Lateral Load Performance of 

Structural Insulated Panel (SIP) 

Diaphragms

Borjen Yeh

Tom Skaggs

Xiping Wang

Tom Williamson

United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

Research Paper

FPL–RP–700

May

2019

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Diaphragm force (lbf)

Midspan diaphragm deflection (in.)

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

2B6

1B6

1B3

5B3

4B6

5B6

3B6

3A 1A

2A

4A 5A
May 2019

Yeh, Borjen; Skaggs, Tom; Wang, Xiping; Williamson, Tom. 2019. Lateral 

load performance of structural insulated panel (SIP) diaphragms. Research 

Paper FPL-RP-700. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 17 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726-2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. 

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, 

offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national 

origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived 

from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by 

USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident. 

Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign 

Language, etc.) should contact the responsible Agency or USDA’s TARGET Center at (202) 720–2600 (voice and TTY) or contact USDA through the 

Federal Relay Service at (800) 877–8339. Additionally, program information may be made available in languages other than English. 

To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at http://www.ascr.usda.

gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in 

the form. To request a copy of the complaint form, call (866) 632–9992. Submit your completed form or letter to USDA by: (1) mail: U.S. Department of 

Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue, SW, Washington, D.C. 20250–9410; (2) fax: (202) 690–7442; or 

(3) email: program.intake@usda.gov. 

USDA is an equal opportunity provider, employer, and lender.

Abstract

Structural insulated panels (SIPs) have been successfully 

used in wall and roof construction for years. Combining the 

strength of facers made of wood structural panels and the 

energy-efficient core made of foam plastic insulation, SIP 

walls and roofs are structurally strong and energy-efficient 

construction systems. However, the data for lateral load 

performance of most SIP systems have generally remained 

proprietary and are covered in code evaluation reports 

held by various SIP manufacturers. The purpose of this 

project was to develop test data needed to characterize the 

lateral load performance of SIP diaphragms. The testing 

program involved structural testing of 12 full-sized SIP 

diaphragms of various configurations that covered a range 

of key variables including longitudinal and transverse SIP 

joints, framing connection, and SIP screw spacing. The 

static load testing of each SIP diaphragm was conducted 

following a monotonic procedure specified in ASTM 

E455-16. Supplementary mechanical tests were conducted 

to determine the lateral resistance of the metal fasteners in 

accordance with ASTM F1575. The results of this testing 

program indicated that stiffness and deformation capacity 

of the SIP diaphragms can be correlated to the number of 

SIP segments used in the diaphragm. As the number of SIP 

segments increased, the SIP diaphragm stiffness decreased 

and deformation capacity increased.

Keywords: diaphragm, fastener, framing, longitudinal joint, 

peak load, structural insulated panel (SIP), transverse joint, 

yield strength

Contents

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

Objective and Scope ............................................................1

Materials and Methods.........................................................1

Results and Discussion ......................................................10

Summary and Conclusions ................................................17

Acknowledgments..............................................................17

References..........................................................................17

English unit

Conversion 

factor SI unit

foot (ft) 3.048 × 10–1 meter (m)

inch (in.) 2.54 × 101 millimeter (mm)

kip (1,000 lbf) 4.448222 × 103 newton (N)

pound, force (lbf) 4.448222 newton (N)

pound per foot 

(lbf ft–1)

1.459390 × 101 newton per 

meter (N m–1)

Nominal lumber 

size (in.)

Standard lumber 

size (mm)

2 by 8 38 by 184

6 by 6 140 by 140
Introduction

Structural insulated panels (SIPs) have been successfully 

used in wall and roof construction for years. Combining 

the strength of facers made of wood structural panels 

(WSPs) and the energy-efficient core made of foam plastic 

insulation, SIP walls and roofs are structurally strong and 

energy-efficient construction systems. However, the data for 

lateral load performance of most SIP systems have generally 

remained proprietary and are covered in code evaluation 

reports held by various SIP manufacturers. The National 

Design Specification for Wood Construction (NDS) 

provides engineering equations for determining the strength 

of mechanical connections for wood structures (AWC 

2018). The Special Design Provisions for Wind and Seismic 

(SDPWS) permits the shear capacities of wood-framed 

diaphragms and shear walls to be calculated by principles of 

mechanics using values of fastener strength and sheathing 

shear capacity (AWC 2015). However, the SDPWS has not 

yet covered SIP diaphragms and shear walls.

In an effort to develop a publicly available database for the 

SIP industry, APA – The Engineered Wood Association; 

USDA Forest Service, Forest Products Laboratory (FPL); 

and the Structural Insulated Panel Association (SIPA) 

conducted comprehensive research in 2015 and 2016 under 

a joint venture agreement (15-JV-11111133-041) to study 

the lateral load performance of SIP walls with full bearing. 

The results were reported in Yeh and others (2018). The 

project reported here was intended to focus on the lateral 

performance of SIP roof diaphragms.

