet retain a feeling of closeness, warmth and security. Typical uses are in great rooms, churches, entries and attached pavilions. When you choose a hammer beam truss you will be locking in the “old” factor. More along the lines of the European style . With heavier beams, angled rather than arched beam detailing, and slightly lower roof slope, the hammer beam truss blends well with the rustic timber frame style.
Notice I said SLIGHTLY, lower roof pitch. Why? Because this stunning timber truss style has a glaring weakness. The strength of the whole roof is stacked upon the lowest knee brace triangle connecting to the outer posts. A familiar phrase among timber frame Guild members is: “With a hammer beam truss, make the principal knee braces as low as you dare! The accumulated thrust and tension loads With the hammer beam truss become daunting indeed! But they are not insurmountable.
If the roof pitch does get too low, the thrust will likely become too great for the lower triangle to resist. One fix is to use a decorative steel tie-rod to eliminate the thrust on the lower knee braces. Some might call this cheating, but I don’t. It is a functional solution which has little impact on the overall inspiring look and feel the hammer beam truss creates. With a tie-rod, normal truss constraints apply, so a 50′ to 60′ span is achievable. Without a tie-rod, a span of 30′ is a stretch, even with a steep roof slope such as 12/12. (45 degree, 12″ run and 12″ rise)
Speaking of creative solutions, many old churches used heavy stone pillars to resist the outward thrust created by the roof trusses. They are tall narrow triangular wing walls, oddly referred to as ‘flying buttresses.’ We have also put this solution from craftsmen of old to good use!
The two biggest reasons to choose a hammer beam truss is to frame a view (a tie-rod could be a distraction in this case) or to create an inspirational feel.
Many people start their timber frame planning with the intent to utilize a hammer beam truss, but as they acquire more knowledge during the process, they change direction. Why? One big reason is intimacy. Space that gets way beyond human scale, needs a lot of people to feel feel right. Imagine having your easy chair, end table, etc set up in a huge vacuous space… just lil’ ol’ you sipping your coffee… I suppose it could evoke a feeling of grand power for some, but not for this guy!
So when people begin the planning process they eventually seek to find their personal balance between WOW and COZY. If the space gets bigger to handle more people, the hammer beam truss gets pretty high. It can begin to feel out of touch for day-to-day living. Because the hammer beam truss is made up of so many pieces, it is easy to add elegant influence by adding curves or arches to the knee braces or soft detailing to various members. But many pieces means many joints, which translates to a larger investment.
Sometimes the investment factor alone nudges people to choose a different truss style. But usually it is a combination of factors . Now if you have a beautiful view you want to frame or have your heart set on a hammer beam truss or are doing an event space, the this could be dynamite! The hammer beam truss has a lot to like!
