In terms of attention per dollar spent, windows typically punch above their weight during the design process. Though usually a lower percentage of our overall contract price than the major trades, windows consume our time and attention throughout preconstruction. That is because even minor design decisions regarding windows can have outsized effects on the aesthetics and performance of a building. Further, windows are tangible to our clients and building residents in a way that an SOE system or a boiler room location, for example, can never be. In this way, although the dollar values can sometimes be low, value engineering decisions regarding windows can be some of the most important that get made. In this article, I will cover window returns, UPVC windows, acoustical specifications, aluminum finishes, performance mock-ups, operation type, bird-safe glass, insect screens, and heat soaking. This list is abbreviated due to space and time available. Some (but not all) of the important value engineering topics left out of this article are: structural performance, air and water performance, thermal performance, metallic paints, tinted glass, balance mechanisms, opening sizes, corner windows, fins, snap trims, true vs. fake divided lites, trickle vents, frit patterns, low e coatings, and the list goes on.

Window Returns vs. Simple Openings

For whatever reason, architects and clients tend to prefer façade returns at masonry openings—in other words, windows that are more deeply inset. Vague pro-return arguments will be made about shadow lines, mass articulation, etc. Regardless of their pretenses towards lofty aesthetic theory, it is this author’s opinion that designers and owners prefer the expense of returns out of pure irrational bias. Whether they understand it or not, architects don’t prefer returns in spite of the returns’ expense—they prefer returns because of their expense. (Thorstein Veblen coined the term conspicuous consumption to describe this type of dynamic and he didn’t mean it as a compliment.) This is because in the past, only expensive projects have been able to afford returns and so architects and owners have grown accustomed to associating this façade feature with buildings and neighborhoods that seem up-market to them.[1]

Ironically, there are in fact many reasons for us, as a contractor, to prefer window returns for general constructability now that all our buildings (due to energy code and sustainability programs) have deep cavities accommodating extra insulation thickness.

Ironically, there are in fact many reasons for us, as a contractor, to prefer window returns for general constructability now that all our buildings (due to energy code and sustainability programs) have deep cavities accommodating extra insulation thickness.

Amongst Other things, eliminating the return creates the need for a Cavity Closure.

Unfortunately for us, despite the constructability advantages, window returns still generate more expense than the alternatives. The cost of the extra brick (or other façade material) is typically great enough to outweigh the cost of heavier clips (or other means to support the dead load of the window which is now cantilevered over the cavity as shown in the detail above to the right) and cavity closures involved in eliminating the return.

UPVC v. Aluminum.

Now that UPVC (plastic) windows have gained more acceptance in NYC (they have been used widely in Europe for a long time now), one of the first value engineering questions regarding windows is often whether to use UPVC windows in lieu of aluminum. There are many ways in which the materials differ when it comes to windows but two of the most important differences for our clients and architects are (1) that UPVC windows typically have thicker mullions and (2) their finish has not been proven stable long term in the same way that high performance organic coatings for aluminum windows have been.

Which project is UPVC and which is Aluminum? Can you tell?

Typical savings involved in switching from aluminum to UPVC windows are in the range of $20 - $35/SF. There are many details that must be resolved and accommodated when making this change—too many and too involved for our purposes here—but we have yet to see this change result in unsatisfied clients or increased costs. Generally, even as costs are reduced and all else being equal, the thermal and acoustical performance of the windows will actually be improved.

Acoustical Requirements.

A project may specify unnecessarily stringent acoustical requirements for any one of many reasons. Sometimes the architect has copied and pasted language from the last project.  Sometimes they have misunderstood the regulatory requirements in force on the project. In all cases, acoustical requirements are something that are important for us to question and verify since stringent requirements can dramatically increase the cost of the windows (whether by triggering the requirement of laminated glass, thicker glass, or even triple glazing).[2] A copy-and-paste error is self-explanatory but the errors that can be committed in relation to regulatory requirements are more complicated. The most common is to misinterpret an overall wall attenuation as a window attenuation. For example, an HPD negative declaration recently specified a “minimum of 31 dBA of window-wall attenuation”. The architect initially interpreted this as requiring a window with an STC rating of 31. The trouble with this approach is that the opaque portion of the wall is far more attenuative than the window and should do more of the attenuation work.  For example, a typical brick exterior wall with stud backup may have an STC of 56. Using a composite STC calculation (which incorporates the values for the opaque wall and the window) we were able to show that, even with a window having an STC as low as 24, the resulting façade would be compliant at 31 dBA. The composite calculation is unfortunately not a strict average, as small areas of low-performing materials can have outsized effect.

The formula above uses STC (Sound Transmission Class). These days, most products are specified and tested in OITC (Outdoor/Indoor Transmission Class). Neither are units. Both are testing/rating protocols expressed in the unit of decibels (dB), specifically A-weighted decibels, or dBA. Because different products may be tested (beforehand) in STC v. OITC, it can sometimes be of financial value to make sure products are specified in STC vs. OITC or vis versa to allow for specific products or manufacturers.

