Snow Retention - The Invisible Code

SHEATHING/ROOFING MATERIAL FAILURE

Roofing Material Is InadequatelySecured for the Shear Created bySliding Snow

If the roofing material is not securelyfastened to the deck (specifically on standingseammetal roofs), added weight can causethe standing-seam metal roof to slide rightoff, along with the rest of the roofingmaterial and snow retention system.There is a code requirement in placefor wind uplift on standing-seammetal roofs but not for shearstrength of the installed panels.

Screws or Fasteners Pull Out

When installing snow retentionon roof sheathing, the thickness and type ofthe sheathing determine the fastener pulloutstrength. If one is installing a snowretention system on ....-in. OSB board, thefastener will fail more quickly than whenusing .-in. plywood. When designing a layoutfor a project, many snow retention manufacturersdo not test for these variations. Ifthe snow retention system was designed for.-in. plywood and the project is using ....-in.OSB board, the entire system needs to beredesigned.

The Fastener Does Not Penetrate theSheathing

If the fastener/screw is not penetratingthe sheathing, the snow guard will not havethe holding strength for which it wasdesigned.

ADHESIVE FAILURE

When using an adhesive, if the surfaceis not free of dust, dirt, oil, or waterproofingor it is not clean and dry, the adhesive willnot bond properly (Photo 2).If the temperature is not above 50ºF(10ºC), the sealant will not cure. If a load isplaced on the snow guard before the 28-daycure time, the snow guard is more likely to fail.

SYSTEM FAILURE

The System Is Not Designed for theRoof Slope and Snow Load

When designing a snow retention system,factors change from project to project:the slope, roof type, sheathing type, androof snow load. If the snow retention systemis not engineered for the variables of theproject, it can fail (Photo 3).

Most Snow Guards Are Not Tested tothe Fail Point of the System

Many snow guard manufacturers claimtheir products are tested, and many of themare, but they are not tested to the fail pointof the entire system. The product may betested to maintain its shape, but was it testedto stay on the roof? It’s great if the productstays in one piece, but not if the fastenerfails, the adhesive fails, and the sheathingfails.

INSTALLATION FAILURE

The Product Was Not Installed toManufacturer’s Specifications

The manufacturer’s instructions needto be followed meticulously in order toensure safety and to keep warranties in effect. Manymanufacturershave specifictorque requirements,as well asplacement andmaintenance instructions.Ifthese are not followed,the systemcan fail andthe manufactureris not at fault.Obviously,there are valid reasons why the UnitedStates should establish codes for snowretention on roofs. Why hasn’t this happened? A few reasons follow:

1. 1. Snowfall occurs in certain areas ofthe country but not nationwide;therefore, the demand for codes issporadic.
2. 2. Not many deaths occur due to slidingice and snow.
3. 3. Property damage is localized.
4. 4. The insurance industry is not pushing for this type of code.
5. There are many other codes in place toprotect people and property, so why not forsnow retention? We have codes for winduplift and ICC test standards for productfailures due to wind and moisture penetrations,to name a few. How many lifethreateningevents (Photo 4) need to occurbefore we do the right thing when it comesto a code for snow retention on roofs? It’s time to make the invisible snowretention code visible.

REFERENCES

1. Surebond Technical Data Sheet SB-190.

Terry E. Anderson has been in the roofing industry for over35 years. He is the owner of Anderson Associates Consultingand president of T.R.A.-MAGE, Inc., a manufacturer of roofsnow and sun accessories. Anderson was sought after tosolve tile roof problems, eventually researching solutions tothe frequent structural damage caused by sliding snow andice. Traveling to Europe, Terry studied how the roofing industrythere successfully dealt with snow and ice issues. Usinghis years of experience and research, he coauthored Concreteand Clay Tile Roof Design Criteria for Cold and Snow Regions. Anderson founded T.R.A.Snow and Sun, now in partnership with MAGE and known as T.R.A.-MAGE, and is recognizedas a leader in snow retention systems. He is a member of RCI, WSRCA, and onthe technical committee for the Tile Roofing Institute (TRI).

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Snow Retention - The Invisible Code