Best Practices for a Successful Natatorium Enclosure

INTRODUCTION
The indoor environment of a natatorium
(indoor pool) presents one of the greatest
moisture-related durability challenges to
enclosures in cold climates. Temperature and
relative humidity levels are elevated compared
to typical commercial indoor environments (for
example, living spaces and offices), resulting
in a high indoor dew point. In high-humidity
environments, the building enclosure is often
subjected to interstitial condensation and
moisture accumulation on indoor surfaces. These
conditions often result in premature enclosure
failures and, in serious cases, structural damage.
This paper reviews strategies for successful
natatorium enclosure design and construction as
well as high-level design considerations for HVAC
equipment. Other challenges and considerations
for indoor pool environments, such as indoor
air quality and corrosion of metals in the pool
space as a result of chlorine exposure, are also
important to the operation of a pool building, but
these are not the focus of this paper.
Over the last two decades, we have
participated in over two dozen projects involving
the design or forensic investigation of pool
buildings and other spaces that are characterized
by high indoor temperatures and high relative
humidity, resulting in high dew points. In most
cases, moisture issues could have been reduced
or entirely eliminated using best-practice design
and construction details.
Our objective in this paper is to provide
guidance on the key design criteria based on
building science principles, field experience, and
industry documents. This guidance is suited to
both architects and general contractors.
INTERIOR ENVIRONMENT
The American Society of Heating, Refrigerating
and Air-Conditioning Engineers’ (ASHRAE’s)
HVAC applications guide1 recommends
design conditions for different types of pool
environments. The ASHRAE recommendations,
reproduced in Table 1, consider different pool
uses and recommend ranges for indoor air
temperature, water temperature, and relative
humidity. The different classifications of use
suggest climate condition ranges appropriate for
Best Practices for a Successful
Natatorium Enclosure
Feature
By Jonathan Smegal, MASc, PEng;
John Straube, PhD, PEng; Chris Schumacher,
MASc, BASc, BTech, BECxP, CxA+BE; and
Aaron Grin, MASc, PEng
This paper was presented at the 2024 IIBEC/
OBEC BES.
each expected activity level. The reader will note
that this guidance provided by ASHRAE is not
based on climate zones.
Relative humidity is not a measure of the
absolute amount of moisture in the air. By
definition, it is relative to the temperature
of the air, so on its own, it cannot be used to
assess moisture risks. Dew point does provide
a measure of the absolute amount of moisture
available. Dew point is the temperature at which
water vapor in the air reaches the saturation limit
of the air and has the capability to condense on a
surface. Hence, dew point is a convenient, more
meaningful, and tangible parameter to use when
comparing the interior moisture loads.
Typical industry standard and building code
recommended indoor conditions for “normal”
buildings in a cold climate are 20 to 22°C (68 to
71.6°F) and approximately 35% relative humidity
(and lower in the far north). These indoor
conditions result in a dew point of approximately
5°C (41°F). This is consistent with dew point
values we measure in winter months in typical
cold-climate commercial buildings with relatively
high air leakage and ventilation requirements.
As shown in Table 1, the indoor conditions for
a pool are necessarily much warmer (to match
the activity and clothing level) and at a higher
relative humidity (owing to moisture from the
pool). Table 1 shows a range in relative humidity
for all pools between 50% and 60%, although
in cold climates we recommend keeping the
relative humidity as close to 50% as possible. If
a typical pool environment were considered to
have an air temperature of 28°C (82.4°F) and a
relative humidity of 50%, the dew point would
be approximately 17°C (62.6°F), which is 12°C
(21.6°F) higher than that of a typical building.
This means that in a natatorium, surfaces that
Interface articles may cite trade, brand,
or product names to specify or describe
adequately materials, experimental
procedures, and/or equipment. In no
case does such identification imply
recommendation or endorsement by the
International Institute of Building Enclosure
Consultants (IIBEC).
©2025 International Institute of Building Enclosure 34 • IIBEC Interface Consultants (IIBEC) September 2025
are below 17°C (62.6°F) will have a high risk of
condensation. Buildings exposed to cold-climate
winters or having long periods of cold weather
require best-practice design, material selection,
and construction to prevent the humid indoor
air from reaching surfaces that are near or below
the dew point. The enclosure design is critical
for all pool enclosures, both residential and
commercial, to minimize the risk of condensation
of the interior air on interior surfaces and within
the enclosure. It is also critical to point out that
to limit the rate of evaporation of the pool,
which adds available moisture to the air and can
exacerbate condensation in the enclosure, the
pool should be maintained at a temperature
2–3°C (3.6–5.4°F) below the air temperature.
If the pool is maintained at a temperature
above the air temperature, it will evaporate
and increase the relative humidity of the space
substantially or add significant latent load to
the HVAC system to meet the design relative
humidity requirements.
