Wind Bracing

8/6/2019 Wind Bracing

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Wind Bracing 1 Last Updated: 8/22/08

WW II NN DD BB RR AA CCII NN GG Fairfax CountyVIRGINIA

L a n d D e v e l o p m e n t S e r v i c e sDepartment of Public Works and Environmental Services

Hours of Operation: Monday - Thursday: 8 a.m. to 4 p.m.Friday: 9:15 a.m. to 4 p.m.

Location: Herrity Building12055 Government Center ParkwayFairfax, VA 22035-5504Telephone: 703-222-0801TTY: 711

Visit us on the web at: w w w .fair fax coun t y.go v/ d pw es

This publication provides guidelines for complying with the wall bracing provisions of the 2006 VirginiaResidential Code so that your new house or addition can adequately resist wind load. These provisionsalso apply to the conversion of an existing deck into a sunroom or living space.

i n t h i s pub l i c a t i on :

WI ND LOAD BASICS ...........................................................................................1AMOUNTS & TYP ES OF BRACING .........................................................................4INTERMITTENT BRACING ....................................................................................6CONTINUOUS SHEATHIN G ................................................................................10BRACED WALL PAN EL CONNECTIONS AND SUPPORTS .......................................17PROPRI ETARY SYSTEMS ...................................................................................19ENGIN EERED DESIGN .......................................................................................20CONSTRUCTION DOCUMENTS ...........................................................................20FREQUENTLY A SKED QUESTIONS ......................................................................21

WI ND LOAD BASICS

WIND LOADAll buildings must be designed to resist wind load. Unlike snow and other vertical loads, wind load isunique in that it acts horizontally and in any direction. Therefore a building must be able to resist loadsacting parallel and perpendicular to any wall of a building.

The design wind load on a structure is basedon the local wind speed. For Fairfax County,the wind speed is 90 mph based on a 50-year storm measured in 3-second gusts at 33feet above the ground. While a 90 mphdesign wind speed might seem extreme, dueto the way it is measured, this only translatesto a weak Category 1 hurricane.

RESISTING WIND LOADAll structures must be designed to transferwind load from where it is applied to theground. For example, in a simple one-storyhouse, as shown in FIGURE 1, wind thatblows against the end wall causes the roof towant to move in the direction of the wind, butthe movement of the roof is resisted by thewall bracing in the side walls.

FIGURE 1: WI ND LOAD APP LIED TO A HOUSE




This process would be similar if the house had multiple floors. In such cases, the side walls of the firstfloor have the added responsibility to resist the forward movement of all the floors and the roof above.Since the walls of the first floor resist more load, they have stricter requirements for their design.

BRACED WALL PANELSAs shown in FIGURE 2, a typical wall will rackdue to wind load if no bracing is provided.When installed along a specified length of awall, bracing prevents this lateral

displacement, see FIGURE 3.

A braced wall panel is a sheathed unit of bracing that is placed in specified lengths andlocations along a wall. Each braced wallpanel must be sheathed for the full height of the wall, up to 12 feet; see FIGURE 4.

FIGURE 3: TYP ICAL WA LLWI TH BRACING FIGUR E 4: BRA CED

WALL PANELBRACED WALL LINES

Braced wall lines are designated"imaginary" straight lines you draw throughthe plan of a house or addition at each levelthat you will use to determine amounts andplacement of bracing.

In most cases, braced wall lines will belocated along all the exterior walls of thehouse or addition. However, braced walllines may need to run through the interiorof the house as the spacing between parallelbraced wall lines cannot exceed 50 feet. Forexample, in FIGURE 5, braced wall lines 1,3, 4 and 5 account for the exterior walls of the house, whereas braced wall line 2 islocated at the interior of the house if thedistance between braced wall lines 1 and 3exceeds 50 feet.

Braced wall lines must begin and end perpendicularly at other braced wall lines except as allowed in theangled wall requirements; see page 3. In FIGURE 5 notice that braced wall lines 1, 2 and 3 begin atbraced wall line 4 and end perpendicularly at braced wall line 5.

spacing must be 50' or less

FIGURE 5: BRACED WALL LI NES

length

wind

wind

FIGURE 2: RACKING DUE TO WI ND LOAD




Since there aren't too many simple rectangular houses built today, the code provides flexibility whendesignating a braced wall line. Wall segments of the house need not align with the designated braced wallline in order to assist in its resistance of the wind load. As shown in FIGURE 6, you may designate thelocation of your braced wall line (the dotted line) to maximize the total amount of wall segments that canbe included on it. However, there are limits. No single offset can be more than 4 feet from thedesignated braced wall line, and the total out-to-out dimension of all offsets can be no more than 8 feet.See FIGURE 6.

FIGURE 6: ALLOWABLE OFFSETS OF A BRACED WALL LI NE

As shown in FIGURE 7, you may even locate your braced wall line such that all wall segments are NOT inalignment with the designated location, but each segment must fall within the limits shown in FIGURE 6.

FIGURE 7: PLACEMENT OF A DESIGNATED BRACED WALL LI NE

ANGLED WALLSDesigners today usually design houses with angled walls and corners. That is why the code allows for thisdesign. Braced wall lines can angle out of plane for a maximum diagonal length of 8 feet. Where theangled wall occurs at a corner, the braced wall line is measured from the projected corner as shown inFIGURE 8. Where the diagonal length is greater than 8 feet, it must be considered its own braced wallline .

