# Maximum Truss Span for Prescriptive Walls and Foundations



## benny (Oct 4, 2013)

Does anyone know where I can find a code reference out of the 2009 IRC limiting the roof truss span / tributary roof load for a building using the prescriptive codes for the foundation and load bearing walls?

Thanks in advance!


----------



## jar546 (Oct 5, 2013)

There is nothing specific to that because trusses are an engineered product.  Each section of floor, walls, etc clearly states that they must be capable of handling the load imposed.  If you have an issue, ask for an RDP to provide proof.  You would have to get quite large to have an issue with this but it can be an issue.


----------



## kyhowey (Oct 7, 2013)

R802.10.2.1 is the only reference in terms of truss limitations.


----------



## steveray (Oct 7, 2013)

I would have no problem limiting them to 40' I imagine......

SECTION 2308 CONVENTIONAL LIGHT-FRAME CONSTRUCTION

2308.1 General.

The requirements of this section are intended for conventional light-frame construction. Other methods are permitted to be used provided a satisfactory design is submitted showing compliance with other provisions of this code. Interior nonload-bearing partitions, ceilings and curtain walls of conventional light-frame construction are not subject to the limitations of this section. Alternatively, compliance with the following standard shall be permitted subject to the limitations therein and the limitations of this code: American Forest and Paper Association (AF&PA) Wood Frame Construction Manual for One- and Two-Family Dwellings (WFCM).

5. Roof trusses and rafters shall not span more than 40 feet (12 192 mm) between points of vertical support.


----------



## jar546 (Oct 7, 2013)

steveray said:
			
		

> I would have no problem limiting them to 40' I imagine......SECTION 2308 CONVENTIONAL LIGHT-FRAME CONSTRUCTION
> 
> 2308.1 General.
> 
> ...


I agree and that is out of the IBC which may apply if the language is not in the IRC and this is a residential question.  I am assuming this is a loading question and not a span question although the two are inter-related.


----------



## steveray (Oct 7, 2013)

And here is how I would get there from the IRC....

R301.1 Design.

Buildings and structures, and all parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code. The construction of buildings and structures shall result in a system that provides a complete load path capable of transferring all loads from their point of origin through the load-resisting elements to the foundation.

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.

1. American Forest and Paper Association (AF&PA) Wood Frame Construction Manual (WFCM).


----------



## mtlogcabin (Oct 7, 2013)

Truss roof framing constructed in accordance with the provisions of this section shall be limited to sites subjected to a maximum design wind speed of 110 miles per hour (49 m/s), Exposure A, B or C, and a maximum ground snow load of 70 psf (3352 Pa).

Unless you are in a high wind *and* over 70 psf ground snow then trusses designed under ANSI/TPI 1 are not limited in size.

Don't try and use the IBC to disallow what is specifically permitted in the prescriptive IRC code

There are similar restrictions for steel trusses and SIPs panel construction, R603.1.1 & R613.2


----------



## steveray (Oct 7, 2013)

MT...it is not the truss I would question, it is the load path through the light frame construction per "shall be constructed to safely support all loads" that I would be questioning....I have had people attempting to post down 30,000+lbs (in a SFD) to the point where I have to question the PT plate and it fails in compression perp. to the grain....

  The fact of the matter is people are building way more advanced homes than they know how to....And as long as  there are gray ares in the code, if there is something I am not comfortable with, I will have no issues sending someone to a (hopefully competent and ethical) design professional.....



			
				mtlogcabin said:
			
		

> Truss roof framing constructed in accordance with the provisions of this section shall be limited to sites subjected to a maximum design wind speed of 110 miles per hour (49 m/s), Exposure A, B or C, and a maximum ground snow load of 70 psf (3352 Pa).Unless you are in a high wind *and* over 70 psf ground snow then trusses designed under ANSI/TPI 1 are not limited in size.
> 
> Don't try and use the IBC to disallow what is specifically permitted in the prescriptive IRC code
> 
> There are similar restrictions for steel trusses and SIPs panel construction, R603.1.1 & R613.2


----------



## mtlogcabin (Oct 7, 2013)

> The fact of the matter is people are building way more advanced homes than they know how to....And as long as there are gray ares in the code, if there is something I am not comfortable with, I will have no issues sending someone to a (hopefully competent and ethical) design professional.....


Agree and in my seismic zone it is easy to require an engineer on an irregular shaped building.

I believe Sections R301.1.2 and R301.1.3  are the best way to handle excessive point loads and other structural items that are not prescriptive in the IRC.


----------

