Metal roof with no snow guards, Poughkeepsie, NY (C) Daniel FriedmanSnow Guard Building Codes & Standards
     

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Snow retention system building codes?

This article discusses standards & codes for snow retention system and answers "no" to the simple question of is there a snow retention system buiding code.

This article series illustrates types of snow guards or snow brakes or other snow retention devices used on metal, rubber, asphalt, and slate roofs and we explain and illustrate in photographs just how and where these devices are attached to building roofs. We give the reasons for snow & ice retainer use and their history.

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Is there a Snow Retention System Building Code?

Metal roof snow brakes - Bard College (C) Daniel Friedman

The short answer: no.

A snow and ice retention system that mounts to a standing seam metal roof by connecting to the roof covering has to resist the forces of snow and ice pressure by transmitting those forces from the snow fence or snow guard to the roof surface and through that roof to the roof mounting clips.

There are building codes for building roof system wind-uplift resistance on metal roofs but there are not building codes that describe the "shear strength" resistance for the fasteners used to secure metal roof panels to the roof deck.

Failures in the mounting system for snow retention devices can occur if the snow retention system is not adequately secured to the building structure itself. Damage to the roof or roof covering can also occur if the total snow and ice load bends or breaks the roof covering (such as a standing seam metal roof).

If the total load causes the roof mounting clips beneath the metal roof to shear. In our OPINION given the total number of clips used to secure the length of a standing seam metal roof panel to the roof deck below, the chances of shearing of all of these roof mounting clip screws, properly screwed to a sound plywood or even OSB roof deck should be minimal.

However it is plausible that high snow and ice loading near the roof edge, imposed against snow guards or a snow fence in that location, could provide a bending force that pulls fasteners out of the roof deck, bending or damaging the roof, and sending snow guards and snow and ice to the ground below.

Adhesive failures are reported by Galow, Anderson, and others as a common snow retention system failure for glued-on snow guards on metal roofs, as we discussed above. [15][20]

Structural damage can occur if the snow retention system is not properly located on the roof. See SNOW GUARD SPACING & PATTERN for an explanation of ice dam loading on roof extensions.

The load on snow guards as well as the relationship of snow loading on roofs and the use of snow guard was investigated by Tobiasson (1996) et als. who concluded that improved design guidelines, standards and performance criteria are needed for snow guards on metal roofs.

There are however recommendations for snow retention system installation from the manufacturers of these systems. See SNOW GUARDS on METAL ROOFS for examples.

References for Snow Guards, Installation Methods, Standards

Metal roof with no snow guards, Poughkeepsie, NY (C) Daniel Friedman

Installing Snow Guards on a Poorly-Secured Metal Roof

Question: snow avalanches off of a poorly-secured standing seam metal roof in Maine

2016/06/07 V Dornan said:

I have a metal roof newly installed, new construction in Maine. Last winter the avalanches of snow and ice coming off the roof were dangerous (for adults and grandchildren) and created snow banks in front of the garage door and entry door.
I am looking at snow bars/guards.

However I have read about the caution of attaching snow bars to standing seam roofs because of structural damage that can happen to the roof. It transpires that the builder used the least expensive materials and quickest methods; I am not sure, but (rather, I am pretty sure)....probably the same shoddy building practice he executed in all other areas of the project...is the same with the roof. It is 29 gauge, snap lock with exposed fasteners along the bottom edge.
My questions are:

1. How wise/unwise would it be to have snow bars installed on a structure that is 32' x 32' with a plain roof half facing north and half facing south?

2. How likely am I to find a metal roofing specialist willing to take this on?

Reply: Do's & Don'ts on repairing & attaching snow guards to a poorly-bonded metal roof

VD

I agree that you pose an important question. When I installed snow bars on the metal roof shown in many of our photos I was confident that the metal roof panels had been very well secured to the roof deck by the contractor: I was present during and even photographed that job.

The snow bar manufacturers warn that if the roof panels are not well adhered snow loads might buckle or damage the roof panels. There *might* be similar concerns even when the snow guard system is not bars clipped to the standing seams but instead snow guards adhered to the roofing panels between the seams.

On the other hand I wouldn't tolerate the snow damage problems you describe either.

