OSB or CDX & why?

[Steves32]

Getting ready to order my garage lumber & this question came up. Entire exterior is shear paneled as well as roof sheeting.
At 1st- I was against OSB but the more people I talk to- the more confused I get. Should I go with OSB for shear & CDX on roof or vice versa or keep it all the same. The difference between the 2 is about $500.00

 

[RoofDude]

Ive torn off 1000+ roofs. I prefer walking on OSB. All things being equal, I havnt seen huge differences in the two, other than cost. When OSB gets wet, it expands, or swells. Repeated moisture, whether it be water intrusion, or condensation, can leave it pretty brittle. When CDX gets wet, it separates, or "delaminates". In my world, it is a little... key words "a little", less noticeable, which in turn, makes it more dangerous.

Another difference... I see more CDX that is "dry rotted". Meaning, poor ventilation has dried it out to the point of being very brittle. Although, I have seen OSB suffer the same issues, just not as much because it wasnt used in the 80's or earlier here. Neither are fun

Having said all that.... CDX has been around a lot longer than OSB. OSB started getting widely used in the early 90's here. So, most of the older structures we tear off have CDX. The OSB roofs we have torn off, seem to be more viable. However, most of em aren't as old either. Time will tell which is truly "better". CDX is considerably more expensive in my area than OSB. As of right now... If I were building a new home, or garage, I would use OSB based on cost, as my experience with both, hasn't left me with a strong opinion one way or the other.

 

[darkk]

What do your zoning regulations require?

 

[mmhouse]

I prefer 1/2" OSB for the walls and 5/8" CDX for the roof. OSB is more subject to sagging, especially when it gets moist (which attic areas do).

 

[Steves32]

What do your zoning regulations require?

Stamped plans call out either 1/2 OSB or 1/2 CDX

 

[70chevellegsp]

OSB has a better perm rating (absorbs less moisture). 7/16 on the walls and 5/8 on the roof. Won't be any sagging. Sagging comes from buiders saving a few bucks using 7/16 on the roof with "H" clips. (trusses 24" OC). A lot of people think OSB is particle board, which it is not. Also if you use Tyvek (or house wrap), tape your seams and flash appropriately, your sheathing should never see moisture.

 

[ddawg16]

I prefer 1/2" OSB for the walls and 5/8" CDX for the roof. OSB is more subject to sagging, especially when it gets moist (which attic areas do).

I agree.....

I went through the same issue/questions with my garage 2 years ago. What I learned was that OSB tends to have more shear strength in all directions where CDX tends to just have a primary shear strength in one direction (call it X) and the y direction is not as strong. That is because the typical 1/2" CDX is typically just 3 layers....

I prefer CDX for the roof because it has more resistance to bowing than OSB....to get an idea...cut two strips of each...support both of them at their ends...guess which one is going to sag more?

 

[trbomax]

My experience dates back to 1973 when all you could use was cdx.The thing about cdx is that its not solid core,which means there are voids in the interior plies.Nowdays ,I'm sure that the voids are larger and more common than they used to be. The voids are a good place to hold moisture,especially if they are opened up on a window or door cut. Osb doesnt have these issues,it's obviously solid core,but the strand alignment is critical when you put it down,its only good in one direction,at right angles to the frameing. Also there are various grades of OSB in regard to the "span rateing". I would always get the highest rated panels no matter what my span actually was.Another thing is that when nailing the OSB down you must NOT "sink" the nail heads even a small ammount,sunken nails reduce the load capacity and in most cases will not pass inspection. When used in the corners as shear panels,I always use adhesive too,thats overkill,but it's how I like to do it.

 

[49stude2r6]

I agree with mmhouse,ddawg16. I am willing to be proven wrong though and trbomx and 70chevelle sound like they have more information than I do. I don't know that either would be horribly wrong, but I built mine with OSB walls and Ply Roof.

 

[trbomax]

If were possible to get the quality of ply that was available 20 yrs ago,ply would be my choice for roofs,but when was the last time you saw a flat sheet of cdx that wasnt full of plugs on one side and open voids on the other? The other thing is that from an economic standpoint, 3 ply is whats there,not 5ply like used to be. I think that even given the shortfalls of OSB,its far more stable dimensionally,and yes if it gets wet or isnt spaced properly the edges will show,but it wont curl like 3 ply might. Just space it correctly,use ice gard all around eves and valleys,then 2 passes of felt,it will be fine for as long as any of us are going to be around.

 

[dipper]

i went with osb for the walls and cdx plywood for the roof decking (roof is on 24" centers with H-clips). Been up for 3.5 years with no problems (tons of rain, snow, ice).

 

[Steves32]

Existing roof is 2x6's on 24" centers that were doubled up when they went from shake to tile roof 18 years ago (with permit). New rafters are 2x12's on 16" centers w/ 1/2 CDX or OSB per plan.

No snow or ice here to worry about.

 

[NUTTSGT]

I used 7/16" OSB for the walls and 1/2" OSB with clips for the roof, trusses 24" O.C.

 

[WVBrady]

OSB has a better perm rating (absorbs less moisture). 7/16 on the walls and 5/8 on the roof. Won't be any sagging. Sagging comes from buiders saving a few bucks using 7/16 on the roof with "H" clips. (trusses 24" OC). A lot of people think OSB is particle board, which it is not. Also if you use Tyvek (or house wrap), tape your seams and flash appropriately, your sheathing should never see moisture.

I found that the 7/16 varied enough in thickness that the "H" clips did not fit right.

 

[southernfriedcj]

I use 7/16 OSB on walls and roof.

What I would use if cost were not an object would be one of the T&G Advantech type sheathing products.

http://huberwood.com/main.aspx?pagename=advantechsheathing

I had an Advantech 3/4 subfloor that was wet for 3 years and was not damaged at all (a leak in a shower migrated between the Durock & Advantech). I was shocked that the Advantech did not absorb any water.

 

[mpraddict]

I prefer 1/2" OSB for the walls and 5/8" CDX for the roof. OSB is more subject to sagging, especially when it gets moist (which attic areas do).

Same here. This is what I specify for residential projects and what I used on my garage a couple years ago. Plywood holds roofing nails better than OSB too.

What do your zoning regulations require?

Zoning has nothing to do with a substrate not visible when the project is complete.

 

[mmhouse]

What do your zoning regulations require?

Zoning has nothing to do with a substrate not visible when the project is complete.

I imagine darkk meant building codes.

 

[tcianci]

There was a lot of OSB used around here years ago and most guys went back to plywood for roofing. We mostly frame on 16 inch centers for roofs here too and you can tell an OSB deck just by looking at the sags between rafters. Today, I would have no problem using Advantech anywhere on a building, it's great stuff and they have a roofing panel with a coating applied thats supposed to only need tape to get you water tight and start the building drying in. The biggest pain using the OSB in the construction process is if you use the OSB on 24 inch centers and try nailing the roofing by hand, it gets VERY bouncy...like trying to nail shingles to a bed pillow

 

[Falcon67]

I used 7/16 OSB on the roof of the 20x24, 2x6 rafters 24" OC. No dip or sags after 14 years.

EDIT - I used screws to attach the decking and clips to space.

 

[sneezer41]

+1 on cdx holding nails better.

 

[Steves32]

Right now- the plan is to use CDX on the roof. Both the framer & roofer prefer CDX. As for the shear walls- I'll decide at the last minute.