PROJECTED CORNER

NOTE: IF THE DIAGONAL WALL IS GREATERTHAN 8 FEET LONG, THEN IT MUST BE TREATEDAS A SEPARATE BRACED WALL LINE.

BRACED WALL LINE 1

FIGURE 8: DIAGONAL BRA CED WA LL LIN ES




BRACED WALL LINE LENGTHThe length of a braced wall line becomes animportant factor when analyzing its compliance.Therefore it is important to recognize where adesignated braced wall line begins and ends: at theintersections of the perpendicular braced wall linesat each end.

As shown in FIGURE 9, on the left side, braced wall

line 3 begins at the projected corner of the angledwall at braced wall line 1 and ends at itsintersection with braced wall line 2 to the right.Therefore, its length is the distance between thosetwo points.

Likewise, the length of braced wall line 2 ismeasured from the intersection of braced wall line3 to that of braced wall line 4. Notice, thisdimension is longer than the actual wall length of the house.

AMOUNTS AND TYP ES OF BRACING

LOCATION, SPACING AND AMOUNTS OF BRACINGBraced wall panels are required to be placed along a braced wall line and must meet three importantcriteria.

SPACING: A braced w all panel must be located at each end of a braced w all line or beginw ithin 12.5 feet of the end. See FIGUR E 10.

FIGURE 10: BRACED WALL PA NELS IN A BRACED WALL LI NE

LOCATION: In each braced wall line, braced wall panels can be a m aximum of 25 feet oncenter. See FI GURE 11.

FIGURE 11: SPACING OF BRACED WALL P ANELS IN A BRACED WALL LIN E

FIGURE 9: BRACED WA LL LIN E LENGTH




AMOUNT: A minimum percentage of a braced wall line's length must contain braced w allpanels.The determination of the minimum required percentage of bracing is based on wind speed (90 mph),floor, the maximum spacing to the next adjacent parallel braced wall line (see FIGURE 5) and thebracing material. Use TABLE 1 to determine the minimum required percentage of bracing required ina braced wall line. Bracing methods are listed in TABLE 2 and TABLE 3. To determine if your bracedwall line is in compliance, the actual percentage of bracing must be greater than the value found inTABLE 1.

TABLE 1: MIN IMUM REQUIRED PERCENTAGE OF WALL BRACINGMIN IMU M REQUIRED PERCENTAGE OF FULL-HEIGHT

BRACING PER WALL LINEBraced wall line spacing less

than or equal to 35'Braced wall line spacing greater than

35' and less than or equal to 50'

SEISMICDESIGN

CATEGORY(SDC) OR

WI ND SPEED

FLOOR

Methods WSP,CS-WSP, CS-G,

CS-PF

All othermethods a

Methods WSP,CS-WSP, CS-G,

CS-PF

All othermethods a

One-story houseor top floor of atwo- or three-story house.

16% 16% 23% 23%

First floor of atwo-story orsecond floor of a

three-storyhouse.

16% 25% 23% 36%SDC A, B

orwind speed

100 mph

First floor of athree-story house 25% 35% 36% 50%

a. For Method GB, the percentage required must be doubled for one-sided applications.

TYPES OF BRACINGThere are two types of bracing in the code, intermittent bracing and continuous sheathing.

Intermittent bracing: bracing material is placed at the braced wall panel locations only alongthe braced wall line. All other areas of the braced wall line can remain unsheathed or infilledwith foam or other nonstructural sheathing. See FIGURE 12.

FIGURE 12: INTERMI TTENT BRACING

Continuous sheathing: Bracing material is placed at the braced wall panels and on all otherareas including above doors and above and below windows. See FIGURE 13.

FIGURE 13: CONTINUOUS SHEATHIN G




INTERMITTENT BRACING

METHODSThe code identifies several unique intermittent bracing methods to construct a braced wall panel. Eachmethod has a specified material type, minimum material thickness and attachment criteria; see TABLE 2.Minimum panel lengths and heights are shown in TABLE 3.

TABLE 2: INTERMI TTENT BRACING METHODS

M ETH OD M ATERI AL MINIMUMTHICKNESS FIGURE CONNECTION CRITERIA

LIB Let-in-bracing

1x4 wood orapproved metalstraps at 45° to

60° angles

wood: 2-8d nails per studmetal: per manufacturer

DWBDiagonal woodboards at 24"

spacing

5 / 8"2-8d (2½" x 0.113") nails or

2 staples, 1¾" per stud

WSP Wood structuralpanel

3 / 8"

6d common (2"x0.113") nailsat 6" spacing (panel edges) and

at 12" spacing (intermediate supports) or16 ga. x 1- 3 / 4 staples:

at 3” spacing (panel edges) and6” spacing (intermediate supports)

SFBStructuralfiberboardsheathing

1 / 2" or 25 / 32 " for16" stud spacing

only

1½" galvanized roofing nails or8d common (2½"x0.131) nails

at 3" spacing (panel edges)at 6" spacing (intermediate supports)

GB Gypsum board 1 / 2"

Nails at 7" spacing at panel edges including topand bottom plates; for exterior sheathing nailsize, see Table R602.3(1); for interior gypsum

board nail size, see Table R702.3.5

PBS Particleboardsheathing

3 / 8" or 1 / 2" for 16"stud spacing only

1½" galvanized roofing nails or8d common (2½"x0.131) nails

at 3" spacing (panel edges)at 6" spacing (intermediate supports)

PCP Portlandcement plaster

See SectionR703.6

1 1 / 2 ", 11 gage, 7 / 16 " head nails at 16" spacing or7 / 16 ", 16 gage staples at 6" spacing

HPS Hardboardpanel siding

7 / 16 "

0.092" dia., 0.225" head nails with length toaccommodate 1½" penetration into studs at 4"

spacing (panel edges), at 8" spacing(intermediate supports)

ABW Alternatebraced wall

See FIGURE 14See FIGURE 14

May only be constructed on concrete.