If you know that the roof panels are not well adhered you should discuss what improvement options the roofing system manufacturer might recommend. The addition of through-roof fasteners is an obvious one but would be a mistake: you'd be changing the fastener design of the roof, restricting thermal movement, inviting buckling and leaks as roof temperature changes. In addition, in my opinion adding through-roof fasteners faces the disadvantage that we are now punching holes in what was otherwise expected to be a long-lived superior roof covering - defeating its purpose.

Unfortunately, as I'll cite below, the only proper and effective repair for poorly-adhered or improperly-locked metal roof panels is to remove them and replace the panels using proper fasteners and faster schedule.

You might get help from an engineer employed by the roofing manufacturer or by the specific snow guard company whose product you want to use. Ask them what they suggest and let me know; we'll both research further.

A different approach might be the use of heating cables on the roof but that needs more thought. A study at Ft. Drum showed that sliding snow simply ripped off the heating cables. (Tobiasson 1996)

I suspect that the best solution would be to install multiple rows of snow guards over the entire roof surface, perhaps 7 or 8 rows on 4 foot centers, thus distributing the loads over a greater area and avoiding concentrating forces in just one or two spots that might deform and damage an inadequately-connected set of roof panels. But this is a general solution not one that's supported by engineering calculations - something that not even a roof engineer can do if she doesn't know the fastener system and schedule that was used on your roof.

A more narrow solution might be to install multiple rows of guards just above the most dangerous areas such as over doorways. I took this approach installing several short rows of snow guards above and around a plumbing vent that had been ripped off of the un-guarded roof. An article about that project is in this InspectApedia snow guard article series.

Your second question about finding the right roofer is not one I can answer. I'm sure there must be some smart metal roofers in Maine but distinguishing the responsible experts from the bullying arm-wavers among any group of contractors can be a challenge. The consumer, unfortunately, is forced to become better informed than she might have elected to be just to know if she can trust the advice she hears. You should use [paraphrasing from the commentator on the article I cite below] only credentialed and well-vetted metal roof installers and should not proceed to allow the work without a pre-issued certificate of insurance that lists the insurer / underwriter so that if the roofer later disappears you have a valid claim against the insurer.

An industry metal roofing association has the following comment on poorly-secured metal roof repair:

Aside from an improper/insufficient roof slope, there could be many other causes of a leaky metal roof; some may be quite obvious, such as a roof leaking due to metal shingles or standing seam panels being blown away by the wind during a storm. – This happens quite often actually, especially to the roofs that were not properly installed, nor properly secured to the deck with appropriate fasteners, in the first place. – If this is the case, you will need to assess the damage to see if the roof can be repaired by sourcing the same type of panels and replacing all the missing panels with new ones. You will also need to identify what caused the failure as most metal roofs are rated for wind uplift of 110 mph or greater. – For instance, you may find that the metal panels were blow away due to improperly interlocked metal panels, or due to the fact that panels were not properly secured to deck with appropriate fasteners. You may also find that there were one too many layers of shingles underneath a metal roof.  - "Metal Roof Repair - Identifying and Fixing Leaks", MetalRoofs.org, retrieved 2016/06/07,original source: http://www.metalroofs.org/metal-roof-repair-identifying-and-fixing-leaks/

A commenter at the end of that article added

that standing seam metal roofs must meet IBC Chapter 15 Criteria, unless a Structural Engineer or someone with Authority and Insurance that Covers Design Stamps and Certifies the assembly as structurally sound and Water Tight.

and

On R, M, and U, and 5V Crimp Panels, the Details are everything. Things such as improperly applied Butyl Tape, over fastened, or under fastened – Fasteners, are a very common source of water Intrusion. Also even when a Roofer uses Neoprene washers on the fasteners they typically have a 7 to 10 year Window before UV Degradation can break down the neoprene washer thus creating a void, hence sealing the fasteners with a dab of a Color Match Metal Caulk can add the extra 10 years years to get the Roof to its full natural / normal 20 year life cycle that the manufacturer warrants the Panels for Color Fade and Against Oxidizing; however there are Kynar 500, and Hylar 5000 baked on Paint Finish Panels out now that are warranted for up to 35 years. Carlisle and Firestone both are in The Metal business too. 

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