Seismic Retrofitting Your Home

Seismic forces on your home

Earthquake forces can affect your home’s integrity in 3 ways [3]

Background: Earthquake Risk in Utah [1, 2]

The Wasatch Fault in Utah runs 240 miles from Southern Idaho (Malad City) to Central Utah (Fayette). It is classified as a normal, vertical motion fault divided into 10 segments. This fault is responsible for the uplifting of our beautiful Wasatch Mountains. The most active segments are located between Brigham City and Nephi, which are associated with the most densely populated areas in Utah. In Salt Lake City, the Fault line runs along 1300 East.

During the past 6000 yrs, a strong earthquake (magnitude greater than 6.5) has occurred approximately once every 350 yrs somewhere along one of the central segments of the Wasatch Fault. The segments that underlie Salt Lake City and Provo produce a large earthquake on average every 1300 yrs. Experts note that the fault is overdue for another major earthquake. “[1].   The last large earthquake experienced in Salt Lake City was more than 163 years ago [2]. The last earthquake associated with this fault in Utah occurred Friday, March 14, 2014 10:03:51 AM MDT 3.5 miles south of Francis, UT (UUSS Shake Maps at quake.utah.edu/shake/60059347/intensity.html).

“Urban areas along the Wasatch Fault lie on the soft lake bed of ancient Lake Bonneville and as such could face severe damage to gas, electric, water, communication and transportation in a major earthquake” [1]. When the major earthquake strikes, at least 42% of all buildings along the Wasatch Front could sustain moderate damage. Hospitals, schools and many unreinforced masonry building (~200,000), including residential homes are particularly vulnerable to violent shaking [1].

Earthquake forces can affect the integrity of your home in three ways [3]

  • Sliding:  house slides off foundation
  • Racking:  Cripple walls buckle and collapse
  • Overturning: House lifts off foundation

What can I do to protect people and my residential home?

Be Prepared for survival [4]
Residents need a minimum of 3 days of Food and water (1 gallon water/day/person). An accessory cooking source is beneficial. Turn off the gas supply (leaking gas causes major fires). Get a dedicated wrench for this purpose and place in a location that is easily accessible. Follow Questar recommendations [5].  Timeline: High density population areas get help first. Residential areas are last.

Assess the Risk of your home [3]

Factor Low Risk High Risk
Footprint Regular, symmetric Multiple additions
Height 1 story, no basement Multiple stories
Profile Simple box Towers, gables, parapets, etc
Foundation Reinforced concrete Rubble, fieldstone
Walls frame Pre and post 1900 masonry
Condition Well maintained deteriorated

Inspection Checklist [4] “the weak links to seismic safety”

  1. Foundation   Signs of settlement of movement. Cracks, sloped floors, leaning walls.  Loose mortar on brick or stone foundations, Deteriorating wood or water damage.  Downspouts dumping water near foundation and/or ground sloping towards foundation
  2. Walls and Columns   Rotted or undersized columns attached to basement floors.  Weak or undersized, unbraced walls or columns in open basement supporting a heavy solid portion of house. Tall, unbraced masonry parapets or gables. Wood studs without structural sheathing supporting the floors or walls above. Cracking in brick walls, spalled or missing mortar between bricks. Cracked, loose, spalled or missing bricks on exterior. Header bricks absent on multiple wythe masonry walls. Large openings in exterior walls. Additions to house not securely attached to hours or pulling away from foundation. Porch columns angled, shifting or unsecure to deck or roof.
  3. Floors and Ceilings   Bridging between joists poorly secured. Floor joists are simply resting on the foundation. Joists are substantially cut away to allow ductwork, wiring, or plumbing installation. Split, twisted, rotted joists.
  4. Roof  Rafters or trusses fastened to the load bearing exterior walls.  Roof decking composed of skip sheathing (gaps between boards) instead of Oriented strand board (OSB) or continuous plywood sheets. Heavy roofing materials such as slate or tiles. Unbraced masonry chimneys, parapet, or gables that are unreinforced or not secured to the roof or ceiling structure. Deteriorated mortar between bricks on the chimney.
  5. Historic and Interior Features   Cracked plaster (more than hairline or seasonal).  Tall furnishings unsecured to the wall. Hanging- or tall-light fixtures that could swing into walls or fall if they swing. Unsecured free-standing water heater to the building structure. Gas supply pipe to water heater is rigid, not flexible. Unsecured cabinet doors that could swing open. Unsecured valuables (knickknacks, computers, TVs) on open shelves.
  6. Site and Building History   Neighboring buildings with chimneys or other site features that could damage your house if they collapse. House damage by previous earthquakes. Heavy, repeated shaking of ground by heavy equipment use. Poor house maintenance over time

Remedies

The primary purpose of earthquake retrofitting is to keep your home from being displaced from its concrete foundation — making the building safer and less prone to major structural damage during an earthquake [3].

