Air Sealing with Open Cell Spray Foam Insulation – Know the Risks

As the latest versions (2012 and 2015) of the International Energy Conservation Codes (IECC) push for more efficient homes, we are getting more questions from architects on how to achieve the air tightness requirements of 3 ACH50. There is no one correct answer, but it can be often achieved through taping of exterior structural or insulated sheathing, air sealing of wall cavities prior to insulating, and/or the use of insulation that is restrictive of air movement. The most common approach that we are asked about is the use of open cell spray polyurethane foam (ocSPF), as it is air impermeable (required thickness is dependent on the specific product, so check requirements in the ICC Evaluation Services Report), reasonably priced, and theoretically, doesn’t require any changes to standard builder practices. While it is true that ocSPF will provide air sealing cost-effectively, we typically do not recommend it in our cold climate region without additional measures due to risk potential over time. To effectively build a home with ocSPF, thoughtful detailing and a high level of execution is required to ensure that it remains effective 5, 10, 15…25 years from now.

ocSFP Window Flashing

While this wall assembly was not insulated with ocSPF, poor window flashing details are a common issue that we see and is one of the reasons we are cautious with this insulation approach.

  • ocSPF is vapor permeable, so there is a greater potential for condensation in the building enclosure than if closed cell spray polyurethane foam (ccSPF) is used. A hybrid approach of ccSPF and an alterative insulation (ocSPF, cellulose, fiberglass, etc.) is often used to keep costs down.
  • ocSPF can absorb 40% of water by volume. Therefore, if bulk water from leaks does make it into the building enclosure, the ocSPF will retain the water until saturated. Pinpointing the source of the leak may be difficult as the water can migrate within the foam.

Our main concern is that the performance of the product requires several trades to meet a high level of quality to ensure success and hope that the homeowners don’t unwittingly cause problems down the road through lack of maintenance. Here’s what we suggest…  Read more

Recalculating Solar Savings

Ten years ago, seeing a solar electric system on a building was noteworthy. Now they’re popping up everywhere. Lower cost is obviously a big driver of this solar surge; photovoltaic (or PV) system costs have dropped 50-70% in the past 10-15 years. Over the past decade, SWA has helped developers and owners install PV systems on hundreds of buildings. The systems are reliable, they have no moving parts, and they will convert sunlight to electricity for decades.

The cost effectiveness of PV, however, is not always clear. In fact, SWA has seen a concerning trend where the cost benefits of PV are exaggerated. Although costs vary with region and application, installed costs of PV are usually $3,000 – $6,000 per kWSTC.

Then there are incentives, including two key federal programs:

Photovoltaic Panels

  • 30% Federal tax credit
  • Accelerated depreciation (for businesses)

Other incentives vary greatly from region to region:

  • State, local, and utility rebates or credits
  • Sale of Renewable Energy Credits (RECs)

The Database for State Incentives for Renewable Energy (dsireusa.org) has a good summary of these regional incentives. Federal and regional incentives can easily lower PV system costs by 50% — often more.

The final piece in assessing cost effectiveness of PV is the electricity savings. With PV generating electricity for your building, you’ll obviously be paying less to the utility. But how much less? Read more

SWA High Performance Design Best Practice: Limiting Shelf Angles in Masonry Buildings

BACKGROUND

The multifamily building industry has adopted a best practice long touted by the building science community: continuous insulation at the exterior of the building. However, even in this ideal circumstance in which the insulation is installed flush and without gaps against the exterior substrate (concrete block or sheathing) with an air barrier applied to this substrate beforehand, the overall performance of the insulation will be vastly reduced by the installation of shelf angles.

Shelf angles (also know as relieving angles) are designed to support the expansion and contraction of the brick coursing; however, this presents a direct challenge to the continuity of exterior insulation. Standard design details interrupt the exterior insulation at every shelf angle, typically at every floor in line with window lintels. Since the shelf angle is made of steel, a highly conductive material, this interruption impacts not only the effectiveness of the insulation in general, it provides a considerable thermal bridge over the entire horizontal band of the building at every occurrence.

A recent article by Urban Green Council, “State Energy Code Clarification Will Stem Heat Loss through Walls,” made it clear that a continuous shelf angle has “about the same poor thermal performance as [an] exposed slab edge.” The full article can be read here.

