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18 2011 Vol 6 No 1 MASONRY EDG E / the storypole Masonry Technology | Innovation masonryedge.com

LEARNING OBJECT IVES

Upon reading the article you will:

1 Compare and contrast three softwareprograms used when performing hygrothermal evaluations.

2 Recognize the importance of materialselection, properties and placementwithin an enclosure system relative to the facility’s exterior climate and expected interior temperature and relative humidity levels.

3 Understand moisture management capabilities of the described wall systems for specific interior and exterior conditions assumed.

Comparison of Static and Dynamic

Analysis MethodsQuickly Displays

Building Performance

To predict and prevent detrimental accumu-

lation of condensation within enclosure

systems, Hygrothermal Evaluations are

performed. Material damage, corrosion,

loss of insulating capacity, organic growth

(mold) and poor air quality can result

from uncontrolled condensation. These

evaluations determine the enclosure’s ability

to MANAGE water transport through the

system under varying conditions.

Hygrothermal: pertaining toHumidity and TemperatureHygrothermal analysis tools, methods

and software programs aid in designing

enclo-sure systems that do not accumulate

moisture, do not exceed the Critical

Moisture Content (CMC), promote drying

if wetting occurs and avoid unintended

conse-quences of improper material selection.

In today’s design and construction field,

elevated interior relative humidity may be

desired for occupant comfort or may be

necessary to properly accommodate the

functions of the building. Facilities such as

museums, hospitals, laboratories, libraries,

arenas, manufacturing, computer centers,

concert halls, green houses, entertainment,

natatoriums and mixed use may require or

experience elevated levels of relative

humidity (RH) and must be evaluated to

determine if water accumulation can occur

within their proposed (or existing) enclosure

systems. If evaluation by modeling indicates

potential for accumulation of condensation,

then revisions to the design must be

implemented to control the condensation.

In the case of existing facilities, remedial

measures may be required.

HygrothermalEvaluation

Evaluation ProcessGood professional practice stipulates thatsome level of hygrothermal evaluation beperformed when designing enclosure systemsthat separate spaces with varying environ -ments. ASHRAE 160 Criteria for Moisture-

Control Design Analysis in Buildings is a recentstandard (2009) developed to provide“performance based design criteria forpredicting, mitigating or reducing moisturedamage to the building envelope…” In somejurisdictions, the standard is referenced as anacceptable method to design enclosures.When a comprehensive evaluation is required,three distinctly different types of software,used simultaneously, are required. Each isdesigned to analyze specific types of condi tionsand to provide specific types of information.Each has advantages and limitations andvaries in complexity. Some are static, somedynamic. Use of multiple analyses concurrentlyallows evaluation of a system’s hygrothermalperformance from a multi-faceted point ofview. Suitable data, knowledge and experienceare necessary to obtain reliable answers. If not available, the evaluation will likely beinaccurate and may present more risk thanbenefit. The level of evaluation depends onrequired performance of the enclosuresystem(s). Not all buildings or occupanciesrequire comprehensive evaluation.

One cannot simply state the level of evaluationrequired for any particular facility. This deter-mination is subject to multiple variables, suchas geographic location, climate type, interiortemperature and RH, enclosure systems andmaterial used and the level of knowledge ofthe design professional. Depending on thefacility’s location, the definition of elevatedinterior RH may vary. In climate zones 4 andabove, evaluation of enclosure systems shouldbe considered in buildings that are activelyhumidified or that can expect an interior RHgreater than 20%-25% during winter months. As the interior RH level increases, the level ofevaluation will increase as well. It requires aknowledgeable and experienced technicalarchitect, mechanical engineer or both todetermine and ensure proper use of the soft-ware, determine the appropriate level ofevaluation and to perform an accurate hygro-thermal evaluation providing accurate results.

Dewpoint calculation is one approach used to predict and prevent detrimental levels ofcondensation. Due to requirements to obtainproduct and weather data and effort toperform calculations, analysis was not oftenexecuted. Computer aided software has been developed to streamline this process.

Standard dewpoint calculation methods arestill being used. However, utilizing advancedsoftware and methods is becoming moreprevalent. More advanced programs originallydeveloped by laboratories to study enclosuresystem performance were typically developedand designed by scientists for scientific use. A wide selection of software readily availabledoes not mean that they are easilyunderstood or used correctly. The criticalcomponent is the user who must understandbenefits and limitations of the software toaccomplish accurate evaluations.

Refer to ASTM MNL20: Moisture Control in

Buildings: A Key Factor in Mold Prevention,ASTM MNL40: Moisture Analysis and

Condensation Control in Building Envelopes andto the US Department of Energy website forBuilding Energy Software Tools Directory foran extensive list of available software. Thisarticle focuses on proprietary dewpointcalculation software, WUFI and THERM 5.2 to describe the evaluation process.

