Better Buildings From Better Fasteners

Better Buildings From Better Fasteners
Gregg Melvin – Senior Applications Engineer
Elco Construction Products LLC
CONSTRUCT 2009

AIA Credits
Elco Construction Products is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members available on request.
This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

Copyright Materials
This presentation is protected by US and international copyright laws. Reproduction, distribution, display, and use of the presentation without written permission of owner is prohibited.
© Elco Construction Products LLC, 2009

Learning Objectives
Identify situations requiring A/E to specify fasteners instead of leaving product selection to contractor or supplier.
Learn techniques for reducing fastener damage due to rust and galvanic corrosion.
Be able to explain causes of hydrogen embrittlement and HASCC.
Be able to specify high performance fasteners that are HASCC resistant.
Explain the role of fasteners in building sustainability.

For want of a fastener…
“For want of a nail, the shoe was lost, For want of a shoe, the horse was lost, For want of a horse, the rider was lost.For want of a rider the battle was lost. For want of a battle the kingdom was lost. All for the want of a nail.”

This old rhyme about a battle being lostdue to one missing nail is a parable about making sure of the details.

Yet it’s specifically about fasteners, because they are a particular kind of detail:
a small thing that holds together larger and more seemingly important things.

Compared to the horse and even the shoe, the fastener is small. Yet without it…

“God is in the details.”
Mies van derRohe

Your reputation hangs onspecifying the right fasteners.
Fastener specification is critical to project success.
The PetronasTowers in Kuala Lumpur, the world’s tallest building, required careful engineering to ensure none of the millions of fasteners used to install cladding would be the installation’s weakest link.

Standard types and grades of fasteners are sufficient in many construction applications.
In these instances, fastener selection can usually be based on industry standards, building code requirements, and design loads.

It may be acceptable in some cases to leave fastener selection to contractors or building product fabricators, allowing them to select fasteners based on cost, convenience, and trade practice.

Other times,fastener selection can be one of the most crucial aspects of building design.
Professional judgment is required to specify fasteners that:
Perform as intended
Are dependable & economical
Last the life of the building

A big job for such a small part
Factors affecting fastener performance include:
Structural capacity and safety factor.
Static and dynamic load resistance.
Pull-out and pull-over resistance.
Shear resistance of fastener and attached materials.

Factors affecting fastener performance include:
Corrosion resistance in conditions of use.
Seal against liquid or gas leakage (if required).
Constructability, practicality, and inspectability.
Compatibility with design intent and aesthetics.
Removability, or other special requirements.
Service life exceeds that of attached materials.

Specifying fasteners is part of designing safe, durable, and practical connections between building components.

HASCCA “New” Threat to Fasteners
HASCC = Hydrogen-Assisted Stress Corrosion Cracking.

HASCC has only been identified as a fastener failure mechanism within the past two decades.

Since then, “Best Industry Practices” have changed to protect fasteners against HASCC.

VISIBLE CORROSION

VISIBLE CORROSION
Before considering HASCC, let’s review some basics of ordinary fastener corrosion:
Oxidation (Rusting)
Galvanic Corrosion

Must it Rust?
Most architectural fasteners are made from grades or alloys of steel that will react with oxygen to create ferrous oxide, commonly know as rust. Rust is a type of corrosion that weakens and deteriorates steel.

Must it Rust?
Rusting is accelerated when steel is also exposed to moisture, especially if the moisture contains chlorides (salts), a condition that is common in marine, industrial, and urban atmospheres.
Once rust starts, it can spread rapidly to adjacent exposed steel surfaces.

Must it Rust?
When designing steel-to-steel connections, both the fasteners and the items being joined must be protected against rusting.
Steel building panels, for example, can be protected by using zinc galvanizing and a high-performance coating.

Must it Rust?
As a general guideline, fasteners should have greater corrosion resistance than items being joined so that fasteners do not become weakest link in connection.

Corrosion-Resistant Plating
Fasteners are often protected with metallic plating.
For example, zinc plating helps protect steel against exposure to air and moisture and provide a sacrificial, galvanic protection to steel.

