High-R Walls for New 

Construction Structural 

Performance: Wind Pressure 

Testing 

A. DeRenzis and V. Kochkin

NAHB Research Center

January 2013
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iii

High-R Walls for New Construction Structural Performance: 

Wind Pressure Testing 

Prepared for: 

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program 

Office of Energy Efficiency and Renewable Energy 

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

Prepared by: 

A. DeRenzis and V. Kochkin 

NAHB Research Center Industry Partnership

400 Prince George’s Blvd. 

Upper Marlboro, MD 20774 

NREL Technical Monitor: Stacey Rothgeb 

Prepared Under Contract Number: KNDJ-0-40335-00 

January 2013 
iv

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v 

Contents

List of Figures ............................................................................................................................................ vi

List of Tables .............................................................................................................................................. vi

Definitions.................................................................................................................................................. vii

Executive Summary................................................................................................................................. viii

1 Introduction........................................................................................................................................... 1

1.1 Background ..........................................................................................................................1

1.2 Relevance to Building America’s Goals ..............................................................................2

1.3 Cost Effectiveness ................................................................................................................2

1.4 Tradeoffs and Other Benefits ...............................................................................................2

1.5 High-R Walls .......................................................................................................................2

2 Evaluating the Wind Pressure Performance of Walls with Exterior Rigid-Foam Sheathing ........ 4

2.1 Background ..........................................................................................................................4

2.2 Methods and Materials .........................................................................................................5

2.2.1 General .....................................................................................................................5

2.2.2 Specimen Construction ............................................................................................8

2.2.3 Test Setup and Protocol ...........................................................................................9

2.3 Results. ...............................................................................................................................13

2.3.1 General ...................................................................................................................13

2.3.2 Pressure Equalization Results ................................................................................21

2.4 Summary and Conclusions ................................................................................................25

2.5 Proposed Additional Testing..............................................................................................26

References................................................................................................................................................. 27

Appendix A: Summary of Test Pressure Traces, Maximum Observed Pressures, and Observed 

Damage for Test Wall Specimens..................................................................................................... 28
vi 

List of Figures

Figure 1. Labeled diagram of out-of-plane test apparatus ................................................................... 10

Figure 2. Testing frame with installed wall specimen .......................................................................... 10

Figure 3. PLAs ........................................................................................................................................... 10

Figure 4. Location of pressure measurements in an exterior residential wall system..................... 11

Figure 5. Pressure transducer locations in 12-ft-long by 8-ft-tall wall ................................................ 11

Figure 6. Example wind pressure traces for various wind speeds...................................................... 12

Figure 7. Comparison of desired and measured chamber pressures................................................. 13

Figure 8. Wall capacities by test group .................................................................................................. 16

Figure 9. Group 1 failure mode................................................................................................................ 16

Figure 10. Group 2A failure mode ........................................................................................................... 17

Figure 11. Pressures on rigid-foam insulation for Group 2 specimens .............................................. 18

Figure 12. Group 2B failure mode (sheathing nail pull-through) ......................................................... 18

Figure 13. Group 3A failure mode ........................................................................................................... 19

Figure 14. Group 3B failure mode ........................................................................................................... 20

Figure 15. Group 3C failure mode ........................................................................................................... 20

Figure 16. Group 3D failure mode ........................................................................................................... 20

Figure 17. Group 4A failure mode, nail pull-through............................................................................ 21

Figure 18. Group 4A failure mode ........................................................................................................... 21

Figure 19. Sample PEFs by individual layers for Group 3 specimens ................................................ 22

Figure 20. PEF analysis for rigid-foam insulation ................................................................................. 23

Figure 21. Envelope PEFs for rigid-foam sheathing for full-wall assemblies (Group 3 specimens) 24

Figure 22. Calculated pressure on the combined system of rigid-foam insulation and vinyl siding 

versus pressures (Configuration 3).................................................................................................. 25

Unless otherwise noted, all figures were created by the NAHB Research Center.

List of Tables

Table 1. Test Matrix of Wall Configurations ............................................................................................. 6

Table 2. Materials and Wall Construction................................................................................................. 8

Table 3. Measurement Sensors ............................................................................................................... 11

Table 4. Summary of Results................................................................................................................... 14

Unless otherwise noted, all tables were created by the NAHB Research Center.
vii 

Definitions

2 × 4 Nominal 2-in.-wide by 4-in.-deep framing lumber dimension

2 × 6 Nominal 2-in.-wide by 6-in.-deep framing lumber dimension

Advanced framing An optimized framing system to reduce extraneous framing 

members while maintaining structural integrity with the goals 

of increased thermal performance and lower cost

Btu British thermal unit

FSC Foam Sheathing Coalition

High-R wall Reference to wall systems generally having an R-value of 1.5 

to 2.5 times that of current energy code requirements for a 

given climate zone

hp Horsepower

Hz Hertz

ICC International Code Council

in. Inch

IRC International Residential Code

IBS International Building Code

LVDT Linear variable differential transducer

NAHB National Association of Home Builders

PEF Pressure equalization factor

PER Pressure equalization rain screen

PLA Pressure loading actuator

psf Pounds per square foot

psi Pounds per square inch

UWO University of Western Ontario

XPS Extruded polystyrene (foam insulation board)

WUFI A menu-driven software program that allows realistic 

calculation of the transient coupled one-dimensional head and 

moisture transport in multilayer building components exposed 

to natural weather. 