BEST-PRACTICE ENCLOSURE
DESIGN
Continuous Exterior Insulation
Residential and commercial pool buildings
can successfully use a range of enclosure
materials (cladding, insulation, control layers,
and structure). Typical structural systems
include wood, concrete, steel, and mass
timber. However, we recommend that pool
enclosures in cool to cold climates employ a
layer of continuous exterior insulation (i.e.,
the thermal-control layer) and that this be
installed over the other control layers (i.e.,
water and air control) and the structure. The
use of continuous exterior insulation keeps
the structure and all other materials inboard
of the insulation warm, reducing the potential
for condensation. This stands in contrast to the
numerous cold spots that are presented when
insulation is installed between the structural
members as a result of thermal bridging.
Further, the application of insulation in the
stud cavities and other framing spaces serves
to insulate the sheathing from the interior,
making it colder and increasing the relative
humidity and potential for condensation and
moisture accumulation at the interior face of
the sheathing.
Construction with continuous exterior
insulation over the structure has been studied
exhaustively over the past several decades. In
1964, Neil Hutcheon2 showed how installing
the insulation on the exterior of the structure
kept the interior surfaces warmer, reducing the
risk of condensation. This concept was further
refined by others. Alberta Infrastructure’s Chris
Makepeace3 promoted the idea of the PERSIST
(Pressure Equalized Rain Screen Insulated
Structure Technique) wall assembly in 1998. In
Alaska, similar exterior insulation strategies have
been referred to as the REMOTE (Residential
Exterior Membrane Outside-Insulation
Technique) wall.4 Building Science Corporation’s
Building Science Insight 0015 employs the
same principles in describing “the perfect
wall” strategy. Many others have documented
research and summarized theory and guidance
to maximize the benefits of this construction
strategy.6,7,8,9
A conceptual representation of an ideal
exterior insulation strategy is illustrated in
Fig. 1. The image shows a schematic identifying
the structural, finish, and control layers in the
enclosure. The structure (concrete masonry unit
[CMU], steel, wood, insulated concrete form,
mass timber, etc.) is covered with continuous
water, air, and vapor control layers, which are
all covered by continuous exterior insulation.
The insulation could be rigid foam, semi-rigid
stone wool, or medium-density (i.e., 32 kg/m3
or 2 pcf) closed-cell spray polyurethane foam
(ccSPF). This strategy ensures the air barrier
system is well supported by the structure and
protected from temperature fluctuations and
ultraviolet light. When this strategy is used in
design and the structure is well constructed,
issues with the wall assembly are rare
because of the continuity of the control layers.
However, as is typical with enclosure issues,
the problems often occur at penetrations and
transitions, which is why it is critical for the
designer to provide clear, constructible details
for all penetrations and transitions within the
enclosure.
Air Barrier System
One of the most critical components of a
natatorium’s enclosure design and construction
is a continuous air barrier system. The air
barrier system must be continuous on all
Figure 1. Schematic for an exterior insulated enclosure wall assembly.
TABLE 1. Typical pool design conditions1
Type of Pool
Air Temperature Water Temperature Relative
Humidity
°C °F °C °F %
Recreational 24 to 29 75.2 to 84.2 24 to 29 75.2 to 84.2 50 to 60
Therapeutic 27 to 29 80.6 to 84.2 29 to 35 84.2 to 95 50 to 60
Competition 26 to 29 78.8 to 84.2 24 to 28 75.2 to 82.4 50 to 60
Diving 27 to 29 80.6 to 84.2 27 to 32 80.6 to 89.6 50 to 60
Elderly Swimmers 29 to 32 84.2 to 89.6 29 to 32 84.2 to 89.6 50 to 60
Hotel 28 to 29 82.4 to 84.2 28 to 30 82.4 to 86 50 to 60
Whirlpool/Spa 27 to 29 80.6 to 84.2 36 to 40 96.8 to 104 50 to 60
September 2025 IIBEC Interface • 35
enclosure surfaces around the pool, including
the roof, the exterior walls, and any interior
partition walls that separate the pool space(s)
from adjoining spaces having different uses
(e.g., offices, community room, gymnasiums,
and especially ice rinks). The design and
construction of the air barrier system in a pool
building in a cold climate demands a higher
standard of care than typical construction,
as even small imperfections can result in
substantial failures. Designers and builders
frequently struggle to achieve the required
airtightness. Many in the industry remain
confused regarding the roles of air and vapor
barriers, and this confusion is propagated in
manufacturers’ literature, industry guidance
documents, construction drawings, etcetera.
An air barrier is always needed, must be
continuous, and, in a cold climate, must be
located on the warmer side of the enclosure to
avoid re-entrant looping condensation. A vapor
barrier is usually required for pool buildings
and can be the same material as the air barrier,
but it does not necessarily have to be.
