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Construction Detail Evaluation

Conventional “thru-fastened” metal roof systems have been around for over a century and still constitute a large sector of the commercial, manufacturing and warehousing roof market today.  They are inexpensive, durable and long lasting with proper maintenance.  These roof systems are typically low slope with a 1:12 to 3:12 pitch.

However, these conventional style roofs have given way to the floating type standing seam metal roofs (SSR) in growing numbers over the last decade in: new installations, retro-fitting and re-roofing.  Much of the change has been predicated upon the SSR concealed fastener and floating / articulating clip attachment design.  Thru-fastened “R” panel systems have a myriad of fastener holes to contend with and a minimal ability to expand and contract.  Conversely the SSR systems use a concealed attachment system and the panels can expand and contract with the assistance of the floating clips that enable relative movement with respect to the secondary support structure.

Thru-fastened metal roofing is just that; it is secured to the underlying secondary support structures by exposed fasteners through the metal panels.  Over time, without proper inspection, maintenance and remedial repairs each fastener is a potential leak point.

The installation of roof penetrations (i.e. curbs & pipe flashings) and ancillary components (i.e. rakes, ridges, high eave and wall flashings, etc.) on these low slope conventional roofs, if not properly installed as specified by the manufacturer, will create premature roof system deterioration and subsequent failure long before their useful life was projected to end.  Ponding water and deficient seals at these roof ancillaries will accelerate degradation.

Manufacturer purlin bracing specifications also have an influence on roof panel horizontal laps, and roof to roof & roof to wall flashing tie-in integrity and performance.  This variable, when influenced by large or sudden thermal swings, can induce sizable internal material stresses and over time can cause loosening of fasteners, joints and seals. Keeping the connections in good condition through regular inspection and appropriate maintenance will help preserve the roof and insulation systems.

Conventional “thru-fastened” roof panel runs of greater than 60’ have been observed to experience higher stress levels due to sizable changes in ambient conditions.  Manufacturers have, over the years, incorporated various design concepts to accommodate roof panel movement for longer runs.  Concealed fastener slots and horizontal expansion joints are two such attempts that have been used to reduce internal stresses and uneven loading of the conventional system.

Galvalume standing seam metal roofs (SSR) are premium systems that cost a little more than the conventional “thru-fastened” roof systems however they come with many advantages over the typical “R” panel roof.  SSR systems, if installed correctly (i.e. on module, proper: backup plates, cinch straps and free to float ancillaries to name a few) will function as designed for an extended life well beyond the manufacturer warranty period if properly inspected and maintained.

Recent studies have indicated that a useful roof life for these systems, beyond sixty years, is very probable due to the advanced design features and the Galvalume coating technology.  Trapezoidal SSR systems have a 3” high rib, and this is usually sufficient to keep most all shed water conditions below the vertical seam.  Additionally, the vertical seam, in most all cases, has a factory installed bead of pliable butyl sealant in the female leg and a mechanical seamer is used to form an integral, water tight lap.  Thru-fastened” roof vertical laps on the other hand have a typical 1.5” vertical high rib that must be secured with fasteners.  So, the advantages and popularity of the SSR systems over conventional “R” panel roof systems are quite evident.

The use of flashing materials to connect non-planar roof to roof and roof and wall systems is critical for a watertight envelope.  Curbs, crickets and water diverters properly installed at roof penetrations minimize ponding water and enhance water evacuation for the roof system.  These ancillary details must take into consideration the relative movement of the roof and wall panel sections to each other as well as to the underlying support structure.  Failure to understand these relationships during the design and constructions phases will ultimately be revealed through moisture breaches during elevated: thermal cycles and water evacuation events.

There are many variations and multiple configurations to the conventional “thru-fastened” and SSR roof systems.  There is insufficient space to address all in this documentation. In either case suffice it to say that no matter the type metal roof configuration that a building employs National Roof has the professional and experienced personnel to inspect, evaluate and provide the owner or manager with a comprehensive report on current roof system conditions and data supported recommendations for preventive maintenance and remedial repairs, as necessary, to ensure an extended roof system life.


The many components of a pre-engineered metal building

Pre-engineered metal buildings and metal roofing systems are more detailed than often meets the eye and can be complex when multiple: elevations, penetrations and roof types are involved.  Give National Roof a call to help simplify the unknown and provide a comfort level of understanding.