Construction Guide on Strengthening Existing Houses in Hawaii Against Hurricanes and Earthquakes

by Civil Defense Division, Department of Defense, State of Hawaii, 1997
This document was funded by FEMA.
This portion is specifically for the island of Hawaii.

INTRODUCTION

The purpose of this guide is to provide information on methods to upgrade and strengthen their existing homes against earthquakes and/or hurricanes. Although an attempt was made to simplify this guide, unless you have some familiarity with construction, you may find it difficult to understand.

The information presented in this booklet is based on a simplified version of a typical residence of less than 1500 square feet in Hawaii. It is likely that your home is more complicated than shown here and that certain parts of its structural framing may be concealed. Important regulatory, architectural, plumbing, or electrical issues also need to be considered. As a result, you may need to consult with a qualified professional (such as an architect or engineer) in order to adapt the techniques illustrated in this guide to your particular situation. For an idea of construction cost, a licensed contractor with home renovation experience should be consulted.

Actual construction should proceed after a set of construction drawings is produced based on your home’s existing condition and site. You should not expect to be able to obtain a building permit based solely on the illustrated structural details presented in this guide.

Home Types Included

The types of homes considered in this guide are limited to homes of wood using construction methods and details felt to be common in Hawaii, and not necessarily characteristic of typical “mainland style” construction. You will find useful information in this guide if your home meets the following criteria:

• Number of Stories - limited to one and two story homes
• Wall Type - single or double wall construction
• Size - less than 1500 square feet under the roof
• Shape - rectangular floor plan
• Foundation Types - "tofu" block footings, concrete slab-on-grade and hollow tile (CMU) walls
• Roof types - hip and gable types with a maximum pitch of 4V:12H (4 vertical to 12 horizontal)
• Roofing Materials - pitch and gravel, asphalt shingles, wood shakes, sheet metal

Home Types Excluded

If your home is better described by the criteria below, this guide was not intended for your use. For help with your home, we recommend that you consult a licensed structural engineer. Also, this guide was not intended for new home construction.

• Wall Type - hollow block, metal stud
• Special Designs - split level, construction on a steep slope
• Building Dimensions - width exceeding 32 feet
• Roof Overhangs - roof overhangs exceed 3 feet
• Roofing Materials - monier tile, clay tile

A WORD ABOUT EARTHQUAKES

• Cause & Effect - During an earthquake, your home will tend to shake, tip, rock and try to slide off of its foundation.

• Building Code - The Uniform Building Code (UBC) first established seismic zones to differentiate seismic hazard. The higher the seismic zone, the higher the hazard. In Hawaii, earthquakes are related to volcanic activity and sea floor plate tectonic movement. Understandably, the Big Island is in the highest seismic zone while Kauai is in the lowest seismic zone.

A WORD ABOUT WIND

• Cause & Effect - During a hurricane, your home will also tend to shake, tip, rock and try to slide off of its foundation. In addition, high winds also cause strong uplift forces. These velocity-related forces are similar to the forces that generate lift on airplanes. These uplift forces will try to lift your roof off. It may even lift your whole house off of its foundation.

• Load Path - To keep your roof on your walls and your walls on your foundation, you will need to strap your roof to your walls and your walls to your foundation. This will form a continuous "load path" to resist uplift forces.

HOW TO USE THIS GUIDE

In Choosing the Upgrade - Consider the following:

• In Hawaii, hurricanes have caused much more damage to homes than earthquakes. Even though Kauai suffered the most damage from Hurricanes Iwa and Iniki, all of the islands are equally susceptible to hurricanes. Consider upgrading your home for wind although it will cost more than a seismic upgrade.
• If you upgrade your home for wind, your home will comply with the requirements of the earthquake upgrade for Zone 4. Thus if you upgrade for wind, you “kill two birds with one stone.”
• If you live on the Big Island, you should definitely consider at least upgrading your home to Zone 4. However, the seismic upgrade shown does not provide a complete load resistance for wind forces.
• If for financial or other reasons, you choose a seismic upgrade instead of a wind upgrade, it is possible to do the wind upgrade at a later date since many of the wind upgrade details are similar to the seismic upgrade details. However, it will involve less effort and be less costly if you can afford to do the wind upgrade initially.

About the Drawings

• There are many details in this guide. Depending on the type of your home construction, some will apply and some will not apply. The details are grouped in like sections; i.e. foundation details are grouped in one section and roof to wall connections are grouped in another section.
• At the beginning of each section is a list of items to be upgraded, an upgrade procedure, a visual key to upgrades and a list of drawings for that section. These should help you sort through the drawings and decide what you need to do.
• On a given sheet, the existing conditions are usually shown on the top or left. (The upgraded condition is usually shown on the bottom or right.)
• If you are confused about a particular detail, you may find it helpful to read the Sheet title and Comments at the bottom of the sheet.