Hot-dipped galvanizing is widely used for large fasteners such as anchor bolts. The thick layer of zinc deposited in this process clogs the threads of smaller screws.
On the other hand, thin coatings of electro-plated zinc applied to some screws do not provide sufficient corrosion resistance for exterior or high performance fasteners.

Other types of metal plating, such as cadmium and chromates, provide greater corrosion-resistance than zinc.
These materials are decreasing in usage, however, due to environmental concerns about heavy metals toxicity.

Plating is no longer considered acceptable protection for high performance fasteners.
In fact, it is counter-indicated for case-hardened fasteners, as will be discussed later in course.

Fasteners are often protected with metallic plating. For example, zinc plating helps protect steel against exposure to air and moisture and provide a sacrificial, galvanic protection to steel.

Corrosion-Resistant Coatings
New types of anti-corrosion coatings can be considered to protect high-performance fasteners.

This type of coating is eco-friendly, minimizing the use of heavy metal in fasteners.

In addition to corrosion resistance, the coatings lubricate threads, making fastener insertion and removal easier. Easier removal is a big plus when doing repairs, remodels, and retrofits.

The coatings can be pigmented to color-match other building materials or to simplify product identification.

Corrosion-Resistant Stainless Steel
300-series stainless steel provides evengreater levels of corrosion resistance.

It should be considered for critical structural connections and in locations with corrosive environments.

Note that even stainless steel requires a coating for protection against HASCC, as will be discussed later in this course.

Galvanic corrosion occurs when dissimilar metals, such as aluminum and steel, are in contact in the presence of an electrolyte, an electrically conductive medium, and form a galvanic cell.
Galvanic Corrosion

These galvanic cells are similar to those in electric batteries. In batteries, however, cells are sealed so galvanic reactions only occur when the the cells are part of a controlled electrical circuit.
Galvanic Corrosion

The same reaction occurs in buildings when two pieces of metal form an uncontrolled short circuit.
It occurs because of the electro-chemical relationship of the metals.
Galvanic Corrosion

Galvanic Series
Metals conduct electricity because they have a tendency to give up electrons easily.
Some metals give up electrons more easily than others.
Cathode (Least Active)
Gold
Silver
Stainless Steel
Bronze
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
Anode (Most Active)

Galvanic Series
They can be listed in order of their potential to yield electrons, a table known as a Galvanic Series.
Gold
Silver
Stainless Steel
Bronze
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
Anode (Most Active)

Galvanic Series
Gold
Silver
Stainless Steel
Bronze
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
Less “noble”(sacrificial and more corroded)
Anode (Most Active)

Gold
Silver
Stainless Steel
Bronze
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
More “noble”(protected and less corroded)
Anode (Most Active)
Galvanic Series

Gold
Silver
Stainless Steel
Bronze
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
More “noble”(protected and less corroded)
Anode (Most Active)
Galvanic Series
Aluminum is more active (anodic) than steel or stainless steel.
Where aluminum and steel form a galvanic cell, aluminum will corrode, sacrificing electrons that will deposit onto and protect the steel.

This aluminum plate received two screws made from 300-series stainless steel, a grade that is highly resistant to oxidation and rusting.
Galvanic Corrosion

It was then exposed to 1000 hours of salt-water spray that acted as an electrolyte to form a galvanic cell between the aluminum plate and stainless steel fasteners. The screws were them removed to allow examination of the plate.
Galvanic Corrosion

Galvanic Corrosion
Stainless Steel Screw WithAnti-Corrosion Coating:Coating prevented formation of a galvanic cell and prevented corrosion of the aluminum plate.
Stainless Steel Screw:The aluminum sacrificed electrons to the steel. The surface of the aluminum is visibly deteriorated.

Galvanic Corrosion
Stainless Steel Screw WithAnti-Corrosion Coating:
Stainless Steel Screw:
Using ordinary steel fasteners in architectural aluminum elements (such as windows, curtain walls, or wall cladding) can create galvanic corrosion of the aluminum, weakening the connection until it fails at well below design loads.

Galvanic Corrosion
Stainless Steel Screw WithAnti-Corrosion Coating:
Stainless Steel Screw:
Avoid this problem by specifying fasteners with high-quality anti-corrosive coatings.