As an example of the confusion in literature
and guidance documents, consider the 2011
ASHRAE Handbook—HVAC Applications,1 which
states that “failure to install an effective vapor
retarder will result in condensation forming in
the structure, and potentially serious envelope
damage,” but it does not make any statements
regarding the need for a continuous air barrier
system within the enclosure, which is even more
critical than vapor control.
Fig. 2 illustrates how much more water
vapor can be moved by air movement than by
vapor diffusion, further emphasizing the need
for a continuous air barrier membrane in the
enclosure. Depending on the height of the
space, stack effect can be substantial and cause
continuous air leakage through the roof system.
In 1966, Kirby Garden wrote Canadian
Building Digest 83 on the topic of indoor
swimming pools.10 Garden wrote, “Air leakage,
a very prominent mechanism operating in most
buildings, transports water vapour into walls
and roofs, producing interstitial condensation.”
Garden also discussed the importance of
preventing air movement from the swimming
pool space to other adjoining spaces in
the building.
Other publications have also emphasized
how critical the air barrier system is. In 1990,
Madeleine Rousseau of the National Research
Council published an article in Home Builder
Magazine11 regarding design and construction
solutions to problems with indoor swimming
pools. Rousseau stated correctly that an airtight
assembly, or air barrier system, is required to
control condensation. She expanded further on
that, writing, “To obtain an airtight assembly
over the enclosure, connect wall or roof air
barrier materials to other air barrier materials
in floors, windows, and skylights and seal the
joints with sealants, adhesive membranes
or gaskets.” She provided a simplified
cross-section view of a house with a pool that
identified an airtight compartment around the
pool space with a continuous air barrier system
and separate mechanical system from the rest
of the building.
Paul Totten, in 2007,12 also wrote on
the importance of properly designed and
constructed air barrier systems in pool
enclosures as well as the need for review
and oversight of the construction of the air
barrier system.
POOL AIR LEAKAGE
CASE STUDIES
We offer the following case studies to further
consider the importance of thermal and air
control in the building enclosure assemblies of
natatoriums and pool buildings.
Case Study 1: Wood-Framed Resort
Pool in the Northeastern US
Case Study 1 is a wood-framed pool building
within a ski resort located in the northeastern
US. The owners had observed some dripping and
staining from the roof assembly onto the glulam
structural beams of the building (Fig. 3), and
the exterior roof surface on the north side of the
building appeared to be uneven. The key issue
related to enclosure durability was air leakage
condensation that led to moisture accumulation
in the roof and, to a lesser extent, in the walls.
The panelized wood-framed roof construction
was assembled on the ground as panels adjacent
to the building and lifted into place onto the
glulam beams. The panels themselves were
constructed to be quite airtight: they were
constructed with 10 in. (254 mm) engineered
wood joists (e.g., TJIs) and were nearly full of
ccSPF insulation. ccSPF insulation is an air and
vapor barrier; however, at any joints where there
is no insulation, such as panel joints, air control
must be maintained. Continuity of the control
layers between panels can be a challenge.
In this case, when the panels were set on the
glulam structure, the air barrier was not made
continuous between the panels. This allowed the
slow movement of moisture-laden air through
the gap between the panels, which reached the
cooler roof surface and then condensed. The
moist conditions resulted in rot and decay of
the wood materials in the roof assembly at the
joints between the panels (Fig. 4), which slowly
spread to the rest of the panel. The deterioration
was greatest on the north orientation, which is
to be expected due to the lower amount of solar
energy available for drying. The deterioration
was so widespread that there was some concern
about the roof collapsing. Dark drips stained
the sides of the glulam beams due to the
condensate that eventually started rotting out
the wood in the roof and turned the condensate
a dark brown color when it drained back into the
building. The glulam beams were structurally
sound, just stained, so the remediation involved
replacing the roof with panelized wood-framed
construction. The replacement required careful
air barrier continuity detail at the joints, as shown
in Fig. 5, and a completely exterior insulated
roof assembly.
Case Study 2: Commercial Pool
Building in Southwestern Ontario
Case Study 2 was a project completed in 2019.
Situated in southwestern Ontario, this project
reminded us that even before the completion
Figure 2. Illustration explaining the relative water vapor movement from vapor diffusion and air
leakage. Source: buildingscience.com.
36 • IIBEC Interface September 2025
of strategies. First, ccSPF was installed into
the void from the exterior, improving the
thermal control, reducing the air leakage, and
significantly reducing the void space. New
gypsum was installed, and a vapor-permeable
air/water barrier was installed in this area of the
wall to increase the future safety factor of the
assembly, particularly to take advantage of the
vapor-permeable stone wool continuous exterior
insulation. A more comprehensive quality
control process using building pressurization
and thermal imaging was conducted to assess
and improve the air barrier system in other
areas of the building while the air barrier system
was exposed.
