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By: John F Mann, PE 1212 Main St, Belmar NJ 07719

I am a professional engineer licensed in NJ and PA, with 30 years experience in structural engineering. I am often involved in review of roof trusses for new construction and investigation of roof truss defects.

I have been following reports in the Island Packet of roof truss problems with Sun City homes, as reported since April. The following comments may be useful for homeowners.

Based on my experience, problems often occur with design and construction of roof trusses, especially when relatively high wind forces must be considered.

For Sun City, problems with connection of the VT (valley) trusses are an indication of more severe defects with design and construction.

Reports to date have not identified the following key players; (1) Truss manufacturer, (2) Truss designer, (3) Truss engineer (if applicable), and (4) Building designer (architect).

The engineer identified in articles was brought in long after building design plans were prepared, indicating that a structural engineer may not have been involved with original building design, or review of truss diagrams.

Roof trusses must resist relatively large wind uplift force at this location, in accordance with standard building code requirements.

Per the standard industry design code by the Truss Plate Institute (TPI), the truss designer is completely responsible for design of all connections between trusses; such as between VT trusses and main roof trusses. Complete design details for the VT truss connections should have been issued by the truss manufacturer, along with truss diagrams, so that construction workers could understand how connections were supposed to be made.

Wind uplift force applied to the top of VT trusses must be transferred down to main roof trusses only through the vertical “web” members of VT trusses. Therefore, connections directly under the vertical web members must resist all the wind uplift force. Toenailed connections between verticals are not effective unless and until connections directly below the verticals were to fail.

Toenails are not appropriate connectors to resist wind uplift for roof trusses, especially at this location where wind uplift forces are very high. As seen in photos, toenails easily split the wood of roof trusses, resulting in complete loss of connection capacity, as well as damage to the roof trusses that may warrant structural repair.

The building designer (architect) is responsible for design of connnections between roof trusses and supporting elements, such as walls. Calculation of wind uplift pressures on roof surface areas, along with forces to be resisted by roof trusses and connections, is relatively complex. An architect should hire a structural engineer to perform design of such connections if the architect is not qualified to determine wind uplift forces and design connections.

For one roof truss, wind uplift pressure to be considered must be calculated using "components and cladding" provisions of the building code. This essential requirement is very often overlooked by building designers. Wind uplift values that are sometimes published on truss diagrams are very often incorrectly calculated using other (mean wind force) provisions of the building code, instead of the correct provisions.

Wind uplift force that must be resisted (per building code) at each end of main roof trusses is very high for this location, assuming main trusses have been designed to be supported only on outside walls. If main trusses are about 50 feet long, spaced at two feet, wind uplift force that must be resisted at each end is more than 1,000 pounds. A strong light gage steel connector (hurricane tiedown) is necessary.

Wind uplift forces must be transferred through the structure, down to foundations. For long roof trusses with relatively large wind uplift forces, this key requirement can mean that very large connections are required at the ends of "header" beams over window openings. For the example noted above, if four (4) main roof trusses are supported by one header beam, a wind uplift force of about 2,000 pounds would be required at each end of the header beam. Another similar connection would be required to connect wall studs to foundation, below end of header beam.

Many more aspects of roof truss design and construction should be evaluated, based on building design plans, truss diagrams and as-built construction. Key requirements are (1) Permanent lateral bracing and (2) Gable endwalls.

Comments 9-5-07

I try to stay informed about truss problems when reported. I first found out about the Sun City truss problems via one of the trade publications that covers the industry.

Although Truswal may be the truss manufacturer, I have not seen any specific description of Truswal as the manufacturer in the Island Packet articles or in the Pulte letters available online.

The valley truss connection drawing by Truswal is only a generic drawing that is not intended, and does not necessarily apply, for any specific Sun City roof. Although this generic drawing could be used to install correct connections, a knowledgeable supervisor would have to provide interpretation for each specific house.

Proper design and analysis of toenailed connections requires knowledge of the standard design code for wood construction (NDS), as well as practice using the detailed provisions of that code for nailed connections. Such knowledge is not generally obtained during undergraduate engineering school study.

