Structural Technologies - Green Building

Article by: Alan Bernstein AIA, ASLA, LEED AP

October 1, 2009



Jonathan Wirthlin, Structural Engineer, AIA Member, Structural Engineering Association of Southern California Sustainable Design Committee, and LEED AP with Coffman Engineers did an outstanding job presenting at the AIA COTE Committee Meeting of September 3, 2009, on how structural engineers can make a project green.



Wirthlin focused on commercial buildings. The Engineers role creates a substantial cost impact on all projects and there are very few LEED points associated with structural engineering. By savings on materials, additional engineering calculations and changes to the building code, the engineering for buildings can become greener. Wirthlin promotes the Green Globes approach rather then the LEEDS, because it is more comprehensive in its approach.


Greener Concrete

Currently a lot of concrete products that are not “green” still have some fly ash content in them. By increasing the fly ash content to 20 to 70% of the cement mixture we are reducing the amount of fly ash that goes to landfills. Fly ash is a byproduct of burning coal for energy, it use to be sent up into the sky before environmental regulations finally stopped or reduced the fly ash into the atmosphere. As a result there is a lot of fly ash in the chimneys coal fire plants. (The best way to reduce fly ash is to reduce coal fire plants.) If a 50% fly ash mixture where used widely, it would reduce the world’s CO2 production by 4% (that is big).



By adding fly ash to the concrete mix we are creating a concrete that works differently than regular concrete, it does not make it worse, and it is less expensive than cement. It takes longer to set and dry- so the engineer needs to create a time line for the “working strength” of the concrete so the job can continue while the concrete is still curing. It takes less water, requires different admixtures, and can have more shrinkage cracks.


Material Reduction

By using fewer materials we can reduce the environmental impact. But there will be more labor involved in carefully calculating each beam individually, as opposed to the current standard of consistent and repetitive beam sizes. This could also reduce the quantity of bolts, welds, reduce shear wall length, and change stud spacing to 24 or 32” on center.



By use of a higher strength concrete, material can be reduced by thinner slabs, shorter and thinner shear walls, reduce deflection, and ultimately building weight.



Using high strength steel is not very practical. Standard steel shapes usually use standard steel strengths. It would be better to reduce the steel weight by increasing the depth of the beams for less deflection and widths of the posts for more efficient strengths.



Less material can reduce construction cost. There will be a learning curve for labor to be more attentive to small and frequent detail changes. More detailed plans will require more construction management and coordination. Wood projects or advance framing techniques will probably benefit the most from these changes. Concrete would benefit the least.


Advanced Systems

Advanced systems like energy dissipaters, system isolators, buckling restrained braced frames and steel plate shear walls can reduce materials and effects of earthquake damage on buildings. These systems require additional engineering and cost.



To justify these costs we need to consider the Life Cycle the building? How long is the building to last? Would it be better to spend more on materials and have a longer building life? Can the building adapt to other uses? And what will be the impact on the building when the earthquake hits – tear it down or replace some isolators?


Green Aspects of Structural Materials

Current LEED credits for engineering are gained in these areas:

Fly ash counts as pre-consumer recycled content, MR4.

Significant use of fly ash has been awarded Innovation in Design credit, ID1.

Crushing existing concrete for aggregate counts as post consumer recycled content credit, MR4.

Using special aggregates, pozzolans and add mixtures can help achieve Innovation in Design credit, ID1.

Showing the extended life of the building may also help achieve Innovation in Design credit, ID1.

LEED does not look at the life cycle, flexibility or reuse of a building.



Recycled wood can go into particleboard, mulch, fuel and firewood. Larger members can be reused, but smaller members like 2x4s will split apart when nailed. Windows and doors can be recovered and reused. Wood is easily deconstructed and reused in some manner. Wood is the greenest building material. Trees store carbon. Wood comes from a “rapidly” renewable resource. The creation of lumber uses relatively low amounts of energy sometimes their own sawdust (biofuel) creates the energy to mill the timber.



Steel is the most recycled material in the world. Over 80% of the steel comes from recycled product. Reusing steel beams is fully practical. Steel can be constructed with deconstruction in mind by using less weld and more bolts. Avoid unusual or custom shapes that are more difficult to reuse. Steel is the strongest per volume building material used. Steel manufacturing has been dramatically cleaned up, most hazardous waste associated with manufacturing is being recovered and used beneficially. Steel is produced more efficiently yet still takes a lot of energy to melt.



Concrete can be reused as base material, gravel, aggregate for new concrete, and the steel can be recycled. Concrete slabs and walls cannot be recycled for structural use. Concrete has the largest carbon footprint. The production and pouring of one ton of concrete creates 1.25 tons of CO2 and significant heat. One 90-pound bag of cement creates 22291 cubic feet of CO2 (a volume equivalent to 28 cubic feet).



Using an existing building can be greener then building a new green building. When we consider all the waste from demolition, existing embodied energy in materials, labor, transportation and time in an existing building we can save more energy through reuse.

Reusing a building has social, economic and cultural impacts. Adding life, strength and safety to an old building often has less impact on the environment. Building design and structural systems should allow for easy reconfigurations and different uses. The envelope or curtain wall system should be removable to allow future renovated or modernized exterior. Simple building shapes would save in renovation costs.



Again special thanks to Jonathan Wirthlin of Coffman Engineers for his presentation.

Thanks to Jonathan Vogel, President of Spectra Contract Flooring for hosting our meeting and providing food. We are always looking for new attendees, please contact Blaire Seibert, AIA, LEED AP, Verde Concepts via email blair@verdearchitects.com for the date and time of our next meeting. Looking forward to seeing you there.