Objective and Scope

The purpose of this research was to develop test data 

needed to characterize the lateral load performance of SIP 

diaphragms. The research program involved structural 

testing of 12 full-sized SIP diaphragms of various 

configurations that covered a range of variables as follows:

• Effect of longitudinal SIP joint (no joint vs. one joint)

• Effect of transverse SIP joint (no joint, one joint vs. 

two joints)

Lateral Load Performance of Structural 

Insulated Panel (SIP) Diaphragms

Borjen Yeh, Director, Technical Services Division

Tom Skaggs, Manager, Product Evaluation, Technical Services Division

APA – The Engineered Wood Association, Tacoma, Washington, USA

Xiping Wang, Research Forest Products Technologist

USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin, USA

Tom Williamson, Technical Committee Chair

Structural Insulated Panel Association, Fort Lauderdale, Florida, USA

• Inclusion of framing connections (with and without 

connection to framing)

• SIP screw spacing (6 in. vs. 3 in. o.c.) between and within 

Series 1B6, 1B3, 5B6, and 5B3

The results obtained from this study provide engineering 

information for the design of SIP diaphragms as lateral load 

resisting systems.

Materials and Methods

The test matrix encompassing the key variables previously 

mentioned is provided in Table 1. The testing program 

contained structural testing of SIP diaphragms alone 

(Part A), SIP diaphragms connected to framing (Part B), 

and supplemental tests for determining the lateral resistance 

of the metal fasteners.

The SIPs were manufactured with 7/16 performance 

category oriented strandboard (OSB) that complied with 

DOC PS 2 and table 2 of ANSI/APA PRS 610.1 (APA 

2018). The foam core was Type I expanded polystyrene in 

compliance with ASTM C578 (ASTM 2018). The adhesive 

complied with ASTM D7446 (ASTM 2017).

SIP Diaphragm Construction

Part A: SIP Diaphragms

The purpose of tests in Part A was to evaluate the capacity 

of a SIP diaphragm as a stand-alone structural element. The 

capacities of SIP diaphragms connected to framing were 

included in Part B of this study. The commonality for all test 

series in Part A was as follows:

Assembly size: 8 by 24 ft

SIP thickness: 8-1/4 in.

Fastener spacing to SIP plates: 8d cooler (0.113 by 2-3/8 in.) 

nails at 6 in. o.c.

Test protocol: ASTM E455 (monotonic)

Replicate: 1
Research Paper FPL–RP–700

2

Series 1A served as the basic diaphragm for Part A with the 

configuration shown in Figure 1a. The diaphragm contained 

no spline and consisted of one SIP panel with dimensions of 

8 by 24 ft.

Series 2A contained one longitudinal joint (block spline) and 

was constructed with two SIP segments with dimensions 

of 4 by 24 ft (Fig. 1b). The purpose of this test series was 

to evaluate the effect of longitudinal joints on lateral load 

performance of a SIP diaphragm assembly.

Series 3A contained one transverse joint (block spline) and 

was constructed with two SIP segments with dimensions 

of 8 by 12 ft (Fig. 1c). The purpose of this test series was 

to evaluate the effect of a transverse joint on lateral load 

performance of a SIP diaphragm assembly.

Series 4A contained one longitudinal joint (block spline) and 

one transverse joint (block spline) and was constructed with 

four SIP segments with dimensions of 4 by 12 ft (Fig. 1d). 

The length of the block spline matched the segment size. 

The purpose of this test series was to evaluate the combined 

effect of one longitudinal joint and one transverse joint on 

lateral load performance of a SIP diaphragm assembly.

Series 5A contained one longitudinal joint and two 

transverse joints. It was constructed with six SIP segments 

with dimensions of 4 by 8 ft (Fig. 1e). The purpose of 

this test series was to evaluate the combined effect of one 

longitudinal joint and two transverse joints on lateral load 

performance of a SIP diaphragm assembly.

Part B: SIP Diaphragms Connected to Framing

The purpose of Part B was to evaluate the capacities of SIP 

diaphragms connected to framing with SIP screws supplied 

by the SIP manufacturer. The screws had a head diameter of 

0.635 in., thread diameter of 0.245 to 0.255 in., and shank 

diameter of 0.190 to 0.212 in. The commonality for all test 

series in this part included the following:

Assembly size: 8 by 24 ft

SIP thickness: 8-1/4 in.

Fastener spacing to SIP plates: 8d cooler (0.113 by 2-3/8 in.) 

nails at 6 in. o.c.

Framing materials: 6 by 6 No. 2 or Better Douglas-fir

Test protocol: ASTM E455 (monotonic)

Replicate: 1

Series 1B6 and 1B3 served as the basic diaphragms for 

Part B with the basic configuration shown in Figure 2a. 

The diaphragm contained no spline and consisted of one 

SIP panel with dimensions of 8 by 24 ft. The diaphragm 

was fastened to the framing with SIP screws at 6 in. o.c. 

for Series 1B6 and 3 in. o.c. for Series 1B3.

Series 2B6 contained one longitudinal joint (block 

spline) and was constructed with two SIP segments with 

dimensions of 4 by 24 ft (Fig. 2b). The purpose of this test 

specimen was to evaluate the effect of a longitudinal joint 

Table 1—Test matrix for structural testing of full-sized structural insulated panel (SIP) diaphragms 

(8 by 24 ft) of various configurations (total number of full-scale diaphragms: 12)

Test 

seriesa Purpose (compared with basic wall)

No. of

tests

SIP 

segment 

size (ft) Deviation from basic diaphragm

1A Basic diaphragm for Part A 1 8 by 24 Basic configuration

2A Effect of longitudinal joint 1 4 by 24 Two SIP segments

3A Effect of transverse joint 1 8 by 12 Two SIP segments

4A Effect of longitudinal and 

transverse joints

1 4 by 12 Four SIP segments

5A 1 4 by 8 Six SIP segments

1B6

Basic diaphragm for Part B

1 8 by 24 Basic configuration with 6-in. o.c. SIP screw spacing

1B3 1 8 by 24 Basic configuration with 3-in. o.c. SIP screw spacing

2B6 Effect of longitudinal joint 1 4 by 24 Two SIP segments with 6-in. o.c. SIP screw spacing