SmithGroup’s Thermal andVapor Analysis Program (SG TVAP)Developed by Curt Songer, PE, SmithGroup, SG TVAP is a steady-state dewpoint calculationsoftware utilized to predict locations of conden -sation that may occur within an enclosuresystem. It requires the R-value and Perm valueof the system’s materials to perform the calcula -tion. Plentiful historic weather data is availablefor use with the software. Due to the staticnature of dewpoint analysis, the materialproperties are not altered due to change intemperature or moisture content. Thismethod also does not account for thermal lagor thermal storage. It is a cumulative analysis(not consecu tive) that determines if the system

by Andrew Dunlap AIA, CDT, LEED AP, NCARB

This article was originally published in MasonryEdge/the StoryPole Vol6 No1.

2011 Vol 6 No 1 MASONRY EDG E / the storypole Masonry Technology | Innovation 19masonryedge.com

experiences a net wetting or net drying for aone year cycle. If net wetting, then the amountfor a one year cycle is predicted. Indication ofexpected condensation locations is representedat locations where the temperature profile linedrops below the dewpoint temperature profile(shaded in black in the sample provided).

Sample output from TVAP Dewpoint Calculation Software (Figure 1)

Output from the dewpoint analysis of arelatively common Brick Veneer Cavity Wall ona Steel Stud Backup Wall is chosen to illustratea common problem. Stud cavity is filled withbatt insulation and the interior vapor barrier islocated directly behind the interior gypsumwallboard. Besides thermal bridging caused by steel studs dramatically reducing theeffectiveness of insulation, the effects ofimproper material selection can also be seen.(Thermal bridging caused by steel studscannot be analyzed with dewpoint analysissoftware and will be discussed in more detailin the example evaluation.) The air/water bar-rier material located outside of the exteriorsheathing was deliberately input as a vaporimpermeable material to show detrimentaleffects of improper material selection. Manyair/water barriers also have properties ofvapor barriers. With an interior temperature of72.5° F, interior RH of 50%, when utilizing dew-point analysis software, substantial conden-sation can be predicted to occur within thebatt insulation and exterior sheathing due tothe vapor tight characteristic of the air/water

barrier. This is indicated by the black shadedarea where the temperature profile line dropsbelow the dewpoint temperature profile line.For this specific condition, selection of a vaporpermeable air/water barrier would haveeliminated the likelihood of condensation fromoccurring. Proper material selection must beconsidered to prevent condensation from anunintended use of a vapor barrier.

WUFI “Wärme und Feuchte instationär” in German(Translation: Transient Heat and Humidity)

Developed and described by the FraunhoferInstitute for Building Physics (IBP) and OakRidge National Laboratory (ORNL), WUFI is a “menu-driven PC program which allowsrealistic calculation of the transient coupledone-dimensional heat and moisture transportin multi-layer building components exposed to natural weather. It is based on the newestfindings regarding vapor diffusion and liquidtransport in building materials and has beenvalidated by detailed comparison withmeasurements obtained in the laboratory and on outdoor testing fields.”

WUFI can be thought of as a continuouslychanging dewpoint analysis. The interior andexterior environments are constantly and morerealistically changing throughout a specifiedperiod of time. It incorporates more precisehourly weather data including temperature,RH, precipitation, wind and solar radiation. It

accounts for changes in material propertiesdue to temperature and moisture content andalso includes the effects of thermal lag andstorage. Moisture movement is calculated intwo directions, to the interior and exterior. Air and/or water leakage can be simulated by injecting a source into individual materiallayers. It considers the hygroscopic nature of materials through absorption/desorption(wetting/drying) which allows for materials to absorb and retain a certain amount of mois-ture. Simulations are typically performed overa five year period to determine if an enclosuresystem is accumulating moisture over anextended period of time. However, due to thecomplexity of material and weather data re-quired for the software, data is often limited.WUFI produces various graphs of the individ-ual materials or the entire system’s temper-ature, water content and RH as a function oftime. It also provides a real-time animationthat simulates the change in system materials’temperature, moisture content and RH as itruns through a given hourly weather tape.

Sample output from WUFI (Figure 2)

A screen capture of the WUFI animationpaused at a winter condition illustrates asimulation performed on the same wall systemas the dewpoint analysis in Figure 1: BrickVeneer Cavity Wall on a Steel Stud BackupWall. Again, thermal bridging of metal studscannot be analyzed. Unlike the results of thedewpoint analysis (indicating location ofcondensation), the WUFI diagram provides theamount of water content and the RH withinthe materials at any given time. The professionalmust determine if these levels are acceptable.