IPF Intermittentportal frame See FIGURE 15See FIGURE 15

May only be constructed on concrete.

All codes sections above reference the 2006 Virginia Residential Code.




PANEL LENGTHSPanel lengths and heights are shown in TABLE 3. Only panels greater than or equal to the lengths perTABLE 3 can contribute to the minimum percentage of bracing from TABLE 1 (Criteria 3).

TABLE 3: MIN IMUM LENGTH OF INTERMI TTENT BRACED WALL P ANELS a,b

HEIGHT OF INTERMI TTENTBRACED WALL P ANELBRACING

METHOD FLOOR

8' 9' 10' 11' 12'

DWB, WSP,SFB, PBS,PCP, HPS

All 48" 48" 48" 53" 58"

GB-two sided All 48" 48" 48" 53" 58"

GB-one sided All 96" 96" 96" 106" 116"

ABW All 28" 32" 34" 38" 42"

One-story house 16" 16" 16" 18" 20"

IPFFirst floor of a

two-story house 24" 24" 24" 27" 29"

a. Interpolation is permitted.

b. When determining compliance with the percentage of bracing required by TABLE 1 , the length of Method LIB isequivalent to 48".

PARTIAL CREDITWhen using intermittent bracing Methods DWB, WSP, SFB, PBS, PCP and HPS, a panel with a length lessthan 48 inches can partially contribute to the required percentage of bracing from TABLE 1. Use TABLE 4below to determine the contributing length for panels between 36 inches and 48 inches. Any panel lessthan 36 inches cannot contribute. For example, if you had a 42-inch panel, you can only contribute 36inches towards the percentage of bracing required.

TABLE 4: PARTIAL CREDIT LENGTHS FOR BRACE WALL P ANELS a

WALL HEIGHTACTUAL LENGTH OFBRACED WA LL

PANEL 8' 9'

48" 48" 48"42" 36" 36"

36" 27" N/Aa. Interpolation is permitted.

MIXING INTERMITTENT METHODSMixing intermittent methods within a braced wall line is permitted. However, when calculating minimumrequired percentage noted in TABLE 1, the method with the greater shall value govern.




1/2" DIA. ANCHORBOLTS BETWEEN 6"AND 12" FROM EACHEND OF PANEL

8d COMMON OR GALV.BOX NAILS @ 12" O.C. ATINTERIOR SUPPORTS

8d COMMON OR GALV. BOXNAILS @ 4" O.C. AT PANEL

EDGES

FOR A PANEL SPLICE (IFNEEDED), PANEL EDGES SHALLBE BLOCKED. ONE ROW OFTYP. SHEATHING-TO-FRAMINGNAILING IS REQUIRED

2X4 FRAMING,MINIMUM DOUBLESTUDS REQUIRED

#4 TOP AND BOTTOM

HOLD-DOWNDEVICE ON EACHSIDE WITH AMINIMUMCAPACITY OF3600 LBS

MIN. 3/8" THICKWOOD STRUCTURALPANELS ON ONEFACE

STUDS UNDERHEADER ASREQUIRED

12" X 12"MINIMUMFOOTING SIZE

PANEL LENGTHSPECIFIED BY

TABLE 3

FIGUR E 14: METHOD AB W

FIGURE 15: METHOD IP FPlease note: Method IPF is not commonly constructed in Fairfax County and

should not to be confused with Method CS-PF; see page 11 for more information.

SEE TABLE 3

HEIGHTSPECIFIED

BYTABLE 3




EXAMP LE 1: How to evaluate compliance of a braced w all line w ith intermittent bracing.1. Determine braced wall panel method(s).2. Determine length of braced wall line and maximum spacing to the next adjacent parallel braced

wall line.3. Determine which floor the braced wall line is located on.4. Based on the above information, choose the highest percentage of bracing for the bracing

method(s) required from TABLE 1.5. Compute the actual percent bracing. Only panels greater than or equal to the lengths per TABLE 3

can contribute.

Actual percent of bracing = sum of all panel lengths (in inches) x 100length of braced wall line (in feet) x 12

6. Compare percentages; ensure the actual percentage is greater than the percentage required fromStep 4.

7. Ensure panels are located at each end of the braced wall line or begin within 12.5 feet from the endand are spaced no more than 25 feet on center.

For example: Using the 35-foot long braced wall line and bracing material shown below, for the first

floor of a three-story house where the next adjacent parallel braced wall line is 25 feetaway, determine if the braced wall line is in compliance.

1. Determine methods: Panel 1 is Method WSP and Panel 2 is Method SFB.2. The length of the braced wall line is 35 feet and the spacing to the next adjacent parallel braced

wall line is 25 feet.3. This is the first floor of a three-story house.4. Using TABLE 1, the highest percent bracing is for Method SFB (all other methods) and equal to 35

percent.