WRB Water-resistive barrier
viii

Executive Summary

Within the U.S. Department of Energy Building America Program, a prominent approach to 

constructing higher R-value walls includes the use of exterior rigid-foam insulation. Although 

this approach has met some success, recent building code changes have raised some performance 

issues for exterior rigid-foam sheathing (e.g., its ability to resist wind pressures) that indicate a 

need for continued wall system performance testing. To optimize performance and lower costs 

when employing exterior rigid sheathing, builders and researchers have investigated alternative 

bracing techniques to eliminate the use of wood structural sheathing. Structural characteristics, 

especially in the direction perpendicular to the sheathing, have been reevaluated for the building 

codes including pressure equalization issues across multiple layers of the wall system. As a

result, exterior sheathings may now need to undergo more extensive design analysis to 

substantiate the capability to adequately resist wind pressures. 

These issues, combined with the importance of limiting cost increases when switching to higher 

R-value wall systems, have prompted the need for structural testing and optimized wall framing 

designs. This technical report describes laboratory testing conducted at the NAHB Research 

Center. The testing evaluated wind pressure performance characteristics for wall systems 

constructed with exterior insulating sheathing. These test results will help to facilitate the 

ongoing use of nonstructural sheathing options and lead to a more in-depth understanding of wall 

system layer performance in response to high wind perturbations normal to the surface. 

Out-of-plane wind pressure testing of various wall configurations with insulating sheathing 

showed that the interactive response of material layers in a whole-wall performance analysis, 

including wall board interior finishes, nonstructural insulating sheathings, and vinyl siding, 

exceeds the wall performance with insulating sheathing alone in resisting wind pressures. The 

research team found that wall material configurations such as the degree and location of air 

sealing play a significant role in equalizing wind pressure. 

Tests of full-wall assemblies with the foam sheathing fully taped along all vertical and horizontal 

joints indicated that the failure of the foam fasteners may become the controlling failure mode. 

Note that this configuration also reached the highest overall capacity. In full-wall assemblies 

with untaped foam sheathing or foam sheathing taped at vertical joints only, the load on the foam 

does not reach levels sufficient to fail at the foam fasteners. Instead, the failure is controlled by 

the wood framing and its connections. 

These test results serve as a baseline of data for further material tests of other high-R wall 

systems and for comparison to whole-house wind pressure testing. This research also lays the 

groundwork for further testing of exterior finish connections to optimized framing systems.
1 

1 Introduction

The NAHB Research Center Building America Industry Team’s research on high-R wall systems 

focuses primarily on increasing the thermal performance of the wall while maintaining current 

constructability and affordability features. Designs of high-R wall systems for residential 

construction have centered on reducing the framing factor of the wall system to allow more area 

for insulation materials. The ultimate goal of this research is to promote options that will

substantially increase wall insulation by cost effectively upgrading from 2 × 4 to 2 × 6 advanced 

framing and by addressing structural performance and wind loading on high performance walls 

constructed with insulating nonstructural sheathing. 

One method of increasing the insulative value of the wall system is to add exterior rigid-foam 

sheathing to the wall design. This design, currently used in many new high performing homes, is 

emerging as one of the preferred ways to increase the R-value of walls. The use of exterior foam 

is expected to grow substantially and even become standard practice in parts of the country 

because of above code energy and green programs as well as more stringent energy codes. 

Increased use of exterior rigid-foam sheathing, especially with nonstructural sheathings on the 

exterior of framing members, has raised a number of design and performance questions, 

particularly in terms of structural performance and attachment. 

This technical report outlines the research and testing of high-R wall systems for out-of-plane 

wind loading to address the questions of structural performance and attachment issues. It 

includes the results of the research outlined in the NAHB Research Center’s Test Plan (NAHB 

Research Center 2011) for this project.

1.1 Background

A trend toward high performing homes, along with increasingly stringent energy codes, has led 

to opportunities for research into increasing wall insulation. Specifically for those approaches 

that include exterior, nonstructural insulating sheathing, a 2009 NAHB Research Center white 

paper reviewed the state-of-the-art performance information about wind pressure resistance of 

rigid foam and cladding systems (NAHB Research Center 2009a). In that paper, the authors 

identified a major code barrier to the use of exterior rigid foam in high-R wall assemblies. The 

study found that research was needed on the wind pressure performance of wall systems with

rigid-foam sheathing. In particular, the authors identified the need for research on the pressure 

equalization between the layers of the wall systems. The research applies to new construction in 

which foam sheathing is attached directly to studs. It also applies to retrofits where foam 

sheathing is attached either directly to studs or over an existing sheathing material with limited 

out-of-plane capacity. 

Most available test information about rigid-foam sheathed wall systems is limited to a single, 1⁄2-

in. foam product. Test programs have focused on capturing the response of the vinyl siding 

instead of the foam sheathing. These limited test results do not provide sufficient information to 

adequately understand the observed response of walls with rigid-foam sheathing. 

Furthermore, no standardized consensus-based test methods or engineering design procedures 

exist for determining the capacity of this type of wall system to resist out-of-plane wind pressure 
2 

loads.1 As an example of the significance of the identified information gaps, the FSC submitted a 

proposal to the 2012 International Code Council (ICC) code development process with 

provisions expanding the use of walls with exterior foam under the International Residential 

Code (IRC) and International Building Code (IBC). The proposal was disapproved, in part, 

because of objections that the out-of-plane structural behavior during wind events is unknown. 

1.2 Relevance to Building America’s Goals

Conducting testing and research to develop test methodologies for ensuring adequate 

performance of insulating products exterior to structural framing will make these products a 

viable option for builders in many climate zones. This research will also yield better empirical 

and design data on which to base methodologies for attaching exterior finishes over nonstructural 

sheathing. In addition, the research will allow prescriptive approaches, which currently have 

limited availability in the building codes, to be formalized. Developing new products and 

establishing test protocols for these products will broaden options for increasing wall system 

efficiencies while limiting cost increases that result from extensive engineering requirements. 

