Saturday, November 30, 2013

Why is Waterproofing Required?

John A. D’Annunzio

The first question that an architect will have to answer is if waterproofing is required on the building that they are designing.  This can be a complex question and the answer could have a significant ramification over the life span of the structure.  Economic and code requirements could also weigh heavily in the decision process.  Waterproofing may be included for a piece of mind, this is the one component of the building that it may be best to caution on the side of err.

There are five reasons why waterproofing is required.  They are:

1.                  Code requirements
2.                  Keep water out of the building
3.                  To protect the structure: concrete and steel
4.                  Hydrostatic pressure
5.                  Economics: the cost of excavation

One: Code Requirements

Certain codes require the use of waterproofing in different conditions.  It is the responsibility of the architect or designer to make certain that the waterproofing component is in compliance with the applicable Federal, state or Local codes.  The primary distinction of the codes in regards to the water table and hydrostatic pressure.  A proper engineering study of the grounds is required to establish this criterion for the design phase.

The IBC code requires dampproofing or waterproofing application when the site ground water table is maintained at an elevation of not less than six (6) inches below the bottom of the ground slab.  The IBC codes also require waterproofing applications where hydrostatic pressure will occur.

ASTM states that dampproofing or waterproofing is required for slabs on ground and foundation retaining walls.

Two: Keep Moisture Out of the Building

The main function of a structure is to protect man from the environment.  This has been the one element that has remained consistent throughout the history of mankind.  Advancements in material technology, application procedures and design have not changed this function.  The main purpose of waterproofing is to serve as a barrier that protects the interior of the structure from moisture intrusion and other environmental ingress. 
Below grade building components are susceptible to moisture intrusion because they can be exposed to moisture from groundwater for weeks – even months – at a time.  Buildings constructed in low-lying areas with high water tables can be exposed to groundwater throughout the life of the structure. 
There are several points where a below grade exterior component is prone to moisture infiltration.  These points require proper design diligence from architects to keep moisture out of the building.  Some of the more common areas of concern are:
·                     Tie-rod Holes
·                     Cold Joints
·                     Expansion Joints
·                     Penetrations
·                     Internal Drains

Three: Protect the Structure: Concrete and Steel

In addition to keeping moisture out of the building, waterproofing serves another equally important role.  It helps protect the structural elements – concrete and steel – from moisture and environmental (chemicals, soils, etc.) related damage.
Deterioration from the elements can occur in the form of cracks and spalling of the concrete or corrosion and rusting of the steel components.  In each case, these deficiencies have an adverse effect on the long-term performance capacity of these components. 
Concrete in its self is not completely waterproof.  If the integrity of the concrete is maintained it can remain waterproof, however, concrete can crack before hardening through construction movement, plastic or drying shrinkage or early frost damage.  Concrete can crack after hardening through settlement, seismic forces, vibration or creep, deflection from soil movement or excessive loading. 

Four: Hydrostatic Pressure

The determination of hydrostatic pressure is an important element prior to the design stage.  This is a basic factor in the choice of a waterproofing system.  By definition, if hydrostatic pressure is present than waterproofing – not dampproofing – is required. 
Aspects demanding consideration regarding hydrostatic pressure include the intensity and duration of the pressure.  This should be defined by a civil engineer and is important in consideration of waterproofing materials that are specified.  Other issues that require clarification prior to design are if the pressure is continuous or intermittent and if the water is stationary or flowing.
The issue of hydrostatic pressure is extremely important in the design of waterproofing systems for several reasons.  Hydrostatic pressure can have adverse effects on waterproofing systems if they are not properly designed or applied.  Hydrostatic pressure can force membranes into voids in the concrete.  Cracking in the concrete that occurs under flexural stress can rupture the membrane and create leaks.
Hydrostatic pressure can also force water into tie-rod holes, cold joints, and rock pockets.  It can also turn minor imperfections into probable sources of leaks.

Five: Economics

In the last decade the term ‘value engineering’ has gained prominence, particularly with General Contractors who look to add to their profit margins through substitution of materials and systems. The term implies that there may be some value in substituting design materials or application procedures with less expensive methods of construction.  This approach is highly cautioned in below grade waterproofing.  The primary reason for this concern is one of risk v. cost.  If a building owner wants to cut costs, the waterproofing system is the last place to do so.  This is because the cost of excavation far exceeds the initial cost.  Due to this fact, the designer should always minimize risk despite any reasonable – or unreasonable – costs.  With waterproofing you only have one chance to do it right!
The architect should stand firm on the waterproofing design and should not accept change orders for materials or systems that they are not familiar (or comfortable) with.  If the building owner or general contractor forces changes to design of materials or application procedures without the designers acceptance, the designer should have those parties sign a release of liability.  As a professional in the industry the designer will assume liability for all design components – even those changed without their consent – unless a release of liability is provided.

Where is Waterproofing Required?
Once it has been established that waterproofing is required, the next important decision is to determine where it is required.  Typically, waterproofing should be applied over all below grade concrete surfaces.  There are several other established building components that require waterproofing protection, they are:
·                     Underground Structures
·                     Elevated Structural slabs over underground spaces
·                     Structural slabs below grade
·                     Structural slabs above grade
·                     Foundations
·                     Lagging walls
·                     Plazas
·                     Terraces
·                     Promenades
·                     Planters

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