Dissimilar metal combinations are common in construction. For example:
Aluminum framed glazing units and cladding get attached to structural steel framing using steel self-drilling, self-tapping screws.
Galvanic Corrosion

Aluminum parts are often attached to concrete or masonry with self-tapping screws made of steel.
Galvanic Corrosion

Even steel-to-steel connections can involve dissimilar metals, if either of the steel parts, or the fasteners joining them, has been coated with zinc.
Galvanic Corrosion

The Schermerhorn Symphony Center looks like solid stone, but it is clad with a thin veneer attached with self-drilling fasteners.
Galvanic Corrosion

It is difficult to prevent electrolytes from contact with fasteners.
Moisture can enter construction due to:
Rain or dew during Construction.
Condensation inside a wall or roof.
Leaks in building envelope
Water from building maintenance or operations.
Plumbing failures.
Flooding and spills.
Perspiration from workers that install the parts.
Air pollutants can make atmospheric moisture more conductive.
Galvanic Corrosion

If dissimilar metals are in contact, assume that an electrolyte will also be in contact with the fasteners.
Galvanic Corrosion

Specifying fasteners with adequate corrosion resistance protects against catastrophic failure, loss of use, injury, death, and liability.
Galvanic Corrosion

HASCCThe Invisible Corrosion

HASCCThe Invisible Corrosion
Hydrogen, a by-product of galvanic corrosion, can weaken standard fasteners and cause failure. It produces a type of corrosion that is not readily apparent…until it is too late.

A Case Study
20 years after installation, screws began snapping for no apparent reason.
The screws complied with building code load requirements.
While they had been exposed to weather due to roof damage, they were not visibly corroded.

A Case Study
They simply appeared to have broken in half.

A Case Study
Scanning electron micrographs (SEM) revealed fractured fastener surfaces and separated grain boundaries in the steel. The screws had also lost ductility.

A Case Study
The Culprit: HASCC!

Hydrogen Embrittlement
HASCC starts with hydrogen embrittlement, which is associated with galvanic action.
However, steel fasteners are not weakened by galvanic corrosion itself.
Rather, hydrogen generated by galvanic action attacks the steel.
Screws attacked by hydrogen embrittlement typically show no visible corrosion.

Hydrogen Embrittlement
Even if steel is protected from galvanic corrosion, hydrogen can attack it rapidly.
Specialized fasteners have been developed to avoid this risk.
Screws attacked by hydrogen embrittlement typically show no visible corrosion.

Galvanic action creates electrical current.
Water in electrolyte separates into oxygen and hydrogen.
Oxygen bonds with the anode and oxidizes the metal. Since oxides have little structural strength, the anode weakens and corrodes.
Hydrogen is attracted to the cathode and penetrates into the metal.
Source of Hydrogen

Source of Hydrogen
This process is similar to the laboratory procedure for separating water into hydrogen and oxygen by passing electrical current through it, a process called electrolysis.

Hydrogen Diffuses into Steel
Hydrogen, the smallest atoms, can penetrate “solid” steel.
Atoms lodge in voids in steel’s crystal structure.
This scanning electron microscope (SEM) image of steel shows enlarged grain boundaries indicative of hydrogen embrittlement.

Single hydrogen atoms are unstable and bond with other hydrogen atoms.
The larger H2 molecules put pressure on the surrounding steel molecules.

This creates internal tension in steel, enlarging its grain boundaries and reducing ductility.
The steel can no longer bear its normal tensile load and becomes brittle.

The Role of Case Hardening
Case Rockwell hardness HRC 52 min.
CoreRockwell hardness HRC 32-40
Hydrogen has little effect on “mild” (soft) steel.
Many architectural fasteners, however, are case hardened.

In case hardening, low-carbon steel is heated in a high-carbon environment to infuse extra carbon into metal’s surface.
This hardens steel’s outer layer (“case”) and makes it brittle.

Case hardening makes self-drilling screws hard enough to drill and tap into structural steel or tap concrete.

HASCC affects steel of Rockwell hardness  HRC 35.
The harder the steel, the more susceptible is it to HASCC.
Case-hardened fasteners are typically HRC 52 on the case and HRC 32 to 40 in the core.