3B6 Effect of transverse joint 1 8 by 12 Two SIP segments with 6-in. o.c. SIP screw spacing

4B6

Effect of longitudinal, 

transverse joints, and 

SIP screw spacing

1 4 by 12 Four SIP segments with 6-in. o.c. SIP screw spacing

5B6 1 4 by 8 Six SIP segments with 6-in. o.c. SIP screw spacing

5B3 1 4 by 8 Six SIP segments with 3-in. o.c. SIP screw spacing

a

The series designation is expressed as nXm, where n is the series number (n = 1–5), X is the part of the study (X = A or B), and 

m (in Part B only) is the screw spacing in inches (m = 6 or 3).
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

3

Figure 1. Configuration of Part A structural insulated panel (SIP) diaphragms: (a) Series 1A, base configuration; 

(b) Series 2A, effect of longitudinal joint; (c) Series 3A, effect of a transverse joint; (d) Series 4A, combined 

effect of a longitudinal joint and a transverse joint; (e) Series 5A, combined effect of a longitudinal joint and 

two transverse joints.

8'

24'

Series 1A (a)

8'

12' 12'

Series 3A (c)

4'

4'

4'

4'

24'

Series 2A (b)

Longitudinal SIP joint

Longitudinal SIP joint

Transverse SIP joint

12' 12'

Series 4A (d)

Transverse SIP joint

4'

4'

Longitudinal SIP joint

8' 8' 8'

Series 5A (e)

Transverse SIP joint
Research Paper FPL–RP–700

4

Figure 2. Configuration of Part B structural insulated panel (SIP) diaphragms connected to framing with SIP screws (DF, 

Douglas-fir): (a) Series 1B6 and 1B3, base configuration; (b) Series 2B6, effect of a longitudinal joint; (c) Series 3B6, effect 

of a transverse joint; (d) Series 4B6, combined effect of a longitudinal joint and a transverse joint; (e) Series 5B6 and 5B3, 

combined effect of a longitudinal joint and two transverse joints.

8'

24'

Series 1B6 and 1B3

6 by 6

DF framing

(a)

8'

12' 12'

Series 3B6 (c)

4'

4'

4'

4'

24'

Series 2B6 (b)

Longitudinal SIP joint

Longitudinal SIP joint

Transverse SIP joint

12' 12'

Series 4B6 (d)

Transverse SIP joint

4'

4'

Longitudinal SIP joint

8' 8' 8'

Series 5B6 and 5B3 (e)

Transverse SIP joint

6 by 6

DF framing

6 by 6

DF framing

6 by 6

DF framing

6 by 6

DF framing
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

5

on lateral load performance of a SIP diaphragm assembly 

with framing.

Series 3B6 contained one transverse joint (block spline) and 

was constructed with two SIP segments with dimensions 

of 8 by 12 ft (Fig. 2c). The purpose of this test series was 

to evaluate the effect of a transverse joint on lateral load 

performance of a SIP diaphragm assembly with framing.

Series 4B6 contained one longitudinal joint (block spline) 

and one transverse joint (block spline) and was constructed 

with four SIP segments with dimensions of 4 by 12 ft 

(Fig. 2d). The purpose of this test series was to evaluate the 

combined effect of one longitudinal joint and one transverse 

joint on lateral load performance of a SIP diaphragm 

assembly with framing.

Series 5B6 and 5B3 each contained one longitudinal joint 

and two transverse joints. They were constructed with six 

SIP segments with dimensions of 4 by 8 ft (Fig. 2e). The 

diaphragms were fastened to the framing with SIP screws 

at 6 in. o.c. for Series 5B6 and 3 in. o.c. for Series 5B3. The 

purpose of these test series was to evaluate the combined 

effects of one longitudinal joint and two transverse joints 

and SIP screw spacing on lateral load performance of a SIP 

diaphragm assembly with framing.

SIP Diaphragm Testing

The SIP diaphragms were constructed and tested at the APA 

Research Center in Tacoma, Washington, USA, which is 

accredited under ISO/IEC 17025 (ISO/IEC 2017). The static 

load testing of each SIP diaphragm was conducted following 

a monotonic procedure specified in ASTM E455-16 (ASTM 

2016) using a loading rate that reached the ultimate load in 

approximately 10 min. Figure 3a shows the diaphragm plan 

view for structural testing of diaphragms, along with the 

loading configuration; Figure 3b shows details of diaphragm 

boundary A-A; Figure 3c shows details of diaphragm 

boundary B-B; and Figure 3d shows the spline detail C-C. 

Test setup for Part A diaphragms (before testing) and Part B 

diaphragms connected to framing (before testing) are shown 

in Figures 4 and 5, respectively.

The attachment mechanism of the diaphragm into one 

of the steel reaction channels is shown in Figure 3b. The 

steel channels were connected to tension reaction rods that 

were mounted to rigid reactions. In this tension train, a 

75-kip load cell was placed inline (Fig. 6). A load cell was 

located at each end of the diaphragm. The reported loads 

were based on the average value of two load cells divided 

by the diaphragm depth of 8 ft to convert to a unit shear 

value in pounds of force per foot. A linear potentiometer 

was mounted midspan on the 2 by 8 chord for each tested 

diaphragm to capture the diaphragm deflection.

