Wood stud height problem

[jar546]

Contractor wants to put an addition on a house that matches the existing elevations. Makes sense. Existing home has 12' ceilings on 1st floor. This is a 2 story addition and he wants to frame the 1st floor with 2x6 studs. I reject the plans stating he needs an architect or engineer to spec out the first floor framing as he exceeds the height requirement. Contractor points to Table 602.3.1 and says 2x6 is prescriptively allowed 18' when supporting 1 floor and 1 roof at 16" o.c.

I reject that claim also. Here are the details.

90mph wind zone

Seismic B

Ground snow load 40 psf

Am I correct?

 

[Yankee]

Contractor wants to put an addition on a house that matches the existing elevations. Makes sense. Existing home has 12' ceilings on 1st floor. This is a 2 story addition and he wants to frame the 1st floor with 2x6 studs. I reject the plans stating he needs an architect or engineer to spec out the first floor framing as he exceeds the height requirement. Contractor points to Table 602.3.1 and says 2x6 is prescriptively allowed 18' when supporting 1 floor and 1 roof at 16" o.c.I reject that claim also. Here are the details.

90mph wind zone

Seismic B

Ground snow load 40 psf

Am I correct?

Assuming 2009 IRC He would be correct if he meets the subnote b. which calls for snow load < 25psf (not gsl, just snow load which I now assume means roof load which will be less than gsl)

 

[jar546]

That table does not apply because his snow load is higher than what that table is designed for. The table specifies ground snow load and does not say calculated live load if converting snow load to live load per ASCE 7.

Therefore, he no usey dat table

 

[steveray]

Here is another section....

R301.3 Story height.

Buildings constructed in accordance with these provisions shall be limited to story heights of not more than the following:

1. For wood wall framing, the laterally unsupported bearing wall stud height permitted by Table R602.3(5) plus a height of floor framing not to exceed sixteen inches.

Exception: For wood framed wall buildings with bracing in accordance with Table R602.10.1, the wall stud clear height used to determine the maximum permitted story height may be increased to 12 feet without requiring an engineered design for the building wind and seismic force resisting systems provided that the length of bracing required by Table R602.10.1 is increased by multiplying by a factor of 1.20. Wall studs are still subject to the requirements of this section.

 

[Yankee]

That table does not apply because his snow load is higher than what that table is designed for. The table specifies ground snow load and does not say calculated live load if converting snow load to live load per ASCE 7.Therefore, he no usey dat table

It was assumed that the wall height would be braced as it is over 10'. I read the snow load to be the roof snow load as the table does not specify ground snow load. "b. Applicability of this table assumes the following: Snow load not exceeding 25 psf, fb not less than 1310 psi determined by multiplying the AF&PA NDS tabular base design value by the repetitive use factor, and by the size factor for all species except southern pine, E not less than 1.6 × 106 psi, tributary dimensions for floors and roofs not exceeding 6 feet, maximum span for floors and roof not exceeding 12 feet, eaves not over 2 feet in dimension and exterior sheathing. Where the conditions are not within these parameters, design is required. "

 

[jar546]

What is the difference between snow load, ground snow load and live load?

If the GSL is >25psf (it was 40), even the live load of that is >30 if you convert it. If we have valleys, the snow load is even more. I am trying to find out how a 40# GSL is equal to or less than a snow load of 25psf.

 

[High Desert]

Footnote b of that table also limits the floor or roof tributary dimension to 6 feet. As steveray pointed out the only way to go taller than 10 feet is to apply Section 301.3.

 

[steveray]

Tables always post like crap...but.....

TABLE R602.3(5) SIZE, HEIGHT AND SPACING OF WOOD STUDSa

STUD SIZE

(inches)

BEARING WALLS

NONBEARING WALLS

Laterally unsupported stud heighta

(feet)

Maximum spacing when supporting roof and ceiling only

(inches)

Maximum spacing when supporting one floor, roof and ceiling

(inches)

Maximum spacing when supporting two floors, roof and ceiling

(inches)

Maximum spacing when supporting one floor only

(inches)

Laterally unsupported stud heighta

(feet)

Maximum spacing

(inches)

2 × 3b

—

—

—

—

—

10

16

2 × 4

10

24

16

—

24

14

24

3 × 4

10

24

24

16

24

14

24

2 × 5

10

24

24

—

24

16

24

2 × 6

10

24

24

16

24

20

24

For SI: 1 inch = 25.4 mm.

a. Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall. Increases in unsupported height are permitted where justified by analysis.

 

[GBrackins]

from Cornell University, how to convert ground snow load to roof snow load calculator

https://courses.cit.cornell.edu/arch264/calculators/example2.3/

 

[GBrackins]

if I have a 12' long stud and provide solid blocking between the studs at their midpoint, what would my unsupported stud height be then?