The requirement for airtightness of the interior
partition walls surrounding a pool is important
in buildings with adjacent spaces to limit the
transport of odors, chloramines, and moisture.
Case Study 3: Community Center
Pool Space Adjacent to Ice Rink
Near Toronto, ON
Case Study 3 was a project in 2006 at a
community center north of Toronto that
included a pool and ice rinks in the same
building, separated by a foyer space. The issue
at this building was mounding on the rink
ice overnight (Fig. 6). The ice mounding was
greatest at the end of the rink closest to the
foyer and pool and diminished with distance
from the foyer. Our investigation determined
that air leakage pathways were created on the
interior near the roof of the building where
the partition walls were not air-sealed to the
underside of the roof. These pathways allowed
Figure 3. Staining from the roof on the interior structure. Figure 4. Rotting of the wood at the exterior of the roof assembly.
Figure 5. Schematic of the roof repair ensuring the air barrier continuity on the warm side of
the insulation.
of the project and the operation of the building,
care is required during construction. The
structure was constructed, and the windows and
membranes were installed. In many locations,
exterior insulation was also installed. The pool
had been mostly filled with water to ensure there
were no issues with the pool systems, although
the mechanical systems were not fully installed
and functional. One of the exterior walls of a
lower roof area had a self-adhered air/vapor
barrier installed on the exterior of the gypsum
sheathing and the steel stud to the exterior of
a CMU structural wall. We observed that the
self-adhered membrane had become loose
over the entire wall surface and was no longer
supported by the gypsum. Further investigation
identified that it was not the membrane that had
released, but the facer on the gypsum sheathing,
and the gypsum core was wet. This failure
occurred because the self-adhered membrane
was a cold-sided vapor barrier during the winter.
Air leakage pathways around the CMU wall
extended into the void space, and since the
continuous exterior insulation had not been
fully installed, it resulted in failure of the wall
assembly. Water was accumulating within the
exterior gypsum, causing the facing to separate
from the core. The repair involved a combination
September 2025 IIBEC Interface • 37
moisture from the pool space and foyer area to
pass through the common space and into the
roof assembly above the ice rink. It condensed
and dripped onto the ice through the joints of
the interior finish, resulting in mounds that
formed every night.
Case Study 4: Community Center
Pool in Southwestern Ontario
Case Study 4 is a pool in southwestern Ontario
that had condensation drainage coming out of
the roof assembly at the lower portions of the
roof. The architectural design for the roof and
the roof-to-wall transition looked adequate:
a self-adhered membrane transition from
the wall to the roof, underneath the parapet,
creating continuity between the roof and wall.
However, when the parapet and adjacent roof
were opened, it was discovered that the backer
had not been peeled from the self-adhered
membrane (Fig. 7). The membrane was not
adhered, and further, there were structural
penetrations through the membrane that were
not sealed. This resulted in air leakage pathways
into the parapet from the interior space. The
schematic in Fig. 9 shows the air leakage
pathway along the structural connection to the
parapet. Condensation on the underside of
the roof membrane was guiding water directly
to the roofing assembly and saturating the
coverboard and roofing insulation. Condensation
was also draining back to the interior of the
building, staining window mullions and the pool
deck (Fig. 8).
THERMAL BRIDGING
Thermal bridging is another important
consideration for the design and performance
of pool enclosure assemblies. Ideally, thermal
bridges are addressed in the design phase of
a project, when they are easiest to remedy.
They become difficult to manage once they
are constructed. Often, the structure will pass
through the insulation layer of the enclosure
to support components of the building on the
exterior, such as soffits, or other architectural
details. In some cases, structural thermal breaks
can be integrated into the structural design to
reduce thermal bridging through the enclosure
early in the design phase.
POOL THERMAL
BRIDGING CASE STUDIES
We offer the following case studies to further
consider the impact of thermal bridging on
building enclosure assemblies of natatoriums
and pool buildings.
Case Study 5: Community Center
Pool in Chicago, IL
Case Study 5 is a pool in Chicago that had issues
with both air leakage and thermal bridging from
the hollow structural section (HSS) that connected
to the structure on the interior of the enclosure
while also supporting the soffit. Significant
condensation and dripping on the interior of the
enclosure at this HSS was a result of a combination
of thermal bridging and air infiltration. The
infiltrating air combined with thermal bridging
cooled the interior steel surfaces sufficiently in
the wintertime that interior air condensed on the
surfaces. The initial design was for the entire soffit
to be wrapped airtight in self-adhered membrane
Figure 6. Mounding on ice formed when air leaked from the common areas and the pool leaked
into the ceiling above the ice rink, condensed, and dripped onto the ice.
Figure 7. Water accumulation and damage in the parapet, and the
backer observed on the Blueskin air barrier.
Figure 8. Staining inside the pool area running down steel columns
from the parapet.
