Exposed trusses are exceptional architectural components, at structural — they hold up the roof — while controlling a space to give it scale and rhythm. But with the many truss types on the market, how do you decide which to use? Even a seasoned architect can get lost in the language of trusses, especially because there are as many variants in truss layout as there are houses.
If you have ever wondered exactly what kind of king post truss is and the way it differs from, say, a queen post truss or a hammerhead truss, here are a couple of answers.
Frederick + Frederick Architects
Before I explain the principle types of trusses, let us define what exactly a truss does.
First, a truss withstands gravity and holds up the roof. That may sound obvious, but it is the one most important criterion. The diagonal rafters of this truss do most of this gravity-defying work. But as gravity pushes back on the roof, the walls behind the rafters are going to want to fall outward.
The horizontal tie beam is what keeps the whole thing rigid. Through the years this tie beam will have a inclination to weaken and sag. That’s where the article comes in, lifting and encouraging to avoid the aging effects of gravity.
The King Post Truss
King article trusses are only about the most frequent truss type. They are so named because there’s 1 post, the king, at the centre that keeps the underside horizontal tie beam from sagging.
Elements of a king post truss:
Rafters: diagonal members who lie against and are parallel to the roofTie beam: at the base of the truss, spanning from wall to wall (or rafter to rafter)King article: connects the tie beam to the point where both rafters matchStruts: diagonals which connect the tie beam to the raftersHow to use it A king post truss is frequently utilized in vaulted spaces in which the designer would like to simultaneously achieve the spaciousness of this vault and, by setting a lower horizontal line of tie beams, the closeness of a lower ceiling.
Ekman Design Studio
The Queen Post Truss
The queen post truss has the same body as the king post truss except that there are two posts off to the sides instead of a centre post. Both of these queen posts do the exact same job the king post: keeping the tie beam from sagging.
How to use it Architecturally, a queen post truss is suited more for a vaulted ceiling which doesn’t rise to a point but to a flat location. The two queen posts can help to define that level point, providing order to the space. A queen post truss can also be excellent for in which the roof climbs up to a clerestory or light track. Again, both vertical poles will establish a rhythm which helps to define a space.
Doreen Le May Madden – Lux Lighting Design
The Scissor Truss
A scissor truss gets rid of vertical and horizontal components. It generates a more spacious atmosphere, because there’s no flat element defining a lesser “virtual” ceiling line.
How to use it A scissor truss is suitable when the ceiling toss, or slope, is not very steep. A shallow pitch, like in this example, can nevertheless be quite spacious every time a scissor truss can be used to support the roof.
David Vandervort Architects
The Hammerbeam Truss
A hammerbeam truss is traditionally utilized to span greater distances. While there isn’t much call for such a kind in residential architecture, it’s some distinctive architectural qualities.
Because of its open centre section, a hammerbeam truss has a stepped quality. Although this example is more of a hybrid of a queen post and king post truss, the metal tie pole visually disappears, providing the truss a hammerbeam appearance.
HEARTHSTONE LOG & TIMBERFRAME HOMES
How to use it Hammerbeam trusses actually come into play in large spaces, in which their quality and scale resonates. A hammerbeam truss is suitable for both baronial-style halls and barns, or any blend of both.
Castro Design Studio
The Arched Brace Truss
The arched brace truss is, like the hammerbeam truss, an open arch. This kind will offer a more spacious and open texture than the king post or queen post truss, that are both considered closed. The defining element is that the arched braces a flat collar tie rests on.
A king post is not a necessary part of this kind of truss. Nevertheless, you may discover that a king post is visually significant as a way to highlight the high point of this vault.
How to use it Because an arched brace truss introduces a curve to the design, it is excellent for situations in which you would like to produce an arch to frame the perspective. It is also the perfect type when you want to create the texture of a barrel-vaulted ceiling.
Robert Young Architects
Mixing It Up
An important point to think about in truss layout is that only about anything goes after you understand what each truss component’s job is. A king post doesn’t need to be made of wood, for example. Sure, that is the traditional material, but a metal rod will do the job just as well. In reality, a metal pole serving as a king post is visually more suitable when the truss elements are visually articulated, as in this example.
Whether the truss starts as a king post, queen post, scissor or hammerbeam, it can wind up being a sort of hybrid. In reality, these days it is rare to find a truss design that is simply one basic kind.
Again, the trick is understand what each truss part does and design accordingly. Metal rods, that are better at resisting tension, are more suitable than timber for tie beams and king or queen poles. And why not pull the tie beam, or in this case the link rod, higher to open up the space, not unlike the struts at a scissor truss?
As stated at the outset, the principle purpose of trusses is to hold up the roof by withstanding gravity. But by being a system that establishes a rhythm and scale at an area, trusses also have an important visual job to do. In reality, there are many instances when the trusses are used only for their visual impact, with something else doing all of the structural work.
Doyle Coffin Architecture LLC
Once freed of its structural function, the truss can take on virtually any configuration. But in the end, the most prosperous trusses will stay true to the language of a truss, using posts, ties, struts, rafters and braces, as was done for centuries.