Fig. 1. An infrared (IR) image that shows the thermal impact of shelf angles

Fig. 1. An infrared (IR) image that shows the thermal impact of shelf angles

 

SWA RECOMMENDATION #1: LIMITING SHELF ANGLES

Not all buildings require relieving angles. Building owners, architects, and structural engineers should first ask themselves whether relieving angles are necessary at all for the building being designed. If it is determined that these angles will be necessary, the next question the structural engineer should ask himself is what the minimum frequency necessary is to support the brick course. Generally speaking, buildings do not need one shelf angle per floor—despite this being common practice.

In addition to the aforementioned energy implications involved in specifying shelf angles, there are other benefits to eliminating these steel members when possible. The most obvious impact is on upfront costs. At approximately $25/foot of angle iron (via Union Iron Works), shelf angles for multifamily buildings in New York City can cost tens of thousands of dollars.

Upfront and operating (i.e. energy) costs aside, there is also the embodied energy of the material to consider. Not only does the manufacture of the steel angle contribute to its embodied energy, but also all of the energy used to transport these pieces to the project site. By reducing the need for the production of these angles, the overall energy expended to construct a new building decreases.

One additional consideration for owners is the maintenance required for shelf angles. The introduction of brick lintels creates an inherent and inevitable need for future maintenance. Since the cost of this upkeep is often considerable, owners may wish to use the opportunity to limit shelf angles during design to reduce long-term maintenance costs.

 

SWA RECOMMENDATION #2: OFFSETTING SHELF ANGLES

In addition to limiting their frequency, consider a shelf angle offset to further reduce thermal bridging. One such system that allows for this is manufactured by FERO called FAST (FERO Angle Support Technology).

Fig. 2. Typical FAST TM system detail

Fig. 2. Typical FAST TM system detail

FAST is designed to offset the shelf angle from the structural backing, allowing the insulation and air barrier installations to be more continuous. More information about this product can be found on their website.

SWA welcomes the input of design teams for other possible solutions to achieve a more continuously insulated wall. By accomplishing this, the building will have a truly continuous thermal envelope. As a result, thermal bridging will be eliminated along with the associated energy losses.

Fig.3. An offset shelf angle

Fig.3. An offset shelf angle

 

Fig.4. A wall section with an offset structural shelf angle

Fig.4. A wall section with an offset structural shelf angle

 

CONCLUSION

To implement best building practices, fulfill the continuous insulation requirements of certification programs, and comply with NYC Energy Conservation and Construction Code, SWA recommends limiting the number of shelf angles in the construction of the envelope. This will help limit upfront material and long-term maintenance costs.

SWA also recommends off-setting the shelf angle to reduce the thermal bridging these steel elements create. Fewer shelf angles means that there are less obstacles imposed on exterior insulation, resulting in less thermal bridging. Limiting the impact of shelf angles produces a more robust and insulated envelope that will, in turn, positively impact the energy performance of the building and comfort of its occupants.

SWA would like to thank Robert Murray for his assistance with this article.

Robert J. Murray, P.E., LEED AP, Principal
Murray Engineering, PC
307 Seventh Avenue, Suite 1001
New York, NY 10001
Telephone: 212.741.1102
Email: rmurray@murray-engineering.com

 

REFERENCES

1. Anderson, J., D’Aloisio, J. DeLong, D., Miller-Johnson, R., Oberdorf, K., Ranieri, R., Stine, T., and Weisenberger, G. “Thermal Bridging Solutions: Minimizing Structural Steel’s Impact on Building Envelope Energy Transfer.” American Institute of Steel Construction. Modern Steel Construction, 1 Mar. 2012. Web. <http://msc.aisc.org/globalassets/modern-steel/archives/2012/03/2012v03_thermal_bridging.pdf>.

2. FERO: Engineered Construction Technologies. Product Catalogue. Edmonton: FERO: Engineered Construction Technologies, 2014. Web. <http://www.ferocorp.com/pages/fast/fast.html>

Accessible Design: Common Mistakes & How to Avoid Them

Part 1: Public and Common-use Areas

After years of inspecting multifamily housing developments across the country for compliance with regulatory requirements for accessible design and construction, our accessibility group has compiled a list of common violations – violations that could easily have been avoided before construction even began. By addressing requirements for accessibility in the early phases of a project, designers can preempt the need for costly remediation during construction and greatly reduce the possibility of potential litigation.

