Choosing Correct Lumber Grade 1

[Teguci]

I am familiarizing myself with multi story lumber construction, but I have limited experience with wood. Given the different species and grades of lumber available, how does an engineer choose the correct species and grade for a particular building?

For instance, (2)2x6 Stud grade hem-fir can be used at 16" ocs for the ground floor or (2)2x6 Standard grade hem-firs can be used at 24" ocs (both dry for shrinkage concerns).

Is there a commonly used cost and availability resource that Architects and Engineers use for pricing wood construction? Rules of thumbs, etc...

Thanks,

 

[frv]

In my neck of the woods, No. 2 is usually specified for flexural members, unless you require # 1 due to loads.

stud grade is typically used for load-bearing walls. Be sure to check axial and bending interaction, as this may bump up your wall studs into No. 2 as well.

 

[woodman88]

First, check out the available construction lumber for the building location.
Second, use single studs down to 8" oc (if you have to go to 6"oc give a option for doubles at 12"oc) before going to double studs. This will decrease the labor.
Third, Be sure to check the double top plates for bending if you use double studs at greater than 12" oc.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[SteelPE]

Most of the numbers I use for wood design is SPF #2. Almost all of the lumber that I have seen on site is this grade. This is the species/grade that is given in the first line of tour general notes.

I have been told by many contractors that they can get any species/grade of lumber you would like but I have never taken them up on that offer (the consequences are just to great).

You will also need to spec and properties of the LVL beams you select as well (Fb, E etc...).

 

[MiketheEngineer]

1. Find the grades that are the most available(cheapest) in your area.

2. Do your calcs

3. Spec what you need.

Basic engineering

 

[msquared48]

It's not lqways the cheapest to use in the design. Sometimes a contractor likies to use a particular species due to greater conformity of individual pieces, such a joists - less splitting, warping, etc.

Sometimes the contractor makes the choice for you. I ALWAYS ask what material and grade they prefer to use. If a particular beam needs a higher grade, then I'll use that. Otherwise, stick to the client's preferences.

Mike McCann
MMC Engineering

 

[AELLC]

The way I understood it is Southern Pine is common in the SE USA and Hem-Fir, Douglas Fir-Larch is common in SW USA.

Don't know about Northern USA.

2x and 4x ledgers, joists, beams and headers are #2 grade
4x posts are #2
All 6x and wider is #1

2x studs are usually Stud grade unless high stress requires #2

DF-L studs not recommended due to lumber twisting, use SP or H-F

 

[MiketheEngineer]

North USA is Doug fir. Some Hem fir
Obviously - consult with contractor on what he prefers - but usually it is the CHEAPEST!!

 

[JAE]

Mike - many areas of north-USA use Spruce Pine Fir as well.

 

[Teguci]

OK, so step 1 is to select the species of lumber to be used. No problem. Step 2 is to select the grade. For a small project, the grade is probably not that important. But, for a four story wood building, the use of stud grade vs #2 could have a significant impact due to the loss of up to 65% of the compressive strength of the stud. However, if the cost difference in grades is double, then stud grade makes sense.

I imagine that the contractor would have a handle on this, I just figured that there would be an engineer's resource that could also quantify this.

Woodman - what is the advantage of tighter spacing vs doubling of the studs (I'd hate to run wiring with 8" oc studs)?

 

[woodman88]

Species - DF-L/SP = shearwalls per tables, lesser species = reduce shearwall table values.
Grade - #2 = straighter walls = easier to finish walls than lesser grades (I am more use to seeing/using the #2 grade for for studs in apartments)
Spacing – Double studs = labor for framer to nail together vs. easier for electrician to run wiring. As an structural engineer I have always had to deal with the framer/contractor more than the electrician, so I try to make the framer/contractor happier. ;-)

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.