For Part A diaphragms, the reaction load path was from 

the diaphragm through two 2 by 8s that were attached 

to the steel channels via Simpson SDS screws (Simpson 

Strong-Tie Co., Inc., Pleasanton, California, USA) 

(Fig. 3b, left). The SIP sheathing nails were only attached 

to the interior 2 by 8. The exterior 2 by 8 was used as a 

spacer to prevent the sheathing from directly bearing on 

the reaction channels. Based on previous SIP tests, when 

sheathing comes into contact with the test frame, the peak 

loads and ultimate deflections are affected. Although there 

was a 6 by 6 that was supporting the diaphragm, for the 

Part A tests, this wood member only served as a spacer to 

maintain the same elevation for all diaphragms for ease of 

applying the four-point loads.

For the Part B diaphragms, the SDS screws connected the 

reaction channel to the 6 by 6 wood members (Fig. 3b, 

right). The diaphragm sheathing was nailed similarly to 

Part A, with SIP sheathing nails installed on both sides of 

the diaphragm. The diaphragm was attached to the 6 by 6 

member with SIP screws at either 6 or 3 in. o.c.

Figure 3c shows the boundary details for Parts A and B on 

the 24-ft-long sides of the diaphragm. Figure 3d provides 

a spline detail for those diaphragms that had splines in 

both Parts A and B. As often occurs in the field, the spline 

was only nailed on one side of the diaphragm, but the nail 

spacing was doubled to transfer the entire shear force of the 

diaphragm through the top of the box spline.

Figure 7 shows the stitch nail spacing of the diaphragm 

chords for the double discontinuous 2 by 8 framing. For the 

Part B diaphragms, additional chord splices for the 6 by 6s 

were provided (Fig. 8). Additional framing connectors were 

used to attach the 6 by 6s that met at a 90° angle on the 

diaphragm corners (Fig. 9).

Supplemental Fastener Tests

Supplemental mechanical tests were conducted to determine 

the fastener yield strength of the SIP screws and the 8d 

cooler nails (0.113 by 2-3/8 in.) in accordance with ASTM 

F1575 (ASTM 2017b) because the bending yield strength 

of the SIP screws could affect the diaphragm shear strength. 

In addition, the lateral resistance of the 8d cooler nails 

was determined following a load-slip test method for 

establishing the sheathing to framing nail characteristics. In 

total, eight 8d cooler nails were driven into 2 by 8 Douglasfir lumber. Figure 10 shows a drawing of the load-slip test 

specimen.

Lateral resistance of SIP screws was determined following 

the principles of ASTM D1761 (ASTM 2012). Figure 11 

shows a drawing of the SIP screw test specimen. The SIP 

screws were screwed through the SIP into 6 by 6 Douglasfir timber. All fastener tests were monotonic using the 

loading rate in the referenced ASTM standards.

An 8d cooler nail test specimen and a SIP screw test 

specimen in the test machine are shown in Figures 12 and 

13, respectively.
Research Paper FPL–RP–700

6

figs 3 through 11

Figure 3. Diaphragm plan view for lateral load testing of structural insulated panel (SIP) diaphragms: (a) diaphragm plan 

view showing the loading configuration of diaphragm testing; (b) diaphragm boundary A-A showing reaction attachment 

scheme for Part A (left) and Part B (right) at the 8-ft boundary framing; (c) diaphragm boundary B-B showing reaction 

attachment scheme for Part A (left) and Part B (right) at the 24-ft boundary framing; and (d) spline detail C-C for Part A (left) 

and Part B (right) framing.

(a)

(b)

(c)

(d)

Diaphragm plan view

Detail C-C for Part A

(spline)

Detail C-C for Part B

(spline)

8d cooler (0.113" by 

2-3/8") at 6" o.c.

Detail A-A for Part A

(8' boundary)

Detail A-A for Part B

(8' boundary)

30 - 10d common 

(0.148" by 3") stitch 

nails (evenly spaced)

20 - SDS screws (0.25" 

by 3-1/2" (evenly 

spaced)

1"

14-3/4"

8d cooler (0.113" by 

2-3/8") at 3" o.c. 

(no nails on bottom) SIP screws, both 

sides of joint at 

12" o.c.

8d cooler (0.113" by 

2-3/8") at 6" o.c.

10d common (0.148" 

by 3") stitch nails 

(see Plan View D for 

nail schedule)

Detail B-B for Part A

(24' boundary)

Detail B-B for Part B

(24' boundary)

P/2 P/4

4'

8'

6' 4' 6' 4'

P/4 P/4 P/4 P/2

12' 12'

C C

A A

B B
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

7

Figure 4. Test setup for a Part A SIP diaphragm (before testing).

Figure 5. Test setup for a Part B SIP diaphragm connected to framing 

(before testing).

Figure 6. Reaction channel 

attachment to load cell.
Research Paper FPL–RP–700

8

Figure 7. Boundary stitch nailing schedule made up of 2 by 8, 8-ft-long framing lumber.

Figure 8. Chord strap from Simpson Strong-Tie CMSTC16 coil straps cut to 6-ft lengths for use in 

Part B SIP diaphragm tests.

Figure 9. Framing anchor (Simpson Strong-Tie MSTI26) 

used in Part B SIP diaphragm tests.

