Snow guard layout & spacing on all roofs.

This article describes how to lay out the snow retainer or guard pattern on a roof in order to provide an effective snow retention system. Spacing requirements for snow retention devices vary depending on the roof slope or pitch.

We give recommended side spacing between individual snow guard devices & we discuss an important consideration to avoid structural damage: how far up the roof from the eaves should the first row of snow guards begin.

This article series illustrates types of snow guards or snow brakes or other snow retention devices used on metal, rubber, asphalt, and slate roofs.

Snow Retention Device Installation Specifications for Location & Spacing

Snow Guard Spacing Distances side-to-side in staggered rows

Experts point out that for the placement of individual snow guards (as opposed to long horizontal snow fences or snow brakes) depends on the pitch of the roof. According to Precision Snow-Guards[2]

[Click to enlarge any image]

• For roofs sloped 0 (flat) to 2 inches in 12 of rise (2/12 Slope), snow guards are placed in one staggered set across the lower roof edge staggered two feet on center. [Why you would need snow retention guards on a flat or 0-slope roof escapes us - Ed.]
  
  Note: Amerimax recommends omission of snow guards on roofs under 3:12.
  
  Do not use Snow Guards on low-slope roofs (those with pitches less than 3:12). Snow guards help reduce the momentum of a potential snow slide.
  
  On low-slope roofs, snow does not typically slide off in the same manner. Under these circumstances, it is often better to allow the snow to naturally clear itself from the roof as quickly as possible or to manually remove it. Therefore, snow guards are not recommended for low-slope roof applications.
  
  Check with the roof manufacturer for specific product application limits and, as always, observe all roof safety guidelines. - Amerimax (retrieved 2014).
  
  Really? for inaccessible low slope roofs, we share the concern for weight (the structure should have been designed for snow loading but may be under-designed, risking collapse) that arguers to "let the snow fall off of the roof". But I have seen damage from snow falling off of low slope roofs, including damage to objects below and damage to on-roof components such as plumbing vents and gutters.
• For roofs sloped more than 2/12 and up to 6/12, install two rows or sets of staggered guards, two feet on center
• For roofs sloped at 6/12 and steeper, install two rows or sets of snow guards in straight lines (not staggered) across the roof eaves
• For metal loop wire type snow hooks or snow guards (photo at left) you can see that to work at all, since these devices have much less surface area than a flat or bar type snow guard, they have to be installed in many staggered rows over half or more of the roof surface.
  
  The snow hooks shown here are installed on a slate roof at the Justin Morrill Smith historic home in Vermont. Metal loop snow guards for shingle,slate, and cedar shake roofs are typically made of copper wire. See Berger Building Products for a source.[1]
• Snow brakes, snow fences, snow rails, or similarly-called continuous bars or fences to retain snow on a building roof are usually installed as a single continuous system across the roof eaves, typically 1 to 3 feet above the eaves.

Snow Guard Row Location: where to place the rows, how to prevent structural damage from accumulated weight of ice & snow

In addition to installing one or more staggered sets of snow guards "across the lower roof edge" with quantity and spacing varying by roof slope (discussed above), we'd like to know how far back from the lower roof edge or eaves should the first row of snow guards begin and how many feet of space should be provided between banks of snow guards on larger roofs with multiple installations of snow guard products.

• Place the first row of snow guards at or above the exterior load-bearing wall.

Watch out: Berger Building Products (ret 2014) warns that

Snow guards should never be placed beyond the bearing wall on an extended roof section. This can result in ice damming and cause structural damage. - Berger Snow Guard Guidelines, op.cit., retrieved 5/2/2014

• Place the second staggered row of snow guards 15 inches over the center of the first row.
• If a third row is used the stagger pattern matches the first row and this row too is placed 15 inches above the center of the second row.

  Note: Alpine Snow Guards (ret. 2014) comments that the top ten feet of rafter length of a roof dfoes not need snow guards except in extreme snow load areas.

• If a second or subsequent group of snow guards is to be installed higher on the roof, space the second group 6ft. to 8 ft. up-roof from the lower set.

Alpine Snow Guards recommends placing a three row pattern on the lower roof, 24" o.c. with the middle row staggerd 12", and covering the remaining roof to within 10 feet of the ridge with evenlyspaced snow guards between the bottom three row pattern and the top un-guarded area. - Alpine (ret. 2014)

5 Snow Retention System or Snow Guard Installation Mounting Methods

Individual snow guard mounting methods vary depending on the roof covering material. All snow retention systems use one of these methods to provide snow and ice retention for building roofs.

In short the methods are:

1. Structurally-connected snow retainer mounts
2. Clamp-on snow retainer mounts
3. Adhesive-bonded snow retainer mounts
4. Clip-on snow retainers
5. Snow-retention coating

...

Continue reading at SNOW GUARD BUILDING CODES? or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Snow Guard & Snow Brake Articles

• METAL ROOFING
• ROOFING INSPECTION & REPAIR - roofing home page
• SLATE ROOF INSPECTION & REPAIR - home
• SLATE ROOF HARDWARE
• SNOW GUARDS & SNOW BRAKES
  • SNOW RETENTION SYSTEM HARDWARE
  • SNOW GUARD FAILURES
  • SNOW GUARD MOUNTING METHODS Details about the five methods for mounting or attaching snow retention systems or snow guard to roofs
  • SNOW GUARDS on METAL ROOFS
    • SNOW GUARD GLUE ON INSTALLATION
    • SNOW GUARD CLAMP ON INSTALLATION
  • SNOW GUARD SPACING & PATTERN
  • SNOW GUARD BUILDING CODES?
  • SNOW GUARD PRODUCT SOURCES

Suggested citation for this web page

SNOW GUARD SPACING & PATTERN at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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