38 • IIBEC Interface September 2025
Case Study 6: Single-Family
Residence with Pool Near
Toronto, ON
Case Study 6 is a residential pool building north
of Toronto. The residents were previously unable
to use the pool in the wintertime because of
the considerable dripping within the space as
a result of poor design and construction details
in the enclosure. The structure was steel with
wood-framed infill and a vented cathedral ceiling.
The roof needed significant improvements to the
thermal control. To minimize the disturbance to
the interior, the exterior surface of the roof was
removed, and ccSPF was used to insulate the
roof assembly and encapsulate all the structural
steel components within the roof assembly
before the roof was reassembled. Following
the reinstatement of the roof, the condensation
and dripping from the interior of the roof was
almost completely repaired. One area had been
missed by the contractor, which was evidenced
by thermal imaging of the interior surface of the
roof. That small section of the roof was reopened,
and additional spray foam was installed around
the thermal bridge to reduce the heat transfer
in the problem area to eliminate the dripping on
the interior.
HVAC DESIGN
This paper is intended to be largely focused on
the building enclosure and not a discussion
of HVAC equipment. However, there are
some high-level HVAC considerations that are
important to consider early in design as well as
during forensic investigations of moisture issues
because they are related to successful enclosure
performance.
Building Depressurization
The ASHRAE HVAC applications guide1 states
that “pool and spa areas should be maintained
at a negative pressure of 15–40 Pa relative to
the outdoors and adjacent areas of the building.”
According to the guide, this negative pressure is
provided to prevent chloramine odor migration.
While controlling odors in adjacent spaces is
recommended, the more important reason for
depressurization is to control the movement of
interior air-based water vapor into the enclosure
and reduce the risk of moisture durability issues.
Quantifying the depressurization may require the
engineers and trades commissioning the HVAC
equipment to use different tools because it was
found through the case studies that large HVAC
balancing is completed to within +/-0.1 in water
column, which equates to only 50 Pa of accuracy.
Both Perkins+Will13 and Jason Der Ananian14
described the importance of depressurizing
the pool space relative to the exterior and to
Figure 9. Schematic of the air leakage pathway and condensation that saturated a large
percentage of the roofing insulation in the roof assembly.
and connected to both the roof and the wall,
but the air barrier layer was not continuous. Air
flowed into the soffit through deficiencies in the
air barrier, and then into the building through
the hollow HSS. Fortunately, the pool had been
operating correctly under negative pressure
(as discussed later in the paper) since it was
constructed; otherwise, there would have been
significant moisture damage to the soffit space.
The recommended fix for this issue (Fig. 10)
was to ensure the air barrier was continuous at
the plane of the enclosure with a fluid-applied
membrane (green coating showing past the ccSPF
on the roof deck) and spray foam on the wall and
in the metal deck flutes, and to entirely wrap the
soffit HSS structural members in ccSPF.
Figure 10. Closed-cell spray polyurethane foam (ccSPF) was installed above the windows at the
transition between the metal roof deck and the enclosure over the green fluid-applied air and
water barrier. ccSPF was also installed around the entire length of the HSS supporting the soffit
and connected to the interior structure to minimize thermal bridging.
September 2025 IIBEC Interface • 39
adjacent spaces to reduce the risk of interior
moisture entering the enclosure. Achieving
depressurization becomes easier with greater
levels of airtightness.
When completing both the design and repair
work on pool buildings, it is our experience that
it is often difficult to convince the mechanical
contractor to provide depressurization of the pool
space. We often get pushback from the contractor,
even when the symptoms and evidence of
moisture issues indicate that pressurization is
contributing to the reported issues.
Stack Effect
The other key criterion to keep in mind when
determining the enclosure pressure is the stack
effect within the building.
Stack effect is the term given to the naturally
occurring interior pressures in a building
related to the height of the interior space and
the temperature gradient across the enclosure.
Fig. 11 shows an illustration of typically occurring
stack effect pressures during the winter months
in a cold climate. Warm air is more buoyant;
it rises to the top of the building and finds its
way out through holes in the air barrier system.
Replacement air is then drawn in at the bottom of
the building. Positive air pressures push air out on
the top of the building, while negative pressures
pull air in at the bottom. The amount of pressure
formed increases with building height as well
as with greater temperature gradients between
the interior and exterior. Stack effect pressures
at the top of the building are the greatest in the
coldest winter months. Therefore, they need to
be considered when the pressure measurements
are taken to ensure that the building is
negatively pressurized all year round. Pressure
measurement should be done during the winter
months when it is cold outside to confirm that the
building depressurization is still effective even
when the stack effect pressures acting within the
space are the greatest.
POOL PRESSURE FIELD
CONTROL CASE STUDIES
We offer the following case studies to further
consider pressure field control and its impact on
the building enclosure assemblies of natatoriums
and pool buildings.