Reminder, The Greenbuild 2009 International Conference and Expo will be held in Phoenix Arizona, November 11 –13. This is a great conference and an incredible number of exhibits about all things green. It attracts a mix of people from all aspects of the construction industry and related fields. Visit www.usgbc.org for further information.





Alan Bernstein is a licensed Architect, licensed Landscape Architect, U.S. Green Building Accredited Professional (LEED, AP) and Certified Green Building Advisor. For questions or comments contact Alan Bernstein at (818-707-9215) or email at alan@abarchitects.com



http://www.concretecontractorlosangeles.wordpress.com



http://www.mikepearsonconstruction.com

Mike Pearson Masonry Contractor Los Angeles

Permeable Interlocking Concrete Pavers

Permeable Interlocking Concrete Pavers
Their Role In Green Construction

We all understand the value of permeable pavers in terms of their ability to give us a hardscape surface that allows water to seap into the water table. But we thought it would be nice to to share some specific information based on our experience with permeable pavers, which will allow you to highlight the important pros and cons related to this product for your customers, specifically in terms of its role in the arena of sustainable design. Below is a general outline of the main points related to this subject, and it should be a quick and easy way to and to put some of the basic facts and figures at your fingertips. If you wish to print this outline, it will also be available on our website as well.

The outline describes, in general, the basic problems with impervious surfaces, what Low Impact Development (LID) is, and how it seeks to address this problems with impervious surfaces, the role of permeable pavers in Low Impact Development, some specific facts about how permeable pavers function in eco-friendly construction, how they conform with ADA standards, and some pointers on how to use permeable pavers to score points in LEED projects.

Problems with Impervious Surfaces: Surfaces that do not permit the penetration of surface water cause two main problems:

1. Overworked storm drains, causing excess, untreated water to run to rivers and lakes.
2. Suspended sediments and heavy metals run directly into storm drains without being filtered by the natural system.

Low Impact Development (LID): A design strategy with the goal of "maintaining and enhancing the pre-development hydrologic regime of urban and developing watersheds." (Taken from the Low Impact Development Center website: www.lowimpactdevelopment.org) One of the goals of Low Impact Development is to reduce the percentage of impermeable surfaces in new construction.

Permeable Pavers Role in LID: Permeable pavers allow water to pass through the upper layer of the pavement and then enter the sub-base reservoir, which acts like a sub-surface infiltration basin. Storm water is therefore treated through filtration, volatilization, microbial activity, storage and ion exchange. The storm water then slowly infiltrates into the sub-grade soils, instead of overunning or storm drains and/or adversely affecting the water supply.

Infiltration: There is considerable debate on the infiltration rate of permeable pavers. The infiltration rate must be calculated based on the overall infiltration that occurs once the pavers have been installed (i.e., when the infiltration rate of sub-surfaces and soil are all factored in.) One study showed a mean infiltration rate of 3.5 inches of water per hour, for clean pavers (free of debris.) This study is here:
http://www.bae.ncsu.edu/stormwater/PublicationFiles/ICPIreport2004.pdf

Some suppliers and manufacturers will claim much higher infiltration rates, including the rate you would expect from the pavers alone (before they are set on soil.) Beware of unreasonably high infiltration claims.

Exfiltration: Rainfall may exceed the exceed the infiltration rate of the soil below. For different densities of soil, different exfiltration methods may be utilized in order to completely re-route water:

Full exfiltration: For use when the soil is expected to fully exfiltrate all of the surface water. All of the water exfiltrates into the soil below, with no additional sub-surface drainage.

Partial exfiltration: For use when the soil may not exfiltrate all the surface water. In this case, a sub-surface perforated pipe is used to redirect the water.

No exfiltration: For use when the soil below has low or no permeability. In this case, an impermeable membrane is used at the bottom and sides of the system, in addition to a sub-surface perforated drain pipe.

Reduction of Pollutants: The aggregate filters and sub-grade soils the allow sedimentation to occur, and contribute through bacterial treatment of the pollutants and cation exchange. Growth of "good" bacteria has been found on established aggregate bases. in addition, because water immediately enters the permeable surface, it maintains a lower temperature, which means that unnaturally heated water does not enter the water habitats of wildlife, where it can cause shock or death.

Where Not to Use Permeable Pavers: Pavers should be installed at least 100 feet from water supply wells, streams and wetlands. They should not be installed in facilities where the by-products of products may contaminate groundwater, such as industrial facilities that store
hazardous wastes, or gas stations.

In addition, permeable pavers are highly subject to clogging when exposed to sediments or fines. The effectiveness of permeable pavers can be significantly reduced due to clogging. (As a side note, permeable pavers should be cleaned on a recurring basis in order to maintain maximum permeability.)

Compliance with Americans with Disabilities Act: There is no express rule for paver spacing in order to satisfy ADA requirements. However, the rule of thumb is that the spacing should be a vertical maximum spacing of 1/2".

LEED Credits:
Credit 6.1 and 6.2: Stormwater Design - 2 possible points (for achieving the appropriate percentage of permeable surface.)

Credit 7: Heat Island Effect Non-Roof - 1 possible point (for using light colored, high albedo materials)

MR Credit 4: Recycled content - 2 possible points (when using pavers that contain fly ash or blast furnace slag)

MR Credit 5: Regional materials - 2 possible points (when using materials that are extracted, processed, and manufactured regionally.


This article is intended as a general overview only. There are a myriad of other factors that we can explore in relation to permeable pavers, and we have included some useful links for those of you who wish to explore the subject in more detail. We always welcome your comments and feedback.

The above article was based in part on information found at the following web links, which you may find useful:

http://www.lowimpactdevelopment.org/
http://www.bae.ncsu.edu/stormwater/PublicationFiles/ICPIreport2004.pdf
http://www.icpi.org/faq/48
http://www.aecdaily.com/en/1647234