Moisture Management and Energy Rating in Building Envelopes / Part II : Effects of two energy retrofit strategies on the wetting and drying potential of wall assemblies

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Moisture Management and Energy Rating in Building Envelopes / Part II

: Effects of two energy retrofit strategies on the wetting and drying

potential of wall assemblies

Moisture Management in Buildings

Part II – Retrofit Strategies

W. Maref, M. Manning , M. Rousseau

Outline

ƒ

Context

ƒ

Field Exposure of Wall Facility (FEWF)

Part II

•

Experimental Approach

–

Construction Details

–

FEWF Instrumentation

•

Results and Discussion

•

Summar

3 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

ƒ

Context:

•

Focus on two energy retrofit scenarios for

exterior walls

ƒ

The question to investigate:

•

What is the effect of the properties of

thermal insulation installed on the exterior of

an existing R20 wall on the wetting and

drying potential of that assembly, particularly

when air leakage is involved?

Adding thermal insulation on the exterior of

an insulated stud cavity wall can …

ƒ

Reduce thermal bridging at the framing

ᄕ

ƒ

Raise the temperature of that cavity, during

cold weather, resulting in lower potential

for condensation in stud cavity

ᄕ

ƒ

Reduce the drying potential to the exterior

ᄔ

ƒ

Promote mould growth in a wet cavity as

the cavity stays warmer over longer

5 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

What Happens Depends On:

ƒ

Vapour permeance and air permeance of added

insulation layer

ƒ

R value of the external layers in relation to the R

value of the internal layers

ƒ

Methods of installation for the insulation and siding

layers

ƒ

Air leakage rates & paths (deficiencies, gaps, cracks

unsealed openings in the assembly)

ƒ

Indoor conditions of RH, T and P

ƒ

Outdoor climate

ƒ

Other factors! e.g. rain penetration bypassing the 1

st

Exterior

Interior

R20 2X6

typical

Addition of a Low Air

and Vapour Permeance

Insulation

Addition of a High Air and

Vapour Permeance Insulation

The 3 Test Specimens – Vertical Section View

7 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Interior

Detail B

Detail A

Wall 1

Wall 2

Wall 3

Wall 1 –

No

exterior insulation

Wall 2

– Lower

Air and Vapour

Permeance

Wall 3 –

Higher

Air and Vapour

Permeance

•

Vinyl Siding

•

Sheathing Membrane (Tyvek)

•

OSB

•

2x6 Stud Cavity with Fiberglass Insulation

•

Plastic Air/Vapour Barrier

•

Drywall

•

Vinyl Siding

•

2 in. XPS Rigid Foam Insulation, 24 in. wide

sections installed horizontally, butt joints

taped

•

Sheathing Membrane (Tyvek)

•

OSB

•

2x6 Stud Cavity with Fiberglass Insulation

•

Plastic Air/Vapour Barrier

•

Drywall

•

Vinyl Siding

•

Sheathing Membrane (Tyvek)

•

¾ in. x 1½ in. Vertical Strapping @ 16 in.

(400 mm) o.c. mounted on blocks, with 2.5 in.

Mineral Fibre Insulation Batts installed

horizontally

•

Sheathing Membrane (Tyvek)

•

OSB

•

2x6 Stud Cavity with Fiberglass Insulation

•

Plastic Air/Vapour Barrier

•

Drywall

Plan View of the Test Specimens in Test Bay

Exterior

Interior

9 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Stripping Down and Harvesting Sensors

Installation of Semi-rigid

Mineral Fibre Insulation

(R10-2.5 in.)

