Building Materials Advances in MultiFamily

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New products and systems help produce greener and better-performing buildings with enhanced design options

Sponsored by CertainTeed Gypsum, Oldcastle® Architectural, Pella EFCO Commercial Solutions, and Tamlyn By Peter J. Arsenault, FAIA, NCARB, LEED AP

Multifamily construction and renovation projects continue to garner a lot of attention whether they are rental apartments or purchased condominium units. The reasons for this attention seem to be driven by a number of different social, economic, and practicalitybased decisions that buoy their continued popularity. Many urban areas are growing in population, creating denser development that combines commercial uses with residential choices in the same building or block. Changing demographics can mean that multifamily housing with all-inclusive maintenance and amenities appear better suited to changing lifestyles and personal budgets. Interest in greener living is causing some people to look at smaller living spaces with less driving or commuting time compared to life in a suburban-sprawl, car-centered environment. And there remains a fair bit of business interest in multifamily real estate from both U.S. and foreign investors. Regardless of the motivation, it becomes incumbent on architects to design multifamily buildings that can respond to the needs and consumer preferences of those spurring the activity. It is equally important to create buildings that use the best and most appropriate building technology to achieve a well-constructed, durable, and efficient end result. Doing so involves an understanding of the availability and workings of building products and systems that can not only meet those criteria, but also contribute to a well-designed, greener, higher-performing building.

Greening of Multifamily Housing

In 2013, an independent study1 was conducted by the firm of Strata Research to “better understand renter purchasing criteria and the importance of sustainability-related apartment features to the overall purchase decision. In order to achieve this, Strata Research was commissioned to test renters’ awareness and importance of various environmentally friendly features, as well as determine their willingness to pay an extra premium if these features were included.” Their findings were quite significant. First, out of their sample of over 1,000 interviewed renters from across the United States, they found that 77 percent believe it is important that their apartment is green. The factors driving this response included cost efficiency (33 percent), protecting the environment (26 percent), and doing their part (25 percent). Further, 65 percent stated that energy efficiency is important and 57 percent value an apartment with environmentally friendly features. In fact this is important enough to renters that 72 percent said that they are willing to trade off an important apartment feature (such as extra storage space or high ceilings) for green features.

Some of this consumer green awareness and preference certainly comes from the general media and interest in sustainable lifestyles. It likely also comes from developers and property owners who have been promoting green buildings for the marketing appeal, the added earnings potential, and, we would hope, the commitment to also do the “right thing.” But it also certainly comes from the growing availability of programs that promote green multifamily housing. The LEED program of the U.S. Green Building Council2 has certainly been embraced by the multifamily housing market with prominent displays of the LEED logo and information on many new and renovated buildings. Recently, ENERGY STAR added multifamily housing3 to their categories of buildings that can be reviewed using their popular Target Finder and Portfolio Manager programs to benchmark a building’s energy performance against similar buildings in the same geographic area. Adding to the interest by developers and owners is the recent availability of lower interest rates from Fannie Mae4 , the national mortgage organization, for multifamily properties with a green building certification, such as LEED or ENERGY STAR.

All of these preferences and actions converge on the design of a new or renovated multifamily housing project since design professionals need to be aware of these drivers to best serve developer clients and end users. But how does this all really play out in a project? It often comes down to a series of design decisions made all along the way related to the building enclosure, the interior, and the integration of innovative technical advances. These decisions will affect the sustainable nature of the building since they will affect different green categories such as energy efficiency, acoustics, indoor air quality, durability, and material choices. In this light, we will review a variety of new or updated building components and services that can help with making some of the best design decisions in multifamily housing projects.

Building Envelope Analysis

The envelope or exterior construction of all buildings directly impacts the energy performance and related energy costs. Therefore, conducting an analysis of a new or existing building envelope is one of the first and best steps a design team can take to understand how to achieve an energy-efficient and environmentally friendly building. This is especially important in the renovation of existing buildings, particularly if the building is being converted from some other use (i.e. warehouse, school, etc.) into multifamily housing that has become very popular in many areas. This analysis can be done in-house by architectural firms using available computer modeling software or by working with manufacturers who have customized software to analyze the options of different systems in a given building envelope system. Either way, a baseline building can be modeled, while the relative changes can be compared using specific envelope designs, types, and options.

