Getting up to speed with Air Sealing Details

Article 103 of the 2009 International Energy Conservation Code (IECC) requires that construction documents include air sealing details. Detailing the building envelope air barrier is a relatively recent challenge for architects, but it is a necessary task for communicating these fussy requirements to builders. The details of laps, connections, splices, and transitions of these thin membranes and tapes are especially important considering the potential downside of an unintended hole in an otherwise tight building envelope. With increased attention to energy conservation and air tightness of the building envelope, a small hole - like a pin hole in a balloon - can wreak havoc in terms of heat loss, vapor transmission, condensation, and moisture damage to construction materials that are concealed from view.

Some architects - already tuned in to our responsibility for construction drawings that show how building materials and products meet and connect with one another - have taken up this challenge by developing a sheet or sheets of details that show typical air sealing conditions that apply to their buildings. Instead of burying this information in other details where it may be hard to read due to the thinness of the air sealing materials, they have developed details specific to the air sealing materials, showing laps and transitions within the air barrier system and at transitions and terminations where the air barrier must connect with other building components like flashings, doors, and windows. Necessary details may include full-size views and exploded views to effectively show proper lapping and isometric views to effectively illustrate 3-dimensional shapes and connections. The details should be designed to effectively communicate the air sealing requirements.

Rethinking the Cost of Time

Building design and construction have been governed in modern history by our perception of time as a cost-based commodity. Both design and construction are assumed to have greater competitive value if production time is minimized. The first cost is generally lower if it takes less time to design and build a project. We can recognize an inverse relationship between first cost and long term cost when we consider building products (e.g., cheap windows vs. expensive windows), where lowest first cost may lead to higher long term costs in energy usage, maintenance, and replacement. Yet, as a profession and an industry, we have not been able or willing to recognize the long term value of time invested in design and construction, such that more available time (if well managed) results in more integrated attention to systems and details that enhance long term building performance and optimize long term operating costs. This issue is most notable in our continuing willingness to commit to abbreviated time periods for design and construction. We talk about the value of high performance buildings in terms of energy efficiency and healthful environments, yet the market continues to demand speed over performance due largely to the long established premise that "time is money" - a premise that is reinforced by the owner who wants the building quicker and by the designer and contractor who must bid low to get the job and then minimize time in order to avoid loss. When minimizing time is the highest priority, long term performance may suffer. Owners, designers, and contractors need to rethink the cost (and focus) of design and construction time as they relate to long term building performance. We have come to recognize long term risks associated with fast food; fast design and construction deserve similar consideration.

Breaking Ground with New Consultants

It can take a few projects to work out the communication kinks with a team of consultants. Consultants who have worked together and with the same team are likely to develop a good understanding of what to expect from other team members: learned and, perhaps, unwritten protocols about information exchange - what to expect and when, and what you have to request. A new consultant may bring both the promise of talent and the risk of problems related to communication. The challenge for both architects and consultants is to spend enough up-front time talking about who will do what and how and when information will be exchanged. It's better to consider your assumptions about what the other party will do and openly discuss details that may otherwise seem too mundane for review, especially if the scope of work is critical to timely project coordination and completion. While a formal consulting agreement may already be in place with an established scope of work and schedule, the details related to scope execution and coordination are not always covered in such an agreement.

Consultants bring not only different talents but also different ways of thinking, so it is best to reach an early understanding about the expectations of each party.

Interdisciplinary Coordination of Construction Documents

Gaps between design disciplines are a common cause of construction change orders. In some cases, the consulting disciplines' standard practices may generate a gap. For example, the electrical engineer may establish an electrical scope of work that "stops" 10 feet outside the building, while the site civil engineer may expect (and indicate on the site drawings) that the electrical contractor will provide power to a sewage lift station that is 15 feet outside the building. Unfortunately, it is quite possible that neither the electrical engineer nor the civil engineer will become aware of this gap in electrical service until the contractor submits an RFI.

Similar gaps can occur between plumbing and site trades, between mechanical and general building trades, between structural steel and miscellaneous metals trades, and between other trades. In most cases, proactive coordination by the project architect during the construction documents phase can help to minimize these gaps."Proactive" coordination means getting involved in finding and highlighting possible gaps and managing document revisions to eliminate the gaps by conferring with the related disciplines, considering applicable trade practices and regulations, and assigning responsibility to the most appropriate party. (It's usually not enough (and not really proactive) to simply tell the consultants to work it out between themselves.)

A Catch 22 Product Specification

Specifications occasionally include unintended contradictions, and in some instances they are related to schedule.

Not long ago, I reviewed a specification for roofing that included a requirement for a particular "ice and water shield" product and allowed no substitutions. The application requirements for the product included a minimum ambient temperature of 40 degrees F. That looked good from a quality control perspective, but the schedule for this fast-track, multi-building project in snow country required construction during the winter, when temperatures were expected to be well below 40 degrees F, and neither the schedule nor the budget allowed for temporary tenting and heating of whole buildings. As a result, in order to meet the schedule, the contractor had to apply the product under conditions that were not recommended by the manufacturer and were not in compliance with the specification.

