National Library, Minsk, Belarus


Main  |  Site Map

Articles

 

Façade Consulting

Our Consulting services touch on many aspects of the development of facades. The client can expect the best results from our Consulting services if we are engaged during the programming and schematic design phase of the project. Because of our broad experience, we can provide initial quantity survey and cost estimates based on global markets and local resources. During the course of developing a project, we can assist with constructability reviews to ensure that what is being designed is adaptable to the local construction market.

Conceptual facade Design
3D-facade Concepts
Specification Development
Contract Drawings
Mock Up Testing
Submittal Document Review
Field Observation Report


When a contractor signs a contract with an owner there is an implied assumption that the building, if built per the documents, will perform under the conditions the environment will impose. A well coordinated and thought out building will perform in this manner. However it is rare that problems do not arise during construction that are the result of conflicts or omissions in the design documents. An inexpensive Peer Review by a qualified facade consultant can save numerous hours of field labor and costly change orders during construction.

The design team discusses coordination issues during the design process. It is assumed that all the team members have listened during the meetings and have incorporated the necessary changes. Perhaps the misconception that generates the most issues when it comes to the building skin is the Architect assumes that the Engineer has designed the structure to accommodate the facade materials the Architect has shown on the elevations. The reality is that the typical Engineer does not consider how the structural system will impact the facade. The structural engineer is more concerned with the stress in the structural members than how their deflections will affect other systems. Many Architects do not know how the building structure can and will impact the facade and thus do not ask the proper questions of the engineer to get the information they need. This lack of understanding between the Architect and Engineer has helped lead the design team to favor Design Build as a solution to ensure a good quality facade.

A majority of the buildings specify the building facade systems as Design Build. The Architect provides schematic elevations and details showing the aesthetics of the building and sometimes the anticipated anchorage of the facade to the building structure. Specifications are written to address the performance expected from the wall and may reference a standard off the shelf curtain wall system. The engineer of record designs the structure with an allowance for the loads imposed by the facade but typically does not indicate how or where the facade will attach. The design of the support and attachment of the facade is left to the selected design build facade sub-contractor.

This process leads to at least one sub-contractor and up to three separate sub-contractors per material type. These sub-contractors typically do not independently coordinate their systems. It is not unusual that the first one to submit their drawings gets the lead and the other sub-contractors have to design their systems around the first. The end result are systems that either interfere with each other as they are being erected or will not accommodate the movements of the surrounding systems as the building moves.

Depending on the design, there may be more than one facade material and support system used on the building. Each material/system has unique design considerations. The system may be supported along the slab edge, it may be attached at or near the columns or it may attach to another facade system. Depending on how the support system is attached, live load floor deflections may or may not be a concern to the facade design. Differential floor-to-floor drift is always a concern although it needs to be addressed differently depending on the configuration and design of the facade. Thermal movements of the facade components need to be accounted for, particularly with aluminum curtain walls. How moisture is directed to the outside, or kept from penetrating to the inside needs to be addressed with proper vapor barriers, weeps and gutters. Systems provided by different suppliers and sub-contractors must be coordinated so that the facade functions as an assembly. The goal of the facade design should be a wall that will perform well for the life of the building with minimal maintenance.

Most problems exist at the interface between systems. A no mans land where neither contractor takes responsibility. Back-up systems become discontinuous with sealant being the only line of defense against environmental intrusion. A Facade Consultant is the ideal team member to coordinate the process. Coordination should begin early in the construction process before the selection of the sub-contractors and the design of the facade products. The Facade Consultant reviews the Contract Documents looking for potential concerns. This "peer review" of the documents would uncover the specific places where additional detailing by the Architect or Engineer will facilitate the design and performance of the facade. It will also uncover issues that concern only the sub-contractors and suppliers such as the sequence of installation of building wrap and flashing. Many of the concerns become rather obvious but it is sometimes surprising the things that get overlooked in the production of details and the drawing process. The focus of the review is meant to facilitate a better building, not to find fault. 

Peer Review

The purpose of the review is to look for discrepancies and thoroughness of the contract documents. Are the documents complete? From a design standpoint do they show the facade conditions adequately? If needed, are isolation joints indicated? How do the facade and other building elements interface? The best time to do this is before the drawings are issued for facade bidding. This allows time for the peer review to be completed and for the incorporation of comments and clarifications to the documents prior to the bid issue.

The facade consultant doing the peer review will look at the specifications, architectural and structural drawings. In addition to this information they should be provided with actual calculated live load floor deflections and differential floor to floor drift. It is important that these numbers be calculated numbers, not the allowable under the code values. Calculated numbers are important because they are often larger than the allowable amount stated in the specifications.

