By Stephen Varone, AIA and Peter Varsalona, PE
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 wood 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 such tools 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 facade, roofing membrane, parapets, boilers, pipes, etc. But not all of a building’s conditions are visible from the surface—such as deterioration of roof deck or back-up masonry—so investigative probes are often required to check underlying conditions and identify potential problems.
Investigative probes entail 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. By providing a view of what’s below or behind the surface, probes uncover hidden conditions in a building. With a more complete understanding of the situation at hand, the engineer/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 Investigative Probes
Probes are identified during the design phase of the project, usually after the engineer/architect conducts the initial site work. Typical locations for probes are areas where the engineer/architect suspects a problem but visual observation is insufficient, such as a spongy part of the roof, which may indicate water damage underneath the membranes, or discoloration on a ceiling, which could mean a leak behind a wall.
Probes are identified during the design phase of the project, after the initial site work.
Other common probe areas include stucco coatings, which hide underlying construction; above windows and doors to determine if lintels are bolted or loosely laid; parapet walls to confirm structural integrity; and at building corners with long vertical cracks to examine the structural steel column.
After analyzing the building conditions and identifying the necessary investigative probes, the engineer/architect prepares an RFP (Request for Proposal) for the probe work and solicits bids from contractors. The contractor chosen to conduct the probes is not necessarily the contractor that will perform the construction work on the project.
Conducting a Probe
In a typical probe, a contractor uses hand-held tools such as a utility knife, hammer or chisel, or small power tools such as hammer drill or electric saw, to remove the outer layer of material. In general, the size of the probe opening is approximately one or two square feet for bricks and about one square foot for a roof. On an exterior wall, the face brick and sometimes another layer of brick (back-up) is removed to reveal underlying construction and waterproofing. If a probe is needed at an interior wall, 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 engineer/architect evaluates the underlying construction and conditions, 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 roofing manufacturer’s instructions so that the roof remains watertight. The engineer/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 depends on the size and scope of the project and building condition. For a roof replacement, approximately two to five probes is standard.
Roof Probes
Given your building’s history of leaks, roof probes are critical to determine if the wood roof deck has deteriorated from years of water infiltration. If the roof deck is found to be structurally compromised in any area, that section could require replacement.
Probes in a roof replacement project also help the design professional determine whether the existing roof deck is sloped for proper drainage, or whether tapered insulation needs to be specified. Installing new insulation to comply with the Energy Code may increase the thickness of the entire roofing system, which may also require raising the counterflashing. In addition, to comply with New York City Building Code, the parapet wall and/or top railing must be at least 42 inches higher than the finished roof surface. Therefore, depending on the new finished roof elevation, the existing parapet walls, as well as bulkhead doors, may need to be raised.
Failing to identify the existing roof slope and/or type of roofing insulation during the design phase could lead to change orders or drainage problems. Furthermore, you could end up with a parapet wall that no longer complies with Building Code. In addition, if your co-op plans on using the roof for recreational purposes, the probes enable the engineer to assess the load-bearing capacity of the roof deck.
For most roof level 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, stucco, etc. If probes are conducted, the Asbestos Investigator can schedule the site visit on the same day so he or she won’t have to come back to take samples once construction begins, saving the client time and money. It also avoids delaying the project if asbestos abatement is required.
Penny Wise, Probe Foolish
While your board may be tempted to forgo probes of your roof to save money in the short run, it would be a shortsighted decision. As a cautionary example, RAND recently surveyed the roofs of a cooperative with two adjacent five-story buildings as part of a Physical Condition Survey. One of the work items we identified was stucco repairs for the parapets. Aside from minor cracking and spalling of the stucco, the parapet walls appeared to be in good shape. Exercising due diligence, RAND requested investigative probes of the parapets for approximately $6,500.
For a roof replacement, approximately two to five probes is standard.
Although the co-op board initially resisted authorizing the probes, we emphasized the importance of confirming the condition of the underlying parapets. The board finally agreed, and when portions of the stucco were removed during the probes, our engineer discovered loose bricks, missing mortar and a parapet wall lacking structural integrity. What was initially estimated to be a $15,000 work item for stucco repairs is now a $250,000 project 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 properly fund the project. The co-op can now plan its financing based on an amount much closer to the actual cost of the program, rather than having to scramble for funding later on 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 with the additional information they provide about a building’s condition and the major surprises they help minimize down the road, properly conducted investigative probes should be considered a cost-effective due diligence measure essential to any major repair program.
Stephen Varone, AIA is President and Peter Varsalona, PE, is Principal of RAND Engineering & Architecture, DPC. This article was originally published in the March 2014 issue of Habitat Magazine.