1.3 Cost Effectiveness

Using exterior nonstructural insulating sheathing presents an opportunity to significantly increase 

the R-value of wall systems. Toward this end, this testing will help solidify the use of these 

products with design data that support alternative approaches to the use of additional structural 

members. The out-of-plane testing described in this report provides the fundamental data set with 

which wall designs incorporating exterior nonstructural insulating sheathing can be compared to 

ensure that they meet minimum wind pressure resistance requirements.

1.4 Tradeoffs and Other Benefits

The study team expects that the results of this research will be used in the design of high-R wall 

systems, especially those incorporating exterior nonstructural sheathings. Additional benefits 

emerge as the testing is evaluated for the performance and failure modes of various wall system 

layers. In particular, the performance of exterior finishes attached through the nonstructural 

sheathing to the framing members can be evaluated. 

1.5 High-R Walls 

Current Building America Program efforts have resulted in heating and cooling savings in new 

homes of 50% and higher. These saving accrue from incorporating advanced high-efficiency 

equipment and incrementally improving building envelopes by raising insulation levels and 

using air sealing. Higher heating and cooling reductions, however, are substantially more 

challenging because of cost and technological constraints. Building envelope improvements that 

a production builder can implement, such as high-R wall systems, are necessary steps toward 

further reductions in home energy use. This comprehensive effort will develop construction 

methodology and design details for the next level of highly insulated wall systems that address

the following in a systems manner: 

• Wall structural issues including wall bracing, structural framing design and optimization, 

wind pressure resistance of walls with exterior insulation, attachment methods for 

 

1 Since this research program started, the Foam Sheathing Coalition (FSC) has initiated an ongoing American National Standards 

Institute process to develop a consensus-based standard for designing walls with exterior sheathing materials. 
3 

exterior insulation and claddings, drainage plane location and installation, and cladding 

installation 

• Performance issues such as moisture and bulk water handling and climate-specific 

optimum thermal characteristics 

• Cost factors associated with material and labor. 

The primary focus will be on developing integrated solutions for light-frame walls to achieve Rvalues ranging from 20 to 40 h∙ft2

∙°F/Btu. Initially, individual measures will be evaluated. As 

systems or component details meet initial evaluation criteria, they will be applied to test homes. 
4 

2 Evaluating the Wind Pressure Performance of Walls with 

Exterior Rigid-Foam Sheathing

Attaching exterior rigid-foam insulation directly to wall studs has been a common residential 

construction practice in parts of the country for many years. Although this practice is permitted 

in Chapter 7 of IRC (2009) under a prescriptive set of conditions, there are currently no 

established consensus-based test methods or engineering design procedures for determining the 

capacity of this type of wall system to resist out-of-plane wind pressure loads (see footnote 1). 

Recent debates at the code and standard development forums have raised questions regarding the 

capacity of these systems to resist out-of-plane wind pressures, and the possible need for 

appropriate limitations on the use of this technology. 

The objective of this research effort was to conduct exploratory laboratory testing to determine 

the out-of-plane performance of wall systems with exterior rigid-foam insulation. The testing 

focused on measuring the pressure equalization characteristics and the capacity of various wall 

systems with rigid-foam sheathing attached directly to the studs. The results will advance efforts 

to develop design procedures and prescriptive code provisions. 

The specific objectives and scope of this study were to: 

• Evaluate the capacity of wall systems with 1-in. extruded polystyrene (XPS) rigid-foam 

sheathing attached directly to studs. 

• Assess the impact of individual wall layers on the performance of XPS rigid-foam 

sheathing. 

• Evaluate the effects of typical exterior residential wall air sealing details on the pressure 

equalization of rigid-foam insulation. 

• Measure the pressure equalization factors (PEFs) across each wall layer.

2.1 Background

The impetus for this testing program is presented in a white paper entitled “Summary of Code 

and Standard Barriers to the Implementation of High Performance Home Systems Designs.” 

(NAHB Research Center 2009a). The white paper discusses the need to characterize the out-ofplane performance of walls with exterior rigid insulation. It also presents results of a literature 

review on the topic including design wind loads, existing test methods and test results, and 

existing design methods, among others. Salient points highlighted in the white paper include the 

following: 

• Typical negative design wind pressures on claddings in exposure B range between –15.1 

and –31.5 psf for 90- to 130-mph wind speeds. 

• The results of limited testing of wall systems with rigid-foam insulation installed directly 

over wood studs demonstrate that the rigid-foam insulation does not experience 100% of 

the applied load at higher pressures. 

• The pressure equalization mechanism observed for rigid-foam insulation is similar in 

principle to that used in design for pressure equalization rainscreen (PER) systems. 
5 

• Direction of the loading can influence pressure equalization across layers and needs to be 

evaluated; however, negative pressures are 25% higher on average and are expected to 

control the design. 

• From single-pulse dynamic testing, the observed range for the PEF for 1⁄2-in. rigid-foam 

insulation installed directly over studs was between 0.15 to 0.35 for wall systems without 

a water-resistive barrier (WRB) and between 0.20 to 0.45 for wall systems with a WRB. 

• A single PEF is expected to apply to a given wall assembly at all performance levels.

2.2 Methods and Materials

2.2.1 General

Testing was conducted at the NAHB Research Center Laboratory Facility in Upper Marlboro, 

Maryland, from November 2010 through February 2011. The researchers constructed wall 

specimens using materials purchased from local suppliers. Table 1 summarizes the test matrix for 

this program and includes a purpose statement for each tested configuration. Four primary wall 

groups were tested:

• XPS foam sheathing attached to 2 × 4 wood studs (no other wall components included) 

• XPS foam sheathing (exterior face) and gypsum wallboard (interior face) attached to 2 × 

4 wood studs. (Note that two configurations of Group 2 were tested—fully taped and 

untaped foam) 

• Full-wall assembly including vinyl siding, foam insulation, 2 × 4 wood studs, batt 

insulation, and interior gypsum wallboard. (Note that several configurations of the full 

assembly were tested with a secondary set of variables including air sealing details at the 

exterior or interior layers or both, installation of a WRB, and installation of electrical 

outlets)

• Gable roof wall assembly with vinyl siding installed over sealed foam insulation attached 

to 2 × 4 studs without interior gypsum wall board. 