Individual material layers are illustrated bylight color-coded shading and are labeledbelow the graphs. For instance, on the far left,solid brick masonry is indicated by light redshading. Indication of temperature, RH andwater content are overlaid onto materiallayers. In the top graph, the dark red line is thecurrent temperature through the system. Lightred shading signifies temperature history asthe system runs through multiple yearly cycles.In the bottom graph, the dark blue line is thecurrent water content, light blue shadingindicates history. Also, in the bottom graph,the dark green line is the current RH. History isrepresented by light green shading. Interiorconditions for this sample are similar to theprevious dewpoint analysis. However, WUFIhas the ability to fluctuate conditions, so forthis sample, interior temperature was set tovary between 70° F to 75° F and 45% to 55% RH.Outside conditions continuously change asdictated by actual recorded weather data. This

Figure 1: Sample Output of SG TVAP Dewpoint Analysis Software. Graph includes temperatureprofile, dewpoint temperature profile through enclosure materials (color coded) at specific interior and exterior temperature and RH.

is a more accurate depiction of what is actuallyoccurring in reality and should yield moreaccurate results. Red and green small hor-izontal triangles to the right and left of boththe top and bottom graphs indicate interiorand exterior temperature and RH conditionsoccurring at the point the simulation waspaused. The clock on the upper right indicatestime when simulation was paused. The bardirectly below illustrates progress of the totalsimulation. Blue arrows between the two

graphs, some to the interior and some to the

exterior, represent the direction of moisture

flow for individual material layers.

Where the animation is paused, a slight

elevation in water content can be seen in the

exterior sheathing. The exterior sheathing and

batt insulation experienced elevated levels

of RH for some period of time. Raw data can

be extracted and analyzed to determine how

many consecutive hours various conditions

occur within the materials

to determine if it is

detrimental. It is the

professional’s

responsibility to determine

if conditions experienced

by the system are

acceptable. To avoid

consequences

of an unintended vapor

barrier, proper material

selection must be

accomplished to prevent

elevated levels of material

RH and water content.

THERM 5.2 Developed and described

by Lawrence Berkley

National Laboratory

(LBNL), “THERM is a

state-of-the-art, computer

program for use by

building component

manufacturers, engineers, educators,

students, architects and others interested in

heat transfer. THERM models 2D conduction

heat-transfer effects in building compo nents

such as windows, walls, foundations, roofs and

doors where thermal bridges are of concern.

Heat-transfer analysis, based on the finite-

element method, allows for evaluation of a

product or system’s energy efficiency and local

temperature patterns, which can help identify

or may relate directly to problems with

condensation, moisture damage and structural

integrity.” While it does not include the

effects of moisture, surface temperatures can

be compared to dewpoint temperatures

determined by other means to verify if there is

risk of condensation.

Explanation of sample output fromTHERM 5.2 (Figure 3) THERM was developed to determine thermalperformance of fenestration systems. How -ever, design professionals have found otheruses for it, such as predicting how adjacentwall construction affects fenestration (and vice versa) and analyzing effects of thermalbridge conditions occurring in enclosuresystems. Figure 3 includes models of a curtainwall head transition to a cavity wall. The twomodels compare effects of a typical fixed steellintel (left) and an atypical thermally brokensteel lintel (right). As indicated, the systemutilizing a thermally broken lintel has warmersurface temperatures, is more efficient and can withstand higher interior RH with less risk of condensation.


Figure 3: Sample Output of THERM 5.2 –Color Infrared Image. Temperature predictions can be identified at any pinpoint location throughout the modeled system and total product (or system) U-factors can be calculated.

Hygrothermal Evaluation

Figure 2: Screen Capture of WUFI Animation of Temperature, RH and Water Content of the materials (color coded) of anenclosure system as it actively simulates a specific time frame of interior and exterior temperature, RH, precipitation andsolar radiation.

Compare and Contrast One principal advantage of dewpoint calculation,

its inherent simplicity, can also be seen as its

primary disadvantage. Due to the static nature

of the method, it must be viewed as a snap shot

in time. Dewpoint calculations analyze systems

at specific interior and exterior temperatures.

Since this method does not account for the

hygrothermal effect of material properties,

it can become problematic and inaccurate.

Professionals could assume they are analyzing

a system at what appears to be the worst

case scenario (winter or summer), when in fact

it may not be the worst. In addition, dewpoint

calculations generally do not account for thermal

bridging of materials within enclosure systems,

i.e. stud wall construction with insulation

placed in the stud cavity. Advanced software

such as WUFI and THERM have been

developed to over come these limitations.

These thermal analysis programs begin to

include other aspects into the evaluation

process of enclosure systems. WUFI provides

comprehensive analysis through out continuous

yearly cycles, assisting professionals from

missing the worst case condition and resulting

in a better and more accurate evaluation.