11 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Insulation and Furring Strips for the Siding

13 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

15 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Insulation and Siding Installation

Open

joints

17 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

19 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

FEWF Instrumentation-W3

Vinyl Siding

FEWF Instrumentation-W3

Exterior WRB

21 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

FEWF Instrumentation-W3

Insulation

FEWF Instrumentation-W3

Interior WRB

23 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

FEWF Instrumentation-W3

OSB Sheathing

FEWF Instrumentation-W2

Vinyl Siding

25 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

FEWF Instrumentation-W2

Insulation

FEWF Instrumentation-W2

WRB

27 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

FEWF Instrumentation-W2

OSB Sheathing

Test Conditions

Condition

Dates

2008

Opening

in ABS of

Walls 2

and 3

Chamber RH

Chamber

Pressure

(Pa)

A2

24-Feb 0:00 to 29-Feb 16:00

3 mm

30%

-B2

29-Feb 16:00 to 18-Mar 12:00

3 mm

50%

-C2

18-Mar 12:00 to 21-Mar 11:30

3 mm

30%

5

D2

21-Mar 11:30 to 27-Mar 11:30

3 mm

~50%

fluctuated

5

E2

27-Mar 11:30 to 9-Apr 14:30

3 mm

~50%

fluctuated

10

F2

9-Apr 14:30 to 30-Apr 0:00

3 mm

50%

-Post Testing

30-Apr 0:00 to 7-Jul 0:00

3 mm

50% to

ambient

-29 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Test Conditions

Condition

Dates

2008

Opening

in ABS of

Walls 2

and 3

Chamber RH

Chamber

Pressure

(Pa)

A2

24-Feb 0:00 to 29-Feb 16:00

3 mm

30%

-B2

29-Feb 16:00 to 18-Mar 12:00

3 mm

50%

-C2

18-Mar 12:00 to 21-Mar 11:30

3 mm

30%

5

D2

21-Mar 11:30 to 27-Mar 11:30

3 mm

~50%

fluctuated

5

E2

27-Mar 11:30 to 9-Apr 14:30

3 mm

~50%

fluctuated

10

F2

9-Apr 14:30 to 30-Apr 0:00

3 mm

50%

-Post Testing

30-Apr 0:00 to 7-Jul 0:00

3 mm

50% to

ambient

-Test Conditions

Interior RH, Chamber Pressure

0

10

20

30

40

50

60

70

24-Feb-08

2-Mar-08

9-Mar-08

16-Mar-08

23-Mar-08

30-Mar-08

6-A

p

r-08

13-Apr-08

20-Apr-08

27-Apr-08

RH (%), Chamber Pressure (Pa)

Room RH

Chamber RH

Applied Chamber P

31 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Test Conditions

Interior and Exterior Temperature

-30

-20

-10

0

10

20

30

40

24-Feb-08

2-Mar-08

9-Mar-08

16-Mar-08

23-Mar-08

30-Mar-08

6-Apr-08

13-Apr-08

20-Apr-08

27-Apr-08

Temperature, °C

Room T

Chamber T

Outdoor T

Interior and Exterior Temperature

-30

-20

-10

0

10

20

30

40

24-Feb-08

2-Mar-08

9-Mar-08

16-Mar-08

23-Mar-08

30-Mar-08

6-Apr-08

13-Apr-08

20-Apr-08

27-Apr-08

Temperature, °C

Room T

Chamber T

Outdoor T

A2

B2

C2

_D2

E2

_F2

Temperature Effects

Coldest Day – February 29

th

33 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Legend

T = Temperature, °C

RH = Relative humidity, %

W = Humidity ratio,

g

/kg

P = Pressure, Pa

Dewpoint T, °C

Coldest Day – February 29

th

Condition A: 3mm opening, 0 Pa, 30% RH

Despite cold OSB surface temperature, air in the stud cavity does

not reach saturation.

Legend

T = Temperature, °C

RH = Relative humidity, %

W = Humidity ratio,

g

/kg

P = Pressure, Pa

Dewpoint T, °C

OSB interior surface temperature is warmer, but still below dew

point of chamber air.

Despite the deficiency in the air barrier, humidity does not enter the

stud cavity due to exfiltration conditions.

Coldest Day – February 29

th

35 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Legend

T = Temperature, °C

RH = Relative humidity, %

W = Humidity ratio,

g

/kg

P = Pressure, Pa

Dewpoint T, °C

Coldest Day – February 29

th

Condition A: 3mm opening, 0 Pa, 30% RH

OSB interior surface temperature is similar to Wall 2, below dew

point of chamber air.