In case-hardened fasteners, only the brittle outer layer is vulnerable to HASCC.
However, a weakening outer layer places the entire load onto the core of the fastener, a significantly smaller diameter of steel than the original design.
Hydrogen Embrittlement & Stress

The design load can overwhelm this reduced fastener diameter, leading to failure.

This cross-section of a failed case-hardened fastener shows the hardened outer case, which was embrittled by hydrogen, and the inner ductile core, which failed under the design load.

A. Application Induced Hydrogen Assisted Stress Corrosion EmbrittlementModeB.Ductile and Embrittlement Mode/ Strength lossC. Complete ductile failure due to reduced cross-sectional area of fastener – unable to sustain application load.

Stress Concentration
Stress increases steel’s susceptibility to hydrogen embrittlement.
Stress concentration occurs at screw heads for 3 reasons:
1. MANUFACTURING: Deformations required to form steel rod into screw heads induces stress into metal.

2. CLAMPING FORCES
When screws are tightened, their heads bear on the surface of the object being attached.
This places the area of the shank immediately under the head into tension, inducing stress.

3. OUT OF ALIGNMENT
Screw holes are rarely perfectly perpendicular to the surfaces they are attaching.
When tightened, uneven pressure is put on the screw’s head.
This puts additional stress on one side of the fastener at juncture of head and shank.

A standard test for resistance to hydrogen embrittlement mimics this real-world situation.
The fastener is screwed through two plates of dissimilar metals. A shim is placed under one edge of the top plate, creating an angle between the two plates and placing the screw at an oblique angle with respect to one of them.

Embrittlement at stress points leads to microscopic cracking.
Micro-cracks further concentrate stress points.
Once propagated, cracks can spread quickly through hardened steel.
Metallurgists call this cracking “Hydrogen Assisted Stress Corrosion Cracking” (HASCC).
Stress Cracking

Plating and HASCC
Case hardened fasteners must still be protected against rust and galvanic corrosion.
Plating should not be used with most case hardened fasteners because the plating process generates hydrogen that contributes to HASCC.
Instead, case hardened fasteners should be protected with a high-performance anti-corrosion coating or with new innovations such as those described in the next section.

Galvanic action between dissimilar metals generates hydrogen.
Hydrogen penetrates steel and creates internal stresses that embrittle and weaken fasteners.
This process occurs primarily in case hardened parts.
Stress concentrations initiate micro-cracking that can propagate across fastener.
HASCC can occur years after fastener installation if connection is exposed to moisture.
Failure is often sudden and without warning.
HASCC Recap

The Remedy for HASCC
Self-Drilling Fasteners have to be case hardened in order to drill and tap substrates – but case hardening makes them vulnerable to failure.
Fortunately, there is a solution to fastener HASCC hazards.

Benefits of Self Drilling Screws
Why use self-drilling screws?
Self-drilling screws require just 25% to 50% of installation time and labor required by nuts-and-bolts, rivets, and other fasteners requiring pre-drilled holes.
Fasteners install in single, fast operation using a power driver.
Installed with
screw gun.

They are much faster than two-handed bolt-and-nut installations, and more practical where the back side is not accessible for installing a nut.
With hundreds of thousands of fasteners used in large buildings, this represents an enormous savings in labor.
Installed with
screw gun.

Use to install windows, cladding, curtain wall, framing, anchors, equipment, fixtures, and other building components.
Installed with
screw gun.

Design of Self Drilling Screws
Select head for easy installation, acceptable profile, and pull-over resistance.
Attaching into Metal: Lead threads tap threads into substrate, so the substrate acts as a nut without requiring the time to tighten a nut.
They are available in many specialized configurations to suit a wide range of construction applications.
Select thread style to hold in substrate.
Lead threads cut threads into (tap) substrate for pull-out resistance.
Tip drills hole and removes shavings.

HASCC-Resistant Fasteners
High performance structural drill screws:
Lower hardness (HRC 28-34)Load-bearing threads for ductilityVirtually immune to embrittlement failures.
Increased hardness (HRC 52 min) point and lead threads for drilling and tapping

HASCC-Resistant Fasteners
High performance structural drill screws:
Lower hardness (HRC 28-34)Load-bearing threads for ductilityVirtually immune to embrittlement failures.
Increased hardness (HRC 52 min) point and lead threads for drilling and tapping
Virtually Immune
to HASCC

There are two ways to achieve this performance:
Selectively Hardened Fasteners
Bi-Metal Fasteners
A Metallurgical Marvel
Hardened for
drilling and tapping.
Ductile for structural performance and HASCC-resistance.