CAUTION

• While some of the details included herein will not affect the general appearance of your home, other details will not only change its appearance but also will change its size and affect other areas as well.
• For example, if you have a single wall home and add wood studs to the inside of your existing walls, affected rooms will become smaller and some things that used to fit may no longer fit.
• On the other hand if you add studs to the outside of your existing walls, some exterior stairs may become narrower, some windows may need to be re-installed to the new exterior face and some portions of the structure may extend into required setback areas (which is not permitted).
• The consequences of your decision to upgrade and how you plan to solve them should be carefully considered before starting.

WARNINGS AND DISCLAIMER

The Construction Guide on Strengthening Existing Houses in Hawaii Against Hurricanes and Earthquakes makes no warranty of any kind, express or implied, Users of the Guide assume all risk and liability in connection with use of the Guide whether used singly or in combination with other information.

The specification of Simpson Products on some of the details should not be construed as an endorsement of the Simpson Strong-Tie Company. Simpson is recognized as an industry standard but other companies manufacture similar generic products. If a different brand is to be used, the substituted product should meet or exceed the strength rating of the Simpson product.

REFERENCES

Department of Commerce and Consumer Affairs, State of Hawaii, “Consumers, Contractors and Contracts”.

Department of Commerce and Consumer Affairs, State of Hawaii, “Acting as an Owner-Builder”

Items to be Upgraded for Earthquake Retrofits

I. Shear Walls
II. Foundation to Wall Connections
III. Wall to Floor Connections
IV. Roof Strengthening

Seizmic Zone 4 Upgrade

Upgrade Procedure

I. Shear Walls: The first step is to determine the length of shear walls required on each side of your home. Shear walls are needed to resist the lateral (horizontal) forces on the house due to an earthquake.

A. The tables on Drawing Numbers (DN) 1A & 2A will help determine the length of shear walls required for one and two story houses respectively. The required length depends on the overall plan dimensions of your house.

B. The minimum length requirement on a given side may be satisfied by one long wall section or the cumulative length of two or more wall sections provided that each wall section is not less than 4 feet long.

C. DN 1B & 2B illustrate how the plywood should be nailed to the studs, plates and headers.

D. DN 10A & 10B show typical stud & plate details used for wall framing.

Dwg. No. Sheet Description
1A Shear Wall Table - Single Story Dwelling
1B Typical Shear Wall Elevation - Single Story Dwelling
2A Shear Wall Table - Two Story Dwelling
2B Typical Shear Wall Elevation - Two Story Dwelling
10A Typical Stud Wall Framing Details
10B Typical Top Plate Details

II. Foundation to Wall Connections: In addition, shear walls must be connected properly to their foundations. Several different upgrade options are provided to the homeowner. Choose one of the following:

A. DN 3A-3G provide an upgrade for a single wall house on a "tofu" block foundation by adding studs interior to the existing walls connected to a new CMU wall foundation.

B. DN 4A-4G provide an upgrade for a single wall house on a "tofu" block foundation by adding studs exterior to the existing walls connected to a new CMU wall foundation.

C. DN 5A-5F provide an upgrade for a single wall house on a "tofu" block foundation by adding studs interior to the existing walls connected to cripple stud walls on a concrete foundation.

D. DN 6A-6F provide an upgrade for a single wall house on a "tofu" block foundation by adding studs exterior to the existing walls connected to cripple stud walls on a concrete foundation.
E. DN 7A provides an upgrade for a single wall house on an existing slab-on-grade foundation.

III. Wall to Floor Connection: Applies to existing two-story houses showing hold down connections.

DN 8A & 9A show upgrade for second floor single wall over existing double wall and CMU wall respectively.

Dwg. No. Sheet Description
8A Single Wall Upgrade on Existing CMU Wall
9A Single Wall Second Story Upgrade - Dble. Wall Below

IV. Roof Strengthening: A roof diaphragm is needed to distribute the lateral forces to the shear walls. Refer to DN 11A for details.

Dwg. No. Sheet Description
11A Plywood Roof Sheathing Nailing Details

Items to be Upgraded for Hurricane Retrofits

I. Shear Walls
II. Foundation to Wall Connections
III. Wall to Floor Connections
IV. Wall to Roof Connections
V. Roof Strengthening

Exposure C Upgrade

Upgrade Procedure

B. The minimum length requirements on a given side may be satisfied by one long wall section or the cumulative length of two or more wall sections provided each wall section is not less than 4 feet long.

C. DN 1B & 2B illustrate how the plywood should be nailed to the studs, plates and headers.

D. DN 13A, 13B & 13C show typical stud, plate and header details used for wall framing.

Dwg. No. Sheet Description
1A Shear Wall Table - Single Story Dwelling
1B Typical Shear Wall Elevation - Single Story Dwelling
2A Shear Wall Table - Two Story Dwelling
2B Typical Shear Wall Elevation - Two Story Dwelling
13A Typical Stud Wall Framing Details
13B Typical Top Plate Details
13C Typical Header Details

II. Foundation to Wall Connections: To resist uplift, walls must be anchored to their foundation. Several different upgrade options are provided to the homeowner. Choose one of the following:

A. DN 3A-3G provide an upgrade for a single wall house on a "tofu" block foundation by adding studs interior to the existing walls connected to a new CMU wall foundation.