Group 1 was used to establish a baseline of the capacity of the XPS foam insulation and its 

fasteners when tested in an isolated configuration without the contribution of any other wall 

layers. Group 2 was designed to determine a baseline for the pressure equalization across XPS 

foam insulation when a rigid, low-air-permeable layer (i.e., gypsum wallboard) is installed on the 

interior face of the wall. Wall specimens of Group 3 were used to benchmark the capacity of the 

entire wall system and to provide the pressure equalization across XPS foam sheathing in fullwall assemblies. Group 4, representing a gable roof wall assembly, provided the capacity of the 

foam sheathing attached to framing with the additional fasteners from the vinyl siding. 
6 

Table 1. Test Matrix of Wall Configurations 

Group Configuration 

Rigid 

Foam 

(Taped/

Untaped)

House 

Wrap 

Vinyl 

Siding

Drywall

(Standard/

Air Sealed 

at Plates)

Electrical 

Outlets Purpose Diagram 

1 A Untaped None None None None 

Benchmark capacity of exterior 

rigid foam and its fasteners 

tested in an isolated 

configuration 

2 

A Untaped None

None 

Standard 

Drywall None 

Evaluate pressure equalization 

across exterior rigid foam when 

rigid, low-air- permeable layer 

(gypsum wallboard) is installed 

on the interior face of the wall

B Taped None 

3 A Taped None 

5-in. 

Double 

Dutchlap 

Standard 

Drywall None 

Evaluate pressure equalization 

effects in a full-wall assembly 

and to determine the full 

system’s capacity
7 

3 

B Untaped Yes

5-in. 

Double 

Dutchlap 

Standard 

Drywall

None 

Same as 3A for a system with a 

house wrap

C Taped None 

Drywall air 

sealed at top 

and bottom 

plates

Same as 3A for a system with 

air sealed drywall

D Taped None 

5-in. 

Double 

Dutchlap

Standard 

Drywall

Exterior 

and 

Interior

Same as 3A for a system with 

electrical outlets and wiring 

installed in predrilled studs

E 

Only 

vertical 

joints 

taped

None 

5-in. 

Double 

Dutchlap 

Standard 

Drywall None 

Same as 3A for a system with 

foam not taped at top and 

bottom plates 

4 A Taped None 

5-in. 

Double 

Dutchlap 

Standard 

Drywall None 

Characterize capacity of a wall 

system without interior 

gypsum, typical of attic wall 

system at the gable end
8 

2.2.2 Specimen Construction

Table 2 summarizes the materials and details used in construction of the wall specimens. All wall 

specimens were 8 ft tall (nine 11⁄2-in. studs and three 11⁄2-in. plates, double top plate and single 

bottom plate) by 12 ft wide. Stud spacing in all wall specimens was 16 in. on center. 

Table 2. Materials and Wall Construction

Material Wall Construction 

Exterior sheathing

1-in.-thick XPS 4 ft × 8 ft panels 

Attachment: 2-in.-long ring shank nails with nominal 1-in.-

diameter plastic cap installed into studs at 12 in. on center 

spacing at sheathing panel edges and 16 in. on center in 

the panel field

Vinyl siding

Double 5 dutchlap (0.042-in.-thick) with single nailing flange

Attachment: 21⁄2-in.-long, 0.12-in.-diameter nail with 3⁄8-in.-

diameter head at 16 in. on center. One nail located at each 

stud 

WRB

(where installed)

XPS foam sheathing with joints taped using 3-in.-wide 

construction tape (all joints were fully taped except Test 3E 

where only vertical joints were taped)

OR

Single continuous layer of house wrap over untaped foam 

sheathing (house wrap with 0.007 air penetration protection and 

moisture vapor permeance of 58) 

House wrap attachment: Two 2-in. ring shank nails with 

nominal 1-in. plastic cap for temporary purposes until 

vinyl siding is installed

Framing Lumber

2 × 4 Spruce-Pine-Fir studs (STUD Grade)

2 × 4 Spruce-Pine-Fir plates (#2) 

Attachment (plates to studs): (2) 16d nails (0.131-in.-diameter, 

31⁄4-in.-long) at each stud end 

Attachment (double top plate): (2) 10d nails (0.148-in.-

diameter, 3-in.-long) at 24 in. on center

Insulation 

Unfaced R-13 batts 

Attachment: Friction fit between studs

Gypsum Wall Board 

1⁄2-in.-thick panel installed horizontally, tape and mud at all 

joints and screw locations

Attachment: 11⁄4-in. Type W screw at 16 in. on center 

Standard drywall detail (Table 1): no seal at top and bottom 
9 

Material Wall Construction 

plates; a 1⁄4- to 3⁄8-in. gap between the edge of the drywall, set up 

not to impede air flow; all vertical joints sealed

Air-sealed drywall detail (Table 1): top and bottom plates air 

sealed with spray foam to minimize air flow

Outlets (Group 3D only)

Exterior outlet: foam sheathing taped at the outlet location; 

outlet has standard rubber gasket 

Interior outlet: no special air sealing

2.2.3 Test Setup and Protocol

Figure 1, Figure 2, and Figure 3 show the test setup, which includes four primary elements: (1) 

specimen, (2) test frame, (3) pressure loading actuators (PLAs), and (4) controls. 

