Roofs are perhaps the most obvious element when one thinks about building waterproofing systems, and across the city by far the most common are low-slope roofs. There are many different waterproofing systems for low-slope roofs, but one thing is consistent across all different systems: they cannot last forever. Eventually, roof membranes degrade and permit water to enter the building interior. Most roof systems have a design life cycle of roughly 20 years before they need to be replaced. However, that number can vary quite a bit due to the design of the system, quality of installation, or type of material installed. Roofs should be periodically inspected to make sure they are free from any major defects.

Most roof systems are comprised of a watertight vapor barrier applied to the deck of the building, insulation, a protection board to protect the insulation, and then a cap sheet. The cap sheet is the main line of defense against water infiltration and the vapor barrier is the backup. In roof systems, there are two main categories of areas: the field of the roof and flashings. The field of the roof is the open section of the membrane in the middle of the roof. Flashings are the terminations of, or penetrations through, the field.

Defects in the field of the system will largely be straightforward to see. Holes or penetrations through the membrane will be the most obvious but can still be hard to spot. Something as small as one nail puncturing the membrane can allow water into the system. The second common deficiency in the field of a roof is open or cracked seams. Most modern roof systems are manufactured in rolls of material about 3 feet across, where these rolls overlap is called the seam. Roofing sheets should be fully adhered to each other, forming a seal at the seams. If you can stick anything in between the cap sheets, water will also be able to get through.

The majority of water infiltrations will occur at the flashings where the system details are more complex so special care should be taken in these areas. Flashings will typically be either cold fluid-applied membranes or rubberized asphalt sheets. Punctures and seams may again present issues but now the system properly adhering to the substrate becomes paramount. Since flashings will extend vertically, there is an increased chance they pull away or delaminate and open the roof up to infiltration if it begins to pull away from the substrate.

Early signs of delamination include open top seams, wrinkling, and blistering. Take note of how high the flashings are above the cap sheet as well. Most manufacturers will require 6-8” of vertical height between the cap sheet and the top of the flashing. This prevents water from building up and overtopping the flashings.

In New York City this is a particular concern during the winter when snow may build up and then melt putting water a good deal above the roof surface. Also check to see if any areas were missed when the flashings were installed, especially around mechanical electrical and plumbing (MEP) equipment on the roof. MEP equipment is typically set on curbs and has various surrounding penetrations for plumbing or electrical lines. The complexity of these areas lends itself to being prone to deficiencies.

A few other things to be aware of: A good inspector will be familiar with the specifics of the roof system they are inspecting. A thermoplastic roof will have different requirements for seam overlaps than a modified bitumen system. Cold fluid-applied flashing will need to be checked for reinforcement while an aluminum-faced, rubberized asphalt sheet needs to be checked more for proper adhesion and mechanical fastening.

If the inspection is for a replacement, design probes should be done in the roof system to understand the current system and the insulation layout. Even low-slope roofs are pitched towards drainage points. This is accomplished with either tapered insulation or a pitched roof deck. The only way to know for sure if a roof system is a tapered or pitched deck is to perform two probes on the down pitch of the other and see if the insulation depth changes. If it remains the same, the deck is pitched; if it changes, there is tapered insulation. Probes should be done at high points in the roof to minimize the risk of standing water sitting on the patch to close the probe.

A good understanding of a roof system leads to a better inspection. It is far easier to find something when you know what you are looking for. To that end, most manufacturers have standard details on their websites and knowledgeable representatives that are happy to answer questions. More seasoned team members will more likely than not be happy to share their knowledge. The more preparation is done and the more familiar one is with roofing, the better the inspection will go and the better the repair recommendations will be.