10 - 10d nails

(0.148" by 3")

20 - 10d nails

(0.148" by 3")

20 - 10d nails

(0.148" by 3")

20 - 10d nails

(0.148" by 3")

20 - 10d nails

(0.148" by 3")

10 - 10d nails

(0.148" by 3")
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

9

Figure 10. 8d cooler nail test specimen.

Figure 11. SIP screw test specimen.

12"

Top view of modified 

load-slip specimen

Front (or back) view of 

modified load-slip specimen

Side view of modified 

load-slip specimen

2" 3"

7"

1"

(8) 8d cooler nails per modified load-slip specimen

Remove 1-1/2" foam from SIP specimen

SIP size = 12" by 7"

2 by 8 length = 7"

(8) 8d cooler nails per modified load-slip specimen

Remove 1-1/2" foam from SIP specimen

SIP size = 12" by 7"

2 by 8 length = 7"

6 by 6 length = 13-1/2"

12"

1" 1"

1-1/2"

4-1/2"

7" 8"

13-1/2"

Top view of SIP 

screw specimen

Front (or back) view of 

SIP screw specimen

Side view of SIP 

screw specimen
Research Paper FPL–RP–700

10

Figure 12. An 8d cooler nail specimen in the test machine.

Figure 13. A SIP screw test specimen in the test machine.

Results and Discussion

Part A: SIP Diaphragms

Typical failure modes of the Part A SIP diaphragms were 

related to nail yielding along the 8-ft-long diaphragm 

chord (Fig. 14). Tests results for Part A diaphragms are 

summarized in Table 2, and the load versus deflection plots 

of all Part A diaphragms are shown in Figure 15.

Series 1A: Peak load for the Series 1A diaphragm, which 

contained no panel joints, was 1,186 lbf/ft with an ultimate 

deflection of 1.16 in.

Series 2A: Peak load for the Series 2A diaphragm, which 

contained one 24-ft longitudinal joint, was 1,220 lbf/ft with 

an ultimate deflection of 1.09 in. Comparing the results of 

the Series 1A and 2A, one can see that adding one single 

longitudinal joint had a negligible effect on diaphragm 

performance.

Series 3A: Peak load for the Series 3A diaphragm, 

which contained one 8-ft transverse joint, was 

1,110 lbf/ft with an ultimate deflection of 1.12 in. Similar 

to the Series 2A diaphragm, the performances of Series 1A 

and 3A diaphragms were comparable. Diaphragms with 

two segments, Series 2A and 3A, had peak loads within 

10% of each other and ultimate deflections within 3%. 

Based on the test results obtained from Series 1A, 2A, and 

3A diaphragms, there was no apparent difference between 

diaphragms constructed with one large SIP having no 

joints and two SIP segments with either a longitudinal or 

transverse joint.

Series 4A: Peak load for the Series 4A diaphragm, which 

contained both a 24-ft longitudinal joint and an 8-ft 

transverse joint, was 1,325 lbf/ft with an ultimate deflection 

of 1.74 in. Peak load and deflection of the Series 4A 

diaphragm was 12% higher and 50% greater, respectively, 

than the Series 1A diaphragm. Based on these results and 

the observed diaphragm stiffness from Figure 13, when both 

longitudinal and transverse joints are included, diaphragm 

stiffness decreased and ultimate deflection increased 

probably because of the increase in panel joints. It is unclear 

if the higher peak load from the Series 4A diaphragm, 

compared with the Series 1A diaphragm, could be attributed 

to material variability.

Series 5A: Peak load for the Series 5A diaphragm, 

which contained one 24-ft longitudinal joint and two 8-ft 

transverse joints, was 1,362 lbf/ft with an ultimate deflection 

of 2.63 in. Peak load and ultimate deflection of the 

Series 5A diaphragm were 15% higher and 127% greater, 

respectively, than the Series 1A diaphragm. The Series 5A 

diaphragm was the least stiff among all Part A diaphragms. 

Intuitively, as additional panel joints are introduced into 

a diaphragm, diaphragm stiffness could be expected to 

decrease and ultimate deflection to increase. It is unclear 

if the higher peak load from the Series 5A diaphragm, 

compared with the Series 1A diaphragm, could be attributed 

to material variability.
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

11

Figure 14. A typical failure mode at boundary framing of 

Part A diaphragms.

Figure 15. Load versus deflection plots for Part A SIP diaphragms.

Table 2—Part A structural insulated panel (SIP) diaphragm test results

Test

series

Purpose (compared with 

basic diaphragm)

SIP segment

size 

(ft)

Deviation from 

basic diaphragm

Peak load

(lbf/ft)a

Ultimate

deflectionb

(in.)

1A Basic diaphragm for Part A 8 by 24 Basic configuration 1,186 1.16

2A Effect of longitudinal joint 4 by 24 Two SIP segments 1,220 (+2.9%) 1.09 (–6.0%)

3A Effect of transverse joint 8 by 12 Two SIP segments 1,110 (–6.4%) 1.12 (–3.4%)

4A Effect of longitudinal and 

transverse joints

4 by 12 Four SIP segments 1,325 (+11.7%) 1.74 (+50%)

5A 4 by 8 Six SIP segments 1,362 (+14.8%) 2.63 (+126.7%)

a

The value in parentheses indicates percentage difference in load compared with the basic configuration (Series 1A).

b

Ultimate deflection is defined as midspan deflection at the 80% post peak load. The value in parentheses indicates percentage 

difference in ultimate deflection compared with Series 1A.