Wall specimens were mounted onto the rigid test frame using a set of pull-action latch clamps 

and TimberStrand® composite lumber members. The interface connections were designed to 

limit air leakage through wall edges and attachment locations. Transparent plexiglass panels (3⁄4-

in.-thick) were used on the test frame face opposite of the specimen to allow observation of the 

response of the specimen’s face inside the chamber during testing.

Through hoses and diffusers, the PLAs deliver suction to the test frame chamber, applying a 

negative pressure to the exterior surface of the specimen. Six PLAs were used to provide 

sufficient air flow to generate high-frequency, high-peak pressure pulses. The PLAs, with a peak 

capacity of ±400 psf, were designed and manufactured by the University of Western Ontario2

(UWO) to generate high-frequency pressure traces that simulate realistic wind loading conditions 

on buildings. 

A computer was used to control the PLAs and the data acquisition system (DAQ). 

 

2 Now Western University.
10 

Figure 1. Labeled diagram of out-of-plane test apparatus 

Figure 2. Testing frame with installed 

wall specimen

Figure 3. PLAs

Table 3 summarizes the pressure and deformation sensors that measured the response of the 

specimen. During construction of the wall specimens, up to 36 pressure transducers were 

mounted throughout the wall system at 12 different locations to measure the pressures at each 

wall layer (see Figure 4 and Figure 5). In addition, five string potentiometers were mounted 

inside two wall cavities to measure displacements of the wall sheathing material relative to the 

framing. Linear variable differential transducers (LVDTs) were used to measure global 

deflections on the interior face (i.e., gypsum side) of the wall at top and bottom supports and in 
11 

the center of the wall relative to the test frame. Measurements were recorded at a frequency of 

100 Hz per sensor. 

Table 3. Measurement Sensors

Instrument (number) Range

Pressure Transducers (39) 37 at ±5 psi

2 at ±1 psi

String Potentiometers (5) 0 to 2.8 in.

LVDTs (5) 4 at ±1 in.

1 at ±2 in.

Figure 4. Location of pressure measurements 

in an exterior residential wall system

Figure 5. Pressure transducer locations in 12-ftlong by 8-ft-tall wall

The chamber pressure was measured by two pressure transducers: one with ±1 psi range and one 

with ±5 psi range.

The pressure inside the test chamber was controlled in accordance with dynamic high-wind 

pressure traces developed from scale-model wind tunnel tests conducted by the UWO. In this 

testing program, pressure traces replicating 60- to 145-mph wind tunnel conditions were used. 

The UWO developed and supplied all pressure traces. Kopp et al. (2010) and Murray and Kopp 

(2010) contain additional information on the pressure traces and their development. Figure 6

shows example pressure traces for four wind speeds. To provide pressure equalization results for 

a range of wind pressures, each specimen was tested using three pressure traces that represented 

incrementally increased wind speeds (exceptions are noted where walls failed before the third 

trace was applied). The wind speeds for the three incremental stages were selected with the intent 

to achieve performance levels ranging from serviceability limit states (i.e., no residual damage) 

at the lower wind speeds to a failure of the specimen at the highest wind speed. Each test 

pressure trace associated with a specific wind speed had a duration of 15 min (900 s). 

LVDT’s

Pressure

transducer

String potentiometers
12 

Figure 6. Example wind pressure traces for various wind speeds

To replicate the target wind pressures, the 11-hp PLA fans were operated at a fan speed of 30 to 

60 Hz. The pressure was controlled through a proportional integral differential using a 

servomotor for adjusting the orifice controlling air flow in the system. The PLAs are capable of 

controlling pressure peaks changing at a frequency of up to 10 Hz. Figure 7 shows a 1-min 

snapshot comparison of the target and measured chamber pressures. 

60 mph trace 90 mph trace 120 mph trace 135 mph trace
13 

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

60 70 80 90 100 110 120

Axis Title

Time (seconds)

Desired chamber pressure Measured chamber pressure

Figure 7. Comparison of desired and measured chamber pressures

2.3 Results

2.3.1 General

Table 4 summarizes the results organized by group and configuration, including test wind 

speeds, peak measured pressures, and descriptions of the observed failure modes. Figure 8 charts 

peak pressures by test group. The results indicate that the capacity of the wall system (Group 3) 

is as much as five times higher than the capacity of isolated foam (Group 1). 

Comparison of the degree of improvement among groups 2, 3, and 4 indicates that both gypsum 

and vinyl siding fasteners contribute significantly to the system’s capacity. The gypsum 

contributes through pressure equalization, whereas vinyl siding primarily contributes through the 

additional fasteners installed through the foam. Pressure, psf
14 

Table 4. Summary of Results

Group Configuration Diagram Description

Peak 

Pressure 

(psf)

Observed Damage/Failure

1 A 

Untaped foam only

Untaped foam 

only –21 Complete failure of the nail plastic caps in the field of the foam sheathing panel 

2 

A 

Foam and gypsum

Foam untaped –89 Complete shear failure of stud to top plate 

connections at two locations 

B Foam taped –51 Complete failure of the nail plastic caps in 

the field of the panel

3 A 

Full assembly

Foam taped –134 

Some damage around interior gypsum 

screws, slight failure at connections of vinyl 

siding and rigid-foam insulation
15 

Group Configuration Diagram Description

Peak 

Pressure 

(psf)

Observed Damage/Failure

3 

B 

 Full assembly

Foam untaped, 

house wrap 

installed

–115 

Complete shear failure in stud to top plate 

connections at one location and stud 

bending failure at one location

C Foam taped, air 

sealed drywall –103 

Slight shear failure in stud to top plate 

connections at two locations and complete 

bending failure of studs at four locations 

D Foam taped, 

electrical outlets –102 Complete bending failure of the studs at 

electrical wiring holes at two locations

E 

Foam taped at 

vertical joints 

only

–104 Bending failure of a stud 

4 A 

Gable end 

assembly, foam 

taped

–73 Failure at connections of vinyl siding and 

rigid-foam insulation
16 

0

20

40

60

80

100

120

140

Group 1 

(foam only)

Group 2 

(foam+gyp) 

untaped

Group 2 

(foam+gyp) 

taped

Group 3 (full 

assembly) 

Press. Range

Group 4 

(foam and 

vinyl)

Peak Pressure, psf

Figure 8. Wall capacities by test group

The peak capacity for the specimen with isolated foam sheathing measured at 21 psf and was 

limited by the failure of plastic cap nails in the field of the panel where the tributary area per 

fastener was the highest. The fasteners’ primary failure mode was associated with the head of the 

nail pulling through the foam with some of the fasteners pulling the plastic cap through the foam 

as well (Figure 9).

