Sidewalk Vaults: Hidden Hazards and Hidden Costs

November 2, 2015 by: Scott L. Weiland, PE

Imagine you are the Building Owner or Property Manager of a commercial building that

is listed on the National Register of Historic Places, and one day you learn that a public

transportation project is planned that could likely impact the stability of your building.

Especially if the building has a degrading underground sidewalk vault, which is out of

sight and out of mind! Do any of your properties have a sidewalk vault, what type of risk

or liability can be associated with maintaining a sidewalk vault; and what should you do

to protect your property?

What is a sidewalk vault?

Sidewalk vaults are a partial

extension of a building’s basement

under the adjacent side walk. They

can extend up to and sometimes

beyond the curb under the

roadway. Introduced in the 19th

century in urban areas, they were

the equivalent of loading docks

today, and are often still in use.

These vaults were typically on city

property and building owners maintained them and paid a tax for their use. The vaults

allowed access to utilities and delivery areas without entering the building. Common

sidewalk construction consisted of a 4″ topping slab or brick pavers on a waterproof

membrane on a 4″ to 6″ structural slab spanning between steel or concrete beams or

masonry arches. Before electricity, cast-iron and precast panels were fitted with glass

lenses to allow daylight to reach otherwise dark vaults. Another common top consisted

of 6″ to 8″ granite panels without waterproofing. Curbs were often faced with steel plate

to protect them from vehicles parked on or driven over them.

How do Sidewalk Vaults present potential risk or liability?

Sidewalk vault slabs constructed in the 19th century lacked the drainage and

waterproofing details in use today. If waterproofing membranes were used, they were

typically poorly installed and/or not easily maintained. They also did not allow for

drainage at the membrane level. Decades of slow water migration into the slab resulted

in freeze-thaw damage and corrosion of reinforcing and support steel. With the decline

in usefulness, sidewalk vaults have been neglected to the point that their structural

integrity is in question.

Additionally, in the 19th century sidewalk slabs were built prior to modern building codes

and were intended to support pedestrians. Today’s building code sidewalk loading

criteria is intended to support parked trucks.

Sidewalk vault degradation is commonly out of sight and out of mind. They are not

subject to ordinances similar to those for building facades and fire escapes. Often, the

unsafe conditions are discovered by accident or partial collapse thus exposing building

owners to tremendous liability and significant cost.

What can you do to protect your property?

Building Owners and Property Managers should consider hiring a structural engineering

firm with expertise in failure analysis and experience in the evaluation of sidewalk vaults

to perform a structural condition survey. The purpose of this survey is to assess the

condition of structural framing, sidewalk slabs, and basement walls along the perimeter

of the subject building.

The condition assessment should include performing a survey and document research

and review of the exterior basement walls and sidewalk support structures, and

performing a structural analysis to determine existing conditions. The structural

engineer should provide a condition assessment report including:

Findings and recommendations for remedial work

Methods used to conduct the investigation

Photographic documentation

Cost estimates for making recommended repairs, and

A professional engineering seal, signature and date

Depending on the results of the structural survey, the engineer should also provide

engineered temporary and/or permanent shoring of sidewalk and basement walls (if

needed) to support any surcharge loading requirements identified during the

assessment. Temporary shoring is only a short-term alternative (band-aid) to alleviate

the most immediate structural concerns, while allowing more time for the development

of other permanent solutions

Innovative Engineering Inc. structural engineers are experts in failure analysis and have

extensive experience with inspecting and analyzing sidewalk vault conditions. We

typically recommend a phased approach consisting of a cursory condition assessment

followed by other phases that may include closer examination, analysis, or

improvements as necessary. In this manner, building owners are able to better control

their expenditures, risk and liability.

For More Information Contact

Scott L. Weiland PE

Innovative Engineering Inc

770-517-5507, x-202

www.ieiusa.com