Although it is a static analysis program,

THERM can be utilized to evaluate effects

of thermal bridging in enclosure systems.

What can and cannot be accomplished Estimation/Prediction of moisture content

of individual materials within a system: A

common misconception is that all condensation

is bad. This is not necessarily the case. Many

enclosure systems can and do experience

condensation within the system throughout

a yearly weather cycle. Certain systems are

able to manage condensation due to the

hygroscopic nature of some materials.

Materials are able to absorb and store/retain

a certain amount of water without having a

detrimental effect on the performance of

the material/system. The system must not

continue to accumulate moisture over time but

to maintain a moisture balance. Provided the

desorption is equal to or greater than absorption,

detrimental effects from accumulation may not

occur. Transient analysis software can deter-

mine if a moisture balance is maintained. This

software can be used at all levels of the design

process to determine, understand and prevent

moisture accumulation within systems.

How much water is too much for a given

material? The simple answer is any amount of

water above and beyond

the critical moisture

content for the specific

material. The CMC is the

point at which damage

could start to occur within

a material. There is not one

particular value; it is

different for various

materials. One source of

information for CMC can be

found in the Proceedings of

the Bugs, Mold and Rot II

Workshop sponsored by

the Building Environment

and Thermal Envelope

Council (BETEC) and the

National Institute of

Building Sciences (NIBS).

Other general guidelines have been developed

over time by various organizations, such as the

developer of WUFI. Some of these guidelines

can be found on the WUFI forum website.

Because it is difficult to assess acceptable

levels of moisture and data is not readily

available, a safe practice is to choose wall

systems that minimize moisture collection.

Experience and careful consideration must be

relied upon to determine the acceptability of

moisture content within materials and systems.

Estimation/Prediction of RH: Similar to the

prediction of moisture content, transient

hygrothermal analysis software can also

predict the RH within various materials of an

enclosure system. This capability can help

predict and prevent microbial growth from

occurring on or in certain materials. In order

to sustain certain types of microbial growth,

four criteria must be present: a nutrient

source, optimum temperature, optimum RH

and time (duration of the temperature and

RH). The RH of a material changes as

environmental conditions surrounding the

material change. If temperature of a material

lowers, but moisture content remains the

same, it will result in a higher RH. Transient

software can simultaneously calculate the RH,

temperature and duration of both throughout

an enclosure system. This data can be extracted

and analyzed with newly developed add-on

software to determine if these conditions are

occurring at a location where there may be a

nutrient source. If data analysis results suggest

potential for microbial growth, the system

must be redesigned and the analysis process

would begin again.

Figure 4 is an isopleth of a microbe that indi-

cates the time, temperature and RH required

for germination and growth. For example,

according to Figure 4, the temperature must

be between 68°F and 100°F and RH between

89% and 98% for at least one full day in order

for germination to occur. As the temperature

or RH range increases, the corresponding days

required for germination must also increase.

Additionally, in order for a growth rate of 2.0

mm/day, a temperature range of approximate-

ly 68°F to 100°F and an RH range of 89% to 100%

must be maintained. If the temperature or RH

ranges increase, the growth rate will decrease.

Prediction of Freeze/Thaw Cycles: Another usefor transient modeling is the prediction of thenumber of freeze/thaw cycles that may occurwithin materials. Clay masonry is oftensubjected to detrimental effects of freeze/thaw cycles. After performing analysis withmodeling software, raw data can be extractedand evaluated separately in software such asMS Excel to determine the number of cyclesthat may occur at a specific location within a particular enclosure system. Additionally,moisture content of the material at time and location of the cycles may be extracted.Software does not output yes/no answers, onlydata. Masonry materials can accommodate acertain amount of moisture without risk ofdamage. In order for masonry to be negativelyaffected by freeze/thaw cycles, moisturecontent at the time of the cycles must begreater than what the specific material canaccommodate, the CMC. Transient modelingsoftware cannot provide this number; it canonly determine whether or not it has been


Figure 4: Isopleth: A line connecting points on a graph that have equalvalues in relation to other specific variables. Shown is an isopleth of a common microbe

THERM can be utilized to evaluate effects

of thermal bridging inenclosure systems.

exceeded. The only way to determine the CMC

is through physical testing of specific brick in

question. This information may be available

from some manufacturers.

Effects of Air/Moisture Sources/Sinks: Some of

the more advanced modeling software include

air and/or moisture sources/sinks within the

enclosure assembly. These can be incorporated

into the modeling to simulate leakage and/or

ventilation of air and/or water. These can

replicate the cladding component of a

rainscreen system that is leaking a certain

amount of air and/or water. This can also be

helpful when evaluating effects of partially

vented cavity wall systems. The potential

drying effect the cavity has on performancecan be more accurately shown with advancedsoftware. Ability for the vented space topromote drying can be predicted or validated.Water sources can be included to show theeffects of a leaking wall to determine if it willstay continually wet or if it has the ability todry. Inclusion of water sources to simulateleaks may also have an effect on the RH ofindividual components of a system which canaffect their thermal performance and ability topromote microbial growth. Similar tocapabilities previously discussed, software cansimulate effects and provide results ofair/moisture sources/sinks. However, littleguidance is available to determine the inputvalue to replicate actual conditions.