5. & 6. Panels 1 and 2 are greater than or equal to 48 inches, therefore both can contribute.Compute actual percent bracing:

% bracing = 48 + 108 x 100 = 37.1% > 35% (required %)35 x 12

7. For this 35-foot wall, the 48-inch panel is located at one end of the braced wall line and the 108-inch panel begins within 12.5 feet from the other end. The spacing between the centerlines of each panel is less than 25 feet. Braced wall line complies!

window

108"

35'

48"

door

10'20'-6"

Panel 2:1 / 2" fiberboard

Panel 1:7 / 16 " OSB




CONTINUOUS SHEATHIN GContinuous sheathing is the second bracing type prescribed by the code to resist wind load. Continuoussheathing requires you to sheath all areas of a braced wall line , including the areas above doors andabove and below windows. In return, you are able to reduce the length of the braced wall panels to aslow as 24 inches. As identified in TABLE 5, there are three continuous sheathing methods.

TABLE 5: CONTIN UOUS SHEATHI NG METHODS

METHOD MATERIALMINIMUM

THICKNESS FIGURE CONNECTION CRITERIA

CS-WSPWood

Structuralpanel

3 / 8"

6d common (2"x0.113") nailsat 6" spacing (panel edges) and

at 12" spacing (intermediate supports) or16 ga. x 1- 3 / 4 staples:

at 3” spacing (panel edges) and6” spacing (intermediate supports)

CS-G a

Wood structural paneladjacent garage

opening supportingroof load only

3 / 8" See Method CS-WSP

CS-PF b Continuous portalframe

3 / 8" See Page 11

a. Applies to one wall of a garage only.b. The number of continuous portal frame panels in a braced wall line cannot exceed four. Continuous portal frame panels

cannot be stacked vertically in multi-story buildings.

PANEL LENGTHSFor Method CS-WSP, the length of a braced wall panel is based on the wall height and the clear height of the opening adjacent to the panel. Use FIGURE 16 and TABLE 6 to determine your panel length. Forexample, a panel adjacent a 76 inch window opening in a 10 foot high wall must have a minimum lengthof 30 inches.

When a panel has an opening on each side of differing heights, the taller opening governs the panel lengthchosen from TABLE 6. Any panels less than the lengths determined from TABLE 6 are NOT consideredbraced wall panels, but by definition of continuous sheathing, must still be sheathed.

For Methods CS-G and CS-PF, the panel length is independent of the adjacent opening height; see TABLE6 for the required lengths.

FIGURE 16: BRACED WALL PAN ELS FOR CONTINUOUS SHEATHIN G

panellength

panel

25'

panel panel

25'

panellength

panellength




TABLE 6: LENGTH REQUIREM ENTS FOR CONTINUOUS SHEATHING M ETHODSWALL HEIGHT

MethodADJACENT

CLEAR OPENI NGHEIGHT 8' 9' 10' 11' 12'

64" 24" 27" 30" 33" 36"

68" 26" 27" 30" 33" 36"72" 28" 27" 30" 33" 36"

76" 29" 30" 30" 33" 36"

80" 31" 33" 30" 33" 36"

84" 35" 36" 33" 36" 36"88" 39" 39" 36" 38" 36"

92" 44" 42" 39" 41" 36"

96" 48" 45" 42" 43" 39"

100" 48" 45" 47" 42"

104" 51" 48" 48" 44"108" 54" 51" 51" 47"

112" 54" 53" 50"

116" 57" 56" 53"

120" 60" 58" 55"

124" 61" 58"

128" 63" 61"

132" 66" 64"136" 66"

140" 69"

CS-WSP

144" 72"

CS-G N/A 24" 27" 30" 33" 36"

CS-PF N/A 16" 18" 20" 22" 24"

METHOD CS-PFWhile similar to Method IPF, Method CS-PF, formally known as the "APA method," can be constructed onconcrete without cast-in-place hold-down devices. Method CS-PF is even approved for use on a raisedwood floor. The benefit to using a portal frame is that it is possible to construct a braced wall panel with alength as low as 16 inches. However, the downside of this desirable dimension is that construction of theportal frame is complex. As shown in FIGURE 17 and FIGURE 18, the connections of the studs, headerand sheathing is quite rigid; this is done in order to limit the amount of movement the portal will seewhen encountering wind load.

FIGURE 17: METHOD CS-PF CONN ECTIONS




FIGURE 18: METHOD CS-PF: CONTINUOUS PORTAL FRAME BRACED WALL P ANELS a

a. All codes sections above reference the 2006 Virginia Residential Code.

6

6




Portal frames can be constructed as a single portal or double portal. A single portal includes the bracedwall panel and header above spanning over the opening to a jack stud. A double portal includes a bracedwall panel at each side of the opening with a continuous header spacing over each panel. See FIGURE 19.

While Method CS-PF can be used on any floor beside any opening, they are commonly used in braced walllines that contain multiple garage door openings. Single and double portals can be used together to framenumerous openings and still comply with wall bracing requirements. See FIGURE 20 for some examples.

single double

FIGURE 19: SINGLE AN D DOUBLE PORTALS

two single portals one single and one double portal

three single portals

FIGURE 20: OPTI ONS FOR GARAGE DOOR OPENIN GS

BEWARE! The most common error in constructing a portal frame is failing to extend the header over thebraced wall panel; see FIGURE 21. There is no fix for this error and Fairfax County will not acceptblocking or an "engineered" solution since the portal frame is a tested assembly.