Where design wind speeds (in accordance with standard building code wind map) are relatively low (such as inland areas), properly installed toenailed connections could be acceptable, at least from a theoretical point of view. However, along the east coast, and especially along the southern east coast, design wind speeds are obviously high, such that toenailed connections are most certainly not adequate for roof trusses.

Wind force (including wind uplift on roof surfaces) varies with the square of wind speed. For example, wind force caused by 80 mph wind speed is four (4) times as large as wind force caused by 40 mph wind speed. Wind force caused by 130 mph wind speed is 2.6 times as large as the 80 mph wind force and 10.5 times the 40 mph wind force.

Comments 9-6-07

Connections between so-called "valley" roof trusses and supporting main roof trusses should be designed by the responsible truss designer / engineer that works for the truss manufacturer. This is required by the industry design code (by Truss Plate Institute) that is referenced in the building code for prefabricated wood trusses.

If the builder / developer is also the truss manufacturer, then the engineer working for the builder can take responsibility for truss-to-truss connections. Otherwise, the builder is effectively voiding the warranty provided by the truss manufacturer.

Whichever engineer is responsible for connection design, that engineer should have prepared a design drawing to clearly specify and show how modified connections are to be made. Inspectors should not be making "design" decisions in the field.

Wood screws of adequate size (gage) and length, might have adequate pullout capacity to resist wind uplift force required by the building code. However, any connector (nail or screw) installed at an angle relative to the vertically oriented uplift force is also subjected to horizontal "shear" force that can greatly reduce the effective pullout resistance.

Net result is that light gage steel connectors (hurricane ties or clips) are a much more secure method of making connections to resist wind uplift, especially in areas subject to hurricanes.

Much more important than the valley truss connections are the required connection at each end of each main (long) roof truss, which must resist much greater wind uplift force than the small valley trusses. There has been no description in any articles to date about inspections of these essential connections or whether the building design plans even specified light gage steel hurricane tiedowns. The building designer (architect; or structural engineer working for the architect) is completely responsible for design of connections between roof trusses and building elements such as supporting walls.

Wind uplift force on roof surfaces must be transferred down to foundations, through roof framing and then through walls and other supporting elements.

Long main roof trusses supported by "header" beams over window openings cause very high wind uplift forces at each end of the header beam. A very strong connection is therefore required to resist wind uplift at each end of the header beam. Another connection is required to connect wall framing to the foundation. These connections should have been designed by the building designer and clearly specified on building design plans.

Comments 9-14-07

The writer correctly identifies adequate inspection as being essential to enforce the building code and building design plans. I have noted the same point in previous comments to various blog posts about the Sun City roof truss connection defects.

However, municipal code officials and inspectors are not more responsible for adequate design and constructon than the building design professionals (architect, engineer) or the builder.

Building defects are essentially due to inadequate design, inadequate construction, or a combination of both.

Licensed design professionals (architect, engineer) have complete responsibility for building design. Municipal code officials are not responsible for design of the building and are not authorized to order design changes. Although code officials generally review design plans, such review is not intended to be a comprehensive analysis of building design, which would require the services of other licensed design professionals.

Municipal inspections should never be considered to alleviate responsibility of the design professionals and builder.

Design professionals are responsible to ensure that the building design plans conform with all requirements of the building code and include sufficient details so that the builder can construct the house without guessing.

The builder is responsible for building the house in accordance with design plans. If plans do not include adequate details, the builder should request clarification from the design professional before proceeding.

Problems such as the reported defects with "valley" truss connections are very likely not the only problem with roof trusses. See my prior online comments to various blog postings for more detailed discussion of potential defects. Homeowners should insist that the County inspect connections at the ends of the main (long) roof trusses, which must resist much, much greater wind uplift forces.

However, homeowners should understand that a complete evaluation of roof truss defects can only be performed by a qualified structural engineer, based on evaluation of building design plans and "as-built" construction.

John F Mann, PE