Life Safety

Wind Resistant Building Design

The lat­er­al (hor­i­zon­tal) and uplift forces caused by thun­der­storms, tor­na­does, and hur­ri­canes attack the integri­ty of build­ings and can dam­age struc­tures with fly­ing debris. A wind resis­tant build­ing design pro­tects a struc­ture by trans­fer­ring the lat­er­al forces that attack the walls and diaphragms (roof, floor, and shear walls) towards the foun­da­tion and ulti­mate­ly into the ground. Wind resis­tant design also pre­vents dam­age to the exte­ri­or of the build­ing from fly­ing debris.

A struc­ture’s abil­i­ty to resist lat­er­al and uplift loads depends on a build­ing hav­ing a con­tin­u­ous load path. A con­tin­u­ous load path uses wood, met­al con­nec­tors, fas­ten­ers and shear walls* to con­nect the roof, walls, floors and foun­da­tion. The con­tin­u­ous load path ensures that when a load or force attacks a build­ing, the load will move toward the foun­da­tion and into the ground. With­out a strong con­tin­u­ous load path that holds togeth­er the roof, walls, floors and foun­da­tion, a build­ing can fail or col­lapse dur­ing extreme winds.

Wind resis­tant build­ing must also con­sid­er the spe­cif­ic ele­ments along the con­tin­u­ous load path. The roof, walls, and floors must indi­vid­u­al­ly have the strength to han­dle all the ver­ti­cal and lat­er­al loads dur­ing severe weath­er. A wind resis­tant build­ing design will ensure the integri­ty of the build­ing, and the safe­ty of those inside, dur­ing hur­ri­canes, tor­na­dos and severe thun­der­storms.

Roof Construction of a Wind Resistant Building Design

Build­ing fail­ures dur­ing high-wind events often begin with dam­age to the roof. Shin­gles or tiles blow from the roof sheath­ing, the roof sheath­ing rips from the roof fram­ing, and the roof fram­ing tears from the sup­port­ing walls. A roof’s main func­tion in a con­tin­u­ous load path is as a hor­i­zon­tal diaphragm that trans­fers the loads imposed by heavy winds to the sup­port­ing walls below. The roof sheath­ing is the first struc­tur­al com­po­nent in the load path between the roof sys­tem and the foun­da­tion. The sheath­ing works in con­junc­tion with the roof fram­ing to trans­fer lat­er­al loads to the building’s shear walls. Accord­ing to FEMA’s Build­ing Fram­ing Sys­tems and Best Prac­tices, com­mon nails can be used to con­nect sheath­ing to sup­port­ing com­po­nents in regions where basic wind speeds are less than 100 mph. Ring-shank nails are required in high­er-wind regions. Wood nails are rec­om­mend­ed in the eaves and cor­ner zones of the roof, where winds can cre­ate large uplifts. Roof fram­ing is the next build­ing ele­ment found with­in the load path.The rafters of a roof’s frame must be sized to resist the weight of the roof sys­tem, and also the loads caused by wind and snow. The roof fram­ing must also trans­fer lat­er­al loads to the shear walls below. It is essen­tial in wind resis­tant roof design that the roof sheath­ing and fram­ing are con­struct­ed and sized for the poten­tial wind forces of the spe­cif­ic region.

Wall Construction of a Wind Resistant Building Design

Exte­ri­or walls of a build­ing must resist wind and pro­vide sta­bil­i­ty for the entire struc­ture. For a con­tin­u­ous load path design, the walls must be anchored to the foun­da­tion. Accord­ing to FEMA, in regions impact­ed by heavy, dan­ger­ous winds, walls con­struct­ed from rein­forced con­crete or con­crete mason­ry units (CMU) are com­mon. How­ev­er, con­crete and mason­ry walls lack the ther­mal per­for­mance required by the IRC and IBC, and typ­i­cal­ly need added insu­la­tion. A bet­ter option over con­crete and mason­ry walls are insu­lat­ed con­crete block wall sec­tions. Insu­lat­ed con­crete block wall sec­tions con­tain ther­mal and struc­tur­al fea­tures with­in a sin­gle, rein­forced con­crete-wall sec­tion. The Bau­tex Wall Sys­tem insu­lat­ed con­crete blocks have the ther­mal per­for­mance along with the strength to resist heavy winds. The Bau­tex Blocks also meet the Fed­er­al Emer­gency Man­age­ment Agency FEMA 320 and FEMA 361 guide­lines in storm zones with pos­si­ble wind speeds up to 250 miles per hour (Zone IV, south­east­ern states).

Fly­ing debris is also a threat dur­ing thun­der­storms, tor­na­does and hur­ri­canes. It can dam­age the exte­ri­or of a struc­ture, and injure the occu­pants of the build­ing. The Wind Engi­neer­ing Research Cen­ter at Texas Tech Uni­ver­si­ty recent­ly con­clud­ed that con­crete wall con­struc­tion is pre­ferred over frame walls for reduc­ing dam­age caused by fly­ing debris. The Bau­tex Block insu­lat­ed con­crete wall sys­tem has the strength and mass to resist the impact to wind dri­ven debris at speeds greater than 100 mph. Tests on the Bau­tex Blocks were done at the Wind Sci­ence and Engi­neer­ing Research Cen­ter Debris Impact Test Facil­i­ty and the Nation­al Wind Insti­tute at Texas Tech Uni­ver­si­ty in Lub­bock, Texas. The Blocks were test­ed for hor­i­zon­tal debris impact. The Bau­tex Blocks sin­gle con­crete inte­grat­ed assem­bly met or exceed­ed the FEMA stan­dards for debris impact**.

Floor Construction of a Wind Resistant Building Design

A building’s floor is a plat­form for the building’s occu­pants. The floor sys­tem is also part of the con­tin­u­ous path that trans­fers the loads to the shear walls in the sto­ries below or, in the case of the low­est floor, to the foun­da­tion. Floor fram­ing typ­i­cal­ly con­sists of dimen­sion­al lum­ber, or floor joists, span­ning an open space. Floor joists must be sized to resist the loads of the entire floor sys­tem along with ver­ti­cal loads. The floor of a wind resis­tant build­ing ensures the loads meet their final des­ig­na­tion — the ground.

A wind resis­tant build­ing design will guar­an­tee the integri­ty of the build­ing and the safe­ty of those inside dur­ing dan­ger­ous winds. A struc­ture’s abil­i­ty to resist lat­er­al and uplift loads depends on a build­ing hav­ing a con­tin­u­ous load path from it’s roof down to it’s foun­da­tion

*A shear wall is a struc­tur­al sys­tem com­posed of braced (shear) pan­els that counter the effects of lat­er­al load act­ing on a struc­ture

**Tests were con­duct­ed on Bau­tex Blocks in accor­dance with the debris impact guide­lines of FEMA P320/P361 (2015) and ICC-500 (2014) for hur­ri­canes and tor­na­dos. ICC-500 includes a hur­ri­cane build­ing enve­lope stan­dard that is required by Flori­da Build­ing Code and Texas Depart­ment of Insur­ance Wind­storm Resis­tant Con­struc­tion Guide.