Dwg. No. Sheet Description
3A "Tofu" Blk. Found. Upgrade w/ Studs Added to Interior Side
3B Typ. Intermediate Shear Wall Condo
3C Typ. Corner Shear Wall Condo.
3D Typ. Corner Shear Wall Condo
3E Upgrade w/ Inter. Studs, Plywd. Shthg. & Tie Strap
3F Angle Connecting 4x Beam to CMU Wall
3G Hold-down Connection to CMU Wall @ Ends of Shear Walls

B. DN 4A-4G provide an upgrade for a single wall house on a "tofu" block foundation by adding studs exterior to the existing walls connected to a new CMU wall foundation.

Dwg. No. Sheet Description
4A "Tofu" Blk. Found. Upgrade w/ Studs Added to Exterior Side
4B Typ. Intermediate Shear Wall Condo
4C Typ. Corner Shear Wall Condo
4D Typ. Corner Shear Wall Condo
4E Upgrade w/ Ext. Studs, Plywd. Shthg. & Tie Strap
4F Angle Connecting 4x Beam to CMU Wall
4G Hold-down Connection to CMU Wall @ Ends of Shear Walls

C. DN 5A-5F provide an upgrade for a single wall house on a "tofu" block foundation by adding studs interior to the existing walls connected to cripple stud walls on a concrete foundation.

Dwg. No. Sheet Description
5A "Tofu" Blk. Found. Upgrade w/ Studs Added to Interior Side
5B Typ. Intermediate Shear Wall Condo
5C Typ. Corner Shear Wall Condo
5D Typ. Corner Shear Wall Condo
5E Upgrade w/ Inter. Studs, Plywd. Shthg. & Tie Strap
5F Hold-down Connection to Cripple Wall

D. DN 6A-6F provide an upgrade for a single wall house on a "tofu" block foundation by adding studs exterior to the existing walls connected to cripple stud walls on a concrete foundation.

Dwg. No. Sheet Description
6A "Tofu" Blk. Found. Upgrade w/ Studs Added to Exterior Side
6B Typ. Intermediate Shear Wall Condo
6C Typ. Corner Shear Wall Condo
6D Typ. Corner Shear Wall Condo
6E Upgrade w/ Ext. Studs, Plywd. Shthg. & Tie Strap
6F Shear Connecting 4x Beam to Shear Wall

E. DN 7A provides an upgrade for a single wall house on an existing slab-on-grade foundation.

Dwg. No. Sheet Description
7A Single Wall Upgrade - Slab-an-Grade Foundation

III. Wall to Floor Connection: Applies to existing two-story houses showing continuous load path connections.

A. DN 8A & 9A show upgrade for second floor single walls over existing double wall and CMU wall respectively.

Dwg. No. Sheet Description
8A Single Wall Upgrade on Existing CMU Wall
9A Single Wall Second Story Upgrade - Dble. Wall Below

B. DN 10A & 10B show upgrade for second floor single walls over existing double wall and CMU wall respectively where the second floor cantilever over the first floor walls.

Dwg. No. Sheet Description
10A Single Wall Upgrade - Fir. Cantilevers Over Existing Dble. Wall Below
10B Single Wall Upgrade - Fir. Cantilevers Over Existing CMU Wall Below

IV. Wall to Roof Connections: Rafter and truss to wall connections required for the first link of the continuous load path.

A. DN 11A, 11B & 11C provide connections for shake, shingle or built-up roofs. Choose appropriate ON depending on whether studs are interior, exterior or existing.

B. DN 11D, 11E & 11F provide connections for metal roofs.

C. DN 11G provides a hip truss/rafter connection at wall corners.

Dwg. No. Sheet Description
11A Upgrade Roof to Wall Connections w/ lnter. Studs
11B Upgrade Roof to Wall Connections w/ Exter. Studs
11C Upgrade Roof to Wall Connections w Existing Studs
11D Upgrade Metal Roof to Wall Connections w/ lnter. Studs
11E Upgrade Metal Roof to Wall Connections w/ Exter. Studs
11F Upgrade 4x Ratter to Wall Connection
11G Hip Truss/Ratter Connection @ Wall Corner

V. Roof Strengthening: Wind damage is most severe at the roof level. Choose appropriate details to strengthen your roof.

Dwg. No. Sheet Description
12A Gable End Upgrade
12B Ridge Upgrade
12C Plywood Roof Sheathing Nailing Details
12D Hip Truss/Ratter Connection @ Supporting Truss

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