The contract documents will be reviewed for constructability and water tightness. The design of the facade will be investigated to determine how the elements of the wall integrate and how they are supported by the building structure. Integration is important since one system may be depending on another for support or weeping of moisture. The support of a particular facade system is usually the same from building to building. Aluminum curtain wall usually attaches to the edge of the slab. Pre-cast concrete, brick panels and stone supported on truss frames typically span between columns attaching either directly to the column or to the slab edge very close to the column. Stone, brick, metal panels, EIFS and other materials supported by metal studs will usually attach along the slab edge. It is important to know how the systems are supported in order to know what affect the building structure is going to have on the facade. The facade has to be designed to work with and accommodate the structural movements. It is essential to the design of the facade to understand these movements and know their magnitude.

Deflection and Drift

The two primary building movements are live load deflection and differential floor-to-floor drift. Facade systems that are supported along
the slab edge need to be designed to accommodate the live load deflection of the floor slab. Curtain wall systems usually have a splice joint every other floor that is sized to allow for both the deflection and thermal expansion. Systems supported by metal studs that attach along the slab edge will usually have an isolation joint at every floor occurring most often at the window head. This joint must also be sized for deflection and thermal expansion. Panelized systems that span between columns usually do not have live load deflection issues. The facade consultant will need to evaluate the design, determine the areas where deflection is a concern, and make sure they are addressed in the contract documents.

Differential floor-to-floor drift is present in all buildings but is especially a concern in parts of the country that are within a high seismic zone. These movements also occur from wind loads causing the building to lean and in tall buildings to sway. The amount of the differential movement from one floor to another is the drift. The facade systems must be able to accommodate this movement. There are various ways to make this happen depending on the type of system.

Basically, stick system curtain walls will lean with the floor drift, panelized systems will either tip and rock or translate. The design of the isolation joints and the facade system needs to address these concerns. The Contract Documents need to provide pertinent information to the facade subcontractors and suppliers in order for them to properly design the wall to accommodate these movements. The facade consultant will identify drift concerns and suggest solutions to the design team. 

The Facade Consultant

Time is a major concern to all parties involved in constructing a building. The shorter the construction time the sooner the owner starts receiving a return on his investment. General Contractors are looking for ways to give them an edge on the completion date and deliver the building sooner. The building skin always sits on the critical path. Facade systems and materials have long lead times. Glass can take 3 to 6 months depending on the coatings and stone can take up to a year depending on the type and complexity of the fabrication. During the design process a Facade Consultant can help to expedite decisions and detailing that impact the timeline. In extreme cases a Facade Consultant can assist in "fast track envelope water tightness" so interior finishes can be installed prior to completing the exterior. If this process is known early in the design process back up systems can be chosen that provide the secondary line of defense in the finished building and provide the primary line of defense for a limited time so interior work can commence.

Performance mock-up testing should be preformed on all projects whether the wall system is a standard design or a custom design. The intent of the performance mock-up is to verify that the design performs as intended. An ASTM 503 field water test should be performed on all buildings. A random sampling of windows should be chosen early in the construction process and tested to insure that the system is being installed correctly. After a system has passed a full-scale performance test the shop drawings need to be revised as required to accurately show how the system is to be erected and sealed. It is important to remember that a system that has passed a performance mock up has proven that the design works when properly executed. Every project has new people installing the system. Some systems rely heavily on sealant to pass a mock up test while others rely on more passive measures. If the technicians in the field do not fully understand what makes the system work even the most proven system will leak. After all systems are installed another round of tests should be preformed. The number of units to test is dependent on the size of the building and the complexity of the system.

A full consulting service package would include submittal and shop drawing review. Part of the submittal package should include copies of historical performance mockup tests for off the shelf systems. These will confirm that the system was tested to the standards that the project has set. A Facade Consultant will also look for incompatibilities in materials being proposed. For instance hydrocarbon-based materials, which are often used as flashings on window and aluminum panel systems, should not come in contact with stone as the oils will leach into and stain the stone. In reviewing the shop drawings the Facade Consultant will help to resolve coordination issues between systems before they become issues.

So how does all this save, as is stated in the first paragraph of the article, hours of field labor and costly change orders? The simple answer is awareness. By performing a careful review out ahead of issuing the documents for bidding and detailing and revising the documents accordingly the building process can proceed much more smoothly. Changes are expensive at any stage and especially once the materials are on the job and installation has begun. A thorough review by a qualified facade consultant can resolve conflicts in advance and reduce the time consumed when conflicts are discovered in the field.

Source: “Facade Consulting for Construction” by Rob Kistler and Tom Kearns