Despite the deficiency in the air barrier, humidity does not enter the

stud cavity due to exfiltration conditions.

15%

30%

Coldest Day – February 29

th

37 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Wind and Pressure Effects

E

S

W

F

E

W

F

N

Wind and Pressure Effects

E

S

W

F

E

W

F

N

39 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Wind and Pressure Effects

Wind and Pressure Effects

Condfiguration A2

41 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Wind and Pressure Effects

Wind and Pressure Effects

Configuration E2

Forced

Exfiltration

43 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Infiltration and Exfiltration

0

1

2

3

4

5

6

7

8

Humidity Ratio (gv/kgda)

Wall 1

Wall 2 (XPS)

Wall 3 (Mineral

Fibre)

vinyl siding

sheathing membrane

OSB

stud cavity with

glass fibre insulation

air / vapour barrie

r

dr

y

wall

insu

lat

ion

sheathing membrane

Condition A2 - Average

(Wall 3

)

(Wall 2 and Wall 3)

Infiltration

Exfiltration

Moisture Effects

Interior and Exterior Temperature

-30

-20

-10

0

10

20

30

40

24-F

eb-08

2-Mar-08

9-Mar-08

16-Mar-08

23-Mar-08

30-Mar-08

6-A

pr-08

13-A

pr-08

20-A

pr-08

27-A

pr-08

Temperature, °C

Room T

Chamber T

Outdoor T

A2

B2

C2

_D2

E2

_F2

Condensation detected on the interior of the OSB

March 29 to 31st

45 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Wall 2 (XPS) - Interior of OSB

Liquid Detection Tape

0

20000

40000

60000

80000

100000

120000

27-Mar

29-Mar

31-Mar

2-Apr

4-Apr

6-Apr

8-Apr

Resistance (k

Ω

)

Wall 3 (Mineral Fibre) - Interior of OSB

Liquid Detection Tape

0

20000

40000

60000

80000

100000

120000

27-Mar

29-Mar

31-Mar

2-Apr

4-Apr

6-Apr

8-Apr

Resistance (k

Ω

)

Liquid detected during

Condition E2

Moisture Effects

Liquid detected during

Condition E2

Note: No liquid was detected in the

stud cavity of Wall 2 (XPS).

47 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Moisture Effects

Conditions in Wall 2 and

Wall 3 when liquid was

detected on the interior

surface of the OSB:

•

The surface of the OSB

is below the dew point of

chamber air for both walls

•

The walls are in a state of

exfiltration, allowing

moisture to enter the stud

cavity

•

High humidity is present at

the surface of the OSB in

both walls

Moisture Effects

Conditions in Wall 2 and

Wall 3 when liquid was

detected on the interior

surface of the OSB:

•

The surface of the OSB is

below the dew point of

chamber air for both walls

•

The walls are in a state

of exfiltration, allowing

moisture to enter the stud

cavity

•

High humidity is present at

the surface of the OSB in

both walls

49 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Moisture Effects

Conditions in Wall 2 and

Wall 3 when liquid was

detected on the interior

surface of the OSB:

•

The surface of the OSB is

below the dew point of

chamber air for both walls

•

The walls are in a state of

exfiltration, allowing

moisture to enter the stud

cavity

•

High humidity is present

at the surface of the OSB

in both walls

Moisture Effects

Differences in wall

performance:

