Roof Truss Tips: How to Set Them the Right Way

Written by Posted On Monday, 21 January 2019 12:28

A roof truss is a structural unit consisting of small members that coordinate together and act as a single large member. The truss functions as a tectonic framework that allows the builder to traverse greater distances between walls without additional center support resulting in larger open spaces.

Nowadays, many builders favor roof trusses over traditional stick-framed roofs mainly because they are quicker to install. Trusses also eliminate the need to cut complicated roof angles. Roof trusses can also be configured to accommodate any roof design and shape. What’s more, they are professionally engineered, which implies that the finer details of the roofing design are constructed with a higher level of precision.

Whereas installing roof trusses is simpler than installing traditional framing, the tradeoff is that it leaves less room for error. Here are some tips on how to set your roof trusses right.

Costs

According to HomeAdvisor, roof truss installation costs fall in the range of $7,200-$12,000 with material costs clocking in at $1.50-$4.50 per square foot. Wood trusses cost $30-$400 each depending on the size of the roof.

Setting the first truss

You can either buy your trusses from a manufacturer or make them onsite. Reclaimed timber trusses such as Timberworks Timber Truss are a popular choice because they are more stable than trusses made from green wood and also add warmth and character to the roof.

 When installing roof trusses by hand, it’s important to make sure all members are fitted perfectly prior to lifting the trusses to the top floor. Glue metal gusset plates to truss joints then nail each point gently taking care not to damage the wood.

With pre-fabricated trusses, the manufacturer provides a diagram and layout of the truss configuration. Each truss member is numbered; the first step is to transfer the numbers to the top wall plates. A crane is frequently used when installing roof trusses because they are usually large and unwieldy.

The manufacturer provides clear instructions for each step of the installation process. Typically, the contractor sets the trusses on the side of the roof opposite the location of Truss #1. The workers manually position the first truss at the end of the roof on the corresponding number on the wall plate. They then nail it to the wall plate and attach temporary braces to hold it upright.

Setting subsequent trusses

The workers then set the second truss in a similar manner to the first and attach a ridge beam at the apex of each truss. This beam extends to the far end of the roof and hangs over the trusses while still sitting there. Subsequent trusses are attached to the wall plates and the ridge beam. Sometimes temporary additional supports might be added.

Truss attachment

Roof trusses are actually designed to move as a unit in order to maintain the structural integrity of the roof. Temperature changes and humidity frequently stress the truss members which can result in the center of the bottom chord lifting upwards.

A common error by builders is to nail the bottom of the chord to the top undesignated interior walls. Unfortunately, doing this prevents the truss moving, can result in truss members cracking and even voids the manufacturer’s warranty. Make sure to nail the trusses only at the points specified by the manufacturer on the layout.

Hip roof trusses

Hip roof trusses are ideal in places that receive heavy snow or rainfall because they slope downward at every point and are able to prevent rainwater from draining into a room. Hip roofing technique is simple and can be done without the help of experts or any specialized equipment. Indeed, hip roof trusses are a good choice when you cannot afford a crane.

Here are some tips to install hip roofing:

  • Common rafters should be measured according to the roof’s pitch angle then cut into perfect shape and installed at a distance 20 inches apart across the wall
  • Jack rafters should also be placed 20 inches apart across the wall
  • Mark the exact spot over the wall to where the rafters will be placed
  • Place the rafters at their respective locations then nail them. You can use extra support for safer installations
  • Cut the plywood sheathing making sure that all facets of the roof are covered
  • Leave some extra space at the bottom edges to hang freely over the walls. These act as extra support and also provide a graceful look

Additional tips

  • Heel height: when placing orders for new trusses to match existing ones, the contractor needs to specify three parameters: slope, span and heel height of the installed trusses. Many frequently forget the heel height which can result in one truss sitting higher than the other.
  • Top plate anchor: Truss screws are highly popular because they are easy to install. However, they might not be adequate when the trusses are extra-long. Check that the restraint used is rated to handle the maximum uplift on the truss. You can get this information from the ‘‘Reaction’’ section of the truss spec sheet.
  • Keep trusses aligned: Most roof trusses need to be installed in a specific direction even when the webbing looks exactly the same. Some trusses are painted so that the framer can see where they need to be installed while others have tags at the bottom of the truss where they require additional load-bearing points.
  • Temporary bracing: Always remember to install temporary bracing on the trusses whenever you leave the jobsite for long periods if the trusses are not fully installed and decked
  • Store trusses on even ground: Storing trusses on uneven ground can lead to bowing resulting in a framing nightmare.

Setting roof trusses right can be challenging and often requires the help of a professional to iron out the more technical snags. Despite the growing prevalence of steel structures, timber trusses remain highly popular because they are more cost-effective, graceful appearance and are more energy efficient.

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