Trends and Realities in Building Façades | Articles & Archives

In many respects, the façade just might be the most important component of a new building. It keeps out the weather and pollution, it admits natural light, it holds in comfortable temperatures and well-processed air, it makes a statement to the outside world, and, if you're really fortunate, it becomes an icon. At the same time the sheer complexity of assemblies, fenestration, materials, even colors these days, has grown exponentially in recent years. There are plenty of ways to make mistakes and plenty of rewards for avoiding them. Recently Healthcare Buildings Ideas Editor Richard L. Peck and Contributing Editor Shannon Powers-Jones posed questions and got multiple perspectives on the challenges involved from key players in healthcare project delivery.

What are some important developments you've seen in use of façade materials?

Rain screen assemblies and double-wall systems are becoming increasingly prevalent in the United States. Water has been an enemy of construction since the pyramids were built, but today's increased concern with healthy buildings that are free of dampness and mold make water-tight façades more important than ever. Even building codes recognize this and are now calling for “drainable exterior assemblies” (IBC Section 1403). But budget is the all-important controller when it comes to choice of materials for the façade, and ultimate decisions always come down to costs.

That said, we're seeing more and more attention being paid to rain screen technology. Rain screens use a variety of materials, but we don't necessarily rely on them for primary weather protection. The technical challenge with rain screen systems however is knitting together the primary wall system to establish an effective weather line-a water/air barrier-that encloses the entire building. It's a challenging process-a lot of detailing is needed here-and that carries cost. But the benefits outweigh those costs: Rain screen systems are either pressure-equalized or pressure-reduced assemblies and, because most building leaks are due to pressure differences between interior and exterior environments, properly detailed rain screens can actually reduce building leaks. Secondly, rain screens offer increased freedom of choice in material palette for the façade. Rain screens can consist of aluminum panels, unitized terra cotta assemblies, cement board, or fiber-reinforced resin panels (some even with natural wood veneers).

Rain screens are not load-bearing and are typically held off from the supporting wall by one and one-half to three inches. Frequently this space can be insulated as well. Exterior insulated walls are much better thermal performers than conventional stud-cavity walls because we eliminate thermal bridging created by metal studs every 16 inches.

Lastly, a lot of the assemblies mentioned are relatively light-weight. Lightweight construction means less cost associated with structure. Often when building owners focus only on line-item costs, they are concerned about rain screens-but when one considers cost of structure and energy costs associated with increased heating and cooling, as well as reducing the potential for mold growth, rain screens present a very smart option indeed.

Double-wall systems are another way to increase performance. Here again building owners must overcome their resistance to buying two walls instead of one and focus instead on energy savings realized by reduced mechanical costs. Additionally, building maintenance walkways can be placed between the two walls and eliminate the need for a powered window washing system. These layered exterior wall systems can also reduce solar heat gain by shaping building apertures and creating layering arrangements. These layers can be perforated or even translucent, providing a light and view without direct sunlight. Whereas horizontal sunshades work well on south-facing exteriors, projected vertical screening works best on west-facing walls, and double-skin walls are an excellent way of achieving this type of vertical screen.

It's conceivable that one could use less expensive glass as a result of this screening, although that decision would be complicated by several factors, including heat loss or gain through conduction, as well as the need for acoustical control in noisy areas and neighborhoods. The glazing decision can be a real balancing act. In my opinion, insulated glazing is such a good way of building altogether that one shouldn't consider moving toward monolithic glazing.

Almost all construction is prefabricated or modularized in some way. Fifty years ago gypsum plaster was the most common interior finish. Today this has been replaced almost entirely with modular sheets of gypsum wall board. The same goes with exterior assemblies. Façades are almost always planned and designed with a module in mind. This module usually lends itself to prefabrication. Being able to hang 5 x 15 or 10 x 15 panels or even terra cotta modules of 24, 36 or 48 in length on vertical mullions can reduce the time needed on-site for craftsman cutting and joining items piece by piece. The important thing is to understand the module you are working with from the very start of design so that no surprises occur.

Cost reductions for this approach are not necessarily straightforward-you might be using more highly skilled labor in the shop constructing a unit than you would in the field, but one gains greater quality control and speed for that increased cost. The real cost impact is on the construction schedule. When a building is going up, construction schedule pressures become enormous. And, in this day and age, when so much of construction is driven by a desire to prevent mold infestation, the sooner one can enclose and “climatize” the building to perform the necessary interior work, the better. You can hang many unitized panels a day and cut weeks or months off the schedule, compared with constructing a building stick by stick, piece by piece, and finding yourself having to delay interior activities until a building is entirely enclosed. That's where the real savings of prefab come in.

Do you see a trend in increased complexity and variety of shape being adopted?

Yes, we often utilize a mix of materials as a tool to help break down the scale on our projects. Healthcare projects are especially challenging because many different types of spaces come together into one building. Whereas bed towers are relatively straightforward repetitive spaces, each with a requirement for daylight, the diagnostic and treatment floors can be endless in their complexity. For various programmatic reasons, many technical spaces require adjacency to other spaces, and this programmatic necessity often yields large floor plates. These big floors, in turn, create massive elevations that usually comprise the base or podium of a building from which bed towers spring. Varying materials on these large elevations is one of several tools architects have available to break down the scale of these building types-sometimes a million square feet or more. There is also increasing use of gardens on roofs and terraces, and even hanging on exterior walls, to further break down scale and enhance appearance.

Owner

Donna Craft

Vice-President Facilities/Plant Operations, Carolinas Medical Center—NorthEast, North Concord, North Carolina

We have increased our palette of materials on the interiors of our facilities to include “art” glass in public areas. Our standard is now to use solid surface materials on our millwork. We now use revolving doors at our main entries for functionality and energy savings. We have also returned to terrazzo in limited public areas. We have tried to balance the use of any new materials with the design intent but with still keeping an eye on the care, maintenance, and the long-term view, so that we are good stewards of our construction and maintenance funds. Maintenance is a continued concern, so materials on the exterior such as brick and precast elements help maintain the long-term viability of our facility.