Figure 9. Group 1 failure mode

Note: the red 

portion of the 

Group 3 bar 

represents a 

range of tested 

values over 

multiple tests.
17 

The addition of gypsum to the wall assembly (Group 2A) more than quadrupled the system 

capacity (89 psf) compared to the isolated foam (Group 1). The plate-to-stud connections of the 

wood frame failed and the gypsum broke (Figure 10), a response caused by the gypsum resisting 

the larger portion of the load. The distribution of the load between the layers occurred because 

air moved through the foam joints and the connections into the wall cavity, which led to load 

sharing between the foam and the gypsum. 

Figure 10. Group 2A failure mode

Taping all horizontal and vertical foam sheathing joints (Group 2B) reduced the permeability of 

the exterior layer. This resulted in higher pressures applied on the foam and reduced the capacity 

of the overall wall system (51 psf). Figure 11 depicts the pressures on the foam layer for the 

Group B specimens plotted relative to the chamber pressure. Figure 11 also shows the upper 

boundary for the isolated foam test (Group 1) as a reference. The maximum pressure on the 

unsealed rigid-foam sheathing (Group 2A test) did not exceed 8 psf, whereas the pressures on the 

sealed foam sheathing (Group 2B test) peaked at about 21 psf—exactly the limit determined 

from the Group 1 test (foam sheathing only). Therefore, because less air moved through the 

joints of the foam sheathing, the foam sheathing layer experienced a higher portion of the total 

pressure. In fact, up to about 15 psf, the pressure on the foam followed the chamber pressure 

(linear portion of Group 2B line) before the onset of pressure equalization. Consistent with this 

observation, the failure mode was associated with the foam sheathing connections. The failure of 

the nail plastic caps in the field of the sheathing panel where the fastener tributary area was the 

highest was followed by the onset of failure of the perimeter nails (Figure 12). Because all foam 

joints (vertical and horizontal, including the specimen boundaries) were taped with a 3-in.-wide 

tape, Group 2B represents the most conservative loading case for the exterior foam. In a more 

typical construction configuration, the boundary joints at the top and/or bottom plates are not 

taped, allowing air to move in and out of the cavity. Results from Group 3 specimens (discussed 

next) indicated that taping only the vertical joints resulted in a range of PEFs for the foam more 

similar to those for the untaped foam configuration than the fully taped foam configuration. 
18 

0

5

10

15

20

25

0 20 40 60 80 100

Pressure on Foam Sheathing (psf)

Chamber Pressure (psf)

Group 2A (Foam Untaped) Group 2B (Foam Taped)

Capacity of rigid foam 

insulation (Group 1)

Figure 11. Pressures on rigid-foam insulation for Group 2 specimens

Washer imprint on sheathing Washer after failure

Figure 12. Group 2B failure mode (sheathing nail pull-through)

Five Group 3 (full-wall assembly) configurations were tested (refer to Table 1 for a description 

of the configurations). Peak capacities ranged from 102 psf to 134 psf. The failure modes varied 

among the specimens, indicating that the system was close to balanced. The Group 3A specimen 

reached a pressure of 134 psf, which was limited by the capacity of the exterior 

sheathing/cladding system (Figure 13). The siding fasteners pulled from the framing and the 
19 

foam sheathing fasteners either pulled out of the framing or pulled through the plastic cap. The 

damage exhibited as bulging of the vinyl siding. 

Figure 13. Group 3A failure mode

The capacity of the rest of Group 3 specimens (B, C, D, and E) was limited by the capacity of the 

framing and/or framing connections (Figure 14, Figure 15, and Figure 16). This led to a collapse 

of the wall system and damage to interior drywall and the exterior layers. Where predrilled studs 

were used for the specimen with electrical outlets, the bending failure of the studs occurred at the 

predrilled holes. Note that a different batch of lumber was used starting on Specimen 3B. The 

observed change of failure mode from the wall’s exterior sheathing fasteners to the framing 

members and connections again indicates that this system was close to a balanced design. 

Although Group 3 test variables had some small impact on the pressure equalization profile as 

discussed later in the report, the variance in capacity of system among the specimens appeared 

more affected by other factors such as the variance in framing lumber strength. 
20 

Figure 14. Group 3B failure mode Figure 15. Group 3C failure mode

Figure 16. Group 3D failure mode

Although the capacity of the Group 4 specimen of 73 psf is a reduction of 30% or more 

compared to the full-wall assemblies (Group 3), it was a 3.5 times increase over the isolated 

foam sheathing test (Group 1). This comparison indicates that the vinyl siding fasteners 

contribute to the capacity of the foam sheathing. The failure mode of the Group 4 specimen was 

associated with pull-through of sheathing and siding fasteners in the field of the center panel 

(Figure 17) and showed on the exterior as bulging of the vinyl siding (Figure 18). 