Case Study 7: Community Center
Pool in Nova Scotia
Case Study 7 is a newly constructed pool in
Nova Scotia, completed in 2022. Lights at the
perimeter of the soffit space above the entrance
were filling with water and failing. Unfortunately,
due to COVID-19, we were unable to travel to the
site to do the investigation ourselves. Instead,
we assisted remotely with the investigation. The
conditioned soffit was part of the interior space
and wrapped in self-adhered membrane as well as
continuous exterior insulation (Fig. 12). The lights
were well protected from driving rain events, and
there was no correlation between rain events and
water in the light fixtures. The accumulated water
was most likely a result of warm, moist interior air
being pushed along the electrical wiring pathway
through the air barrier discontinuity into the light
fixtures, resulting in condensation and moisture
accumulation. Fig. 12 shows a section of the
exterior edge of the soffit with the membranes
on the gypsum sheathing, and over the flashing,
and thick layers of continuous exterior insulation.
Fig. 13 shows a photograph of water accumulated
in the light fixture at the edge of the soffit.
Our recommendation was to negatively
pressurize the pool space to prevent
moisture-laden interior air from entering the
light fixtures. The mechanical contractor assured
us that the pool space was depressurized and
was not willing to make any adjustments to
the mechanical system. A simple assessment,
holding the exterior door open an inch, resulted
in air moving out of the building, readily
confirming that the space was, in fact, positively
pressurized at grade.
To ensure that a building is depressurized
correctly, the pressure must be measured
across the enclosure with a manometer and not
determined by measuring the flow rates at the
mechanical equipment. We have found that many
times, the HVAC contractor will provide evidence
of depressurization by using measured flow rates
of supply and exhaust, but these do not always
correlate to the desired enclosure pressures.
AIR DISTRIBUTION
OVER WINDOWS
HVAC design and distribution are also factors
contributing to window condensation issues.
As a result of the high interior moisture loads,
it is common in cold climates that the glazing
systems’ surface temperatures will fall below
the dew point for extended periods. The risk
of condensation on glazing systems can be
countered with high-performance glazing and
framing systems, but reducing condensation
more commonly relies on air distribution over
the glazing from the HVAC system.
POOL AIR DISTRIBUTION
CASE STUDIES
We offer the following case studies to further
consider HVAC system air distribution and its
impact on the performance of building enclosure
assemblies in natatoriums and pool buildings.
Case Study 5 (Revisited): Community
Center Pool in Chicago, IL
Case Study 5 in Chicago, previously discussed
because of the thermal bridging and air leakage
at the soffit, also had issues with condensation
on the windows. The lack of air distribution from
the mechanical system over the windows and
the deep interior mullions disrupted the airflow,
promoting condensation. As part of the repair
strategy for the building, additional fans, separate
from the HVAC supply ducts, were installed
specifically to blow air over the windows (Fig. 14).
Figure 11. Illustration of wintertime stack
effect with naturally occurring drawing of air in
the bottom of the building and exhausting it
out the top. Source: finehomebuilding.com.
Figure 12. Many of the light fixtures at the perimeter of the soffit were filling with water and
failing because of air leakage from pressurization of the building.
40 • IIBEC Interface September 2025
Case Study 4 (Revisited):
Community Center Pool in
Southwestern Ontario
Case Study 4, previously discussed because
of the moisture accumulation in the parapet
and roofing, also had issues with mechanical
distribution. Air supply grilles and ductwork
were provided around the perimeter of the
pool with linear diffusers to supply air to the
glazing at floor level (Fig. 15). A few years
following the construction of the building,
there were some issues with the masonry on
the exterior of the building with crumbling
mortar as well as staining of the masonry,
mostly around windows (Fig. 16). The parapet
cap was removed during inspection to look
down into the drainage/ventilation cavity
behind the masonry. The air coming out of the
gap was humid and smelled of chlorine. The
high humidity air in the masonry veneer cavity
resulted in icicles and moisture accumulation
at the top of the wall under the parapet flashing
during the wintertime (Fig. 17). The masonry
wall issue was the result of a combination
of factors, including, most importantly, the
lack of air barrier continuity. However, it also
involved installation deficiencies in the HVAC
ductwork, since in some locations, the air from
the ductwork was blown directly into the brick
veneer cavity, resulting in premature failure
of the masonry on the building. The building
repairs included air barrier replacement and
improvements to control airflow and eliminate
air exfiltration.
Case Study 8: Multi-Family Building
with Pool in Vancouver, BC
In Case Study 8, the importance of air
movement over the interior of glazing was
highlighted. The design of the visually
stunning Butterfly Westbank pool project in
Vancouver did not follow the best-practice
recommendations of keeping window areas
small and of providing large ducts with lots
of air to the window areas. RDH Building
Science worked with a company that provided
extensive computational fluid dynamic analysis
modeling on the airflow, analyzing interior
surface temperatures to determine the best
strategy to provide airflow over the glazing
with the concealed ductwork. Many iterations
and variables were run in the analysis, with
Figure 13. Photograph of water within the light fixtures at the edge of
the soffit.