Efficiency of insulation: Performance of manyinsulation products decreases as the moisturecontent increases. Ample moisture dependantR-value data is available. However, whenperforming a traditional dewpoint analysis, it can be difficult to determine what R-value to use. As a result, analysis can be quiteinaccurate depending on the enclosure systembeing evaluated and type of insulation used.Transient modeling is beneficial for this. As transient simulation is a consecutiveprocess, insulation conductivity is continuouslyrecalculated and based on material moisturecontent at that particular moment. Dependingon the makeup of the enclosure system,interior and exterior temperature/RH conditionsand location of the insulation, moisturecontent can have dramatic fluctuations,corresponding to variations in thermalperformance. If elevated levels of moisturecontent occur, performance loss is probable.Current simulation capabilities providesubstantiation of performance loss. Recentlydeveloped add-on software can be used topredict the changes in thermal performance of the system shown on an average monthlybasis through a year cycle.

Example Evaluation

Further illustrating characteristics andcapabilities of hygrothermal analysis software,the following is an example of an evaluation of three different, but similar, commercial wallsystems. Interior and exterior conditions arethe same for each. The following conditionsare assumed.

• Facility is in a northern climate (Climate Zone5) with elevated levels of interior RH.

• Effective air barrier is provided. In all casesthe vapor barrier can also be the air barrier.

• Includes the effect of moisture migrationthrough diffusion, not through air leakage.

• Interior surface coating (paint) is consideredto be a vapor transmitting material thatdoes not impede water vapor frommigrating in either direction.

Temperature and RH Conditions

• Interior Temperature: 72.5° F, +/- 2.5° F

• Interior Relative Humidity: 50% set point, +/-5

• Exterior Conditions: Recorded weather datafor Detroit

Wall Types:

Wall Type One: Brick/Steel Stud Cavity Wallwith Stud Space Insulation

Wall Type Two: Brick/Block Cavity Wall withCavity Insulation

Wall Type Three: Brick/Steel Stud Cavity Wallwith Stud Space Insulation and Cavity Insulation



Figure 6: Section Detail of Wall Type One

Figure 8: Output Results from SG TVAP for Wall Type One. The Temperature profile line does notdrop below the Dewpoint temperature profile line. Condensation should not occur.

Figure 7: THERM 5.2 Plan Detail Model of Wall Type One. Results in Infrared Mode show thermal bridging.

Many wall systems contain two zones, the wet zone and the dry zone. Typically, thesezones are divided by a material that serves as the water (resistive) barrier. This materialcan sometimes also serve as the air and/orvapor barrier. Materials used in the dry zonegenerally cannot tolerate elevated levels of RHor moisture content. Materials used in the wetzone can be expected to be wet at some pointand must be able to tolerate effects ofelevated levels of RH and moisture content.

Extruded polystyrene, spray polyurethanefoam and some polyisocyanurates areinsulation products generally consideredacceptable for use in the wet zone of a cavitywall type construction provided they meet allapplicable building codes and ASTM materialstandards. Multiple materials that can be usedfor the water barrier can often also be the airbarrier. Generally these should be self adheredsheets or fluid applied materials. Compositionof these materials can vary greatly and cansignificantly affect the water vapor permeance.Many of the liquid or sheet synthetic rubberizedor polymer modified materials are typicallyvapor impermeable (barriers) whereas the acrylics and the spun or heat bondedpolypropylene or olefin materials are oftenvapor permeable (breatheable).

WALL TYPE ONEBrick / Steel Stud Cavity Wall with

stud space insulation

Wall Type One includes steel stud backup,continuous vapor permeable air/water barrierapplied directly on exterior sheathing, non-continuous batt insulation installed in the steelstud space and a vapor barrier installed directlybehind the interior gypsum wall board. Thissystem may not meet certain energy codes incertain climate zones. For example, a contin-uous layer of insulation with an R-value of 3.8or more is required in climate zones 5-8 whenusing International Energy Conservation Code(IECC) 2006 as the energy code (Figure 6).