 Create a continuous load path to maximize safety first, then maximize saving house integrity second [4-8]

  1. Anchor roof to house URM (unreinforced masonry) walls.  Attach top plates (2 x 8 boards laid horizontally on top of house walls) by installing high-tensile strength helical pins (HELIFIX is one brand) through the 2” x 8” boards into the double-wythe masonry walls. Install two pins (one pin per wythe) to a depth of at least 12 inches into the bricks. Fold over 3-4 inches of remaining pin above the top plate at a right angle and secure with an electrical staple or other anchor. Install a pair of helical pins every 16 inches around the perimeter of the house. (This is in-lieu of the ¾ inch diameter anchor bolts set in epoxy recommended in most guides).  Use OSB or plywood sheathing to tie the ends of all the roof framing members (rafters, ceiling joists, top-and bearing-plates, etc) together at the top of the wall. Use metal framing anchors such as Simpson™ hurricane uplift anchors to further connect the rafters to sheathing). This item may add 20% of roofing cost to the overall project. Hire a general contractor to do this work and coordinate with their roofing sub-contractor
  2. Anchor rafter to rim board.  Attach floor framing to the concrete foundation and double-wythe brick walls with through bolts and steel angles OR use Simpson™ FJA (Floor Joist Anchor) to connect floor joists to foundation. Use wedge anchor bolts or epoxy anchors at concrete. Use epoxy anchors only at brick, block and stone masonry. Space anchors every 4 feet maximum around footprint.
  3. Create shear walls.  Install structural rated OSB or plywood over 2” x 4” wood framing on interior walls and nail at 4“ on the edge of the panels and 6“ in the centers. Connect the shear walls to the exterior masonry walls or concrete foundation walls with anchor bolts or Simpson™ connectors. Install blocking between floor or ceiling joists at the tops of shear walls and attach the shear walls to the blocking.
  4. Anchor chimney to roof with steel brace   Install steel straps around chimneys and tie back to the roof structure with diagonal steel braces [7]
  5. Anchor/brace water heater [8]   Tether gas-fired water heaters to concrete foundation walls or interior stud walls with steel straps or proprietary braces.  Install flexible tube connector to gas line.

Timeline Approach to Retrofitting

FEMA encourages phased approach-take advantage of scheduled house repair or remodeling projects to improve seismic retrofits, one project at a time.   Substantial retrofits may require professional assistance of a licensed engineer, architect or general contractor.  Words to the wise   Contact several firms. Evaluate their expertise with historic residential structures. Check references. Have a legal, clear contract. Get the required permits.

Earthquake Insurance

Insurance may be expensive. Retrofit your home first because it improves personal safety, then get insurance if desired. Insurance should cover the remaining mortgage on the house and allow some of the rebuilding. Can borrow additional money for rebuilding against the cost of the property lot, since it retains property value post-earthquake.

20% Utah state tax credit for rehabilitation of homes in a National Historic District

Utah state Tax Credit Program gives a 20% state tax credit of your expenses to retrofit, repair, replace infrastructure for a residential home on the National Historic Register. Yalecrest was listed on the NHR in 2007.  Obtain a State tax credit application from Utah Division of State History at http://heritage.utah.gov/history/state-tax-credit/attachment/historic-preservation-tax-credit-application-april-2013

Caveats to the 20% Utah state tax credit program

  1. The building use after rehabilitation must be residential.
  2. The building must be listed on the National Register of Historic Places at the time of application or within three years of the approval of the completed rehabilitation project.
  3. A minimum of $10,000 must be spent on rehabilitation over, at most, a three-year period.
  4. All work must meet appropriate rehabilitation standards; one “wrong” modification voids the entire tax credit.
  5. This application form must be completed before the rehab project is finished—preferably before work is started in order to avoid problems with ineligible work.

For more information, contact Nelson Knight, nwknight@utah.gov, Tax Credit Program, Utah Division of State History, 300 S Rio Grande St (450 West), Salt Lake City, UT 84101, Hours of Operation: Office 8:00 AM-5:00 PM, M-F, 801.245.7244.  Website at http://heritage.utah.gov/history/federal-tax-credit.

References and Sources

Expert Speaker, Don Hartley   Has lived in Yalecrest since 1995. He isaregistered architect with extensive experience in rehabilitating historic buildings. He has been employed as an Historical Architect with Utah Division of State History, Historic Preservation Department, since 1989. He was the project architect for Salt Lake City & County Bldg restoration using the seismic base isolation technology.

Contact information: Don Hartley, dhartley@utah.gov, Historic Preservation, Utah State Division of History, 333 S. Rio Grande St (450 West), Salt Lake City, UT 84101, Hours of operation: 8:00 AM-5:00 PM M-F, Office: 801.245.7240

