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Hurricane Ties/Clips

R802.10.5 Truss to wall connection.

Trusses shall be connected to wall plates by the use of approved connectors having a resistance to uplift of not less than 175 pounds (779 N) and shall be installed in accordance with the manufacturer’s specifications. For roof assemblies subject to wind uplift pressures of 20 pounds per square foot (960 Pa) or greater, as established in Table R301.2(2), adjusted for height and exposure per Table R301.2(3), see section R802.11.
 
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michaelj,

They are not required in or by the IRC. If the structure is located in

an area of high winds, then the ' hurricane ties ' will need to be

specified by a DP ( see Section R301.2.1.1 in the IRC ).

Section R301.1.3 in the IRC refers to "a building of otherwise conventional

construction... " R301.1.1 Alternative provisions: "As an alternative to the

requirements in Section R301.1 the following standards are permitted subject to the

limitations of this code and the limitations therein. Where engineered design is

used in conjunction with these standards the design shall comply with the International

Building Code.

Section 2308.10.1 [ from the `06 IBC ] - WIND UPLIFT:

Roof assemblies shall have rafter and truss ties to the wall below. Resultant uplift loads

shall be transferred to the foundation using a continuous load path. The rafter or truss

to wall connection shall comply with Tables 2304.9.1 and 2308.10.1.

TABLE 2308.10.1 REQUIRED RATING OF APPROVED UPLIFT CONNECTORS (pounds)a,b,c,e,f,g,h



b. The uplift connection requirements are based on the framing being spaced 24 inches on center. Multiply by 0.67 for framing spaced 16 inches on center and multiply by 0.5 for framing spaced 12 inches on center.

c. The uplift connection requirements include an allowance for 10 pounds of dead load.

d. The uplift connection requirements do not account for the effects of overhangs. The magnitude of the above loads shall be increased by adding the overhang loads found in the table. The overhang loads are also based on framing spaced 24 inches on center. The overhang loads given shall be multiplied by the overhang projection and added to the roof uplift value in the table.

e. The uplift connection requirements are based upon wind loading on end zones as defined in Figure 6-2 of ASCE 7. Connection loads for connections located a distance of 20 percent of the least horizontal dimension of the building from the corner of the building are permitted to be reduced by multiplying the table connection value by 0.7 and multiplying the overhang load by 0.8.

f. For wall-to-wall and wall-to-foundation connections, the capacity of the uplift connector is permitted to be reduced by 100 pounds for each full wall above. (For example, if a 500-pound rated connector is used on the roof framing, a 400-pound rated connector is permitted at the next floor level down).

g. Interpolation is permitted for intermediate values of basic wind speeds and roof spans.

h. The rated capacity of approved tie-down devices is permitted to include up to a 60-percent increase for wind effects where allowed by material specifications.

michaelj,

Essentially, either the jurisdiction has adopted a standard to require the use of approved

type of ' hurricane ties ', or a DP will have to specify them. Does this answer

your question? ;)

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The IRC does require what is commonly refered to even here in Montana as "Hurricane Clips" My own house equated out to over 500 lbs of uplift in a 90 mph wind load

R802.11 Roof tie-down.

R802.11.1 Uplift resistance.

Roof assemblies which are subject to wind uplift pressures of 20 pounds per square foot (960 Pa) or greater shall have roof rafters or trusses attached to their supporting wall assemblies by connections capable of providing the resistance required in Table R802.11. Wind uplift pressures shall be determined using an effective wind area of 100 square feet (9.3 m2) and Zone 1 in Table R301.2(2), as adjusted for height and exposure per Table R301.2(3).

A continuous load path shall be designed to transmit the uplift forces from the rafter or truss ties to the foundation.

TABLE R802.11

REQUIRED STRENGTH OF TRUSS OR RAFTER CONNECTIONS TO RESIST WIND UPLIFT FORCESa, b, c, e, f

(Pounds per connection)
 
We make them provide truss specs with the uplift on them. Then we know which trusses need uplift connectors and how big they need to be for things like girder trusses.
 
lateral loads are tougher... most hurricane clips only address uplift (generally the dominant load)... you need to look carefully for the lateral loads (more important in hurricane prone and seismic prone areas).

Doesn't matter if it's an interior non bearing wall.. don't connect it
 
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You need to go to a separate reference, wcfm, (wood construction frame manual, or astm-7

It is all based on average wind speed, each state code should give you a wind ma
 
the reference standard that defines lateral loads is ASCE 7. The design of the wood members to resist the forces are addressed in the AF&PA National Design Specification and theAF&PA Special Design Provisions for Wind and Seismic.

While the proscriptive provisions in the IRC are relatively simple they do not cut it if you have significant wind or seismic loading or unusually configured building. There is some differences of opinion about the dividing line beyond which you need to perform an engineering design but there is only so much you can acomplish with prescriptive code provisions.
 
Since the code puts everything pretty much in the 90 mph wind zone, which I believe pretty much equates to 20 psf uplift load.. so they are pretty much required everywhere. You need to look at the actual loads, which should appear on the truss drawings.

Girders are always higher (duh.. since they generally transmit all the loads of the trusses or joists tied into them).. so it's not going to be a little clip that holds them down. Cantilvered trusses for porches are always high at the bearing point (which is where they are meant to be tied down).. always ask for the truss plans... if it happens to be rafters, at least require a clip of some type (or learn to do the calculations - at PLAN REVIEW).
 