It is critical to evaluate and understand boththe plan and section views of any enclosuresystem. Figure 7 is an infrared plan detail ofWall Type One modeled in THERM 5.2 whichillustrates thermal bridging effects of steelstuds. If this were modeled in a section view(Figure 6), thermal bridging of the studs would not be evident. As can be expected, the effectiveness of insulation is dramaticallyreduced. As calculated by THERM 5.2, systemU-factor for all components in the wall isapproximately 0.0915, which equates to an Effective R-value of approximately R11, less than half the calculated R-value of

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Figure 9: Screen Capture of WUFI Animation Film paused during a summer condition on Wall Type One. Elevated levels of water content and RH are present in the exterior sheathing and batt insulation located in the “dry zone”.

Figure 11: Wall section at interface of exterior wall and roof slab. Infrared image produced fromTHERM model indicates thermal bridging due to the roof slab.

2011 Vol 6 No 1 MASONRY EDG E / the storypole Masonry Technology | Innovation 23

Figure 10: Wall section at interface of exterior wall with floor slab. Infrared image produced fromTHERM model indicates thermal bridging due to the floor slab.

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approximately R23 at the center of the studspace. In addition, the system’s ability to resistcondensation at the surface is also reduceddue to lower surface temperatures. Thermalbridging can also potentially cause staining onthe interior surface of the wall.

Figure 8 is the results graph of the SG TVAPanalysis performed at a winter condition.Dewpoint analysis does not include effects ofthe thermal bridging from the steel studs. Asindicated, the Temperature Profile Line doesnot drop below the Dewpoint TemperatureProfile Line as they progress through individualmaterials. As a result, dewpoint analysismethod would suggest that detrimentalcondensation should not be expected for the specific conditions in which the simulationwas performed. Dewpoint calculation wasintentionally only performed during a wintercondition to illustrate that when used alone, it can sometimes be misleading.

Figure 9 demonstrates areas of concern duringsummer months that would not have beendiscovered if relying solely on dewpointcalculation. WUFI simulation indicates highlyelevated RH levels throughout exterior sheath -ing and batt insulation. Elevated levels of watercontent are also occurring in exterior sheathingand batt insulation. Both of these conditionsare occurring in the dry zone of the wallsystem (to the right of the air/water barrier).

It is critical to analyze end results of the WUFIsimulation after it has computed multiple yearsof weather data. In this case, the wall systemdoes not continue to accumulate watercontent over multiple yearly cycles. Exteriorsheathing and batt insulation consistentlybecome wetter during summer months anddryer in winter months. This is because thesummer moisture drive is inward. Due to theplacement of the interior vapor retarder,higher levels of summertime atmosphericmoisture cannot dry to the building interior.

It is not good practice to have "wet" materials in the dry zone even if they may dry out over a yearly cycle. Effectiveness of insulation is reduced due to elevated RH, becoming lessefficient. If the RH level is maintained, it maypromote and sustain microbial growth. Datacan be analyzed to determine if optimumtemperature and RH levels for microbial growthare present for a substantial period of time.Even if microbial growth is determined to notbe a concern, accelerated deterioration of somematerials can occur due to the elevated RH.

Wall Type One can also cause other problemsnot evident in static or dynamic hygrothermal


Figure 15: Screen Capture of WUFI Animation Film paused during a winter condition. No indication of elevated levels of RH or moisture content in the “dry zone”.

24 2011 Vol 6 No 1 MASONRY EDG E / the storypole Masonry Technology | Innovation

Figure 14: Output Results for Wall Type Two from SG TVAP. The Temperature profile line does notdrop below the Dewpoint temperature profile line. Condensation should not occur.

Figure 12: Section Detail of Wall TypeTwo: Brick and Block Cavity Wall

Figure 13: THERM 5.2 Plan Detail Model of Wall TypeTwo. Results shown in Infrared Mode. No thermalbridging.

analysis programs. In Figures 10 and 11, effects ofnot using continuous insulation in the wall cavitycan easily be observed – thermal bridg ing atthe floor and roof slabs and discontinuousinstallation of the interior vapor barrier.

Depending on interior RH, thermal bridgingmay cause localized condensation, damagingmaterials within and adjacent to the wallsystem. Thermal bridging also reduces overall efficiency of the exterior enclosure’sthermal performance.

Buildings utilizing this type of wall systemoften have perimeter steel beams installedquite close to the exterior wall. These limitaccess needed to provide a quality installationof the vapor barrier and insulation directlybelow floor and roof slabs. This installation canbe extremely difficult to achieve, if possible atall. In addition, due to the vapor barrier’slocation, it will inherently be discontinuous atthe floor and roof slabs. The vapor barriermust rely on the concrete slab to maintain thecontinuity of the vapor barrier system.Depending on the building’s interior RH level,this may not be acceptable.

WALL TYPE TWOBrick/Block Cavity Wall with cavity insulation

Wall Type Two is a typical Brick and Block Cavity

wall with interior gypsum wall board. It

includes a continuous air/water/vapor barrier

applied directly on the exterior of the CMU

wall, a continuous layer of 2" extruded

polystyrene insulation, 2" air space and

exterior veneer brick (Figure 12).