 

[Francis Vineyard]

Tables always post like crap...but.....TABLE R602.3(5) SIZE, HEIGHT AND SPACING OF WOOD STUDSa

Copy and paste from the ICC website.

TABLE R602.3(5) SIZE, HEIGHT AND SPACING OF WOOD STUDSa

[TABLE=class: MsoNormalTable, width: 512]

[TR]

[TD=width: 66]STUD SIZE(inches)[/TD]

[TD=colspan: 5]BEARING WALLS[/TD]

[TD=colspan: 2]NONBEARING WALLS[/TD]

[/TR]

[TR]

[TD=width: 85]Laterally unsupported

stud heighta(feet)[/TD]

[TD=width: 96]Maximum spacing when supporting a roof-ceiling assembly or a habitable attic assembly, only

(inches)[/TD]

[TD=width: 92]Maximum spacing when supporting one floor, plus a roof-ceiling assembly or a habitable attic assembly(inches)[/TD]

[TD=width: 92]Maximum spacing when supporting two floors, plus a roof-ceiling assembly or a habitable attic assembly(inches)[/TD]

[TD=width: 84]Maximum spacing when supporting one floor heighta

(feet)[/TD]

[TD=width: 85]Laterally unsupported stud heighta(feet)[/TD]

[TD=width: 84]Maximum spacing(inches)[/TD]

[/TR]

[TR]

[TD=width: 66][/TD]

[TD=width: 85][/TD]

[TD=width: 96]

[/TD]

[TD=width: 92]

[/TD]

[TD=width: 92]

[/TD]

[TD=width: 84]

[/TD]

[TD=width: 85][/TD]

[TD=width: 84][/TD]

[/TR]

[TR]

[TD=width: 66]2 × 3b[/TD]

[TD=width: 85]-[/TD]

[TD=width: 96]-[/TD]

[TD=width: 92]-[/TD]

[TD=width: 92]-[/TD]

[TD=width: 84]-[/TD]

[TD=width: 85]10[/TD]

[TD=width: 84]16[/TD]

[/TR]

[TR]

[TD=width: 66]2 × 4[/TD]

[TD=width: 85]10[/TD]

[TD=width: 96]24c[/TD]

[TD=width: 92]16c[/TD]

[TD=width: 92]-[/TD]

[TD=width: 84]24[/TD]

[TD=width: 85]14[/TD]

[TD=width: 84]24[/TD]

[/TR]

[TR]

[TD=width: 66]3 × 4[/TD]

[TD=width: 85]10[/TD]

[TD=width: 96]24[/TD]

[TD=width: 92]24[/TD]

[TD=width: 92]16[/TD]

[TD=width: 84]24[/TD]

[TD=width: 85]14[/TD]

[TD=width: 84]24[/TD]

[/TR]

[TR]

[TD=width: 66]2 × 5[/TD]

[TD=width: 85]10[/TD]

[TD=width: 96]24[/TD]

[TD=width: 92]24[/TD]

[TD=width: 92]-[/TD]

[TD=width: 84]24[/TD]

[TD=width: 85]16[/TD]

[TD=width: 84]24[/TD]

[/TR]

[TR]

[TD=width: 66]2 × 6[/TD]

[TD=width: 85]10[/TD]

[TD=width: 96]24[/TD]

[TD=width: 92]24[/TD]

[TD=width: 92]16[/TD]

[TD=width: 84]24[/TD]

[TD=width: 85]20[/TD]

[TD=width: 84]24[/TD]

[/TR]

[/TABLE]

[TABLE=class: MsoNormalTable]

[TR]

[TD]For SI:1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 square foot = 0.093 m2.

a. Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall. Increases in unsupported height are permitted where justified by analysis.

b. Shall not be used in exterior walls.

c. A habitable attic assembly supported by 2 × 4 studs is limited to a roof span of 32 feet. Where the roof span exceeds 32 feet, the wall studs shall be increased to 2 × 6 or the studs shall be designed in accordance with accepted engineering practice.

[/TD]

[/TR]

[/TABLE]

 

[jar546]

if I have a 12' long stud and provide solid blocking between the studs at their midpoint, what would my unsupported stud height be then?

I do not believe typical blocking is the same as lateral support.

 

[Sifu]

if I have a 12' long stud and provide solid blocking between the studs at their midpoint, what would my unsupported stud height be then?

12'. I consider support to be an intervening floor, ceiling or roof structure, but I have come up with that from my own experience. I have had engineers design a kind of sideways "beam" around the peremiter of some large rooms at the midpoint as an alternate.