1. Selectively Hardened Fasteners
DUCTILE WHERE NEEDED
HARDENED WHERE NEEDED
Selectively hardened fasteners are made from special, high-carbon steel.
Since the alloy already contains the carbon needed to harden the steel, fasteners do not have to be placed in a high-carbon environment during heat treatment.

1. Selectively Hardened Fasteners
DUCTILE WHERE NEEDED
HARDENED WHERE NEEDED
This makes it possible to heat selectively harden fastener tip.
The tip of the screw is passed through an electrical induction coil that heats and hardens drill-point and lead-threads without affecting the rest of the shank.

2. Bi-Metal Fasteners
StainlessSteel Head andShank
High-CarbonSteel Tip,Selectively Hardened
Use where stainless steel is required for increased resistance to corrosive environments.
Recommended for exposed fasteners.

Stainless steel is not suitable for selective hardening. Instead, a high-carbon steel tip is fused onto a stainless shank.

The high carbon tip is then selectively hardened using induction-coil heating.

Bi-Metal Fastener: Before coating, above. After coating, below.
Even stainless steel is not immune to galvanic corrosion and the elements.
Non-metallic, anti-corrosion coatings are recommended on both selectively hardened and bi-metal fasteners to provide additional protection and lubricate the threads.

Bi-Metal Fastener: Before coating, above. After coating, below.
Coating can be color matched as required.

PROOF
Steel and aluminum plates are connected by fasteners and sprayed with saltwater, an electrolyte.
HASCC-resistant fasteners are not affected
Standard
case-hardened fasteners failed

PROOF
Conventional fasteners fail due to stress concentration at screw heads that accelerates embrittlement.
Standard

PROOF
Neither selectively-hardened nor bi-metal fasteners fail.
Standard

PROOF

PROOF
US Bank Building
Los Angeles, CA
Pei Cobb Freed Partners
HASCC-resistant fasteners, securing roof-top panels, have been exposed to marine and urban atmosphere and earthquakes during two decades of service.

Best Industry Practices
In applications where dissimilar metals will be in contact, specify selectively-hardened self-drilling fasteners to resist HASCC.

Best Industry Practices
In aggressive environments requiring stainless steel for protection against visible corrosion, specify bi-metal self-drilling. fasteners with a selectively-hardened tip to resist HASCC.

FASTENERS FOREXTREME LOADS
Fasteners exposed to extreme loads also require special attention to HASCC.

Extreme Loads
During extreme loading, structures are briefly subjected to loads far higher than normal operating loads.
Determinationof Risk
Estimate of Risk Loads
Risk-Resistant
Design

Extreme Loads
Risks can include:

Hurricane & Tornado, including windblown missile impact
Earthquakes
Accidents (industrial accident, vehicular collision, etc.)
Redistribution of load due to failure of other building elements
Explosion, including boiler, natural gas leaks, & attacks.

Risk-Resistant
Design

Extreme Loads
If there is reason to suspect a risk, it should be designed for.
Risk-Resistant
Design

Hurricane and Tornado Loads
Use building codes and regional history to predict loads.

Hurricane and Tornado Loads
High-speed winds create extreme atmospheric pressure differentials between the interior and exterior of building enclosures.
High-velocity, windblown missiles create extreme impact loads.

Blast (Explosion) Loads
Blast resistance should be designed into structures:
Containing volatile materials.
With high-security profile.
With strategic importance to an organization or mission.
The attack on Oklahoma City Federal Building provoked rethinking of the need for blast-resistance.

That are or have occupants considered targets for attack.
Located near possible targets.

That are “Essential Facilities” that must remain functional after disasters due to importance to public health and safety:

Hospitals
Fire/rescue/police stations
Toxic-material storage
Air traffic control
Critical defense installations.