0

200

400

600

800

1,000

1,200

2A

3A

1A

4A 5A

1,400

1,600

Diaphragm force (lbf)

Midspan diaphragm deflection (in.)

0 0.5 1.0 1.5 2.0 2.5 3.0
Research Paper FPL–RP–700

12

Part B: SIP Diaphragms Connected to Framing

Typical failure modes of the Part B SIP diaphragms are 

shown in Figure 16. One common failure was related to the 

SIP screws that fractured close to the intersection of the SIP 

and the timber framing (Fig. 16a). Figure 16b shows the 

results of a screw fracture with the screw head appearing 

to have “popped.” Another common failure mode was 

the screw head pulling through the face of the OSB facer 

(Fig. 16c). A tension splice fracture is shown in Figure 16d. 

Finally, yielding of the framing anchors (Fig. 9) was also 

commonly observed in Part B diaphragms.

Test results for Part B SIP diaphragms are summarized in 

Table 3, and the load versus deflection plots of all Part B 

SIP diaphragms are shown in Figure 17. Parts A and B SIP 

diaphragms combined are shown in Figure 18.

Series 1B6: Peak load for the Series 1B6 diaphragm, which 

contained no joints but with the SIP screws installed at 

6 in. o.c., was 2,332 lbf/ft with an ultimate deflection of 

1.91 in. Clearly, the SIP screws into the timber framing 

increased diaphragm shear strength. Compared with 

Series 1A without connection to framing, the Series 1B6 

diaphragm had a 97% increase in shear strength and a 65% 

increase in ultimate deflection.

Series 1B3: Peak load for the Series 1B3 diaphragm, 

which contained no joints but with the SIP screws 

installed at half the spacing of Series 1B6 (3 in. o.c.), was 

3,740 lbf/ft with an ultimate deflection of 2.01 in. A simple 

principle of mechanics would suggest that doubling the 

SIP screws would double the shear strength. However, the 

shear strength for the Series 1B3 diaphragm was only about 

60% higher than that for the Series 1B6 diaphragm. It is 

unclear why doubling the number of SIP screws did not 

double the diaphragm shear strength. The lack of dowel 

bearing capacity from the foam plastic insulation core might 

have affected the load distribution between the SIP facers. 

Ultimate deflection between these two series of diaphragms 

was within 5% of each other.

Series 2B6: Peak load for the Series 2B6 diaphragm, which 

contained one 24-ft longitudinal joint, was 2,346 lbf/ft with 

an ultimate deflection of 1.71 in. Shear strength for the 

Series 2B6 diaphragm was within 1% of shear strength of 

the Series 1B6 diaphragm, whereas ultimate deflection was 

10% less. One longitudinal joint appears to have minimal 

impact on diaphragm performance.

Series 3B6: Peak load for the Series 3B6 diaphragm, which 

contained one 8-ft transverse joint, was 2,041 lbf/ft with an 

ultimate deflection of 2.04 in. The Series 3B6 diaphragm 

had 13% less peak load and 7% greater ultimate deflection 

than the Series 1B6 diaphragm. Comparing the two tests, 

it appears that one transverse joint has minimal effect on 

diaphragm performance.

Figure 16. Typical failure modes of the Part B diaphragms: 

(a) a typical fracture location of SIP screws (a hinge 

forming on inside face of the bottom OSB facer); (b) SIP 

screws fracture and then pop out; (c) SIP screw head 

pulled through the face of OSB facers; (d) a tension splice 

fracture.

(a)

(c)

(d)

(b)
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

13

Figure 17. Load versus deflection plots for Part B SIP diaphragms.

Table 3—Part B structural insulated panel (SIP) diaphragm test results

Test

series

Purpose (compared with 

basic wall)

SIP segment

size

(ft)

Deviation from 

basic diaphragm

Peak load

(lbf/ft)a

Ultimate

deflectionb

(in.)

1B6

Basic diaphragm for Part B 8 by 24

Basic configuration with 6-in. 

SIP screw spacing 2,332 1.91

1B3 Basic configuration with 3-in. 

SIP screw spacing 3,740 2.01

2B6 Effect of longitudinal joint 4 by 24 Two SIP segments with 6-in. o.c. 

SIP screw spacing 2,346 (+0.6%) 1.71 (–10.5%)

3B6 Effect of transverse joint 8 by 12 Two SIP segments with 6-in. o.c. 

SIP screw spacing 2,041 (–12.5%) 2.04 (+6.8%)

4B6

Effect of longitudinal joints, 

transverse joints, and SIP 

screw spacing

4 by 12 Four SIP segments with 6-in. o.c. 

SIP screw spacing 2,290 (–1.8%) 2.08 (+8.9%)

5B6

4 by 8

Six SIP segments with 6-in. o.c. 

SIP screw spacing 2,094 (–10.2%) 2.51 (+31.4%)

5B3 Six SIP segments with 3-in. o.c. 

SIP screw spacing 3,347 (–10.5%) 2.72 (+35.3%)

a

The value in parentheses indicates percentage difference in load compared with the basic configuration (1B6/1B3).

b

Ultimate deflection is defined as midspan deflection at the 80% post peak load. The value in parentheses indicates percentage difference in 

ultimate deflection with respect to the basic configuration (1B6/1B3).

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Diaphragm force (lbf)

Midspan diaphragm deflection (in.)

