Insulating Steel Stud Insulating Steel Stud BackBack--Up Up

for Masonry Veneerfor Masonry VeneerHerbert Slone

Registered ArchitectTechnical Manager, Commercial Insulation

1.5 Hour, HSW

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©Owens Corning 2007

Learning Objectives

For steel stud/foam sheathing/brick veneer,

1. Understand thermal performance.

2. Understand vapor migration and simple evaluation methods to estimate potential moisture build-up.

3. Understand bracing and brick tie methods.

4. Understand code/fire design considerations.

1 “ci” = Insulating Sheathing

What is the benefit?¤ Minimizes thermal

bridging¤ Minimizes transverse

flow

1

Total R-ValueCalculation Method

w/ Gypsheathing

Series 14.75

7.75

7.45

Correction FactorModified Zone Method

w/ “ci”sheathing

18.10

11.10

11.90

Effective “R” for Steel Stud Walls w/ “ci”

INTERIOR AIR FILM

1/2” GYPSUM BOARD

STEEL STUD R-13 BATT INSULATION

R-3.8 FOAM INSULATION

AIR SPACE

MASONRY

EXTERIOR AIR FILM

3.5” stl stud @ 16”o.c., R13 Batt + R3.8 continuous insulation

Wall Plan Section

Warm Interior

An insulating sheathing, “ci”, reduces heat loss by minimizing lateral heat energy transfer through the large sheathing surfaces of the wall.

1 Thermal Performance: Summary

2 “ci” must be water resistant…….

the Brick Industry Association recommends the use of “inherently moisture resistant”sheathing such asclosed cellextruded polystyrene.

Due to expected exposure to moisture……

2“ci” joint treatment……..

must be water resistant.

Batt Insulation

Sealant under brackets

T&G Joint w/Tape or SealantXPS Sheathing

Brick TieBrick VeneerVapor RetarderGypsum Board

Foundation Wall

Steel Stud

2 Static Dewpoint, “Glaser Method”

Where Actualfalls below Dew Point, condensation is suspected under that set of static conditions.

2 Change to low perm facer on FG…Winter Conditions: Exterior, 0OF, 50% RH; Interior, 72OF, 30% RH

1” XPS Sheathing0.02 (low) perm Faced FG

No Dew Point in FG or XPS. VERY GOOD

Per Modified Zone Method RT= 12.2

0

10

20

30

40

50

60

70

80

90

100

Tem

pera

ture

(F)

Foil

Face

d FG

Bat

t R11

Inte

rior A

ir Fi

lm

1/2"

Gyp

sum

1/2"

Gyp

sum

1" A

ir Sp

ace

4" B

rick

Ven

eer

Exte

rior

Air

Film

Actual Temp. Dew Point Temp

2 Summer/Southern, Internal VR

Gyp Exterior Sheathing0.5 perm Foil Faced FG

Dew Point at retarder,UNDESIRABLE.

Summer Conditions: Exterior, 95OF, 95% RH; Interior, 72OF, 50% RH

3 Carefully Consider Bracing of Studs

In theory, all components act together………brick veneer, sheathing, studs, act as a composite assembly, resisting out-of-plane loads by each taking a portion of the load relative to it’s stiffness, span length, and the ability of the brick ties to transfer load between brick and framing.

3In reality, they don’t………over time, the brick and sheathing are continually flexed. Brick cracks, sheathing to stud connections deteriorate around fastener heads, sheathing wetting may occur. Composite action is lost.

Wind Load

Carefully Consider Bracing of Studs

3Deflection Bracing

for all Sheathing TypesAssume that the entire out-of-plane load must be resisted by the steel stud and bracing.

3 Brick Ties for XPS Insulating Sheathing

Anchors and ties:

•Connect directly to steel studframing.

•Don’t rely on the compressive strength of the sheathingsurface to maintain a stable base for the tie.

3 Penetrating Brick Tie Types

These types penetrate the sheathing layer, making a solid connection to transfer wind loads directly to the steel stud framing.

3 Unacceptable Brick Tie Types

Some minimize steel through the insulating layer to minimize thermal bridging, however, efficient load transfer must be the critical priority.

Steel Stud/Brick Veneer Fire Resistance

System fire resistance ratings must be established.

• Exterior Wall Rating (Time, ASTM E119)• Non-Combustible Wall w/ Combustible

Components (Pass/Fail, NFPA 285)• Perimeter Joint (Time, ANSI/UL 2079)

4

Exterior Wall Fire Resistance Rating4ASTM E119 Fire Resistance Furnace

Underwriters Laboratories, Northbrook, IL

Exterior FaceExterior Face Interior FaceInterior Face

Foam & fiber glassFoam & fiber glassgone after 3 hourgone after 3 hourexposureexposure

Exterior Wall Fire Resistance Rating4V434; 1 hour interior.1 hour exterior.Steel stud.Load bearing.

Foam sheathing (directly over stud).

Fiber glass or mineral wool in cavity.

Brick veneer.

4 NFPA 285: Multi-Story Test

Stud CavityFiber Glass

Type IV XPSSheathing

Test Window Opening

Mineral Wool Fire Safing

4 NFPA 285: Window Head

MW Fire Safing

4 NFPA 285: Fire Exposure

4 NFPA 285: Test Result, PASSNo flame propagation. Limited melt back.

4 ANSI/UL 2079 Perimeter Joint

Unrated Rated

Sill Detail

PerimeterJoint:assumes nonatural firestop.

Head Detail

4 Rated Joint Schematic

Mineral woolcovered with spray sealant

Gypsum insideand out.