Energy Efficient Building For Facility Managers
BECx provides Energy Efficient Building and Savings For Facility Managers
Building Enclosure (or Envelope) Commissioning (BECx for short) originated in Canada in the 80’s and came to the US in the 90’s. The General Services Administration and the US Army were amongst the early adopters. They started commissioning enclosures on their building projects in 2006. Since then, it has gained traction on the East Coast and in other areas of the country with higher heating and cooling needs. It is now finding its way into California’s Energy Code too, due to the fact that it enables building owners and facility managers to garner an energy efficient building with enhanced air quality and lower ongoing maintenance costs.
So how does a BECx Help Facility Managers Design an Energy Efficient Building?
Why do you need a BECxA (building enclosure commissioning agent) when you already have an architect and contractor on the team?
A BECxA, as the name implies, is entirely focused on the exterior shell of the building. S/he has a triple mandate of (a) reducing air leakage, (b) eliminating thermal bridges and (c) controlling water intrusion in the building.
A. Reducing air leakage in/out of the building skin not only significantly reduces energy usage, it also helps greatly with mold mitigation. A considerably greater amount of moisture escapes into wall and roof assemblies by piggybacking on leaking air, than as vapor diffusion through building materials. This moisture can condense out of the air when it comes in contact with a cold surface and may cause mold, rot, and eventually failure of the building material. The graphic below shows a common location of air leakage. The top of a concrete slab or foundation is very rough and uneven and when the steel (or wood) bottom track sits on it, it creates areas of significant air leakage unless sealed.
Graphic above shows recommendation for expanding foam under steel bottom track to prevent air infiltration/ exfiltration. Cant strip is recommended to facilitate water drainage.
B. Similarly, when you have a “thermal bridge” like a structural steel member penetrating the building skin, (or a concrete slab cantilevered out to form a deck or balcony) it can conduct cold temperatures from the exterior to the inside of the wall or roof assembly (unless it has been appropriately detailed), causing condensation and eventually mold and rot. In summer, the penetrating steel member can conduct higher temperatures indoors, increasing the load on the HVAC system. Eliminating these thermal bridges also enhances occupant comfort. Below are two examples of common thermal breaks found in buildings when steel fasteners are used to attach the steel member to the framing and a concrete slab on grade.
Graphic above shows detail recommendation for steel fasteners penetrating exterior skin.
Graphic above shows recommendation for under-slab rigid insulation to mitigate heat loss in winter.
Facility Managers Want Energy Efficient Buildings
C. The benefits of controlling water intrusion, i.e. waterproofing, in an energy efficient building needs no explanation. It is the main reason for contractor callbacks and construction litigation. Well detailed and installed waterproofing can significantly increase the building’s lifespan and reduce ongoing maintenance costs. The detail on the left below addresses a problem seen with architectural drawings. Boiler plate construction details may be inadequately modified for the project without thinking through the actual installation. This can leave the actual construction to the worker in the field who may choose to improvise instead of issuing a request for further information (a.k.a. RFI). This potentially becomes a problem, especially if repeated over numerous window installations.
Graphic above shows recommendations to improve window head waterproofing.
To achieve energy saving goals for facility managers and owners, the BECxA works with the architect to determine components of the wall and roof that will work best to control air leakage, heat transmission and moisture. These “control layers” can be achieved by a single material such as taped exterior rigid sheathing, or multiple materials, depending on various factors. Ensuring the continuity of these “control layers” at changes in building cladding, intersection of the wall and roof planes, pipe/ utility penetrations, fenestrations, etc. is the single most important task in building enclosure commissioning and is responsible for obtaining the 3 objectives outlined above. This approach looks at the building skin as a complete and inter-dependent system, as opposed to approaching each construction detail in isolation and focusing only on waterproofing, as is the case with architectural drawings or a waterproofing consultant’s details. The BECxA brings to bear the building science principles for heat, air and moisture control as they apply to various climates and different building materials, to the design of the wall and roof. This is not the way architects have traditionally developed their wall and roof configurations. This is one of the many tasks of the BECxA during the design phases. It is beyond the scope of this article to discuss all the other tasks as stipulated in NIBS Guideline 3 (NIBS: National Institute of Building Sciences), which is the guiding manual for BECx.
During construction of an energy efficient building, the main focus is again on the quality installation of the control layers, and the various products and materials that make up these layers such as sealants, membranes, coatings, sheathing, insulation, etc. The quality installation of the cladding is very important as well since it is the first line of defense against water entry. This quality assurance is achieved through periodic construction site visits and observation logs, quality control meetings with sub-contractors, submittal reviews and testing. The intent is to ensure critical details and specifications that have been meticulously developed during the design phase, are fully adhered to, during construction. Special attention is given to details where multiple different trades are responsible for ensuring an airtight or watertight installation, or materials being installed are new and unfamiliar to the installers, or different systems come together such as exterior wall cladding interface with roofing. Mock ups built during the pre-construction phase are regularly tested for water intrusion on most construction projects, but the actual construction can also be tested in various ways to validate that goals for air tightness, water tightness, thermal conductivity (or lack thereof), have been achieved. There are different tests for a variety of conditions and materials. The selection and implementation of these tests depends on how high the quality requirements are for the building and on the construction budget. Water intrusion tests can be very expensive.
At the end of the construction phase for an energy efficient building, the BECxA conducts training for the owner’s personnel and facility managers on the maintenance of the various components of the exterior walls and roofing. S/he also conducts a comprehensive warranty review of all products and systems that are a part of the building exterior. This training and warranty review is generally absent from projects that do not have a BECxA as part of the team.
Ultimately the effectiveness of BECx is determined not just by the experience and competence of the agent but by a whole hearted embrace of the BECx process by the owner, architect, contractor and facility managers. The owner needs to recognize that the BECxA is acting as his/ her representative and proactively discuss the BECxA’s concerns during design and construction with the project team members. The BECxA’s role is also to act as a bridge between the design and construction phases. Well executed BECx has the potential to offer many benefits, not just on new construction, but the underlying principles of building science as they relate to heat, air and moisture are also effective for a variety of tenant improvement projects. In labs, where maintaining pressurization relative to adjacent spaces is crucial; an air tight lab space is a big help in HVAC system design and function.