How venturesome are healthcare facility façades becoming? Are there limits to this?

When part of your original building that was constructed in 1938 is still in use, and in consideration that North Carolina is the brick capital of this country, it may seem that we are not very venturesome. We try to respect the facility as a whole and keep the facility in context with our community. We accomplish this by using brick as the main material on our exteriors. Where we have been venturesome in our exteriors is under the skin. We have changed the exterior wall assembly to have the insulation installed on the exterior of the sheathing instead of in the interior side in the stud space of the wall. In our mixed North Carolina climate this gives us the ability to keep any condensation or water infiltration on the exterior of the sheathing and effectively out of our building. This is in hopes of eliminating mold in our buildings so that we provide better indoor air quality for our patients, some of who have compromised immune systems.

Prefabrication for a “prototype” is sometimes difficult, if not more costly, when the buildings are so specialized. However, where we have the opportunity-such as our parking decks-we take every advantage of prefabrication that we possibility can. Our parking decks are all prefabricated concrete structures. We have stretched that to include the use of “thin” brick in the façade of decks. This provides the appearance that we desire, but maximizes prefabrication because the thin brick is installed in the panels at the precaster's plant instead of on-site.

We have, as has any owner, enjoyed the reduction in construction costs. However, we try to be conscious that the downturn in the economy has had more adverse effects than benefits, such as costs. We are in an area that has experienced much more than our share of layoffs and plant closings. We know that the downturn in construction costs will not be long lived, so we are really trying to be realistic for the long-term and plan accordingly.

How venturesome are healthcare facility façades becoming? Are there limits to this?

I am seeing a great deal of glass and light-colored stonework being used. Both create cleaning issues due to pollutants in the atmosphere, especially in large urban areas. This is neither practical nor cost-effective. In addition, large expanses of glass can be an energy cost issue if not installed correctly with the right glazing and angles.

What progress has been made in disaster-proofing façades (e.g., earthquake- and hurricane-resistant)?

I know that current building codes address seismic issues and wind shears, and that there have been improvements in these areas. Not being a structural engineer, I do not feel competent to really discuss this.

Prefabrication is becoming a major factor in all construction sectors, not only healthcare buildings, as there are significant program, build quality, and safety related advantages in exploring a prefabricated approach to external cladding.

These are important factors as construction schedules are increasingly becoming more compact, and the building design lead-in times are being reduced with a preference for design and build construction agreements.

Prefabrication requires sufficient lead-in time prior to the installation of the cladding starting on-site, to allow the design to have been developed to a level of resolution, typically with subcontractor input, and also to allow the cladding elements to be fabricated and delivered to the site to meet the construction program requirements. However, if sufficient time is available to enable this to be accommodated, the cladding installation period can be significantly reduced. This allows the exterior envelope of the building to be made weather-tight and water-tight as quickly as possible, and it also enables the internal fit-out of mechanical and electrical services to commence. This is particularly important for healthcare buildings where the amount and quality of installation and equipment, and internal services and machinery required, is typically greater than what is required for a standard commercial office building.

The off-site fabrication of the unit in factory conditions ensures that the build quality of the prefabricated units and the workmanship is improved, minimizing the need for any on-site fabrication or installations, in uncertain or inclement weather conditions, which thereby reduces the risk of water leakage through the façade.

Prefabrication can also reduce or negate the need to externally scaffold the building for the cladding installation, subject to interface design, and allows for large areas of the building to be clad quickly with significant benefits to the program and sequencing of the cladding installation.

What progress has been made in disaster-proofing façades (e.g., earthquake- and hurricane-resistant)?

Prefabrication has provided a means to address a number of issues related to disaster-proofing building façades, primarily in how the façade cladding transfers applied loads back to the primary structure, and how the movement between the primary frame and the cladding is accommodated. Prefabrication of the cladding elements also allows the façade components to be designed to accommodate significant disaster scenarios, including earthquakes and hurricanes, as well as man-made acts such as terrorism, which primarily concern the life-safety of the building occupants and those in the immediate vicinity of the building during an event. However, depending on the requirements of the building owner, building envelopes can be designed to limit damage to the building and exterior walls by understanding the performance criteria required from the building envelope from the outset, the prefabricated units and in particular, the panel-to-panel joints, can be designed to accommodate a range of movements, including primary frame, superstructure, movements-such as slab edge deflections-and building sway.

The individual material components, such as window or glazing elements, can also be designed to accommodate specific, known, design loads that will ensure that they do not break or allow wind-borne debris into a building, in the event of a hurricane for example.

Cost remains the biggest factor in the development of the building design, and while the range and palette of materials available to the architect has significantly increased in the last 5 to 10 years, current market and world financial conditions are typically driving the design process.

Developers and clients are seeking maximum value for their investment to minimize their financial risk/exposure, while the specialist contractors, when in a competitive tendering process, are submitting low bids in order to secure work in difficult times. This has led to many façades being developed utilizing proprietary systems and materials that have a proven track record and are fit for purpose, rather than bespoke systems that may be relatively untried or proven in a specific location or environment under the required performance criteria.

However, the increase in the number of buildings in the United States pursuing LEED have significantly reduced the cost of highly efficient materials and systems (such as high-efficiency windows) and systems fitted to the façade, such as integrated building photovoltaics and shading devices. The market today is seeing more competitive costs and more choices in this regard, as well as more standardized methods to verify building claddings performance (thermal) and their “green-ness.” HBI