Figure 14. Fans were added during the building repairs to blow air
directly over the windows to reduce condensation on the interior
surfaces of the windows.
Figure 15. Linear grilles adjacent to the windows are designed to apply
airflow to the window area, reducing condensation.
Figure 16. Around the windows, there was greater mortar damage and
efflorescence as a result of the lack of deficient air barrier details.
September 2025 IIBEC Interface • 41
3. Thermal Bridges: Limit all thermal
bridging through the insulation layer as
much as possible in design. In instances
where the structure must pass through
the insulation layer, design structural
thermal breaks or other strategies to control
the interior surface temperatures of the
structural elements.
4. Continuous Air Barrier System: We
have concluded based on the case studies
as well as other previous research that a
continuous air barrier system across all
surfaces of the enclosure (that is, roof,
walls, floor, and partition walls) that is
also continuous at all penetrations, such
as windows and doors, is required to be
nearly perfect to minimize the risk of
enclosure durability issues.
5. Negative Pressurization of the Building:
In a cold climate, to minimize the risk of
interior air entering the enclosure, the pool
space should be kept at a negative pressure,
which will reduce the risk of condensation
of interior air within the enclosure. This is a
requirement for pool buildings.
6. Airflow over Glazing: Windows in pool
buildings in cold climates often require air
to be directed at the surface of the windows
to minimize condensation on the interior
surfaces.
7. Construction Quality Control: It is crucial
to always be aware during construction of
the modifications/penetrations to the air
barrier system. Any penetrations that are
required should be reported and tracked, and
repairs should be done by the responsible
trades. Airtightness testing with the use
of thermal imaging or tracer smoke can
also help identify potential air leakage
pathways and is recommended as a quality
control tool prior to covering the air barrier
system, although this is often difficult in
reality due to construction sequencing on
the project.
two of the simulations shown here. Fig. 18
shows the model output for the plan view of
the roof. The entire roof/skylight area is red,
indicating condensation is expected to cover
the entire skylight/ceiling assembly. Fig. 19
shows the predicted surface temperature
and condensation results with a higher
temperature set point as well as additional
fans blowing air over the glazing surfaces. This
approach significantly reduced the predicted
condensation risk over most of the skylight/
ceiling of the pool space, as indicated by the
mostly blue and white coloration of the surfaces.
RECOMMENDATIONS FOR POOL
ENCLOSURE DESIGN
The authors have been involved in many
natatorium enclosure designs and failures
over the past two decades. Our experiences
are distilled into the following seven
recommendations that will minimize the risk
of enclosure and durability issues in a pool
building.
1. Early Design: Communicate the importance
of the key design criteria such as continuous
exterior insulation, continuous air barrier
system, and accurate construction details
early in the process when these strategies can
still be incorporated into the project budget
and construction scope.
2. Continuous Exterior Insulation: Wrapping
the structure in control layers and installing
continuous exterior insulation with as
few penetrations as possible is typically
the lowest-risk design for all enclosures,
especially buildings with high-humidity
interior environments, like pools, in
cold climates.
Figure 17. At the top of the wall, icicles, wetting, efflorescence, and mortar damage were all
present as a result of air leakage.
Figure 18. The predicted temperature margin and condensation risk on
the skylights of the pool without any fans indicates that the other ceiling
will be covered in condensation.
Figure 19. The predicted temperature margin and condensation risk
on the skylights of the pool with a higher temperature setpoint and
additional fans shows a significantly decreased risk of condensation.
42 • IIBEC Interface September 2025
REFERENCES
1. American Society of Heating, Refrigerating
and Air-Conditioning Engineers, 2011 ASHRAE
Handbook—HVAC Applications. (Atlanta, GA:
ASHRAE, 2011).
2. Hutcheon, Neil, Canadian Building Digest 50:
Principles Applied to a Masonry Wall. Ottawa, ON:
National Research Council of Canada, 1964.
3. Makepeace, Chris B., and Dennis, Barrie T.,
“PERSIST—Pressure equalized rain screen insulated
structure technique—Design approach.”
Thermal Envelopes VII (1998): 767–772.
4. Cold Climate Housing Research Center, “CCHRC
Snapshot 07-03: REMOTE Residential Exterior
Membrane Outside-Insulation Technique.”
Retrieved June 26, 2024, from https://gwscientific.
com/cchrc/snapshot07-003remote.pdf.
5. Lstiburek, Joseph W., “Building Science.com
Insight-001: The Perfect Wall.” Retrieved June
26, 2024, from https://buildingscience.com/
sites/default/files/document/bsi-001_perfect_
wall_2010rev2_0.pdf.