Figure 13 Infrared plan detail of Wall Type Two

as modeled in THERM 5.2. No thermal bridging

is present as the insulation is continuous in

the cavity. System U-factor for all components

in the wall is approximately 0.067, which

equates to an Effective R-value of approximately

R15. This software does not include benefits

provided by thermal mass of masonry in the

Effective R-value calculation.

Figure 14 Results graph of SG TVAP analysis

performed at a winter condition. Temperature

Profile Line does not drop below the Dewpoint

Temperature Profile Line as they progress

through individual materials of the wall system.

Dewpoint analysis method would suggest that

potential detrimental condensation should not

be expected for specific conditions in which

the simulation was performed. Note: there is a

point at the back side of the masonry veneer

in which the material temperature and dew -

point temperature nearly cross. This minor

amount of moisture is not considered

detrimental as it is in the cavity of the wall

system, the wet zone, which by its nature

has some venting capabilities.

Figure 15 Screen capture of WUFI animation

paused at a winter condition. There is no

indication of elevated RH or moisture content

(green and blue lines and shading) in the dry

zone (right of vapor barrier). Depending on

material type, a certain amount of water

content may always be present. For example,

concrete layers that make up concrete block

consistently show approximately 2 lbs/ft3. The

key is that water content does not continue

to accumulate over time.

Defining elevated may be difficult as it is

dependent upon many factors, such as

material in which RH is being evaluated,

corresponding temperature and duration of

the elevated condition. However, if occurring

in a material that could support microbial

growth, if the RH begins to approach 70% with

a corresponding temperature of approximately

50°F to 100°F for an extended period of time,

this could be considered elevated. Refer to

figure 4 for other possible ranges.

Note: A brick cavity wall utilizing a steel stud

back wall could perform in a similar manner as

this wall system as long as it also utilizes

continuous insulation in the cavity only and

continuous air/water/vapor barrier installed

directly on the exterior sheathing of the steel

stud wall assembly. However, the benefits of

the thermal mass from the CMU backup wall

would not be included.

Figure 16 indicates the importance of utilizing

continuous insulation installed in the cavity.

Unlike Wall Type One, thermal bridging does

not occur at floor and roof slabs as the cavity

insulation is continuous, keeping slab edges

warm. The vapor barrier is also not interrupted

by the slabs with this type of wall. Brick relief

angles are not included in figures 10 and 16. It

is important to understand that if brick relief

angles are required, they should also be

installed in a manner that will thermally break

the steel from interior to exterior. Cavity

insulation must remain as continuous as possible.

Proprietary products are designed specifically

for this application or it can be achieved by

holding the steel angle away from the wall

with intermittent steel clips allowing insulation

to be installed behind the angle. No matter

how this is achieved, additional and atypical

detailing is required to ensure that thermal

bridging is not occurring at relief angles, lintels

or any other conditions that may produce a

system breach. (Note: This type of detailing

is not considered standard practice. However,

in buildings with high humidity, it is critical to

follow through and evaluate all atypical detail

conditions beyond the typical wall system

details, looking for potential areas of thermal

bridging similar to what can be found at floor

slabs, roof slabs, steel lintels and relief angles.)


Figure 16: Wall section at interface of exterior wall and floor slab. Infrared image produced fromTHERM model indicates no thermal bridging due to the floor line.

Because it is difficult to assess acceptable levels of

moisture and data is not readilyavailable, a safe practice

is to choose wall systems thatminimize moisture collection.

WALL TYPE THREEBrick/Steel Stud Cavity Wall with Stud Space

Insulation and Cavity Insulation

Wall Type Three, a cavity wall with continuous

air/water/vapor barrier on exterior sheathing

and continuous insulation installed in the

cavity, sometimes created as an afterthought,

begins as good design. Assuming there is no

insulation installed in the stud space, the wall

would perform similar to Wall Type Two, just

not with the added benefit of thermal mass

from the CMU backup. However, this wall type

now includes insulation in the steel stud backup.

Note: there is not a vapor barrier installed on

the interior side of the insulated stud assembly.

Often, someone has an idea to fill steel studs

with insulation to gain additional thermal

performance. However, the air/water/vapor

barrier that is in the cavity is now effectively

insulated from the heat of the interior. Without

adding another vapor barrier on the interior

side of the stud assembly, this condition can

allow elevated interior RH to condense on the

interior surface of the exterior sheathing. If a

vapor barrier were installed on the interior

side of the stud assembly, then similar issues

as described in Wall Type One occur (Figure 18).