FIGURE 21: PORTAL FR AMEHEADER REQUIREMENTS

optionalfalsewall




CORNER FRAMINGCorners of braced wall lines with continuous sheathing must be framed as shown in FIGURE 22.

gypsum wall board as required andinstalled in accordance with Chapter 7

8d common nails (0.131" x 2-1/2")@ 6" o.c. on all panels' edges

(c) Garage door corner

(b) Inside corner detail(a) Outside corner detail

8d common (0.131" x2-1/2") @ 6" o.c. on allpanel edges

16d nail (0.131" x 3-1/2")2 rows @ 24" o.c.

optional blocking forgypsum wall board

8d common nail (0.131" x2-1/2") @ 3" o.c. on bothstuds at each panel edge

minimum 24" woodstructural panel sheathing

braced wall line withcontinuous sheathing

optional non-structuralfiller panel

orientation of studsmay vary; see FigureR602.3(2)

16d nail (0.131" x3-1/2") @ 12" o.c.



gypsum wall board as requiredand installed in accordance withChapter 7

orientation of studs mayvary; see Figure R602.3(2)

8d common nails (0.131" x2-1/2") at 6" o.c., on allpanels' edges

minimum 24" woodstructural panelsheathing


optional non-structuralfiller panel

8d common nails (0.131"x 2-1/2") @ 6" o.c. on allpanels' edges

8d common (0.131" x2-1/2") @ 6" o.c. on allpanel edges

16d nail (0.131" x3-1/2") @ 12" o.c.

8d common (0.131" x 2-1/2")@ 12" o.c. on all intermediatesupports

8d common (0.131" x2-1/2") @ 12" o.c. on allintermediate supports

8d common (0.131" x 2-1/2") typical @ 6"o.c. at panel edges and @ 12" o.c. on allintermediate supports


FIGURE 22: CORNER FRAMI NG REQUIREMENTS FOR CONTINUOUS SHEATHING a

a. All codes sections above reference the 2006 Virginia Residential Code.

CORNER PANELSEach end of a braced wall line with continuoussheathing must have a 24-inch panel on bothsides of a corner: a return panel and an end

panel; see FIGURE 23.

In many cases, the end panel will also be abraced wall panel. This panel is called Option1; see FIGURE 24(a). Option 2 allows theelimination of the return panel provided an800 pound hold-down device is providedinstead. See FIGURE 24(b).

FIGURE 23: TYP ICAL CORNER PAN ELS




Option 3 allows the first braced wall panel to begin 12.5 feet from the end of the braced wall line;however, the 24-inch end and return panels must still be provided. See FIGURE 24(c).

Option 4 allows for the first braced wall panel to begin 12.5 feet from the end of the braced wall line andfor the elimination of both the corner panels. In their place an 800-pound hold-down must be provided atthe location of the first panel. See FIGURE 24(d).

800 lbshold- down

braced wall line with continuous sheathing(all framed portions of wall are sheathed)corner detail per Figure 22

braced wall line with continuous sheathing(all framed portions of wall are sheathed)

end panel is alsobraced wall panel (24"minimum)

braced wall panelwithin braced wallline

end panel is alsobraced wall panel (24"minimum)

braced wall panelwithin braced wallline

(a) Option 1: end and return panels provided; endpanel is also braced wall panel

(b) Option 2: hold-down device provided; end panel is alsobraced wall panel

minimum

24" returnpanel

braced wall panelwithin braced wall line

12'-6" max.

corner detail per Figure 22

braced wall line with continuous sheathing

minimum 24"end and returnpanels

(all framed portions of wall are sheathed)

12'-6" max.

800 lbs hold-down device

(all framed portions of wall are sheathed)braced wall line with continuous sheathing

braced wall panel upto 12'-6" from end ofbraced wall line

(c) Option 3: end and return panels provided; firstbraced wall panel begins up to 12.5' from end

(d) Option 4: hold-down device provided; first braced wallpanel begins up to 12.5' from end

braced wall panel > 24"and up to 12'-6" from endof braced wall line

FIGURE 24: END PAN EL AND CORNER RETURN PAN EL REQUIREMENTS




EXAMP LE 2: How to evaluate compliance of a braced w all line w ith continuous sheathing.1. Determine braced wall panel method(s).2. Determine length of braced wall line and maximum spacing to the next adjacent parallel braced wall

line.3. Determine which floor the braced wall line is located on.4. Based on above, choose the percentage of bracing for the bracing method(s) required from TABLE 1.5. Evaluate the length of each full height panel to determine if the panel qualifies as a braced wall panel

based on the lengths from TABLE 6.6. Compute actual percentage of bracing, as follows:

Actual percent of bracing = sum of all panels lengths (in inches) x 100length of braced w all line (in feet) x 12

7. Compare percentages; ensure the actual percentage is greater than the minimum percentage requiredfrom Step 4.

8. Ensure panels are located at each end of the braced wall line or within 12.5 feet with the appropriatecorner return panels and/or tie-down devices and are spaced no more than 25 feet on center.