6. Tsongas, George A., “The effect of exterior insulating
sheathing on wall moisture.” In Insulation
Materials: Testing and Applications, 2nd Volume,
ASTM STP 1116, pp. 401–414. (Philadelphia, PA:
ASTM, 1991).
7. Trainor, Trevor. 2014. “The Hygrothermal
Performance of Exterior Insulated Wall Systems.”
(Master’s thesis, University of Waterloo, 2014.)
8. Kane, Robert, and Titley, Guy, “Case histories
of moisture monitoring in residential walls.” In
Thermal Insulation: Materials and Systems, ASTM
STP 922, pp.615–629. (Philadelphia, PA: ASTM,
1987).
9. Smegal, Jonathan, et al., “Moisture-related durability
of walls with exterior insulation in the Pacific
Northwest.” Paper presented at ASHRAE Buildings
XIII, Clearwater, FL, 2013.
10. Garden, Kirby. 1966. Canadian Building Digest
83: Indoor Swimming Pools. Ottawa, ON: National
Research Council of Canada, 1966.
11. Rousseau, Madeleine, “Design and construction
solutions to problems with indoor swimming
pools.” Home Builder Magazine, July 1990, pp. 23,
48.
12. Totten, Paul, and O’Brien, Shane, “Air barriers
in high interior RH specialty buildings:
Considerations for control of moisture-laden air
in museums, labs, and natatoriums.” Paper presented
at 2007 ASHRAE Conference, Clearwater,
FL, 2007.
13. O’Sullivan, Philip, and Fenech, Phil, “Design
Considerations for Pool Environments.”
Perkins+Will Research Journal (2010): 97–104.
14. Der Ananian, Jason S., and O’Brien, Sean M.,
“Avoiding problems in aquatics facilities: Atypical
design for atypical buildings.” The Construction
Specifier, no. 12 (2013): 42–52.
ABOUT THE AUTHORS
Based in Waterloo, Ontario,
for nearly 20 years,
Jonathan Smegal,
MASc, PEng, is an
associate principal and
senior building science
consultant at RDH Building
Science. He leads projects
related to laboratory
research, forensic analysis
of building failures,
litigation, hygrothermal
modeling, and field
monitoring of building
enclosure performance.
He has authored multiple
peer-reviewed papers and has frequently shared his
work through industry publications, webinars, and
speaking events.
John Straube is
a principal at RDH
Building Science and a
cross-appointed faculty
member in the School
of Architecture and the
Department of Civil
and Environmental
Engineering at the
University of Waterloo.
He conducts forensic
investigations, assists
with the design of new
high-performance
buildings and
building products,
and leads research projects in the areas of
low-energy building design, building enclosure
performance, hygrothermal analysis, and field
performance monitoring.
Chris Schumacher
is a principal and
senior building science
specialist with RDH
Building Science,
Inc. His current work
focuses on forensic
investigation; testing
and development
of materials and
systems; and applied
hygrothermal analyses
to address unique
problems in new
construction and
existing building
retrofit. Since 2001 Schumacher has led the
design and implementation of dozens of
lab- and field-testing programs for academic
and government research; for industry-driven
materials-and-methods demonstration
projects; and for litigation- support work. He
has a special interest in heritage buildings
and enclosures, focusing on preserving their
heritage features while designing updates
to improve durability, energy performance,
and occupant comfort. Through his work
with three North American universities,
Schumacher regularly teaches undergraduate,
graduate, and continuing-education courses
on the topics of building science, enclosure
design, enclosure performance, and
hygrothermal analysis.
Aaron Grin is a
Canadian building
scientist, professional
engineer, and
researcher with an
academic background
in building science and
structural engineering.
His creative
problem-solving,
extensive and in-depth
knowledge of building
materials and systems,
and experience with
root-cause analysis of
hundreds of in-the-field
forensic failures across all building typologies
and North American climates enable him to
effectively address challenging questions and
develop practical solutions. Prior to joining
DuPont, he was a principal and the practice area
leader for research and development at RDH
Building Science Inc. Grin is also an adjunct
professor at the University of Waterloo School
of Architecture.
JONATHAN SMEGAL,
MASC, PENG
Associate, Senior
Building Science
Consultant
RDH Building
Science Inc.
JOHN STRAUBE, PHD,
PENG
RDH Building
Science Inc.
University of Waterloo
Faculty of Engineering
CHRIS SCHUMACHER,
MASC, BASC, BTECH,
BECXP, CXA+BE
Principal, Senior
Building Science
Specialist
RDH Building
Science Inc.
AARON GRIN, MASC,
PENG
Global Residential
Applications
Technology Leader
Dupont Performance
Building Solutions
Please address reader comments to
chamaker@iibec.org, including
“Letter to Editor” in the subject line, or
IIBEC, IIBEC Interface Journal,
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September 2025 IIBEC Interface • 43