Figure 19 indicates the infrared plan model of

Wall Type Three. Due to the continuous layer

of cavity wall insulation, effects of steel stud

thermal bridging are not as significant as in

Wall Type One. However, effectiveness of the

batt insulation is still dramatically reduced. Batt

insulation added to this system has an R-value

of 19. The System U-factor for all components

included is approximately 0.046, which equates

to an Effective R-value of approximately 22.

This is only R7 more than Wall Type Two,

not an additional R19 as might be expected.

Figure 20 is the results graph of the SG TVAP

analysis performed at a winter condition. As

indicated, the Temperature Profile Line drops

below the Dewpoint Temperature Profile Line

as they progress through the system’s

individual materials. This would suggest that

potential detrimental conden sa tion could be

expected within batt insula tion and exterior

sheathing for specific conditions in which the

simulation was performed.

Figure 21 is the screen capture of the WUFI

animation for Wall Type Three paused at

a winter condition. Simulation indicates

elevated RH levels in exterior sheathing

and batt insulation. Water content is also

elevated in the exterior sheathing. Both of

these conditions are occurring in the dry zone.

Similar to Wall Type One, it is critical to analyze

the end results of the simulation after it has

computed multiple years of weather data. In

this case, the wall system does not continue to

accumulate water content over multiple yearly

cycles. However, exterior sheathing and batt

insulation consistently become wetter during

winter months and dryer in summer months.

A primary benefit of using transient software

is that there is no longer a need to perform

multiple dewpoint calculations at multiple

times throughout a year. Transient software

essentially performs calculations at all times

throughout a year.

The difficulty with this simulation is

determining if moisture content has exceeded

the critical moisture content for the system.

Again, it is not a good idea to have "wet"

materials in the dry zone even if they may dry

out throughout a yearly cycle. Effectiveness of

the insulation is reduced due to elevated RH

and material damage such as corrosion of steel

studs may occur.

It should be made clear; using steel stud

backup walls is not the concern. The problem

is when studs are filled with batt insulation and

used in facilities that contain higher levels

of interior RH. Unintended consequences



Figure 20: Output Results from SG TVAP. The Temperature profile line drops below the Dewpointtemperature profile line. Condensation may occur within exterior sheathing and batt insulation.

Figure 18: Section Detail of Wall TypeThree: Brick, Steel Stud Cavity Wall withStud & Cavity Insulation

Figure 19: THERM 5.2 Plan Detail Model of Wall TypeThree. Results shown in Infrared Mode

of these decisions may result in substantial

material and property damage.

Future DevelopmentSophistication of analysis programs hasoutpaced information that is readily available.When used carefully and correctly, they canprovide more useful data than ever before.Additional, more accurate and comprehensivematerial and weather information is needed.More information is also needed for the CMC of various materials and various materials’resistance to freeze/thaw damage.Organizations such as ASTM, ASHRAE and ORNL continually work to meet thisdemand. However, as the requirements for the evaluation process continues to increase,the demand for material data will increase as well. Manufacturers can assist this byproactively testing their materials andproviding the necessary material data.

How much water is too much? Professionalsmust first understand that analysis softwarecannot provide simple answers. Carefulconsideration is required to determine whichsystems will work for which applications.Hygrothermal evaluation can help usdetermine if our systems will perform withoutrisk of detrimental condensation. In addition,they offer a method to compare multiplesystems to provide the best possible solutionfor any given situation. There are sources ofguidance and reference regarding variousmethods of hygro thermal evaluation fromorganizations such as ASHRAE, ASTM, ORNL andLBNL. There are varying opinions throughout

the industry about the types of methods thatare most accurate. However, the one item thatis typically agreed upon is that evaluation isrequired. Predicting problems before theyoccur is a primary goal of this process.

For more information and additional resources,visit masonryedge.com nnn

masonryedge.com

Figure 21: Screen Capture of WUFI Animation Film paused during a winter condition. Elevated levels of water content and RH are present in exterior sheathing and batt insulation located in thedry zone of the wall system.

Andrew Dunlap, AIA,CDT, NCARB, LEEDAP, is an associatewith SmithGroup’sBuilding Techology Studio. His workfocuses on the analysis and developmentof exterior building envelopes, specializingin the thermal and vapor analysis of wall,window and roof systems. Dunlap servesas Vice President and Programs CommitteeChair for the Building Enclosure Council –Greater Detroit Chapter and as an adjunctprofessor at University of Detroit Mercy. Hehas also served on the Steering Committeefor Development of a new degree programat the University, for what is now theArchitectural Engineering Bachelor ofScience program. Dunlap holds BS degreesin Mathematics and Architecture and aMasters of Architecture from the Universityof Detroit Mercy. [email protected]

2011 Vol 6 No 1 MASONRY EDG E / the storypole Masonry Technology | Innovation 27

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