For example: Determine compliance of the braced wall line fully sheathed with 7 / 16 inch OSB shownbelow for a one-story house with a 20-foot spacing between braced wall lines. Assumethere are 24-inch return panels at each end.

1. The method is CS-WSP.2. The length of the braced wall line is 50 feet and the spacing is 20 feet.3. This is a one-story house.4. Using TABLE 1, the required percentage bracing required is 16 percent.5. From left to right, evaluate each panel:

Panel 1 is adjacent an 80 inch opening and per TABLE 6 must have a length of at least 31 inches.Actual length is 34 inches. This panel can contribute.Panel 2 is adjacent an 80 inch opening and a 64 inch opening, but the taller opening governs.Therefore the panel must be at least 31 inches. The actual length is 24 inches. This panelCANNOT contribute!Panel 3 is adjacent 2-64 inch openings and must have a length of at least 24 inches. Actual length is24 inches. This panel can contribute.Panel 4 is adjacent a 64" opening and has a length of 24 inches. This panel can contribute.

6. & 7. Compute actual percent of bracing:

% actual bracing = 34 + 24 + 24 x 100 = 13.67% < 16% (required percentage)50 x 12

Braced wall line FAILS!

34"

50'

24"door window 1

Panel1

Panel2

Panel3

Panel4

24"24" window 1

24'-7" 23'




MIXI NG METHODSIn addition to being able to mix intermittent methods within the same braced wall line, mixing continuoussheathing methods on the same braced wall line, mixing methods per floor and mixing methods perbraced wall line is permitted. However, you must analyze each braced wall line separately and ensureeach method’s requirements are met. Look for return panels, hold-downs, etc. Pleas e note: you maynot mix intermittent and continuous sheathing methods in the same braced w all line.

HORIZONTAL BLOCKINGFor intermittent bracing and continuous sheathing, when bracing materialis installed to construct a braced wall panel such that a horizontal spliceoccurs between the sheathing material, blocking is required. Verticalsplices must occur at stud locations. See FIGURE 25.

Blocking must be equal to the adjacent stud size. Sheathing must beedge nailed at all joints in accordance with the connection criteria of TABLE 2 and TABLE 5.

Any horizontal splice in sheathing for Methods IPF or CS-PF must occurwithin 24 inches of the mid-height of the portal braced wall panel.

Blocking is not required when the amount of bracing provided in a bracedwall line is at least double that required by TABLE 1.

INTERIOR FINISHESAll braced wall panels must have 1 / 2 -inch minimum gypsum wall board or equivalent installed on the sideof the wall opposite the bracing material. This requirement does not apply to intermittent Methods GB,ABW and IPF and continuous sheathing Method CS-PF. This requirement may be ignored when theamount of bracing provided in a braced wall line is at least 1.5 times that required in TABLE 1.

BRACED WALL PA NEL CONNECTIONS AND SUPPORT

Braced wall panels must be attached and/or supported as noted below.Where framing is perpendicular to a braced wall panel, a rim joist or blocking must be providedalong the length of the braced wall panel as shown in FIGURE 26.

Where framing is parallel to a braced all panel, a rim joist, framing member or blocking must beprovided along the length of the braced wall panel as shown in FIGURE 27.

When a braced wall panel with a length up to 48 inches is supported by a masonry stemwall,the masonry must be reinforced per FIGURE 28.

Elevated post or pier foundations supporting braced wall panels must be designed by aregistered design professional. See Engineered Design on page 20 for more information.

FI GURE 25: HORI ZONTALBLOCKING




FULL HEIGHT BLOCKINGCONTINUOUS ALONG LENGTH

OF BRACED WALL PANEL

FULL HEIGHT BLOCKINGCONTINUOUS ALONG LENGTHOF BRACED WALL PANEL

PERPENDICULAR FRAMING

PERPENDICULAR FRAMING

8d @ 6" O.C. ALONGBRACED WALL PANEL

BRACED WALL PANEL

3-16d @ 16" O.C. ALONGBRACED WALL PANEL


BRACED WALL PANEL


CONTINUOUSRIM JOIST

CONTINUOUSRIM JOIST

FIGURE 26: BRACED WALL PAN EL CONNECTION W HENPERPENDICULAR TO FLOOR/ CEILING FRAMIN G

ADDITIONAL FRAMINGMEMBER DIRECTLY BELOWBRACED WALL PANEL

ADDITIONAL FRAMINGMEMBER DIRECTLY ABOVEBRACED WALL PANEL

FULL HEIGHT BLOCKING@ 16" O.C. ALONGBRACED WALL PANEL

BRACED WALL PANEL

CONTINUOUS RIMOR END JOIST

CONTINUOUS RIM OREND JOIST

FULL HEIGHTBLOCKING @ 16" O.C.

ALONG BRACED WALLPANEL



BRACED WALL PANEL



TOE NAIL 3-8dNAILS AT EACHBLOCKINGMEMBER

3-16d AT EACHBLOCKING MEMBER

BRACED WALL PANEL

2-16d NAILSEACH SIDE

FIGURE 27: BRACED WALL PAN EL CONNECTION W HENPARALLEL TO FLOOR/ CEILING FRAMING




OPTIONAL STEM WALL REINFORCEMENT

TALL STEM WALL REINFORCEMENTSHORT STEM WALL REINFORCEMENT

3" COVER

20" MIN. TYP.3" COVER3" COVER

BRACED WALL PANEL

MIN. 2" CUT WASHERS

BOND BEAM WITH 1-#4 BAR

#4 BAR

BOND BEAM

1/2" ANCHOR BOLTS PERBRACED WALL PANELREQUIREMENTS

BRACED WALL PANEL

20" MIN. TYP.

