Tag Archives: ANSI/ASBE S618

Will I Need to Use Double Trusses?

Will I Need to Use Double Trusses?

Reader DALE in TOMPKINSVILLE writes:

“On an open front 5 bay tool shed, roof length 60 feet, width 40 foot, height of 10 foot, 12foot, trusses on 6×6 columns, 12/4 pitch located in southern Kentucky zone 6 will I need to double the trusses?”

Need and want are two different things. In all likelihood, single trusses will support your climactic loads. Double trusses do have some distinct advantages however.

ASABE (American Society of Agricultural and Biological Engineers) published ANSI/ASABE S618 “Post Frame Building System Nomenclature” in December 2010. For those who are unfamiliar ANSI stands for American National Standards Institute (www.ansi.org). ANSI is a private non-profit organization overseeing development of voluntary consensus standards for United States products, services, systems and personnel.

In ANSI/ASABE S618, a Metal plated connected wood truss would be described as, “A truss composed of wood members joined with metal connector plates (also known as truss plates). Metal connector plates (MCP) are light-gauge, toothed steel plates. The most common type of light wood truss.” Ganged wood trusses are defined as, “A truss designed to be installed as an assembly of two or more individual light wood trusses fastened together to act as one.”

nailing trussesFor Hansen Pole Buildings, any time we are using a “real” double (more specifically ganged) truss system, we specify top chords to be a minimum of 2×6, regardless of loads. I say “real” because placing a single truss along each side of a column is not a double truss. They are two single trusses, acting independently from each other. A true double truss system, such as used by Hansen Pole Buildings, features trusses physically attached face-to-face by means of mechanical connectors (e.g. nails, bolts, etc.). This allows for two members to actually load share, reducing probabilities of one weak single truss failing and pulling a roof system down with it.

True ganged trusses, due to their load sharing capabilities, often are able to utilize smaller steel connector plate, smaller or lesser dimension lumber for chords and/or webs, and require far less lateral bracing. Often utilization of two-ply ganged trusses results in a less expensive overall structural design solution, when all factors are taken into consideration.

Three sided buildings also pose their own unique set of structurally challenges, please read more here: https://www.hansenpolebuildings.com/2014/03/three-sided-building/

See the Pretty External Wall Girts?

See the Pretty External Wall Girts?

Readers of my latest two episodes are probably beginning to feel familiar with this commercial post frame building. As well as its challenges.

I will first point out something in this photo I find to be odd, although not (surprisingly) necessarily a structural deficiency.

Outside board on this building’s roof eave line is known as a fascia or edge purlin. A fascia purlin is defined (in ANSI/ASABE S618 “Post Frame Building System Nomenclature”) as, “a purlin that helps form the fascia of a building”. An edge purlin is, “A purlin in the most outer row of purlins. All fascia purlins are edge purlins but not all edge purlins are fascia purlins.” Looking at this fascia purlin, note there is a dark portion roughly 4-1/2 inches in width aligned with each wall column. These are truss ‘tail’ ends. This builder installed fascia purlins between truss tails, rather than across them as indicated on engineer sealed plans and our Construction Manual.

Effectively this should have made precut soffit panels all 1-1/2 inches too long, leading me to believe it is possible this building is three inches narrower than planned!

How fascia purlins are attached is yet another issue, as through nailing into truss tail ends was specified.

Now onto what is really an issue, not structurally, but from a functional standpoint. This commercial building’s owner is planning upon climate controlling it. As part of being able to effectively insulate walls, materials for commercial bookshelf girts were provided (as well as specified on plans by the engineer).

For extended reading on commercial bookshelf girts, please see https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/.

As we have seen from previous articles, this particular builder was not too savvy when it came to looking at plans. I suspect they are neatly tucked away behind a rear seat in his crew cab pickup.