Envelope Analysis Portal

One common and critically important component of building envelopes is fenestration. Hence, it is not surprising that some window manufacturers have embraced its importance and seek to partner with design professionals on conducting a building envelope analysis. Doug Phelps, Director of Commercial Business Development for Pella EFCO Commercial Solutions, points out that they work with designers on a “whole building analysis which is truly unique from the component approach. This way, we’re able to analyze and run ‘whatif’ scenarios to compare potential envelope improvements in terms of energy savings, occupant comfort, and building aesthetics. Every project has specific goals, and we are able to support the project team with flexible, realtime analysis.” He also notes that this interest in full analysis came from occupants commenting that their spaces felt more comfortable after replacing windows. By adding the analysis of occupant comfort as part of the envelope analysis, it is also possible to quantify that improvement while showing projected energy savings for the building.

This process is available to any design team and supported by the national, independent energy engineering firm, The Weidt Group. According to David Eijadi, Principal in Charge of Energy for The Weidt Group, “The envelope analysis identifies potential problem areas and offers solutions to make buildings more energy-efficient and comfortable. In the process it leverages some of the best technology available in software for computing hourly energy simulations.”

Air and Water-Resistive Barriers (WRBs)

One significant part of a building envelope is its ability to be sealed completely. Hence, building codes require barriers be incorporated into envelope assemblies to prevent unwanted air infiltration and water penetration. Waterresistive barriers (WRBs) are commonly used that are synthetic, non-woven building wrap products. The high-performance advantages of this modern solution include a barrier that is more breathable, more durable, and more easily sealed along the seams. Further, this type of synthetic WRB can also double as a continuous exterior air barrier, meeting the code requirements for both in a single layer.

Drainage Gap on Water Resistant Pavers

Using a high-performance building wrap in a multifamily housing project takes advantage of several innovative characteristics. First, as an engineered product, it creates a weather barrier behind exterior cladding to protect the sheathing and reduce water intrusion into wall cavities. This is important since all exterior cladding will likely allow some degree of water intrusion at some point. It is also particularly important in rainscreen assemblies where water is expected to enter behind a cladding material and is allowed to drain away. Second, as a vapor permeable or breathable product it will allow water or moisture to escape, thus allowing any damp or wet materials to dry in a relatively short amount of time. During this drying, WRBs can maintain their water resistance because they are constructed with pores that are large enough to allow moisture as a vapor to pass through but too small for water as a liquid to pass. Third, as an air barrier, a WRB will be an energy-efficient means to stop air infiltration and exfiltration through walls.

A further innovation has come about by enhancing building wraps to serve as an effective drainage plane set back from the cladding with a gap. The conventional means to create a drainage gap in a framed wall system is to use furring channels or strips. The alternative is to use a drainable WRB building wrap that provides its own integrated method of drainage. For example, at least one manufacturer creates this gap by bonding 1.5 mm propylene spacers to a high performance WRB building wrap. This depth is large enough to provide a true drainage space between the sheathing and cladding material, allowing it to act as a full rainscreen system in miniature, without the added labor or cost. Further, it will work with all types of cladding systems, particularly those that can be moisture sensitive such as wood or fiber cement siding.

When specifying WRBs or building wraps for multifamily housing projects, it is important to recognize that there are literally dozens of building wrap products available with wide variations in performance and cost. They can also vary in water resistance, drainage efficiency, water vapor transmission or breathability, ability to impede air flow, durability, tear resistance, cold weather flexibility, flammability, and smoke developed ratings. Beyond that, however, it is important that the WRB can be sealed properly and fully along the seams without undue penetrations from staples or nails. Some manufacturers offer full sealing systems that avoid the use of nails and staples and instead use a compatible adhesive, sealant, or tape. Equally important are the details of how the WRB deals with openings in the wall such as doors and windows. Being able to flash and seal the WRB properly with window and door flashing materials will assure that water draining down the face of a drainable WRB will flow away properly and not behind other building elements into the wall.