•

Wall 2 (XPS) has a very

high level of humidity,

approaching saturation at

the exterior of the OSB

•

Wall 3 (Mineral Fibre) has

a lower humidity at the

exterior of the OSB

•

Need to investigate the

drying potential of the XPS

assembly

51 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Moisture Effects

Moisture Effects

Interior and Exterior Temperature

-30

-20

-10

0

10

20

30

40

24-F

eb-08

2-Mar-08

9-Mar-08

16-Mar-08

23-Mar-08

30-Mar-08

6-A

pr-08

13-A

pr-08

20-A

pr-08

27-A

pr-08

Temperature, °C

Room T

Chamber T

Outdoor T

A2

B2

C2

_D2

E2

_F2

Moisture detected on the exterior of the mineral fibre

insulation on six occasions

53 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Moisture Effects

Wall 3 RH & T Sensors - Relative Humidity

0

20

40

60

80

100

120

25-Mar

0:00

27-Mar

0:00

29-Mar

0:00

31-Mar

0:00

2-Apr

0:00

4-Apr

0:00

6-Apr

0:00

8-Apr

0:00

10-Apr

0:00

12-Apr

0:00

Date and Time

Relative Humidity (%)

Exterior

Exterior of Mineral Fibre

Insulation at Top of Wall

Wetting corresponds to peaks in relative humidity of the air

between the mineral fibre and exterior sheathing membrane.

55 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

ƒ

Phase 3 of project:

•

April 27- June 11, 2008

•

50% RH indoor (until May 22nd), 0 Pascals

•

3 mm opening in air/vapour barrier

Moisture

Effects-Inward flow in springtime

Interior and Exterior Conditions

-30 -20 -10 0 10 20 30 40 50 60 70 30 -Ap r-08 0: 00 2-Ma y-0 8 0_:0 0 4-Ma y-0 8 0_:0 0 6-_Ma y-08 0 :0₀ 8-_Ma y-08 0 :0₀ 10 -M ay_-0 8 0:0₀ 12 -Ma y-0 8 0_:0 0 14 -M ay_-0 8 0: 00 16 -M ay_-0 8 0: 00 18_-Ma y-08 0: 00 20_-Ma y-08 0: 00 22 -Ma y-0 8 0_:0 0 24 -Ma y-0 8 0_:0 0 26 -M ay_-0 8 0: 00 28 -M ay_-0 8 0: 00 30_-M ay -0_{8 0:} 00 1-J un-08 0: 00 3-_Ju n-08 0_:0 0 5-_Ju n-08 0_:0 0 Date and Time

R H ( % ), C h amber Pressure ( P a) , Temperat ure ( °C ) Chamber RH Chamber T Room T Outdoor T Chamber P Post Testing

Chamber removed

(missing data)

Reversing of moisture flow toward the inside was observed in

June 2008

57 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

The lower vapour permeance of XPS foam (compared to that of semi-rigid

mineral insulation ) resulted in a lower flow of vapour transmission inwards

Larger drop in

absolute moisture

content across

XPS than across

mineral fibre

insulation

Conclusions

ƒ

Temperature effects:

•

Both retrofit walls had similar temperature profiles,

creating a warm interior surface temperature for

the OSB

ƒ

Pressure and wind:

•

Without applied chamber pressure, infiltration

conditions dominated

•

Even with a 10 Pa applied chamber pressure

(above room air), westerly winds in excess of 30

km/h were capable of generating infiltration

59 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

Conclusions

ƒ

Interstitial condensation requires:

•

Exfiltration pressure conditions

•

A deficiency in the air barrier

•

Humid chamber/room air

•

Cold outdoor conditions, to cause surface

temperature to drop below the dew point of the

chamber/room air

ƒ

During the test, these conditions were only

met briefly for Walls 2 and 3 in Configuration

E2 (10 Pa pressure, 3 mm opening, 50% RH)

Conclusions

ƒ

Moisture effects:

•

Condensation was detected on the interior surface

of the OSB of both walls equally

•

Condensation was also detected at the bottom

plate in the stud cavity of Wall 3 (mineral fibre)

•

High humidity was detected between the XPS and

OSB of Wall 2, and requires further investigation

•

There was evidence of moisture accumulation

behind the exterior WRB of Wall 3 in the early

spring

61 – Moisture Management in Buildings / Gestion de l’humidité dans les bâtiments – 12th_{CCBST/ 12 CCSTB Montréal, May 2009}

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