Underground Parking Garages

Parking Solid State Inspections Inc

With the increased density of homes and the desire by city planners for increased community green spaces and community beautification, moving car parking underground is an increasing trend. However, while moving parking underground can solve a lot of issues above ground, it creates a lot of complexity and risks underground.

Underground Parking Garage Design

When builders start a new building complex, there are many stages of site preparation followed by construction of  the first useable part of the structure, the underground parking garage. To maximize building space, builders will the parking garage right to the property lines even though above ground the buildings may be set back from the property lines.

The parking garage forms part of the load bearing structure for the buildings above but it also carries the landscaping on the property above it. This landscaping presents a challenge to water management on the site as uncontrolled water will flow with gravity downwards towards the parking garage. Water is one of the natural enemies of all buildings, even concrete parking garages, and it will look for any crack to enter the building.

Why is Underground Parking and Water a Concern?

In order to increase the strength of concrete for large open spans, like in parking garages, steel bars call 'rebar' are laid in the concrete forms before the concrete is poured. It is this rebar that needs to be protected from water penetration as when steel rebar gets wet, it will rust. When steel rusts, it expands, and the force of expanding rebar in the concrete will cause the concrete to 'spall' and fall off, sometimes in large chunks. When enough concrete spalls off, the structural integrity of the concrete, and the building, is compromised. 

Two situations that make this process worse are first, climates where salt is used in winter to clear ice as salt speeds the oxidization (rusting) process. Second, 'post-tensioned' concrete construction uses rust susceptible steel cables in addition to rebar to increase the strength of the concrete and both are at risk of possible rust erosion and structural failure.

How Do Underground Garages Prevent Water Penetration?

Underground parking garages are surrounded by water like a submarine as soils in the ground carry water which pushes hydraulic pressure from all sides. In addition, water that flows from irrigation and rains on the landscaping above needs to be repelled by the parking structure. To accomplish this, condo builders apply water proof membrane systems to the outside of the parking structure to make the garage water tight. These membrane systems are designed to last for 25+ years but as water can penetrate even the smallest weaknesses, failures in these systems are common. 

Failures in the waterproof parking membrane can be caused by poor original design or installation, damage from tree roots, or just deterioration over time. Typically buildings start to see some signs of failure around 10-15 years old however leaks are occasionally seen in newer construction. With BC's 2-5-10 year new home warranty, builders are required to fix any water ingress leaks in the first 5 years of construction.

Fully repairing and replacing a membrane is a very disruptive and expensive process as it requires removing all the landscaping materials and digging down to the top concrete slab of the parking garage. There are repair processes such as injecting expanding sealant into cracks from below however these repair processes usually just divert water in time to other weaknesses in the membrane. 

Aren't Strata's Responsible for the Building?

When you buy into a condo building, you are becoming a co-owner of that building and you are partially responsible for the costs of strata repairs. The exterior elements of condominiums have much higher repair costs than any repairs in suites will typically be.  Condo buyers need to have a condo inspector evaluate the exterior of their condo purchases when buying real estate to protect themselves from unexpected costs.

While strata's ultimately make the decision to spend money on repairs and the work is done by contractors working for the strata, the funds for all repairs come from the owners.  Repairing a parking garage membrane is one of the most expensive special assessment costs that condo owners can face.

What Do Home Inspectors Look for in an Underground Parking Garage?

Parking garages give condo inspectors visibility to signs of water ingress, a portion of the structure of the building, and should also be evaluated for safety of the residents. Any signs of water ingress should be documented in the condo inspection report and potential buyers should follow up by checking with the strata on any engineering reports or potential upcoming costs. Garage structure should not be showing any unusual cracks or shifting at the columns. Cracking in concrete is normal as concrete shrinks when it cures however a qualified Condo inspector will be able to identify unusual cracking which will need further evaluation by structural experts for the strata. If a condo inspector is suggesting further evaluation in parking garage areas, these could be red flags for potential buyers of major building failures and buyers need to protect themselves by getting satisfactory follow up information from experts on the building.

Condo inspectors should also comment on the safety and security of the garage for residents. Garages should be well lit, stairs should have handrails and good clearances, and there should be some form of ventilation for car exhaust fumes. Security cameras and security gates are also good for preventing crimes in underground parking areas.

Final Thoughts

The most expensive issues condo owners can face are leaky condos, replacing roofing, and replacing underground parking membranes. If you are looking at buying a condo, always call in a professional condo inspector so you know your home will be safe and solid.  

By James Bell - Owner/Operator of Solid State Inspections Inc.