Continuously Insulated Wall Systems

An innovative trend in multifamily housing projects has been the increased use of coordinated, high-performance wall systems with multiple components from a single manufacturer. According to John Cicciarelli of Oldcastle® Architectural National Masonry Sales, “Over the past few years, we’ve seen two innovations in multifamily housing projects: an increase in high-performance wall systems and an uptick in masonry veneers being specified.” In many cases, this system approach gives the designer the benefit of a total wall assembly that allows for better insulation solutions for increased energy efficiency. One such system uses a continuous insulating foam layer over a prepared substrate, typically in a framed wall, that is formed specifically to accept veneer stone or masonry products. In this way, it provides a full layer of continuous insulation outside of the framing while solving the common problem of how to best finish the exterior surface. The insulation in such systems can achieve thermal resistance R-values above R-13 and also provide an integrated moisture management design. The exterior finish can be selected from the wide range of veneer stone colors and patterns that are on the market or from the equally broad range of masonry and brick products. Of course, the finish stone or masonry products need to be selected to be compatible with the patterned insulation that is designed to receive them.

Exterior Wall System

This type of wall system can be used on either new or existing buildings. In new construction, the framed wall assembly would need to be complete to the sheathing or substrate level with the appropriate air and water-resistive barrier in place as needed. In a renovation, existing cladding may be able to remain if it is fairly flat and intact. Otherwise it may need to be removed and the substrate adequately prepared. Then the installation of the formed foam insulation takes place using specially designed fasteners and screws. Next, the selected veneer stone or masonry is set into the formed openings of the insulation in a pre-selected pattern and held in place by friction between the foam panels and the manufactured teeth of the veneer. As in most veneer installations, anchors are used to affix the masonry and mortar to the substrate or structure of the building. The wall is finished using a Type-S mortar to assure proper bond strength, adhesion, flexibility, and stability. When finished, the wall is lighter in weight than a full masonry or stone wall, provides a full layer of continuous insulation, and offers a broad range of finished appearance choices. Further, the nature of the masonry and mortar makes the exterior surface more durable and longer lasting than some other cladding choices as well.

Multifamily Acoustics

In a multifamily housing unit, good acoustics are important to ensure noise control between residential units or between indoors and outdoors. This has increasingly been recognized as a part of indoor environmental quality in green building standards but also as part of a general quality of life aspect associated with multifamily living. Occupants expect a reasonable sense of separation from neighbors that is necessary for comfort and privacy. Acoustically designed and installed walls and floor/ceiling assemblies can substantially decrease sound transmission through them and improve residents’ satisfaction, which often leads to less turnover and fewer expenses associated with filling vacancies.

One of the common means of measuring sound transmission through walls is to test an assembly for its Sound Transmission Class (STC) rating. In simplest terms, it is a measure of how many decibels of sound are absorbed or reduced (i.e. sound attenuation) when sound passes through an assembly. The higher the STC rating, the more sound attenuation, meaning a quieter environment on the other side. There are many common design choices to achieve some degree of sound attenuation in framed interior walls that use gypsum board over studs with soundabsorbing insulation between the studs. The STC ratings typically improve as more attention is paid to details such as penetration offsets, sealants, and separation of studs from gypsum board using resilient channels. A fairly new option has also become available in the form of noise-reducing gypsum board which is specifically designed to reduce airborne sound transmission between two adjoining spaces when used in wall or floor/ ceiling assemblies. This type of product features a viscoelastic polymer layer placed between two specifically formulated dense gypsum cores that collectively dampens sound energy. The result is a combination that significantly improves sound attenuation and is ideal for systems requiring high STC performance, such as multifamily housing.

Noise-reducing gypsum board is an excellent acoustic solution for meeting STC ratings without the need for techniques such as isolation clips or resilient channels. Clips and resilient channel can easily be shortcircuited during the construction process and even afterwards, during picture hanging or pressing of heavy objects against the wall, negatively affecting acoustic performance. These risks are eliminated when using noisereducing gypsum board, thus providing more consistent acoustic performance. If used in systems with resilient channels, noise-reducing gypsum board can reduce the negative effect of short circuits. It can also help reduce material usage versus traditional multi-layer gypsum systems. The high acoustic performance of noise-reducing gypsum board makes it possible to build effective noise-reducing walls with a single layer of material, gaining valuable square footage from thinner walls, and saving both construction time and material cost. Less material used also means a more sustainable structure in keeping with green building practices.

