What are Roof Trusses?
Roof trusses are the primary building elements of a roof system. It used to be that when the framing carpenter built a house, part of that construction ALWAYS consisted of building the roof system. They did so with rafters. It was time consuming and if the framer was not that great, he may not have properly calculated what was necessary to build a strong roof. This may be why in old neighborhoods there are sagging roofs. Rafters start as straight wood members but over time, since there is not typically mid-beam support they begin to sag. This is especially true in areas where there is snow and the roof may have to hold additional weight for weeks or months at a time.
As home construction became more and more specialized, so did the building materials used. Roof trusses became more the norm.
I've decided to cite the professionals at artruss.com for a good definition of a roof truss.
“A roof truss is a rigid, strong framework made up of wood members, such as 2" x 4"s, fastened and held together by metal connector plates. This framework accounts for the shape of your roof and supports the roofing materials. Roof trusses are designed according to ancient geometric principles. Many of the bridges you drive over were designed using the same principles.”
Why are Roof Trusses Better?
Because each truss is individually engineered to be a part of a roof system. They are designed for whatever area the build will take place. If the house is built in an area that receives snow, trusses will be engineered and designed to withstand snow loads. If heavy tile is used for roofing material, that calculation is made. Also, because of technology and the exacting manufacture of trusses in manufacturing plants, the owner builder has a number of options for the inside of their home. Vaulted ceilings, coffered ceilings, attic space areas, etc, can be caculated into truss plans. It may cost more, but it can be engineered.
Trusses also go up much faster than a rafter built roof. Normally, roof trusses are “swung” in one day. After the walls are complete, the framing contractor will schedule a crane for a day or for several hours. It is important that the job site is clear of non-essential personnel and there is access. Cranes are EXTREMELY expensive and delays can be aggravating and costly for your framers. The ground personnel take each truss ( marked individually for it’s proper placement and purpose), strap a chain to it and hoist it up to framers who are working the top plates of the house. These framers move the trusses into position and nail them into place.
If it is windy or rainy, do not expect your framing crews to swing trusses. It is probably one of the most dangerous jobs in residential construction. Each truss is like a 500 lb sail and will knock a man off the top plate easily. Remember, Safety is Paramount!
Any material should be ordered using the same principles as obtaining construction bids. Be sure to go to at least 3 suppliers. It is best to go directly to truss companies for a bid. Sometimes your lumber supplier can get a better price due to their volume discount but typically the truss company will be able to give the best price.
The process is simple. Call the truss company and make an appointment. Take in your blueprints with you when you go. The truss company will probably want to review your plans with you. You will leave a set of drawings and they will engineer a truss plan for the house. They will put together a bid. Be sure to discuss lead times for manufacture and delivery of the truss package. When all the calculations are complete, they will submit the truss plan and the bid to you for review.
Because each package is engineered, your decision can be based on fewer items. First, check with some local contractors and see how happy they are with product delivery and timeliness. Second, compare the bid prices. If the company has a good record for on time delivery and suitable placement of materials, you can go with the lowest bid. Roof Trusses may be ordered with your lumber package.
When Do I Get My Truss Bid?
Do not wait to submit your plans to truss companies for bids. In many municipalities it is a requirement to have your engineered truss calculations before you apply for building permits. Waiting to get truss bids will hold up the approval process. Also, some companies charge to do a truss bid and some do not. If there is an initial cost, it is charged to you when you pick upthe bid but credited if you order trusses from that company. However, if their proposal is higher than another, you may not award the contract to that company. Seek out suppliers that offer a free estimate.
Delivery and Staging
Roof trusses should be delivered the day before it is scheduled to swing trusses. Trusses should not sit out for a prolonged period in the elements. Waterlogged trusses are heavier on connection joints and increase the risk of possible separation of the members. Having material sitting out on the job site also increases the risk of manmade damage. Vehicles could be inadvertently driven over corners, etc.
Do not place the truss pack on uneven ground. Again, this has the potential of stressing the connections and compromising the overall engineered strength of the truss. Stage the truss package close to the building in a position advantageous for access by the crane. Discuss and coordinate this with your supplier and your framing contractor.
Roof Trusses and Home Design
When designing your home, consider these truss related facts. You may be required in your area to have a higher pitched roof due to substantial snowfall. If the pitch is less, a variance MAY be possible if the engineered strength of the trusses is increased. Some designs, such as Santa Fe style homes with 1/12 pitch and parapets, may not be practical or within code in a high snowfall area. Also, identify how much of an overhang you would like on your trusses. A longer overhang can contribute to energy cost savings by adding more hours of shade per day.