Exactly:)
David and Marcel have the info that has been in place for years.
If bracing is required it is labeled on the truss locations and, at the very least, was specified in the engineering documents traveling with the trusses.
Same issue with piggy back trusses mounted on the top of other trusses. Some require 2x4 scabs to connect the two together and some do not. It depends on the sizes involved and whether or not a seam in the roof sheathing is within one foot of the truss joints. It’s better to have a photographic memory of houses than a photographic memory of the IRC when it comes to engineered structures.
I would say it would be a call out if there was bracing and it was cut away to accommodate the AC guy or some other obvious modification. But if they were engineered trusses, Its on the engineer not the home inspector. The trouble with writing beyond the SOP is that now you are speaking as an expert in the field. if there is another engineering deficiency that may not be visible or recognizable, you could be held accountable because you already made a statement that would present yourself as an expert in the field.
Good advice but does not apply to those who have the right inspection agreement wording.
Everyone should have something to this effect in their agreement: Any issues reported that are beyond the scope of the SOP are included as a courtesy and not intended to change this agreement in any way.
I doubt any inspector can inspect more than a few houses without finding a problem that technically, he does not have to report but will anyway to protect the client and himself.
Mold like substances are not part of the SOP but would you leave it out of the report? :shock:
The compressed cords could buckle due to snow load;-)…
Lateral bracing would not affect that possibility though, failure due to compression would be due to inadequate truss design for conditions.
NBC 9.23.13.11 (3) Where the length of compression web members in roof trusses described in Sentence (1) exceeds 1.83 m, such web members shall be provided with continuous bracing to prevent buckling.
(4) Bracing required in Sentecnce (3) shall consist of not less than 19 mm by 89 mm lumber nailed at right angles to the web members near their centres with at least two 63 mm nails for each member.
Rarely ever see truss bracing here.
Any snow in AZ?
Lot’s in the Northern end of the State. Snow there now…
It comes down to training and experience… the purpose for bracing of trusses has more to do with initial installation and at times the area the home is built…manufacturers do not differentiate between the two in order to CTA.
Unless there is something unusual about the roof design, I typically do not call it out.
Jeff
This week, I am attending ICC training on the 2009 IRC. It’s an all week course. As luck would have it, today we discussed truss bracing. I specifically asked the instructor, John Gibson (an engineer), if the code below required some sort of bracing in all circumstances. His answer: “Yes”.
He interpreted the code, as I do, to say that trusses “shall be braced”. If it’s not addressed in the truss design drawings, then the TPI/HIB bracing requirements apply. Bottom line, he said, is that you should see some degree of bracing somewhere for a truss built roof structure. Additionally, he said that the sheathing is not considered bracing, although it certainly does add stability.
That still does not make me change my stance on truss bracing… It’s not my job to red flag engineered truss designs.
That’s not lateral bracing through, that’s basically 2x4s nailed flat to the edge of the webs, so that the cross section forms a “T”. knowing when to call out the need for additional compression bracing to be installed is for an engineer.
I’m not familiar with the “NBC”, is that the Canadian building code?. Even if the IRC called out for “some bracing” that’s way too vague for me to ever call lack of bracing a defect.
THE NEED FOR BRACING IS UP TO THE BUILDING DESIGNER (see below).
** Wood Truss Bracing**
by Dr. Frank E. Woeste, P. E.
While metal-plate-connected (MPC) wood trusses have become to a large extent the standard way to frame residential and light-commercial structures, the responsibility for bracing design is still fuzzy for some truss users. For example, one common misconception is that the truss design drawings contain permanent bracing design specifications for the roof system. The purpose of this article is to clarify the bracing design responsibilities when using MPC wood trusses.
Permanent Truss Bracing
Permanent bracing is required to stabilize the truss members (chords and webs) in the vertical plane of each truss for the life of the structure. Permanent bracing must be designed to resist design loads that are specified by the Building Designer. With respect to wood trusses, ANSI/TPI 1-1995 defines the Building Designer as follows:
2.2 BUILDING DESIGNER
Building Designer - is the design professional individual or organization having responsibility for overall building design, in accordance with the state’s statutes and regulations governing the professional registration and certification of architects or engineers. This responsibility includes but is not limited to foundation design, structural member sizing, load transfer, bearing conditions, and the structure’s compliance with applicable building codes. Also referred to as registered architect or engineer, building designer, and registered building designer, but hereinafter will be referred to as building designer.