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

2B6

1B6

1B3

5B3

3B6

4B6

5B6
Research Paper FPL–RP–700

14

Series 4B6: Peak load for the Series 4B6 diaphragm, 

which contained both a 24-ft longitudinal joint and an 8-ft 

transverse joint, was 2,290 lbf/ft with an ultimate deflection 

of 2.08 in. The Series 4B6 diaphragm had 2% less peak 

load and 9% greater ultimate deflection than the Series 1B6 

diaphragm, indicating little effect of the joints on diaphragm 

performance.

Series 5B6: Peak load for the Series 5B6 diaphragm, 

which contained both a 24-ft longitudinal joint and two 

8-ft transverse joints, was 2,094 lbf/ft with an ultimate 

deflection of 2.51 in. The Series 5B6 diaphragm had 10% 

less peak load and 31% greater ultimate deflection than the 

Series 1B6 diaphragm.

Series 5B3: Peak load for the Series 5B3 diaphragm, 

which contained both a 24-ft longitudinal joint and two 

8-ft transverse joints but with the SIP screws installed at 

half the spacing of the Series 5B6 diaphragm, was 

3,347 lbf/ft with an ultimate deflection of 2.72 in. A simple 

principle of mechanics would suggest that doubling the SIP 

screws would double the shear strength. However, the shear 

strength for the Series 5B3 diaphragm was only about 60% 

higher than that for the Series 5B6 diaphragm. Similar to the 

case of Series 1B3, the lack of dowel bearing capacity from 

the foam plastic insulation core might have affected the load 

distribution between the SIP facers. Ultimate deflections of 

Series 5B3 and 5B6 diaphragms were within 8% of each 

other, with 5B3 being the larger of the two. Also, ultimate 

deflection for the Series 5B3 diaphragm was the greatest 

Figure 18. Load versus deflection plots for Part A and Part B diaphragms combined.

of all diaphragms tested in this study, and this diaphragm 

experienced a tension splice fracture (Fig. 16d).

Yield Strength of SIP Screws and 

Nail Fasteners

The average yield strength of the ten SIP screws was 

186,500 lb/in2 with a coefficient of variation of 2.1%, and 

the average yield strength of the ten 8d cooler nail was 

118,000 lb/in2 with a coefficient of variation of 2.6%.

Figure 19 shows a typical lateral load versus deflection plot 

from the 8d cooler nail test where the plot has been adjusted 

to a load per nail basis, as opposed to the total load. A 

summary of the test data is provided in Table 4.

A reasonable approach for determining the allowable lateral 

nail design properties is to divide the mean value by a 

safety factor of 5.0 based on the NDS (AWC 2018). This 

results in an allowable lateral nail design value for the 8d 

cooler nails of 61 lbf/nail. This value matches well with 

the lateral nail design value for 8d cooler nails published 

in table 12Q of the 2018 NDS of 56 lbf/nail (AWC 2018). 

Given that SIP thickness did not affect lateral performance 

of the facer framing, this value is appropriate for all SIP 

thicknesses when SIPs are fabricated with facers meeting 

the requirements specified in ANSI/APA PRS 610.1 (APA 

2018). In addition, based on the principle of mechanics, 

shear strength of the Part A diaphragms can be estimated as 

the average nail strength value of 305 lbf times 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Diaphragm force (lbf)

Midspan diaphragm deflection (in.)

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

2B6

1B6

1B3

5B3

4B6

5B6

3B6

3A 1A

2A

4A 5A
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

15

Figure 19. A typical lateral load versus deflection plot for the 8d cooler nail specimens.

Table 4—Results of individual 8d cooler 

nail test specimens

Specimen

no.

Deflection at 

peak load (in.)

Peak load

(lbf/nail)

1 0.384 255

2 0.618 324

3 0.488 296

4 0.467 334

5 0.549 325

6 0.267 282

7 0.596 338

8 0.584 339

9 0.441 284

10 0.299 272

Number of tests 10 10

Mean 0.469 305

Maximum 0.618 339

Minimum 0.267 255

COVa (%) 26.2 10.0

a

COV, coefficient of variation.

50

100

150

0.0 0.1 0.2 0.3

Specimen deflection (in.)

Applied load (lbf/nail)

0.4 0.5 0.6 0.7

200

250

300

350

0
Research Paper FPL–RP–700

16

4 nails/ft, which yields an ultimate unit shear of 

1,220 lbf/ft. This estimated value agrees well with the 

observed load values from Part A diaphragms (Table 2). 

This analysis was based on ultimate loads with multiple 

nails, and the diaphragm factor, Cdi, of 1.1 (as defined in 

section 12.5.3 of the 2018 NDS) was not used. Nonetheless, 

it is interesting that the NDS published value of 56 lbf/nail 

times a diaphragm factor of 1.1 leads to an allowable lateral 

nail design value of 62 lbf/nail, which compares well with 

the value of 61 lbf/nail obtained from this study.

Figure 20 shows a typical lateral load versus deflection plot 

for a SIP screw test. Table 5 summarizes the results of the 

individual SIP screw specimens.

When dividing the mean peak load value from Table 5 by a 

safety factor of 5.0, the allowable lateral SIP screw design 

value is 176 lbf/screw. Given that SIP thickness probably 

affects SIP screw behavior, additional evaluation is needed 

for SIPs with different thicknesses.