  1. Wasatch Fault. en.wikipedia.org/wiki/Wasatch_fault
  2. For Information and reports about Utah’s earthquakes and their hazards from Utah Geological Society Web site: http://geology.utah.gov/utahgeo/hazards/eqfault/index.html
  3. Earthquake Safety at http://www.earthquakesafety.com/earthquake-retrofitting.html
  4. Bracing for the Big One: Seismic Retrofit of Historical Homes. By Utah Division of State History at http://heritage.utah.gov/hisotory/earthquake
  5. Advice about earthquake preparation. “Putting Down Roots in Earthquake Country” by Utah Seismic Safety Commission at http://ussc.utah.gov/putting_down_roots.html
  6. “Building a continuous load path” www.safesstronghome.com/protect/02.asp
  7. Structural upgrades for unreinforced masonry houses: “The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings” by Structural Engineers Association of Utah at www.seau.org
  8. Earthquake Preparedness and Natural Gas at http://www.questargas.com/brochures/59503.pdf.
  9. Retrofitting contractors  Home-Tech, Inc., 333 W Hope Ave, Salt Lake City, UT. 84115.  Contact: Michael Mahffey, T 801.484.9360, F 801.461.0110 at http://www.hometechincorporated.com

 

–Lynn Kennard Pershing, Ph.d.

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Yalecrest Doors

Have you seen these doors on your neighborhood walks? yalecrest doors 1

Where are they located?

Do you know its architecture style?

What type of entry door do you have? 

As I take my daily dogwalk in the Yalecrest neighborhood, I marvel at the beauty, craftsmanship and diversity of the original doors on our homes.  The character of the original front entry doors are intimately associated with the houses’ architecture.

Homes in Yalecrest are represented by Early 20th century residential types, which include Bungalows (1905-1925), Period Cottages (1910-1935), and CapeCod (1925-1945).

Within those building types are a variety of styles, which are characterized by architectural detail that adds to the basic form.  Bungalows include Arts and Crafts and Prairie School.  Period Cottage styles include Colonial Revival, Neoclassic, English Tudor, Period Cottages, French Norman, Spanish Colonial Revival and ModernClick here for more information

Bungalows (1905-1925) both Arts and Crafts and Prairie School styles are characterized by a wood framed, one story (sometimes two) home, with a low-pitched roof containing partially exposed framing wood members in its gable ends and decorative motifs.  A Bungalow home often accentuates the texture of its material and features abstract patterns in stained and leaded glass.  The local architect Taylor Woolley, who apprenticed with Frank Lloyd Wright in the Oak Park, Illinois studio is associated with many of the finest examples of this architectural style in Utah and  we have some in Yalecrest! The front entry doors associated with this building style are often constructed wider than a traditional front exterior door and are made with solid oak with decorative art glass inserts or side panels.  See examples

Period Cottage Revivals

Colonial Revival (1890-1940) is influenced by Dutch (gambrel roof designs) and English (Georgian and Federal periods of the 18th and early 19th centuries) designs.  The Cape Cod cottage is a subtype of the Colonial Revival built during the 1930’s.   Colonial revival styled homes have hip, gable or gambrel roofs, with symmetrical front facades, porches, with shingles, wood siding or brick surfaces, bay windows, side and transom lights around the front entry, and broken, segmental pediments.  See examples

Neoclassical (1900-1925) has uninterrupted cornice and /or pedimented porticos and symmetrical front facades.  Doors associated with this architecure are often paneled and have glass transoms above and to the sides of the front entry door.  See examples

English Tudor (1915-1935) is characterized by an asymmetrical façade and timber-frame architectural detail (stucco wall panels with exposed wood framing members).  English Tudors have a picturesque irregular massing, a variety of window shapes, diamond-pane and/or bottle-glass lights, tall casement windows, clay chimney pots, and a steeply pitched gable roof.  Doors associated with this style are often a single piece of quarter-sawn oak (sometimes walnut) with or without small art glass inserts and with or without wrought iron details.  See examples

English Cottage (1920-1940) is characterized by an all brick exterior without the timber frame architectural detail of English Tudor, but is similar in all other aspects.  English Cottages are typically smaller than English Tudors but have a picuresque irregular massing, a variety of window shapes and steeply pitched gable roof.  Doors associated with this style are either rectangular or rectangular with curved heads.  They are constructed from Douglas fir, quarter-sawn oak wood from either a single piece of wood or multiple conjoined linear planks with a window insert of diamond-pane, art glass or large circular glass.  See examples

Spanish Colonial Revival (1915-1935) is based on the architectural styles of Mexico and are characterized by red tile roofs, white stucco-covered wall surfaces with low relief ornament, decorative cornices and parapets, wrought iron grills and balconies. Doors associated with the Spanish Colonial Revival style are heavily paneled in oak with wrought iron detail.  See examples

French Norman (1915-1935) style was originally popularized by architect Richard Morris Hunt in the first 3 decades of the 21st century.  This style is loosely based on the vernacular of Normandy and Brittany.  Its design elements incorporates stone, brick and stucco with half-timbering and decorative brick patterns, wall dormers, steeply pitched slate roofs, and round towers with conical-shaped roofs.  The doors associated with French Norman Revival are often heavily paneled with wooden spindle inserts over a glass window.  See examples

Modern styles (1930-1940) are characterized by rounded edges or rectilinear corners, constructed in cement or stucco with butterfly or flat roofs and large glass windows with or without fenestrations.  Doors associated with this building style are typically flat rectilinear in shape without embellishment but occasionally contain a circular piece of glass.  See examples

—Lynn Kennard Pershing