Stud failure at 

predrilled hole
21 

Figure 17. Group 4A failure mode,

nail pull-through 

Figure 18. Group 4A failure mode

2.3.2 Pressure Equalization Results

The pressures measured inside the wall assemblies were used to calculate a PEF for each layer of 

the wall system. The PEF is the percentage of the total applied pressure resisted by an individual 

wall layer according to Equation 1: 

(1)

Figure 19 gives sample PEF graphs by layer for Specimen 3C (taped) and Specimen 3B 

(untaped) under a single wind pressure trace. These charts demonstrate that the PEFs are a 

function of the chamber pressure trace and the configuration of the wall system. For example, at 

pressures below 40 psf for the wall assembly with foam fully taped, the peak PEF across the 

foam sheathing layer was as high as 1.0 (Figure 19b). This means that the foam resisted as much 

as 100% of the total pressure at specific times along the pressure trace. As the pressure increased, 

the peak PEF for the rigid-foam insulation dropped below 0.7. For the wall assembly with 

untaped foam insulation and a house wrap (Figure 19a), the pressure gradient across foam was 

substantially reduced with the PEF trending below 0.40 at chamber pressures above 40 psf. 
22 

Blue • – Vinyl siding and house wrap

Red • – Untaped rigid-foam sheathing

Green • – Interior gypsum

Blue • – Vinyl siding

Red • – Taped rigid-foam sheathing

Green • – Interior gypsum

(a) Sheathing joints taped (Group 3C) (b) Sheathing joints not taped, house wrap installed 

(Group 3B)

Figure 19. Sample PEFs by individual layers for Group 3 specimens 

Figure 20a compares PEFs for 12 pressure sensor locations in the same wall for one of the 

specimens (refer to Figure 5 for locations of pressure sensors). The chart shows consistent results 

between various locations, indicating that there was little variability in response between 

different locations in the same wall. This conclusion holds true for all tested specimens. 

To characterize the PEF of a wall layer over the range of test pressures and to enable consistent 

comparison of PEFs among different wall assemblies, PEF envelope curves for each wall layer 

were developed as follows: (1) for each pressure trace, individual envelope curves were 

generated for each of the 12 pressure sensors in a wall specimen, (2) envelope curves were 

averaged across the 12 pressure sensors, and (3) the highest PEF factor for a given pressure was 

selected among all pressure traces (Figure 20b). 
23 

(a) PEF envelope curves for exterior rigid foam for 12 

locations in a wall specimen

(b) Average and maximum PEF envelope curves

Figure 20. PEF analysis for rigid-foam insulation

Figure 21 plots the envelope PEFs for rigid-foam sheathing for all Group 3 configurations (fullwall assembly). For configurations with foam fully taped (configurations A, C, and D), the PEF 

trends for the foam sheathing ranged from 1.0 at low pressures (0 psf to 30–50 psf) to 0.55–0.70 

at peak pressures (80+ psf). For configurations with foam untaped (Configuration 3B) or taped at 

vertical joints only (Configuration 3E), a more rapid decrease in the foam sheathing PEF was 

observed. Here, the PEF started at lower pressure thresholds (less than 5 psf) and reached levels 

below 0.2 at system capacity. For Configuration 3B, house wrap was applied as a continuous 

sheet and taped at the edges of the specimen. This effectively functioned as an air barrier and 

imposed a larger load onto the siding fasteners (refer to Figure 19b). For Configuration 3E, the 

gypsum sheathing resisted more than 80% of the load at pressures above 20 psf... This suggests 

that systems that are not fully taped respond more as untaped systems, allowing the air to move 

behind the foam. 
24 

Figure 21. Envelope PEFs for rigid-foam sheathing for full-wall assemblies (Group 3 

specimens)

For Group 3 specimens, Figure 22 shows the relationship between the total pressure gradient 

across the entire wall assembly (i.e., chamber pressure) and the pressure resisted only by the 

combined system of the rigid-foam sheathing, vinyl siding, and their associated fasteners. In 

addition, the horizontal dash line representing the capacity of the foam only (Group 1A) is 

included on the chart as a reference boundary. Of the five full-wall specimens of Group 3, only 

Configuration 3A approaches the capacity of Group 4A. This suggests that this is the only group 

in which the fasteners of the foam sheathing and siding system limit performance. None of the 

other wall systems experienced pressures approaching the capacity of the combined foam/siding 

system; failure in these walls, then, occurred in the framing. Because the capacities of Specimens 

3B–3E were lower than the capacity for Specimen 3A, the research team concluded that the fullwall assemblies with foam sheathing are a relatively balanced system. Other factors, such as 

variability of lumber bending properties, have a greater impact on the overall system’s capacity 

than air sealing details. Configuration 3E again indicates that for systems with only vertical 

joints taped, the exterior assembly is resisting less than 20% of the total pressure with the 

majority of the load resisted by the interior gypsum.
25 

Figure 22. Calculated pressure on the combined system of rigid-foam insulation and vinyl 

siding versus pressures (Configuration 3)

2.4 Summary and Conclusions

This testing program was designed to evaluate the wind pressure performance of energy efficient 

walls constructed with exterior rigid XPS foam insulation used as the primary wall sheathing 

material. Several 8 ft × 12 ft wall specimens of different configurations were tested under highfrequency dynamic wind pressures traces that closely replicated the loading conditions during 

real-life wind events. Pressures were measured in multiple locations and at each layer in the 

walls to characterize the pressure distribution across the wall assembly. The results of the 

pressure distribution were used to characterize the behavior of each wall layer and its 

contribution to the system. The results also yielded pressure equalization factors for rigid-foam 

insulation when used as an insulating layer along with a WRB and when used solely as an 

insulating layer. Based on the testing, the following conclusions can be made: 

• The capacity of the complete wall system (siding-foam-studs-gypsum) is five times 

higher than the capacity of the isolated foam sheathing (foam studs). 