#4 BAR MIN.; FIELD BEND 6"EXTENSION INTO BOND BEAM

BOND BEAM WITH 1-#4 BAR

5/8" THREADED RODS MAY BESUBSTITUTED FOR ANCHORBOLTS AND REBAR

1/2" ANCHOR BOLTS PER BRACEDWALL PANEL REQUIREMENTS

#4 BAR

BRACED WALL PANEL

8" MIN. CMUFACE BRICKOPTIONAL

TYPICAL STEM WALL SECTION

BRACED WALLPANEL

BOND BEAM

NOTE: GROUT BOND BEAMS AND ALL CELLS WHICH CONTAINREBAR, THREADED RODS AND ANCHOR BOLTS.

48" OR LESS

48" OR LESS

48" OR LESS

FIGURE 28: MASONRY STEM W ALLS SUPPORTIN G BRACED WALL PA NELS

PROPRIETARY SYSTEMSProprietary systems are pre-designed, pre-manufactured panels that can be used to resist wind load.Acceptable products in Fairfax County are those listed by a testing agency with a code evaluation report inaccordance with International Code Council-Evaluation Service (ICC-ES) Acceptance Criteria.

The ICC-ES itself currently has several products listed. Go to www.icc-es.org to obtain product evaluationreports which will list manufacturer contact information, limitations for use and design loads. Reportsmust be included with your plan submission during the permit application process. Proprietary systemsmust be installed in strict conformance with the manufacturer's recommendations and the evaluationreport.




Listed below are some of the available proprietary products.

TABLE 7: PROP RIETARY SYSTEMSAvailable Lengths

ProductICC-ES

EvaluationReport # As a P ortal Frame As a Braced Wall

PanelSimpson Strong Tie Steel Strong Wall 1 ESR-1679 12", 15", 18", 21", 24" 12", 15", 18", 21", 24"

Simpson Strong Tie Shear Wall PFC-5485 16", 22" 18", 24", 32", 48"

Weyerhaeuser iLevel TJ Shear Panel ESR-1281 16", 22" 18", 24", 32", 48"

Weyerhaeuser iLevel Shear Brace ESR-2632 12", 18" 12", 18"

Hardy Panels 1 PFC-5342 12", 18", 24" 12", 18", 24"1 Panels can be stacked for two-story walls; restrictions apply. See manufacturers' literature for more information.2 Fairfax County does not endorse any of the products listed above.

ENGIN EERED DESIGNIf you wish to deviate from the prescriptive code requirements, then you must have your wall bracingdesigned by a registered design professional licensed in the commonwealth of Virginia.

Determine wind load using Section 1609 of the 2006 International Building Code. The basic wind speed forFairfax County is 90 mph. Most residential construction in Fairfax County qualifies as Exposure B with anImportance Factor ( I w) of 1.00. Please note: wind load must be applied to both windward andleeward sides simultaneously.

DESIGN METHOD AND CALCULATIONSSection 2305, "General Design Requirements for Lateral-Force-Resisting Systems," and acceptedengineering practice shall be employed in the design professional's calculations. Calculations, at aminimum, must:

Show a detailed analysis of the wind load determination.Show a detailed design of the building diaphragms (Section 2305.2) and shear walls (Section2305.3).Specify the sheathing thickness, nail sizes and nailing pattern for diaphragms and shear walls.Ensure there is an adequate load path to the foundation.Show a detailed analysis of all connections along the lateral load path.Show an analysis of the existing lateral load resisting system with the new applied loads whenutilizing an existing structure to resist lateral loads of an addition.Ensure post-to-beam connections are capable of resisting shear and rotation.Bear the original signature and seal of the registered design professional.

Calculations which do not meet the above requirements w ill not be approved by Building PlanReview during the permit application process.

CONSTRUCTION DOCUMENTSAll plans submitted to the county for permit application and plan review must have all braced wall lines,braced wall panels and method(s) clearly identified. Plans will not be approved otherwise.

When submitting plans for a building that utilizes a proprietary product or an engineered design, therelated evaluation report and/or calculations must be attached to the plans. The drawings must alsoinclude comprehensive details outlining the construction requirements of the diaphragms and shear walls.These detail sheets must also bear the original signature and seal of the responsible registered designprofessional.




FAQS: FREQUENTL Y A SKED QUESTION S

There have been no major catastrophic events in Fairfax County due to wind. What hasprompted theses new w ind bracing requirements?One driving force for wind bracing provisions has been the insurance industry who's involvement inbuilding code development intensified after Hurricane Andrew in 1992 and the Northridge Earthquake in1994. While Fairfax County has not recently experienced a widespread and devastating wind event, thecode requires all residential construction to be designed to resist the potential for such events. A

jurisdiction's probability for wind events is based on its proximity to the coastline and/or other high windregions. Hurricane Isabel in 2003, and the tornados from Hurricane Ivan in 2004 are just a few remindersof the potential in Fairfax County for high winds.