Window Performance

Windows are an integral and important part of any multifamily wall system and as such, they need to address a variety of design criteria. The desire to provide views and natural light needs to be balanced with energy efficiency in the wall system. To achieve the best energy efficiency and overall performance, a window system should be selected based on the performance of the total unit, not just the components. An option to consider in low- to mid-rise buildings with larger window sizes is a wood-framed window rated to meet AAMA performance classification CW. This performance level assures that the window can withstand design pressures from wind of at least 30 pounds per square foot (psf) and in some cases on the order of 50 psf or higher. It also assures that the windows will seal and prevent drafts in most situations while holding up to wind and weather conditions on upper floors of buildings. Aluminum-clad wood windows are often used where design flexibility is desired, where the warmth of wood will complement other interior woodwork, where low-maintenance exteriors are important, or in older existing buildings that require an authentic look.

Noise Reducing Gypsum Board

The glass options for windows have increased significantly in the past few decades but often choices can be limited by the window system used. For residential multifamily situations that prefer the aesthetic and energy performance of wood over other choices, the glazing choices do not necessarily need to be limited. It is now possible to specify and select up to triple glazing for wood-framed windows for greater energy efficiency and sound rol. Further, the insulating glass units can be treated for greater heat or solar gain resistance and the insulating space filled with inert gas such as krypton. Altogether, a triple-glazed, kryptonfilled, wood-framed window can deliver thermal performance values on the order of a U-factor as low as 0.16 or an R-value of approximately R-6.25.

Exterior Joining

Among the details to address on exterior walls, the means to join or connect cladding materials along joints, corners, and seams is worthy of design attention. Some products, such as masonry, have their own, well-established means of dealing with these details. Other products such as cladding panels or siding, require a separate trim product to deal with those transition areas. A design trend in this regard is to achieve clean modern lines that have become popular with younger generations and more urban multifamily projects. Hence, it has become common to see the use of extruded aluminum shaped trim pieces that make strong design statements while assuring the proper functioning of the cladding material.

Energy-Efficient Aluminum Clad Wood Windows

Selecting aluminum trim can be based on its capability as a resilient material that can adjust and flex to meet the needs of building material expansion and contraction. From a design perspective, it is extruded in a wide variety of profiles, allowing for choice in appearance from recessed to pronounced. Manufacturers have made many different sizes available, allowing the trim to be used with multiple panels from different sources. And, it is available in multiple finishes including primed, clear anodized, and pre-painted.

Different aluminum trim profiles are available for different placement locations. Horizontal and vertical reveal pieces can be coordinated for a consistent appearance that maximizes or minimizes the lines between cladding panels. Outside and inside corners can similarly be treated to accent a corner condition or help it to blend in with the rest of the building. Transition pieces are available that connect special corner conditions and the junction of soffits to walls. When properly used and installed, these products not only provide for a complete, finished design appearance, they help with the overall performance and durability of the exterior cladding as well.

Stone Veneer

A fast-growing type of exterior wall treatment that has been specified on multifamily housing in recent years involves the use of masonry veneers. We have already discussed how they can be used as part of a wall system, but the details of the veneer itself warrant some further discussion. Masonry veneers are comprised of thin pieces of stone or brick but give the appearance of solid masonry without the weight or cost. Stone veneers provide a natural surface exposed to the weather that allows the finished building to emulate the great aesthetics of solid stone or brick but in fact they are non-structural. This means they install much quicker than natural stone or brick due to their simplified installation process with much less weight and potentially less cutting.

Extruded Aluminum Trim

The options on the market for veneer masonry are broad and varied. Available choices range from a standard smooth or split face unit to veneers that look just like natural stone in varying sizes. The range of colors of the finished units is equally extensive and includes stone earth tone colors of grays and browns, a range of brick reds and oranges, and even white cast stone products. It is worth noting that these products have advanced considerably since they were first introduced several decades ago such that many have integral color worked into their makeup so the product color is consistent throughout each unit. The shapes and sizes are also varied to allow for details to be more authentically addressed. 

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