Here are just a couple of examples of common violations that we come across on a regular basis:

  1. Slopes of Accessible Routes
    At least one accessible route is required to connect site arrival points, accessible building entrances, various site and building amenities, and dwelling units in the project. All too often, we arrive on site to find that the slopes of these accessible routes are not compliant (sometimes more than twice what is allowed), necessitating the ripping up of sidewalks and flooring materials – an undertaking that can quickly become expensive. When considering an accessible route, there are two important slopes to keep in mind: cross slope and running slope.

    — Cross slopes of accessible routes must be no more than 1:48 (2%). Areas where two accessible routes intersect, as well as the clearance at doors, must not exceed 2% when measured in any direction.
    — Running slopes of accessible routes must be no more than 1:20 (5%). If the running slope of an accessible route exceeds 5%, it is then considered a ramp and all ramp criteria apply, including the requirement for handrails on both sides of the ramp.

    By identifying the required accessible routes on the drawings, and providing notes and slope indicators along these routes rather than spot elevations, it is possible to greatly increase the chances of compliance once the concrete is poured and the building is constructed.

  2. Protruding Objects
    Sconces are common examples of protruding objects.

    Sconces are common examples of protruding objects.

    Accessible design isn’t just about ensuring equality for those with mobility impairments. Another important, and often missed requirement, applies to those with visual impairments. A protruding object can be something as basic as a wall sconce, bar countertop, or drinking fountain; and as seemingly innocuous as a piece of artwork on the wall. Any element that is located 27-80 inches AFF and projects more than 4 inches from a wall can prove hazardous to someone who does not have the ability to see it. The projecting objects themselves may seem small, but the cost of replacing hundreds of lighting fixtures throughout a building can be astronomical.

    While the best method of avoiding protruding objects is to specify wall-mounted sconces and other fixtures with a low profile, there will of course be situations that require other solutions. Where a protruding object exists, a cane-detectable barrier must be provided below it to ensure that a person with a visual impairment will be able to identify and avoid the potentially hazardous object. This can be as simple as positioning a planter or built-in piece of furniture below a wall sconce or piece of artwork, or installing a foot rail or knee wall below projecting bar countertops. Locating drinking fountains within alcoves is another method of achieving compliance.

By addressing these common violations in the design phase of a project, it is possible to greatly reduce the need for change orders and costly delays once construction begins. A little planning ahead can save a lot of time and money in the long run.

Stay tuned for Part 2: Dwelling Units – coming soon!

The $300 Investment Every New Construction Home Should Make

Whether code built or energy efficient, if your new home has a poured concrete foundation and floor slab, please pay particular attention to the following. While older, leaky homes result in low interior moisture levels (thus the desire for humidifiers on central furnaces); newer, tighter homes will typically have relative humidity levels in the 25-50% range naturally.

Window

Moisture from construction materials in new homes must be managed to avoid problems like interior condensation and mold.

In some cases, there is a need to actually dehumidify to maintain relative humidity below 50% during the winter. In the first 1-2 years after the home is built, concrete foundations expel massive amounts of moisture as part of the concrete curing process called “hydration”. As the concrete cures, some of the water in the concrete mix reacts chemically with the portland cement and forms the hardened concrete, and some of the water evaporates to the surrounding air. The exterior water resistant/proof coating on the below grade portion of the foundation prevents moisture from escaping that way. Typically only a 1-2 foot tall area along the perimeter of the above-grade portion of the foundation is available for drying to the exterior.  It is more likely that the moisture will be expelled to the interior of the home and therefore, must be managed to prevent deleterious moisture-related problems such as condensation, mold, wood rot, etc.  Framing lumber also contributes: lumber that starts out kiln-dried at 18% moisture levels, will eventually end up at 6%.

How to deal with that moisture? Here is that cheap investment alluded to: an ENERGY STAR dehumidifier with a built-in humidistat.  This unit should be plumbed to a drain to allow continual operation (without having the occupants empty a bucket).  In addition, the dehumidifier should be installed in the basement or crawlspace as soon as the structure has been enclosed and power is available. In terms of the construction process, it is recommended that the foundation be the last item to be insulated to allow for the internal construction moisture to be removed prior to enclosing. After a year or two of occupancy, construction material moisture levels will become stabilized at “normal” levels. In the interim, remember to “build-tight and ventilate right”, but also manage that construction moisture.