• Wind pressure is redistributed between the wall layers as a result of the pressure 

equalization effects. The degree of redistribution depends on the detailing of the exterior 

air barriers and, to a lesser degree, the interior air barrier (level of air sealing).
26 

• Gypsum wall board contributes to the total wall capacity and the degree of the shared 

load depends primarily on the air-tightness of the exterior foam layer.

• The full-wall assembly is a relatively balanced system with failure modes ranging from 

failure of framing members and their connections to the failure of the exterior foam 

sheathing connections.

• The PEFs across the foam sheathing are a function of the total pressure applied to the 

wall. As the pressure increases, the PEFs decrease (i.e., a greater degree of pressure 

equalization occurs in the wall). 

• The PEFs across the foam sheathing decrease with increased permeability of the foam 

sheathing layer. The walls with the foam sheathing untaped or taped only at vertical 

joints show an onset of equalization at low pressures (about 5 psf) and the levels of PEFs

below 0.2 at higher pressures. 

• In full-wall assemblies, the failure of the foam fasteners is the controlling failure mode 

only in the systems with the foam sheathing fully taped along all vertical and all 

horizontal joints. This configuration also reaches the highest overall capacity. In full-wall 

assemblies with the foam untaped or taped at vertical joints only, the load of the foam 

does not reach the levels sufficient to fail at the foam connections. In these cases, the 

failure is controlled by the wood framing and its connections. 

2.5 Proposed Additional Testing 

Further testing of other wall materials and configurations is recommended for a more complete 

representation of wall system PEFs. The additional testing combined with the completed testing 

can be used to develop more complete design guidelines for walls using foam sheathing. The 

recommended testing will

• Characterize the performance of a variety of plastic cap fasteners

• Determine the capacity of different field fastener spacings

• Characterize the performance of other rigid-foam insulation types (i.e., expanded 

polystyrene and polyisocyanurate) and brands 

• Characterize the performance of 24-in. on center stud spacing. 

A targeted and parallel effort is proposed to evaluate the moisture performance of high-R wall 

systems through laboratory testing at the Forest Products Laboratory, simulations using WUFI 

software, field testing of walls using the Research Center’s Test Huts, and monitoring of wall 

moisture conditions in high performance homes. 
27 

References

IRC (2009). 2009 International Residential Code® for One- and Two-family Dwellings. Country 

Club Hills, IL: International Code Council, Inc. 

Kopp, G.A.; Morrison, M.J.; Gavanski, E.; Henderson, D.J.; Hong, H.P. (2010). “Three Little 

Pigs Project: Hurricane Risk Mitigation by Integrated Wind Tunnel and Full-Scale Laboratory 

Tests.” Natural Hazards Review (11:151). 

Morrison, M.J.; Kopp, G.A. (2010). “Performance of Toe-Nail Connections Under Realistic 

Wind Loading.” Engineering Structures (33:2011); pp. 69–76. 

NAHB Research Center (2011). Test Plan: High-R Wall Systems – Structural Performance 

Testing. Deliverable Number 2.1.1. Upper Marlboro, MD: NAHB Research Center. 

NAHB Research Center (2009a). Summary of Code and Standard Barriers to the 

Implementation of High Performance Home Systems Designs. Deliverable Number 4.2.2.1 Under 

NREL Subcontract Number AXL-9-99208-01. Upper Marlboro, MD: NAHB Research Center. 

NAHB Research Center (2009b). Gate 1B–System Evaluations & Specifications: Advanced 

Header Framing Design for High-R Wall Systems. Deliverable Number 4.2.1.2 Under NREL 

Subcontract Number AXL-9-99208-01. Upper Marlboro, MD: NAHB Research Center.
28 

Appendix A Summary of Test Pressure Traces, Maximum 

Observed Pressures, and Observed Damage for 

Test Wall Specimens

Group Configuration 

Wind Speed 

Pressure 

Trace 

(mph)

Maximum

Negative Chamber 

Pressure 

(psf)

Observed 

Damage/Failure 

1 A 60 –21 

Complete failure of the nail 

plastic caps in the field of 

the panel

2 

A 

73–125 –27 to –89 None

125 –82 

Complete shear failure in 

stud to top plate 

connections at two 

locations

B 

60 –27 None

90 –51 

Complete failure of the nail 

plastic caps in the field of 

the panel

3 A 

60 –27 None

90 –53 None

120 –108 Slight damage around 

interior gypsum screw

135 –124 

Complete failure at 

connections of vinyl siding 

and rigid-foam insulation

90 –54 None

120 –97 None

135 –125 Slight damage around 

interior gypsum screws

145 –134 

Increased damage around 

interior gypsum screws 

slight failure at connections 

of vinyl siding and rigidfoam insulation

3 B 

90 –53 None

120 –95 Slight damage at vinyl 

siding fasteners

135 –115 

Complete shear failure in 

stud to top plate 

connections at one location 

and stud bending failure at 

one location
29 

Group Configuration 

Wind Speed 

Pressure 

Trace 

(mph)

Maximum

Negative Chamber 

Pressure 

(psf)

Observed 

Damage/Failure 

C 

90 –53 Slight damage around 

interior gypsum screw

120 –95 Slight damage around 

interior gypsum screws

135 –103 

Slight shear failure in stud 

to top plate connections at 

two locations and complete 

bending failure in the studs 

at four locations

D 

90 –53 None

120 –92 

Slight failure at 

connections of vinyl siding 

and rigid-foam insulation

135 –103 

Complete bending failure 

at electrical wiring holes in 

the studs at two locations

4 A 

60 –27 None

90 –55 None

110 –73 

Failure at connections of 

vinyl siding and rigid-foam 

insulation
DOE/GO-102013-3627 ▪ January 2013

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