Frequently Asked Technical Questions
What level, if any, of responsibility does a CM assume if the contractors on the jobsite use our layout plans to do more than just put the walls together? Specifically on the job in question, the panel layout was used to place plumbing for a kitchen island. Unfortunately, the layout had the pony wall for that island out of place by 11”. As a result, there is additional work needed to relocate the plumbing. We send the layouts as a guide for the framers to know what goes where numerically and have never implied that the layouts were specific enough to use in place of the actual engineered prints. Has this issue come up before? If so, how was it handled?
Some truss lumber repair nailing patterns call for 16d common nails. Most nail guns do not support 16d nails, but have an equivalent to a 12/10d nail. Is there a substitution guide or ESR report that could help us?
I recall seeing a design recommendation several years ago regarding installation of hanger nails above the neutral axis of the bottom chord of a plated girder truss. The intent was to avoid dumping large loads into the bottom chord, below the neutral axis. Can you tell me where I can find this information?
If you use hurricane clips to secure roof trusses from uplift, are you allowed to use fewer than the typical three nails in the bearing heel of the roof truss? I am concerned because we want to do the right fastening schedule, but three nails in addition to the hurricane clip splits the wood. What is the standard recommendation?
What is the correct method of attaching scissors trusses to the top plate? I read recently in a trade magazine that this type of truss should be toe-nailed on one end and attached with slotted clips on the other end. According to the article, this is to allow for movement of the truss. We require PE stamped spec sheets from the truss manufacturer to verify trusses meet wind and snow loads. These sheets give bracing requirements but never give recommended attachment requirements.
Are there any trusses that are supported strictly by the wood itself without any mechanical connections such as brackets?
I am a building inspector and have some questions regarding how to apply IBC 2012 2308.8.5 (IRC 2012 R802.8) (similar IBC 2015 2308.4.6 & IRC 2015 R802.8) to trusses, especially those with high heels:
2308.8.5 Lateral support. Floor, attic and roof framing with a nominal depth-to-thickness ratio greater than or equal to 5:1 shall have one edge held in line for the entire span. Where the nominal depth-to-thickness ratio of the framing member exceeds 6:1, there shall be one line of bridging for each 8 feet (2438 mm) of span, unless both edges of the member are held in line. The bridging shall consist of not less than 1-inch by 3-inch (25 mm by 76 mm) lumber, double nailed at each end, of equivalent metal bracing of equal rigidity, full-depth solid blocking or other approved means. A line of bridging shall also be required at supports where equivalent lateral support is not otherwise provided.
Commentary: When the depth-to-thickness ratio (based on nominal dimensions) of joists and rafters exceeds 5:1, as would be the case in members larger than 2 inches by 10 inches (51 mm by 254 mm), the minimum lateral support required by Section 2308.8.2 is not sufficient to prevent lateral buckling between supports. Additional restraint is required. Sheathing, subflooring, decking and similar materials attached to each joist or rafter are considered to provide edge restraint. These requirements are cumulative. The lateral support required by Section 2308.8.2 applies to all joists. Additionally, members greater than 2 inches by 10 inches (51 mm by 254 mm) must have one edge held in line, and members greater than 2 inches by 12 inches (51 mm by 305 mm) must have one edge held in line as well as a line of bridging at each 8 feet (2438 mm) of span (which may be omitted if both edges are held in line). The section also prescribes acceptable bridging methods.
Is this requirement for framing true for all truss end bearing conditions regardless of truss heel height? What are the proper methods to achieve solid blocking? Is the combination of roof sheathing, gypsum wallboard on the ceiling and a hurricane clip on one side of a truss an acceptable substitution for solid blocking? How would one solid block a truss at intermediate bearing points? Do truss engineers account for rotation and lateral displacement in their truss design or is this the responsibility of the structural engineer or building designer?
Would you please inform me of the specified requirements of the size and the amount of nail attachments from the truss to the top plate?
The industry suggests notching the gable end truss to support the overhang. Is this wise? What about a structural gable, or a gable designed with drag loads, or one with only partial bearing? How safe is it for a framer working with a truss that has the top chord cut repeatedly?
I am remodeling a 16-year-old ranch style home. The roof consists of 4/12 26 ft. span trusses, 24 in. O.C., over 2x4 stud walls. What is the recommended means of affixing the top plate of new interior partitions to provide the lateral support needed for the partition? Also, I want to hang a soffit above and overhanging the new kitchen cabinets (recessed lighting placed within). What is the recommended means of attaching the soffit to the underside of the trusses so as not to interfere with the designed movement of the trusses under the variable live load experienced (snow load)?