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Structural Evaluations

By Stephen Varone, AIA and Peter Varsalona, PE

My apartment in a pre-war cooperative shares a lot line with an adjacent property on which a new building is being constructed. (Our building abutted the now demolished building that was on the site.) Hairline cracks have started appearing in my bedroom wall and so has a new gap between the wall and the floor. Our superintendent says he also notices new cracks in our basement on the same side of the building. The board is worried that the construction next door is causing these conditions and that they could worsen as time goes on, especially given that our building is old and the exterior walls have not been maintained that well over the years. How do we determine if the construction next door is to blame for the cracking walls and gap, and what should we do in the meantime?

Damage from adjacent construction work is an all-too-common problem, and older buildings with potentially weaker walls such as yours are particularly vulnerable. Although the responsibility for protecting surrounding properties rests with the developer/owner of the new project, it behooves boards to take precautionary steps when construction is planned next door.

Pre-construction Survey
One strongly recommended measure is to have a survey conducted of the building before any demolition or excavation begins next to it. A pre-construction report serves as a record of the building’s overall structural condition, which the board can then use as a baseline to compare against any new damage that may be subsequently caused by the adjacent construction.

To establish proof of pre-construction conditions, the engineer should take plenty of photos throughout building. The more detailed and thorough the report (especially the photographic documentation), the stronger the board’s case will be should damage occur.

Even if a survey was not conducted before construction began (as in your building’s case), it does not mean that it’s too late to have one performed now. It’s still important to document the damage that you think may have been caused by the construction work next door, so it’s recommended that the board undertake a survey as soon as possible before any further problems develop.

Problem Signs
Obvious problems that an engineer conducting a survey would look for are shifted walls; cracked, loose, or spalling bricks; deteriorating mortar joints; loose or missing coping stones; deteriorated or missing base flashing or counterflashing on the roof, deflected lintels and relieving angles; and improperly spaced or non-existent expansion joints. Some of these conditions may be structural in nature, while others could be the result of water penetration, which in turn can slowly wreak havoc on a building and lead to structural problems if not addressed.

Inside the building, the engineer looks for cracked or bulging walls, sloping or sagging floors, gaps between walls and floors or walls and ceilings, rotted or defective joists or beams in the basement, and any out-of-plumb structural elements.

If the survey identifies structural deficiencies, the next step would be for the engineer to perform tests to determine the extent of the damage. One way is to sound out areas by lightly tapping a hammer to detect soft spots or loose material. The engineer may also want to conduct investigative probes of problem areas by having a contractor remove a small section (approximately one square foot) of surface brick or masonry to better determine underlying conditions. Depending on the condition of the wall, several or more probes could be in order.

Shaky Foundation
Because the former building on the adjacent site abutted your cooperative, chances are both buildings shared the same foundation wall (also called a party wall). If so, it is possible that the building’s demolition and the subsequent excavation have had an adverse effect on your building. Vibrations from demolition of the adjacent building, for example, could have been transferred to your wall. In addition, removing soil next to the foundation wall—especially if the digging went deeper than your basement—could have caused your building as a whole to shift and settle.

Given the age of your building, the foundation wall is probably the standard stone-rubble type of the pre-war era. If the existing foundation wall—your basement wall, which now has cracks—is in poor condition, the developer of the adjacent property should have taken precautionary steps to protect it. One method is to pressure grout the wall by coating it with a layer of cement, which strengthens the wall and protects it from cracking or crumbling. The developer should have also provided temporary shoring to support the wall and keep it from shifting. If neither of these measures were taken, it is more likely that your building has been adversely affected by the demolition and excavation.

According to New York City Building Code, a new building being erected cannot bear on an existing party wall but instead must rest on a new foundation wall, usually made of reinforced concrete. There should be a space between the two walls, typically filled with a foam material, to keep loads from transferring from the new to the existing building. In addition, if the new structure’s basement is deeper than the adjacent one, the developer is required to install an underpinning below the existing building’s basement to help prevent the building from settling.

If your building is more than six stories tall, you can also compare the survey’s findings to the most recent Local Law 11/98 facade inspection report. The report won’t detail conditions inside the building, but it should have reported any major exterior defects and subsequent repairs, which could then be evaluated in light of any defects that have become visible since then.

Monitoring Defects
In the meantime, keep an eye on the hairline cracks in your bedroom wall and the gap between the wall and the floor. If the cracks and/or gap become larger, or you see signs of water penetration, bulging, or other deficiencies, you may have to have a structural engineer investigate further. The finished wall will likely need to be removed to examine the underlying structure and the extent of damage. Any sheared or cracked brick on the inside or outside face of the wall will need to be replaced. If the damage extends beyond the immediate area, structural reinforcement measures, such as supporting damaged beams with new beams (called sistering) might be necessary.

The areas around the lintels (the horizontal structural elements that span the top of window and door openings) are especially vulnerable to structural forces, so they should be observed for any defects, such as sagging, bulging, cracking, or leakage. The basement wall—the building’s foundation—also bears the brunt of any additional loads on the building, so that should be monitored daily as well.

A post-construction survey should be conducted to compare your building’s previous condition against its condition after the demolition, excavation, and new construction are completed. However, if the first survey clearly shows that the developer of the adjacent property is already causing damage to your building, exacerbating existing damage, or not following proper building code procedures for demolition, excavation, or new construction, your board may have to take legal action to have the work stopped.

In the meantime, the board should take the proper safeguards and make any necessary repairs to keep the damage from getting worse and ensuring that your building is structurally sound.

Stephen Varone, AIA is president and Peter Varsalona, PE principal of RAND Engineering & Architecture, PC. This column was originally published in the September 2006 issue of Habitat Magazine.

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