Roof Design Basics for Snow Country

Leaks from ponds created by ice dams can frequently be traced to roof design. Roof designs that funnel snow to narrow spaces and narrow eaves are likely to promote the development of ice dams and resulting roof leaks. Roof designs with changing slopes that drain steep roofs to flatter roofs are likely to promote the development of ice in the area where the roof slopes meet. Standing seams of metal roofing can restrict snow runoff and promote the development of ice dams near the lower ends of valleys. Roof designs that include opportunities for warm interior air to reach the underside of the roof are likely to cause roof snow to melt and allow melt-water to run down and refreeze at the eaves, forming ice dams and leak-producing ponds behind the ice dams.

Some design principles to minimize the risk of ice dams and resulting leaks include the following:

1. Keep the roof design simple. Avoid complex roof architecture that requires runoff to change direction or follow circuitous paths to get off the roof. 
2. Avoid or minimize 'waterfall' conditions where runoff dripping from a high eave can freeze on a lower roof.
3. Avoid roof configurations that include a high, steep roof intersecting a lower, flatter roof surface.
4. Make way for snow. Remember that snow cannot get through tight spaces easily passed by water. Roof designs should allow wide paths for snow movement. Avoid tight dormer spacing, tight valleys, and other roof configurations that would restrict snow movement. 
5. Avoid standing seam configurations that restrict snow movement. Snow may move down-slope easily in a direction parallel to standing seams, but standing seams in valleys and roof slope changes can act like brakes, restricting snow movement toward eaves. Snow movement around chimneys and similar items can be restricted by standing seams, so special consideration should be given to a seam layout that will promote effective snow movement.
6. Keep the roof surface cold - especially up-slope from eaves - by keeping warm interior air away from the underside of the roof. Paths for interior air to reach the underside of the roof must be effectively blocked by a complete air barrier on the warm, interior side of the insulation (or by a properly installed, complete air barrier type of insulation).
7. Include support for underlayments, flashing, and roofing membranes at intersections between roof surfaces and related construction. Do not expect watertight integrity where a design calls for a dormer eave to intersect a main roof plan at a point without special construction to support underlayments, flashing, and roofing transitions.
8. Consider roof orientation and exposure when designing a roof. Snow will generally melt sooner on a roof exposed to sunlight than on a more shaded roof. As noted in 2 above, snow melt from an exposed roof can meet colder temperatures and refreeze as ice on the more shaded roof.
9. Minimize use of skylights and roof windows. Even the most energy efficient of these will melt snow that lands on them, and the melt-water is likely to refreeze as ice as it runs down on colder roof surfaces.
10. Do not expect an underlayment product like "ice and water shield" to compensate for design features that promote ice dams.
11. Consider the need for snow removal maintenance. Designs with features that promote ice dams may require frequent snow removal to minimize leaks.

Aesthetics and structural integrity are commonly the first considerations in roof design. Roof designs for snow country should also include basic considerations and accommodation of snow behavior in order to minimize problems caused by ice dams.

Bidders Trust Bid Documents for Take-off

Estimating quantities from a set of plans prepared by another architect reminds me that bidders are likely to rely on the accuracy of the drawings when preparing a take-off for a bid. If the drawings are inconsistent or include discrepancies, those are likely to affect the bids, and they may lead to claims of extra cost during construction, if the successful bidder determines that actual construction of the design requires more material (and related labor) than the drawings clearly indicated. The claims may be disputed as unreasonable based on a documented requirement for the bidder to consider the greatest quantity in the event of a discrepancy, but the limit of practicality may be exceeded where determination of actual quantity for bids would require exhaustive review and computation based on various plans and details. Bid preparation is typically limited to a short period of time due to a combination of the scheduled bid period and bidder attention. This is stated not for the purpose of blaming either the designer or the bidder but instead to suggest that accuracy in bid documents should be optimized in order to obtain accurate bids and to minimize discrepancies and the related disputes. There is an old saying that close bids are an indication of tight documents, meaning that the bidders all saw and bid the same scope. Of course, experience also shows that bids vary for reasons that have nothing to do with the bid documents, but that does not detract from the advantages of well coordinated bid documents.

Building Science and the Risks of Experimentation

Science is experimental; it consists of hypothesis and experiment. The path to success can be littered with experiments that fail. Scientists learn to expect failure along the way and to live with experimental failure as the cost of progress. Scientific design is experimental, and it is accompanied by an expected risk of failure.

The growing popularity of building science today brings increased risks of experimentation to the mainstreams of the building industry and the practice of architecture.

Historically, building design decisions were based on long established and proven practices and material selections. Expectations of reliability rested on proven performance over years or decades or - in some cases - centuries. The practice of experimentation was left mostly to the fringes and outliers. Main-streamers tended to avoid products and systems that lacked a good track record. Established building technology was a focus of learning and skill building; architects and builders could expect to learn from a previous generation and practice for decades with a building technology that would remain essentially the same.

More recently, we have seen and become obsessed with an increasing pace of change. Many equate faster with better, making decisions based on the latest available product or on predictions of the next invention or innovation - perhaps even with a belief that it must be better simply because it is new and not established. However, this kind of experimental approach to building design and construction dramatically increases the risk of building failures, in large part because it discredits time-tested performance and avoids or dismisses time-consuming consideration of the multiple roles played by building materials and the roles played by parties in the construction process.

Valid interest in (and popular incentives for) conservation and quality of resources and processes may have led to a willingness on the part of some to take more risks with experimentation. But questions need to be answered: Who assumes the risk? How much risk? Is there awareness and consent of assumed risk? and, If it fails, who owns the failure? Further, If it fails, how can it be considered a sustainable practice?