The responsibility for permanent truss bracing design is stated in ANSI/TPI 1- 1995 National Design Specification for Metal Plate Connected Wood Truss Construction. ANSI/TPI 1-1995 was adopted by the three model codes, and thus it is the appropriate code reference for matters involving MPC wood trusses unless the local authorities have alternate provisions. Section 2.2.2 (d) and (e) of ANSI/TPI 1-1995 specifically addresses permanent truss bracing:
2.2.2 As this Standard does not cover the design for the complete structural system of a building, the Building Designer shall provide for the following in the design and detailing of the building:
(a) Truss deflections (b) Truss movement due to moisture and temperature change (c) Truss supports and anchorage accommodating horizontal, vertical or other reactions or displacements
(d) Permanent truss bracing to resist wind, seismic and any other lateral forces acting perpendicular to the plane of the truss (e) Permanent lateral bracing as specified by the Truss Designer, to prevent buckling of the individual truss members due to design loads.
ANSI/TPI 1-1995 contains additional information on permanent truss bracing and can be purchased from the Truss Plate Institute (608) 833-5900.
The Truss Designer specifies on the Truss Design Drawings the members that are assumed to be sheathed and the assumed points of lateral support for members without sheathing, if support is required. For example, if a 10-foot web is overstressed in compression, then the truss designer may indicate on the Truss Design Drawing that the center of the web is to be braced against lateral movement. It is up to the Building Designer to determine how that point should be stabilized under the specified design loads. The most common way is to use a continuous lateral brace (CLB) in combination with diagonal braces at some interval.
The Building Designer must determine the spacing of the diagonal braces needed to stabilize the CLB’s. Figure 5.3.3.2(c) of ANSI/TPI 1-1995 depicts how a CLB is stabilized in the roof structure by the use of diagonal braces.
Another option for stabilizing the center of the example web is the use of a T- brace, usually a 2x4. Typically, T-braces extend the full length of the web minus a few inches on each end. The Building Designer must specify the T-brace size, grade, length, and nailing schedule. The advantage of the T-brace approach is that only one member is needed to brace a point on a truss member versus the CLB approach that requires both a CLB and diagonals. In instances where only one truss of a kind is installed and neighboring webs (or chords) don’t line up, a T-brace may be the only practical option.
Some Building Designers incorrectly assume that if a brace is attached to the “bracing points” shown on Truss Design Drawings, then the roof system is braced. The fallacy of this assumption can be explained by the concept of “load paths.” When a CLB is only nailed to a series of webs (or chords), it does connect the webs but the CLB has no load path. The CLB is free to translate in space, either left or right, with no resistance. The CLB must be stabilized by connecting additional members to it, that transfer loads to another part of the roof structure, that is connected to yet another part, and so on. When diagonals are used to stabilize CLB’s, the load path would be
• Web to CLB • CLB to diagonal(s) • Diagonal(s) to truss panel points • Truss panel points to roof, ceiling, or other diaphragm • and eventually to the foundation.
A new publication, Commentary for Permanent Bracing of Metal Plate Connected Wood Trusses, is available from the Wood Truss Council of America (WTCA) by calling (608) 274-4849. This 26-page document points to typical cases where permanent bracing is needed, and gives some strategies for providing the required lateral support to members.
Excerpt from the Commentary:
“Wind loads acting perpendicular to the side walls will cause lateral forces acting across the width of the building. These lateral loads are usually designed to be transferred through the stiffness of the roof/ceiling/floor diaphragm into the end walls, or into interior shear walls, portal frames or partitions. The choice of how to resist these lateral forces is the responsibility of the Building Designer.”