Extreme Loading-Building Envelope
Hurricane, tornado and exterior blast loads are applied first to building cladding and fenestration.
These elements either absorb the load - by deformation or failure - or transfer load to other structural elements.

Seismic Loading
Violent, cyclical accelerations place extreme loading on all building components, not just structural members.
Failures of non-structural elements can injure or kill people and make buildings unusable.

Extreme Loading of Fasteners
Under extreme loading, if a structural element does not fail, and it does not deform sufficiently to absorb all the load energy – that is, if it is designed to withstand the load – then the load is transferred to the fasteners that hold it in place and connect it to other structural elements.

Extreme Loading of Fasteners
If the fasteners are ductile in nature, they will deform, absorbing some or all of the blast or impact energy, but may still keep in place the element they are attaching.
If fasteners are brittle, extreme loading may cause them to fail.

Case-Hardened & Extreme Loads
Hardened(brittle)case
Core diameter < fastener diameter
Soft(ductile)core
Cross-section of case-hardened fastener.
The outer layer of case-hardened fasteners is brittle and less ductile.
Under extreme loads, the brittle outer case fails first, leaving the inner core to bear load.

Soft(ductile)core
Even though the core may be ductile, its smaller area can becomes overloaded and fail.
Fasteners with incipient HASCC are even more likely to fail during extreme loading.

Soft(ductile)core
Using ductile, HASCC-resistant fasteners helps assure full design strength of fasteners can be used to resist extreme loads.

Where to Specify
Blast resist windows.
Curtainwall framing.
Building equipment.
Critical life safety and communications equipment.

OTHER TYPES OF FASTENERS
HASCC-resistant fasteners can be used to simplify a wide range of special construction applications.

Concrete and Masonry Screws
Specifying concrete and masonry anchors also requires consideration of dissimilar metals and corrosion resistance.
Choice of head styles
Hi-Lo thread taps into masonry
Concrete Masonry

Concrete and Masonry Screws
A variety of special designs are available to satisfy most construction requirements.
Choice of head styles
Hi-Lo thread taps into masonry
Concrete Masonry

Pressure-Relief Fasteners
In buildings with potential for interior explosions, special panels can be designed to blow off and relieve pressure, a built in safety valve.

Examples include places where highly volatile liquids are in use, or storage for extremely fine, dry materials subject to dust-explosion.

Pressure-relief panels are not actually held in place by fastener heads. Panels have an attachment-hole larger than the fastener-head, and a special aluminum washer retains the panel in position.

Under explosive pressure, washers fail and allow panels to blow off, venting the pressure.
The panel is loosely tethered to keep it from becoming a dangerous missile.

HASCC-resistant fasteners can be used in assembly.

Pressure-Relief Venting
Video at: http://www.dablackcompany.com/images/explosion.swf

Threaded rods are used to support fire-sprinklers and other essential building services. These fasteners simplify installation while protecting against HASCC.
Threaded Rod Anchors

Sealing Washers
High performance washers help prevent leaks in the building envelope.

SUMMARY

SUMMARY
Fasteners are critical components of buildings.
Architects and Engineers must be aware of their professional responsibility to specify fasteners that fulfill design intent and provide safe and durable connections.

HASCC-Resistance
HASCC can cause sudden, catastrophic failures when self-drilling or self-tapping screws are used in conditions with dissimilar metals and the potential for exposure to moisture.
It is not safe to assume that contractors will be aware of this issues and will select anything other than standard fasteners. Specify accordingly.
Selectively hardened and bi-metal self-drilling fasteners mitigate risk because their load-bearing sections remain ductile and less vulnerable to HASCC.

Economy
The lowest cost fastener may not be the most economical when labor and service life are considered.
Specialty fasteners can sometimes save money by providing lower installed cost.
Fasteners are less than 2% of total building cost, but specifying inadequate fasteners can cause up to 100% of construction defect costs.

Sustainability
Most metal fasteners have recycled-material content and are recyclable.
New corrosion-resistant finishes eliminate toxic heavy metal plating.
Durability over the life of a structure is the most important measure of sustainability.

Thank you!
This concludes the American Institute of Architects
Continuing Education Systems Program.
Any Questions?
Gregg Melvin, Elco Construction Products
(815) 979-3249 - gmelvin@acument.com