In addition, similar to the Part A diaphragms, the 

predicted ultimate strength for Part B diaphragms can be 

calculated as 880 lbf times the number of screws per foot, 

which results in an ultimate unit shear strength of 

1,760 lbf/ft for the diaphragm with SIP screws spaced at 

6 in. o.c. (two screws per foot) and 3,520 lbf/ft for the 

diaphragms with SIP screws spaced at 3 in. o.c. (four screws 

per foot). These calculated shear strengths for the Part B 

diaphragms underpredict the test results shown in Table 3 by 

14% to 25% for SIP screws spaced at 6 in. o.c. However, for 

SIP screws spaced at 3 in. o.c., the calculations predict the 

Figure 20. A typical lateral load versus deflection plot for the SIP screw specimens.

Table 5—Results of individual structural 

insulated panel (SIP) screw tests

Specimen

no.

Deflection at 

peak load (in.)

Peak load

(lbf/nail)

1 1.062 961

2 1.403 888

3 1.388 909

4 1.014 968

5 0.851 981

6 1.391 778

7 1.414 707

8 1.500 749

9 1.380 914

10 0.816 940

Number of tests 10 10

Mean 1.222 880

Maximum 1.500 981

Minimum 0.816 707

COVa (%) 21.1 11.2

a

COV, coefficient of variation.

test results fairly accurately, on average. Further research 

on modelling of shear strength of SIP diaphragms installed 

with SIP screws is recommended to optimize the correlation 

between single SIP screw lateral load strength and SIP 

diaphragm performance.

100

300

200

400

0.0 0.2 0.4 0.6 0.8

Specimen deflection (in.)

Applied load (lbf/screw)

1.0 1.2 1.4 1.6

600

500

700

900

1,000

0

800
Lateral Load Performance of Structural Insulated Panel (SIP) Diaphragms

17

Summary and Conclusions

Part A Diaphragms

Shear strength of SIP diaphragms alone can be reasonably 

estimated using single fastener lateral strength and the 

principles of engineering mechanics.

A difference between SIP diaphragms constructed with one 

segment and two segments could not be detected with the 

limited tests conducted in this study.

There was a positive correlation between ultimate deflection 

and number of SIP segments. Although a difference between 

one segment and two segments was not discernible, a 

significant increase in ultimate deflection was noted when 

the segment number was increased to four and six.

There did not appear to be an apparent impact on diaphragm 

shear strength with a change in the number of SIP segments.

Part B Diaphragms

Shear strength of SIP diaphragms connected to framing 

was underpredicted by 14% to 25% using single SIP screw 

lateral strength and the principles of engineering mechanics 

for screw spacing of 6 in. o.c. However, for screw spacing 

of 3 in. o.c., values were well-predicted on average.

Increasing the number of SIP screws from a spacing of 6 in. 

to 3 in. o.c. resulted in a 60% increase in the diaphragm 

shear strength. It is unclear why doubling the number of 

SIP screws did not double the diaphragm shear strength.

There did not appear to be an impact on diaphragm shear 

strength with a change in the number of SIP segments when 

SIPs were connected to framing.

Stiffness of SIP diaphragms can be correlated to the number 

of SIP segments used in the diaphragm. As the number of 

SIP segments increased, SIP diaphragm stiffness decreased.

Acknowledgments

This project is a cooperative effort between APA – The 

Engineered Wood Association; the USDA Forest Service, 

Forest Products Laboratory; and the Structural Insulated 

Panel Association (SIPA). This research is partially funded 

by the Forest Products Laboratory through the Coalition for 

Advanced Wood Structures (CAWS) (16-JV-11111133-039). 

CAWS brings together representatives from universities, 

industry, and government to work together in a cooperative, 

complementary manner to foster sustainable, efficient 

use of forest resources while improving the economy and 

performance of wood structures.

Literature Cited

APA. 2018. Standard for performance-rated structural 

insulated panels in wall applications. ANSI/APA PRS 610.1. 

Tacoma, WA: APA – The Engineered Wood Association.

ASTM. 2012. ASTM D1761-12. Standard test methods for 

mechanical fasteners in wood. West Conshohocken, PA: 

American Society for Testing and Materials International.

ASTM. 2016. ASTM E455-16. Standard test method 

for static load testing of framed floor or roof diaphragm 

constructions for buildings. West Conshohocken, PA: 

American Society for Testing and Materials International.

ASTM. 2017a. ASTM D7446-09. Standard specification 

for structural insulated panel (SIP) adhesives for laminating 

oriented strand board (OSB) to rigid cellular polystyrene 

thermal insulation core materials. West Conshohocken, PA: 

American Society for Testing and Materials International.

ASTM. 2017b. ASTM F1575-17. Standard test methods 

for determining bending yield moment of nails. West 

Conshohocken, PA: American Society for Testing and 

Materials International.

ASTM. 2018. ASTM C578-18. Standard specification 

for rigid, cellular polystyrene thermal insulation. West 

Conshohocken, PA: American Society for Testing and 

Materials International.

AWC. 2015. Special design provisions for wind and seismic. 

Leesburg, VA: American Wood Council.

AWC. 2018. National design specification for wood 

construction. Leesburg, VA: American Wood Council.

ISO/IEC. 2017. General requirements for the competence 

of testing and calibration laboratories. ISO/IEC 17025. 

3rd ed. Geneva, Switzerland: International Organization 

for Standardization and the International Electrotechnical 

Commission. 30 p.

Yeh, B.; Skaggs, T.; Wang, X.; Williamson, T. 2018. Lateral 

load performance of SIP walls with full bearing. Gen. Tech. 

Rep. FPL-GTR-251. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

23 p.