How To Verify Building Envelope Performance

Published: May 29, 2014 By: McIntosh Perry

Caulking Wall With the industry push towards higher efficiency building envelopes, designers are using new materials to their maximum limits and designing spaces and systems within buildings for maximum efficiencies.  While the theoretical envelopes are being pushed these design expectations are often not matched by actual performance.  This session will discuss a range of performance confirmation technologies including thermography, electrical vector mapping, smoke testing, air and water leakage testing and other methods used to verify execution of the design intent.

Roof Systems:

Green roofs, amenity areas and paved podium levels to meet the expectations of modern users has resulted in greatly increased complexity and costs should systems not perform

Wall and Window Systems:
Ever increasing building heights and the desire for more daylight in spaces is pushing the performance limits of systems
Mechanical Systems:

Although not a building envelope element , the sometimes conflicting battle of energy performance and acceptable comfort often become critically highlighted when the envelope does not perform as theoretically conceived and a tightly designed mechanical system is expected to pickup the slack.

Roofs

The three areas of concern for roofs are:

  • Leak testing prior to installation of overburdens
  • Active monitoring of roofs for early detection of leakage.
  • Thermographic scanning for wet insulation

Green Roof Requirements

City of Toronto Green Roof Standard, and good practice, requires a leak test of the roof prior to installation of the overburden.  Accepted options for this verification include the following:

Flood testing

Flood testing is exactly what it sounds like.  After blocking the roof drains the area is flooded with water and watched for a period, usually 12-24 hours, to see if it leaks.

Pros:

  • Cheap, usually just the cost of the water and can be done by a range of people

Cons:

  • If it does leak, can cause significant damage to the building below, or even the roof itself
  • Improper execution or lack of consideration of the structure can cause structural collapse
  • With minor defects may not show within the period of the test, particularly with systems bonded to the roof deck, such as most high-rise projects and green roofs.

Thermographic scanning

Using a thermographic camera which presents a thermal image of the roof a technician complete a scan looking for variations in temperature.

The concept is that wet insulation or moisture absorbing substrates in the roof system heat up and cool at different rates than dry areas.

The scans are done at night after a day of warming so that the variations in the cooling become visible.

Pros:

  • Large areas of roof can be scanned relatively quickly, relatively affordable.

Cons:

  • Highly dependent on ideal weather conditions to highlight the defects (warm dry day, cooling at night), and a skilled operator to see them.
  • Leaks in new roofs being scanned may not have had time to wet substrates to a point where there is any visible thermal variation.

Electrical vector scanning

Electrical Vector ScanningNewer technology, although various proprietary systems exist, the fundamental concept is that where penetrations through a roof exist that water is leaking through, the electrical resistance between the top roof surface and a conductive material below, such as metal decking, will be at a minimum at the point of the leak.

Pros:

  • High accuracy for location of the defects, can locate them within inches in many cases.
  • Can identify small penetrations even on new roofs
Cons:
  • Proprietary systems, you are tied to just a few suppliers of this service, some of the pioneers of which started in the GTA.
  • On non-conductive decks, such as concrete, you need to incorporate conductive elements below the membrane during construction of the roof

Building Envelope Elements

Wall and Window Systems

Ever increasing building heights and the desire for more daylight in spaces is pushing the performance limits of systems. Changes in height have affected tests and designs. Many tests and standards developed over the years top out at building heights of about 25-30 stories. Designers have a choice of performance levels when they select systems, but all systems have limits. Another consideration is that lab results do not always reflect what is delivered to the site.

There are four site verification options for windows and walls:
  • Water penetration tests
  • Air leakage testing
  • Structural tests
  • Thermographic scanning

Water Penetration TestsWindow Only Testing

The interior of the window or wall area is isolated and depressurised using a calibrated exhaust fan.  For small scale testing most common for windows individual sections of the window are isolated, on larger scale tests entire suites or floors can be de-pressurized.  Once a pressure difference is established water is sprayed on the window or wall using a calibrated spray rack to deliver a known volume of water.  The pressure is typically cycled and the testing is typically run for a set period.

Pros:

  • When just windows are tested the testing provides results relatable to the manufacturer’s lab testing.  Provides assurance that the installed windows meet the design specifications.

Cons:

  • For window only tests it does not provide any data regarding the performance of the adjacent interfaces.
  • This confirmation testing is limited to just the areas tested.  On a large building even a half dozen tests may not be statistically significant.

Air Leakage Tests

This testing is often done in conjunction with a window water leak test.  As with the water leakage testing the interior of the window or wall area is isolated and depressurised using a calibrated exhaust fan.  Rather than spray water the exterior of the window is covered with a poly sheet sealed to the window frame and the interior depressurised again.  The difference between the initial air leakage flow rate and the rate after covering the exterior is used to estimate the amount of air leakage through the window at the test pressure.

Pros:

  • As with the water testing the testing provides results relatable to the manufacturer’s lab testing.  Provides assurance that the installed windows meet the design specifications.

Cons:

  • This confirmation testing is limited to just the areas tested.  On a large building even a half dozen tests may not be statistically significant.
  • For window only tests it does not provide any data regarding the performance of the adjacent interfaces.

Larger scale testing can be completed using blower doors in the suite entrances, or entire floors exhausted or pressurized.  The blower door is calibrated to provide a set pressure difference across the opening and is provided with calibrated openings to estimate the air flow required to maintain that pressure.  Used in combination with smoke pencils to find isolated air leaks, or if the suite is pressurized smoke machines can fill the space with smoke detectable from the exterior to establish paths of air flow.

Pros:

  • Can test an entire suite or floor and all associated sources of air infiltration regardless of whether it is through the windows, walls, or even from an adjacent suite or back-drafting of the exhaust fans.

Cons:

  • As with other methods this testing provides only a sample.
  • There are design assumptions made with regard to air leakage which can be confirmed, however the numbers provided by this testing to not relate to equivalent lab testing.

Window Thermographic Scan

Thermography

  • Thermographic cameras have been used for decades to review the thermal image of a wall to assess thermal performance.  In the 80’s thermal imaging cameras cost upwards of $75k and required dry ice to function.  Changes in technology have brought the price down to the point where basic systems can be purchased for less than $1K.As noted previously these cameras present a thermal image of the surface you are looking at.  Although this appears simple enough it requires skill and knowledge of material properties, such as emissivity, and construction methods to know what the images are in fact showing.A comparison I like for thermography is having a whole body scan done when you have no specific problem they are looking for.  The scan will invariably show some variations or unexplained anomalies, as no one is perfect.  The skilled radiologist or doctor can separate the shadow of a childhood scar from the cancer, similarly a skilled thermographer can separate the missing insulation or defective air seal from a normal variation.

Pros:

  • From the exterior from a distance you can view large areas of walls.
  • Provides an easy image of the entire surface you are looking at with all elements

Cons:

  • Misuse, or use by an unskilled person has been known to spark significant destructive investigations of no value.
  • Generally a qualitative test, observations are not easily translatable to a measured performance variation

Mechanical System Impacts

As noted at the beginning, mechanical systems are not part of your building envelope, but a building should always be viewed as a holistic system.  Efforts to maximize efficiency, coupled with the precision of sizing computerized design has brought to the industry means many systems are very precisely sized based on the defined parameters of your building performance.

One of the large issues we are encountering is that with the heights of current buildings minor amounts of unplanned air leakage compounded by the stack effect of the tall structures overwhelms mechanical systems.

Confirmation early in construction that the systems deliver what is specified and can provide the performance planned saves everyone in the long run.

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