Does Section R602.10 apply to sunrooms an d cold-formed steel construction?No. Section R602.10 applies only to light framed wood construction. Sunrooms constructed of aluminumor steel and any house or addition construction using cold-formed steel requires an engineered solution.

What does the county expect to see in a engineered shear wall design during permitapplication?As noted in Engineered Design on page 20, a set of calculations meeting the requirements therein mustbe submitted to the county. In addition, the shear wall design detail must be shown on the drawings witha minimum aspect ration of 3.5 to 1 (height to length) and must show, at a minimum, material thickness,fastener spacing, stud size and spacing, hardware requirements and a signature and seal of the registereddesign professional.

Can I construct a stud/ pony w all above a portal frame at a garage door opening?No. A stud/pony wall above a portal frame weakens the wall and creates an undesirable condition called a"hinge." The ability of a wall with a hinge to resist wind load is severely reduced.

What are the requirements for w ind bracing if I construct an enclosed room atop my deck?The walls of your new room must meet the requirements of this publication. However, the posts of thedeck below must be designed by a registered design professional to resist lateral loads using acceptedengineering practice.

Can I construct a two-story braced w all panel using the prescriptive requirements of the code?No. The maximum height of a braced wall panel using the Virginia Residential Code is 12 feet. See theFAQ below for potential options.

If my design does not meet the prescriptive requirements of the code, what are my options?You have two options. The first is to use a proprietary system such as those from Simpson Strong-Tie,Weyerhaeuser or Hardy Frame. See Proprietary Systems on page 19 for more information. The secondis to have the structure designed by a registered design professional licensed in the commonwealth of Virginia. See Engineered Design on page 20 for more information.

Are Simpson Strong-Tie, Weyer haeuser and Hardy Frame w all bracing products available on theeast coast?Yes. Representatives from all companies have indicated that their products are available to builders in ourarea. For more information, contact Simpson Strong-Tie at 1-800-999-5099, TTY 711 , Weyerhaeuserat 1-800-242-4854, TTY 711 , and Hardy Frame at 1-800-754-3030, TTY 711 . A full list of bracedwall products acceptable in Fairfax County can be found at www.icc-es.org .

Can Thermoply be used as a braced wall panel?Yes. Thermoply (Blue) Structural Grade is considered equivalent to Method SFB for intermittent bracingand can be an additional method for continuous sheathing. However, installation in either case must be instrict conformance with the product's ICC-ES Evaluation Report (ESR-1122 ).



Can sheets of OSB be placed with the long dimension horizontal to construct a braced wallpanel?Yes. OSB can be placed horizontally provided all vertical joints are located at studs, horizontal joints areblocked and all joints are edged nailed.

Does Fairfax County require an added inspection for w all bracing elements such as sheathing,framing and nailing prior to the house or addition being w rapped?No. Wall bracing elements will be inspected during the framing inspection.

If I call a braced wall line intermittent bracing with Method WSP (OSB) and infill the areasbetween the braced w all panels with more OSB, am I required to analyze this braced wall lineas if it w ere continuous sheathing, Method CS-WSP?No. This is the advantage to Method WSP. If you meet the three criteria for a braced wall line withMethod WSP and each panel is greater than or equal to the minimum panel length, then you can infillbetween the panels with any material, even the same material as the panel itself, in this case OSB.Analyzing this as Method CS-WSP is simply over designing the braced wall line and could possibly requirehold-downs, return panels and/or end panels.

Is there a fix for a portal frame, Methods IPF or CS-PF, that was constructed without theheader spanning atop the panel?No. Both Methods IPF and CS-PF are laboratory tested assemblies that could not be proven usingstandard engineering principles. Therefore, any fix would also require laboratory testing which mostbuilders do not have the capacity to do. So it is imperative to construct a portal frame correctly the firsttime.

If I have a braced wall line w ith continuous sheathing on the second or third floors and I opt touse a hold-down instead of a return panel (Options 2 or 4), how do I attach the hold-dow n?Hold-downs, if installed per the manufacturers' recommendations, require a connection from the hold-down device to an anchor bolt into the masonry or concrete foundation. Obviously this becomesproblematic for a braced wall line on the second floor. In this case, a galvanized strap, with an 800-poundcapacity, attached on the exterior side of the sheathing into a stud on the second floor and the first floorwill suffice.

Can a braced w all panel from a portal frame (Method IP F or CS-PF) w ith a length less than 24

inches be used as the return panel for a perpendicular braced w all line w ith continuoussheathing?Yes. A portal frame braced wall panel is considered equivalent to the return panel for an adjacent bracedwall line with continuous sheathing.

Can braced wall panels be constructed on a cantilevered floor?Yes. Braced wall panels can be constructed on a cantilevered floor provided blocking is provided back atthe bearing wall and the cantilever limits of Section R502.3.3 of the Virginia Residential Code are followed.

Sources: International Code Council-Evaluation Service, APA – The Engineered Association, SimpsonStrong-Tie

Fairfax County is committed to a policy of nondiscrimination in all county programs, services and activitiesand will provide this document in alternative formats and in different languages upon request. Please call703-324-5033, TTY 711 or write Department of Public Works and Environmental Services, Suite 659,12055 Government Center Parkway, Fairfax, VA 22035-5506. Please allow at least seven working daysfor preparation of material.

A Fairfax County, Virginia Publication

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Wind Bracing