A Diagnostic Scan for Walls and Roofs

I sit on the board of a six-story co-op in Inwood, and we recently hired an engineer to design and administer the replacement of our roof system over a wooden deck, which over the years has suffered serious water damage and created persistent leaks. The engineer has requested several investigative probes, which will cost us an additional $4,500. I know that doesn’t sound like a lot for a $350,000 project, but the co-op’s finances are tight, so we’re wondering if probes are really necessary. What exactly are the probes for, and how are they done?

Think of your building as a patient and your engineer as its doctor. A doctor assesses a patient’s health by visually examining his or her external parts: skin, limbs, eyes, ears, mouth, etc. But to get a fuller understanding of the patient’s condition, the doctor sometimes needs to look “inside” the person using tools such as X-rays, MRIs, CAT scans, etc.

Similarly, an engineer or architect can evaluate a building’s systems by examining the visible systems and components: the façade, roofing membrane, parapets, boilers, pipes, etc. But some of a building’s underlying conditions may not be visible – such as the deterioration of a roof deck or backup masonry – so investigative probes are often required to identify potential problems.

This entails carefully cutting an opening in a building element to access another building element for evaluation, such as a steel beam or column behind a wall or a roof deck underneath roofing membranes. With a more complete understanding of the situation at hand, the engineer or architect can develop a realistic scope of work, draft precise construction details, and prepare an accurate specifications package for bidding. In this way, investigative probes help minimize surprises during construction and lessen the number and costs of change orders later in the project.

Identifying the Problem

Probes are identified during the design phase of the project, usually after the initial site work. Typically, probes are done in areas where the engineer or architect suspects a problem but cannot confirm it with visual observation. For example, a spongy part of the roof may indicate water damage underneath the membranes, and discoloration on a ceiling could mean a leak behind a wall. Other common areas for a probe include stucco coatings, which hide underlying construction; windows and doors, to determine if lintels are bolted or loosely laid; parapet walls, to confirm structural integrity; and building corners with long vertical cracks, to examine the structural steel.

After analyzing the building conditions and identifying the necessary probes, the engineer or architect prepares an RFP (request for proposal) for the work and solicits bids from contractors. The vendor chosen to conduct the probes is not necessarily the contractor that will perform the construction work on the project.

The Hole Opens

During the probe, a contractor uses hand-held tools such as a utility knife, hammer, chisel, or small power tools such as a hammer drill or electric saw, to remove the outer layers of material. The size of the opening is usually one square foot or two square feet for bricks, and about one square foot for a roof. On an exterior wall, the face brick and another layer of backup brick may be removed to reveal underlying construction and waterproofing. If an interior wall needs to be probed, a section of the drywall is cut away to reveal studs, beams, piping, wires, ducts, insulation, and any other elements behind the wall. On a roof, the entire thickness of the roofing system (roofing membranes and any underlying insulation) is removed down to the roof deck.

After the evaluation, the contractor seals the probe opening with new materials, returning the wall or roof to its original state. To properly seal a roof probe, the roofing membrane must be patched according to the manufacturer’s instructions so that the structure remains watertight. The engineer or architect should be on-site to oversee the opening and sealing of the probes, which nonetheless remain the contractor’s responsibility.

The number of probes specified will depend on the size and scope of the building condition. For a roof replacement, about two to five probes is standard.

Plugging the Leak

Given your building’s history of leaks, a roof probe is critical to determine whether or not the wooden roof deck has deteriorated from years of water infiltration. Any section of the deck found to be structurally compromised may need to be replaced.

Probes in a roof replacement project also help the designer determine whether the existing deck is sloped for proper drainage, or whether you need to install tapered insulation – pre-formed rigid insulation used on roofs at drains or roof intersections that require a slight change in elevation at the surface. Installing new insulation to comply with energy codes may increase the thickness of the entire roofing system, which may necessitate raising the counterflashing. In addition, the parapet wall and/or top railing must be at least 42 inches higher than the finished roof surface to comply with city building codes. Therefore, the existing parapet walls and bulkhead doors may need to be raised.

If your co-op plans to use the roof for recreation, the probes also allow the engineer to assess the load-bearing capacity of the roof deck.

For most roof construction, a certified New York City asbestos investigator must take samples of materials that will be disturbed by the work, such as bricks, mortar, caulking, paint, roofing membranes, tar, and stucco. If probes are conducted, the asbestos investigator can schedule the site visit on the same day, so he or she won’t have to return to take samples after construction begins. This saves the client time and money, besides preventing delays to the project if asbestos abatement is required.

Penny-wise, Probe-foolish

While your board may be tempted to forgo a roof probe to save money, it would be a short-sighted decision. As a cautionary example, Rand recently surveyed the roofs of a cooperative with two adjacent five-story buildings. Aside from minor cracking and spalling of the stucco, the parapet walls appeared to be in good shape. Exercising due diligence, we requested investigative probes of the parapets for roughly $6,500.

Although the co-op board initially resisted the idea, we emphasized the importance of confirming the condition of the underlying structure. The board finally agreed. When portions of the stucco were removed during the probes, our engineer discovered loose bricks, missing mortar, and a lack of structural integrity in the parapet wall. What was initially estimated to be a $15,000 project for stucco repairs is now a $250,000 job to completely replace the parapets.

While that’s harsh news for any board to hear, it’s much better to know upfront the true scope of work and how much will be needed to fund the project properly. The co-op can now plan its financing based on an amount much closer to the actual cost, rather than having to scramble for funds later when hit with the sticker shock of a huge change order.

Investigative probes may seem like a bothersome extra step in a project, and bypassing them might appear an easy way to trim costs for boards on a tight budget. But they provide additional information about a building’s condition and help minimize major surprises down the road. So they should be considered a cost-effective, due-diligence measure essential to any major repair program.