The misconception about roof penetrations
Like the old saying “it’s not the fall that hurts, it’s the sudden stop at the bottom”, it can be said that it’s not the roof penetration that hurts, it’s the painful leak that results. It is understandable that people hate roof penetrations and try to avoid them at all cost. A commercial roofing system is expensive and the thought of poking holes in it sends shivers down one’s spine. But instead of simply avoiding roof penetrations altogether, consider that if done properly, those painful leaks can be eliminated and rooftop equipment can be mounted securely. In fact, roofs are full of penetrations. Skylights, A/C units, air vents, and plumbing vents, to name a few, all involve roof penetrations. However, those instances aren’t usually problems because they are typically roofed in during new construction or renovation when properly designed by an architect or roof consultant, and installed by a qualified roofing contractor.
Leak problems occur when non-qualified contractors penetrate the roof with improperly designed attachments.
It is rare for a roofing system originally installed during construction or renovation to leak, assuming a reputable roofing contractor did the work. It is work that takes place after the roofers are gone that can create some real problems. An electrician runs a conduit through the roof, an HVAC contractor adds a small AC unit, an equipment screen gets installed; these are all common events with high potential for poor workmanship and resultant leaks.
Bad ideas people use to avoid roof penetrations
With this widespread perception that roof penetrations will cause leaks, people have resorted to solutions that seem to solve the problem, but can actually cause more harm to the roof. To make matters worse, these solutions can also pose significant safety risks.
The most common solution is to let equipment sit on the roof held down by its own weight, or add ballast like concrete blocks to hold it down. It is obvious for objects like equipment screen walls, signs and large HVAC units to be mechanically attached to the roof structure, but it is also very common for smaller equipment and other roof accessories to be placed directly on the roof, or to be held down with ballast.
Wind is a powerful force and anything with surface area acts as a sail. Not only could equipment completely tip over or even blow off the roof, there are other less obvious problems that occur. Constant movement from wind and thermal expansion will grind and wear on the roof under the equipment. If it is heavy ballast, indentations can also form. Water, dirt and gravel can collect in the indentations, further contributing to roof wear and premature failure. Another major concern is weight. Many roofs are designed for minimal loading and adding heavy ballast blocks can overload the structure quickly. An unexpected heavy rain or snow, or a simple clogged drain on an overloaded roof can result in major disaster.
When adding any type of equipment to a rooftop, primary concerns are safety, waterproofing and preserving the service life of the roofing. Using an inferior method of mounting equipment to avoid roof penetrations may solve the waterproofing concern, at least for the short term. However, adding heavy ballast, restricting water flow or leaving unattached equipment exposed to wind forces can seriously compromise building safety. True, these methods won’t cause immediate leaks, but that is shortsighted. Restricted water flow and roof wear from ballast will shorten the service life of the roof.
Roof penetrations are a good thing if you follow these two rules
Anything installed on a commercial roof that is subject to wind and seismic loading should penetrate the roof and mechanically attach to the roof structure. But don’t think of it as something you have to do, think of it as something you want to do in the same way that you want the roofing to last a long time and keep occupants dry and safe.
Rule #1: Have a qualified licensed roofing contractor do the roofing portion of the work.
Don’t make the mistake of leaving the roofing up to an installing contractor without proper roofing skills and license. If the roof is under warranty, the contractor may need to be certified by the roof material manufacturer. Before any work takes place, all proposed roof penetration details should be submitted to the manufacturer for approval. But roofers are not miracle workers. You have to give them something good to work with, which leads us to the second rule.
Rule #2: Properly design the roof attachment.
Any roof penetration needs to be roofed and sealed by a qualified, licensed roofing contractor. But to ensure a roof penetration doesn’t leak, it needs to start way before the roofing contractor steps foot on the roof. Items penetrating the roof must be properly designed so they can be roofed in using industry standard best practices. Don’t expect that if a contractor penetrates the roof with a wood beam or perforated Unistrut channel, that the roofer can properly seal it for long term service. Coordination between the installing contractor and roofing contractor, combined with properly designed roof attachments, can result in completely water tight roof penetrations that require no maintenance.