Roof Penetrations

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.