Is the aluminum finish standard for the windows over-specified?

The finish that is specified for an aluminum window is another place where it may be possible to save money. The typical finishes we see specified are AAMA 2603, 2604, and 2605. Here is an excerpt from a recent specifications book:

AAMA 2603, 2604, and 2605 are performance classes based on a set of criteria for durability and longevity—summarized by the following table:

Certain combinations of paint types, procedures, and thickness are required to achieve the various classes. For example, as you go up in class, higher percentages of fluoropolymer content in the paint may be required along with additional coats. Sometimes a specification book will provide the paint chemical content and coat quantity rather than the performance class. (And sometimes they provide both the class and the requirements and fail to coordinate those two sets of requirements, leading to confusion.)

Needless to say, reducing the required class can often result in cost savings. We frequently provide AAMA 2603 windows but at the same time also have many clients who insist on 2605.

If lab testing is specified, is it truly necessary? Similarly, is the field-testing protocol specified reasonable? 

Almost every project these days requires third-party reports (supplied by the manufacturer) demonstrating that the proposed window complies with the specified performance requirements. These are sometimes called “off the shelf” reports—reports commissioned by the manufacturer long in advance. However, many projects—particularly ones with custom aspects, unique installation details, or high-performance requirements—will require a project-specific third party off-site (laboratory) report (or reports)—so called Performance Mock-Ups (PMUs). Testing may include operation cycling, air infiltration, static water infiltration, dynamic water infiltration, structural, inter-story differential, dynamic wind load, acoustic, thermal, thermal cycling, condensation, and life cycle testing.

Since these are time-consuming and expensive, we must question whether they should truly be required in every case (no doubt they sometime will be). Sometimes the PMU can be eliminated altogether. If not, maybe the testing regimen proposed can be reduced. For example, structural performance is far more predictable than water infiltration or acoustic performance. Some of our projects have avoided structural testing on this basis. Similarly, dynamic wind loading and inter-story differential testing may not be needed and have also often bene avoided even when other testing is required.

For field testing protocols—this is not so unusual or onerous that we might question it occurring altogether. In fact, we have generally been including our own, in-house field testing of windows in our initial general conditions budgets on all budgets. However, we do question the field testing protocols when they are unnecessarily stringent. For example, we don’t recommend testing 15% of windows, or ne window on every floor. But three to five windows (depending on the project size) might be reasonable.

Is the window operation specified cost-effective?

In order to least expensive to most expensive, the typical window operation (for operable windows of course) we see are: (1) Double Hung, (2) Sliding, (3) Casement, and (4) Tilt-and-Turn.

Double-hung windows used to be relatively standard for affordable housing. They are common, cleanable, and can accommodate window air conditions easily. As owners’ façade expectations and performance requirements have become greater, double-hung windows have become far less common. Although we still provide sliders frequently, the superior energy performance of casements has made them far more prevalent. In fact, the new UPVC companies that have been springing up typically manufacture only casements or tilt and turns.

If Bird Safe Glass is specified, is it really required?

Apparently, millions (or billions) of birds die every year by flying into buildings’ glass facades that they cannot see.

And so bird-safe glass has been a threatened addition to building code for a while now. It has come up repeatedly in design meetings over the last few years, with no one totally sure whether forthcoming projects will need to comply and what compliance will actually mean. As far as we can tell, complying with early versions of the regulations using frit coating patterns or films would add anywhere from $25 - $50 per square foot of window (truly extreme numbers that can sometimes double the cost of the window itself). We have no track record of value engineering solutions because it has so far not been required of any of our projects. However, if implemented in the future these regulations will necessitate a lot of work on our part in determining the most cost effective and aesthetically acceptable methods of compliance.

If insect screens are specified, are they really required?

Our environmental beneficence towards birds does not extend to insects so specification books typically include requirements for insect screens. This is regardless of the fact that insect screens are rarely actually required for mid-rise and high-rise projects. Even on low-rise projects, management companies will often prefer not to deal with the seasonal installation and removal of insect screens. Further, some clients and architects prefer building without them given their aesthetic impact on the façade. Screens are low hanging fruit for value engineering.   

If Heating Soaking is specified for glass, is it really required?

Heat soaking is a process whereby glass is subjected to extremely high temperatures with the intention of reducing the chance of spontaneous breakage. The high temperatures cause any nickel sulfide inclusions that may be present in the material to expand and the glass to break. In this way it is more like a quality assurance process than a process to modify the glass itself.

If nickel sulfide inclusions remain in the glass material, there is a chance it can spontaneously break after or long after installation. Heat Strengthening the glass, a less expensive process, is sometimes a viable middle ground in terms of cost.

To this author’s knowledge, Monadnock has never actually purchased heat-soaked glass. Nevertheless, it is a perennial specification requirement and low-hanging fruit for value engineering. Based on recent pricing, heat soaking can add $3.50 - $4.50 in material cost per square foot of window.