Reading this thread prompted me to read the relevant sections and study the tables in Chapt. 3. I can usually figure out the prescriptive requirements but after spending about an hour I can not figure out how to calculate the psf of uplift from the tables. Can anyone give an example referenceing the table and explain how the calculation is done?
 
Table 802.11

Column 1 go down till you find the wind speed Example 90 mph

In the 90 mph row go across till you find the width of the roof Example 40 ft

This gives you a wind uplift of -302 pounds per truss based on 24" OC

I am in Exposure "C" so Footnote "a" sends me to Table R301.2(3)

My mean roof height is 25 ft so I have to use the 1.35 coefficient factor for exposure "C"

-302 x 1.35= -407.7

Now move to the last column for overhangs it is -43.2 footnote "d" says this is per foot of overhang

2.5 X - 43.2= -108 overhang load

-108 + -407.7 = -515.7 pound uolift connector per truss/rafter

Footnote "e" will allow a reduction for some of the internal trusse/rafters.

http://www.strongtie.com/products/connectors/H.asp

Look at the uplift loads even 515 pound is not hard to meet
 
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Stirring up an old thread

Hi gents, Hoping to find an answer to the question here. I have been requiring "hurricane clips" on trusses here since day one. However, the question has surfaced as to whether or not they are needed with the newer "raised heel energy trusses" when the exterior sheething is installed continuous up past the top plate and fastened to the outer chord of the raised heel section of the truss. Theoretically providing the truss to wall connection through the exterior sheeting. Anyone else been there done that? seems logical to me but I feel like I need solid evidence that this method could be an "approved connection". Thanks for any input. :D
 
Here is a little excert i found searching the web. Sounds like it is still up in the air (no pun intended) as to whether or not it is an "approved connection".

Framing Details The 2009 International Residential Code, and to a greater extent its recently released 2012 version, require extensive blocking—perhaps even a shear wall detail—between trusses with heels higher than 15-1/4 inches to guard against truss uplift and seismic forces. Previously, builders and framers could extend ventilation baffles to enclose the heel and create the attic insulation cavity. But recent testing at the National Association of Home Builders (NAHB) Research Center in Maryland indicates that a section of 7/16-inch OSB extending from the top plate to the underside of the top chords (thus enclosing the cavity and connecting multiple trusses laterally) may meet the performance threshold of the code.

A full or extended OSB panel covering the heel cavities and extending far down the sidewalls appears to further enhance lateral stability, and may even eliminate the need to install metal connectors at the heel-plate junction to guard against uplift. “A tall OSB panel that connects to the wall structure might serve as a continuous load path,” says Drew DeRenzis, a structural engineer with the Research Center. “If it saves builders money and time not having to apply metal connectors, they’re all for it.”
 
Excerpt #2 Not necessarilly from a credible source though Sheathing—No Splice In this case, the connection is made by the wall sheathing itself. If the sheathing is continuous over the truss/top plate intersection, as shown, a hurricane clip is not needed. This method requires a block large enough to be edge nailed to both the roof sheathing and the wall sheathing.View attachment 1450

View attachment 604

View attachment 604

/monthly_2012_10/572953c508d9c_Trusstowallconnection.jpg.e76dc6d5d390dd6fbabda7b64226a483.jpg
 
Mr. Inspector (and others),

In that picture, there is a "cut out" section to allow for ventilation (I presume).

Is that framed element a custom made, "on site" product or is that part of the

truss assembly, or other?

Essentially, how will the soffitt ventilation (which is 1/2 of the ventilation

equation) be achieved?

.
 
Not sure about Mr. Inspector's question, but,

Looking at the 2012 IRC it looks to me like "hurricane clips" are not required until you exceed a 200 lb. uplift force as detemined in Table R802.11. Table R802.11 determins the uplift force by Exposure Category, Roof Pitch and Roof Span. Looks like it is not a cookie cutter answer and in Category B, unless you go to 24" o.c. with your rafters or trusses and have a pretty good roof span, you are allowed to go with the toe nailing (fastener schedule) in Table R602.3(1)

I haven't adopted the 2012 code yet but we are reviewing it for adoptioned at the 1st of the year.

If anyone has already adopted the 2012 IRC an read this differently, I woud appreciate being corrected before I start enforcing this section.

Thanks
 
Also, in applying the wind loads factors, in my AHJ the hurricane clips

would not be required either, however, we DO experience significant

tornado activity on a regular basis.

How do others apply the need / requirement for uplift resistance

considering tornados in your area?

.
 
Mr Inspector

Figure R602.10.6.2(3) in the 2009 IRC depicts what you described

Can it replace the mechanical fasteners required in the code for certain wind loads. I bet most engineers can make.
 
Alright guy's, I have beaten myself up with this one but I think I have it figured out. According to the 2009 IRC section 802.10.5 Truss to wall connection; Trusses shallbe connected to wall plates by the use of approved connectorshaving a resistance to uplift of not less than 175 pounds and shall be installed in accordance with the manufacturer's specifications.(period) Therefore, I am concluding that clips/straps with 175 lbs of uplift resistance are required at each truss as a connector no matter what and a toenail(fastener)is not a connector.
 
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