Timber Frame Trusses
A timber frame truss is one of a framework of timbers that help support roofs and cover the area above rooms. They are, simply speaking, exposed beams, which makes up the popular open beam concept style house. Whether they add space to a room or make your living room more cozy, exposed timber frame roof trusses are an excellent and versatile way to add a rustic and attractive look and feel to your home.
There are two timber frame truss styles: closed and open. Closed means that there is an extra beam, the tie beam or crossbeam, connecting to the bottom of the truss and posts, while in open variations the tie beam is absent. Some of the more common types of closed timber frame trusses include the king post truss and the queen post truss, while some of the most common open timber frame trusses include the arch-braced truss, the scissor truss, and the hammerbeam truss.
- King post trusses are some of the most simple trusses. The king post is positioned vertically between a triangular shaped truss at the top and a horizontal tie beam at the bottom. There it forms a classic shape often seen in the construction of open bridges. A less simple form can also see two additional beams extending out from the king post and connecting upward to the triangular truss. The king post can also be replaced with a wrought iron rod and made into a variation known as a king bolt truss.
- Queen post trusses are shaped like half-hexagons, with two queen posts extending vertically from a horizontal tie beam to the two inner vertices of the shape. They can generally span a greater distance than a king post truss and are often seen in the construction of things like covered bridges. The queen post can also be replaced with a wrought iron rod and made into a queen rod truss. This style comes with a quaint, at-home feel.
- Arch-braced trusses are similar in shape to king post trusses, except they are open and lack a tie beam. Instead, they have a horizontally running beam connecting to the truss. Underneath that are two curved beams (known as collar beams) which also connect to the truss and the underside of the scissor beam. The style is sleek, simple, and modern.
- Scissor trusses are shaped like a pair of shearers or scissors, hence the name. This roof truss design is wide open and has crossed beams in the middle, which connect to the sides and bottoms of the truss, making up the blades of the scissors. On each side of the truss, there is a vertically connected tie beam, making up the scissor handles.
- Finally, hammerbeam trusses are a derivative of the arch-braced truss, except a bit more complex and decorative. This truss design allows them to span wider gaps than the arch-braced beam, however, as with the queen post truss to the king post truss. They are the main component of the roof of Westminster Hall in London which was constructed in the 1390s by Hugh Herland, royal carpenter to King Richard II. The style is evocative of Medieval England, lavishness, and royalty.
Although trusses are a decorative and popular addition to your home, safety measures must also be taken into account. Proper joinery is key in the durability of a heavy timber truss and frame. One must take into account the steepness, or pitch, of the actual roof that the beams will be a part of, which will be predetermined by the climate in which a house is built. A house that is built in a snowy climate will have a steeper roof to prevent snow from building up and a roof collapsing. So, more than ever, we need to make sure our trusses are secure and properly joined if being secured to a high pitched roof.
How do we achieve a proper truss joining? First of all, if a joint is properly constructed it will, or should, remain tight forever, even with the natural shrinking, checking, or cracking of the wood truss itself over time. A joint must be made with this in mind, and with the ability to contort and conform to these natural deformations as time goes by. To accomplish this, there is a variety of joints to choose from, be it traditional all-wood joints to joints with steel bolts and plates.
Hardwood pegs are frequently used to pin together traditional joints, where the shape, or geometry, of the joint carries the brunt of the weight of the
truss and the pegs hold the joint itself in place and together. However, when the trusses span a distance greater than 16 feet, it is recommended using steel to secure your joints to keep in line with proper safety measures and building codes. The steel can either be hidden or exposed, though, depending on the preference of the client or homeowner, so all is not lost for those large rooms and areas that we still want to look traditional and rustic.
When working with an extraordinarily large load, or when it is aesthetically pleasing or desired, it is recommended to use heavier steel plants, rods, and bolts, which can also either being hidden or exposed. This is an industry standard across multiple companies and will help promote better safety and keep your home up to the building codes in your city and state.
We have now learned about different timber frame truss styles and types, their applications in your home, and how to properly secure them for optimal safety and aesthetic purpose when we install our trusses. They are a stylish and lavish addition to any home. Timber frame trusses can bring out the quirks in your home and transform any room or space into something exciting, new, and extravagant, evocative of Medieval England, cozy covered bridges, a quaint Maine cottage, or even royalty.