In summary, when a Truss Design Drawing shows that a point on a truss member is to be laterally restrained (by the assumptions of the truss design), then the Building Designer must provide a design for the lateral restraint of the point and the forces generated by the restraint must have a load path to the building foundation. When compression member is braced by only one CLB, it is a common practice to assume that 2% of the axial member force is required to stabilize the member. The contractor is responsible for installing the permanent bracing design for the roof system.
Temporary Bracing
As life-safety is involved, the importance of effective temporary truss bracing can not be overstated. The responsibility for temporary bracing design and installation is also stated in ANSI/TPI 1-1995:
**
GENERAL**
Metal plate connected wood trusses are planar structural components. Structural performance depends on the trusses being installed vertically, in-plane, at specific spacing, and being properly braced. The installer is responsible for receipt, storage, erection, installation, field assembly, and bracing.
Four industry documents currently provide recommendations for temporary bracing. The documents include DSB-89 Recommended Design Specifications for Temporary Bracing of Metal Connected Wood Trusses
(TPI, 1989), HIB-91 Commentary and Recommendations for Handling, Installing, and Bracing Metal Plate Connected Wood Trusses Pocketbook (TPI, 1991), HIB-91 Summary Sheet (TPI, 1991), and HIB-98 Post Frame Summary Sheet (TPI, 1998). All documents are available from the Truss Plate Institute.
Alpine Engineered Products, Inc.(1996) in cooperation with WTCA produced a temporary bracing video that contains a segment on “buckling behavior” of a compression chord. A 60-foot parallel chord roof truss was placed in a testing laboratory, and inadequately braced by a series of temporary lateral braces only. The bottom chord was loaded with buckets containing weights that simulated the weight of truss installers. With one bucket lowered onto the bottom chord, no noticeable truss movement was visible in the video. Next, the second bucket was lowered onto the truss. The top chord slowly buckled into the classic S-shape, with the chord severely bending between points of lateral support. Finally, a third bucket was lowered onto the truss and the truss violently collapsed. Reviewing this sequence can be very educational for erection personnel. The video can be purchased on the Internet at WWW.WOODTRUSS.COM, or by calling WTCA.
Frank E. Woeste, P. E. is a professor of wood construction and engineering at Virginia Tech University, Blacksburg. He specializes in the engineering and performance of wood buildings. He can be contacted by e-mail at fwoeste@vt.edu
or by telephone (540)231-6093.
I agree with Randy, unless you see failure or read the truss installation requirements you can’t suggest upgrades or additional bracing. The most comon CYA Ploicy used by HIs is (The home received a Cerfiticate of Occupancy, it met local code.) Above your SOP!
Well Wward, that wouldn’t apply on a framing inspection / pre drywall inspection, now would it? We are talking about if it’s right or wrong, not if it received the C of O.
Good post started here Joe F, interesting, good info, thanks. Actually it is applying to an inspection I’ve got. House trusses had the lateral bracing tag w/ no lateral bracing.
National Building Code (NBC) is for Canada; some provinces improved on the NBC, for example the Ontario Building Code (OBC).
Trusses manufacturers have drawings and specifications for builders but some builders cut corners…
If no drawings and specifications are available on site from the trusses manufacturer and compressed cords are longer than code would permit without proper braces then it is reported…
Cheers,
Wow, that is kind of refreshing NBC actually calls out a minimum. Here in the states because of the fear of litigation most of our authorities ie the ICC do not put a lot of definitive requirements in the code. Most generally it is referenced to a testing standard or another a trade organisation.
As far as wood truss construction is concerned the ICC deflects all requirements to the building designer and to meet the requirements of WTCA/TPI. So theoretically the only required permanently installed bracing is bottom cord permanent lateral support (rat runs) installed 10’ o.c. which includes diagonal bracing installed at 20’ intervals.
With that said the need for compression bracing (web) is directly related to the design. Many times I have sent a plan to bid and have ended up awarding the job to the higher bidder because after considering the hidden costs (labor and material for bracing) the high bid in the long run was actually cheaper. Required bracing has a direct relationship to the size of truss plates and the grade and species of lumber used in the design
Mark, you say Building designer. I would hope you mean Architect or Engineer. Anyone can be a designer, not everyone can be an Architect or Engineer. (takes lots more education and a license)