Roof Sheating, Span Ratings, Boca 96

Grumpy

I'm bidding a project with plywood replacement. 7 buildings about 20 squares each. This is phase II of the project. Another roofer was a disaster on Phase I, so they are trying to replace him.

THis old roofer used 3/8" sheathing on the roof. I bid for 1/2" CDX. They want me to adjust my bid for 3/8".

I spoke with the building inspector who said he doesn't care what the thickness is, he cares what the span rating of the wood to be used is. I am looking at the Boca 96 code, but I'm confused here.

Can someone explain this to me? I think I know what I am looking at, but not sure.

I believe the roof is 24" OC 2"x4" rafters. Some rafters are 26' long.

Unregistered

I was old once by an inspector in Plymouth Minnesota the numbers on some plywood have something to do with what it is rated for like Example 15/32 should be 15 inches on center for walls and 32 inches on center for roof sheathing possibly the other way around but this would mean you need at least 1/2 inch plywood for the roof decking at 24 OC - (which brings me to this point i would never use 3/8 inch plywood on any roof for decking unless re - decking over existing decking of 1/2 inch or greater.) 15/32 is just like saying 1/2 inch. so if you took 3/8 found the common denominator of 3 you have 9/24 so this would mean 9 inch on center for walls and 24 on center for roofs or vise versa. I have been roofing here in Minnesota for 12 years and have only heard this once but it kinda makes sense. especially when you have lines on the plywood at 15 inches and 32 inches. and why else would they make a 15/32 plywood and not a standard 1/2? i will continue to read these posts I am curious on this subject.

Grumpy

I pretty much insisted I use 1/2. I don't want quality to suffer for the sake of a few bucks.

hatchet

You've got the right idea Grumpy. I would decline the job if they want you to use 3/8". If you get the job you are covered by them requiring you to use the 3/8" but it's bad publicity for your company when a year down the road the roof fails.

__________________
Rich
WIT Construction Co.
Superior MT Contractor

Glasshousebltr

What's up with the 3/8's crap......Back in my days nobody would put 3/8 on a roof, now I'm running into it all the time. Don't the homeowners realize thier sacrifice?

Bob

Mike Finley

I understand Hatchet's response but if it is built to code and passes inspection you are off the hook.

So this inspector is referring to the fact that you could use different types of products as the roof sheathing so he is concerned with the individual products specs more than just a general 12 inch on center, 16 inch on center or 24 inch on center. Sounds like he is on the ball to me, but what the hell do I know. What other materials are available for roof sheathing that are up to code in your area, partical boards?

In regard to the guest, those plywood thicknesses have more to do with saving money then some kind of archaic code. A 1/2 inch thick piece of plywood would also measure 16/32. 15/32 is 1/32 thinner and cheaper over millions and millions of sheets of plywood. All the plywood I see is now 1/32 thinner, except for tonge and groove which has remained true to the old thicknesses.

Unregistered

As far as being off the hook i can agree to a point. i know quite a few builders in the area and have done some building of my own. as far as code goes you may be off the hook. but at the same time the city and state are immune to prosicution so even if say you use 3/8 and it is found out years down the line that this is unacceptable who pays? City is off the hook. so are you. insurance companies wont cover it. so the homeowner is stuck flippping the tab. We have this issue in Minnesota with mold vapor barrier inside wall outside wall any crack is filled. windows taped. nowhere for walls to breathe we all followed city code. everbody is off the hook but the homeowner is stuck big time. especially with homes that were constructed with wood foundations. 12 year old $200,000.00 homes have to be torn down and rebuilt. at homeowners expense. bad business for us all.
I have been reading a few of your guys other posts and have noticed you like the grace ice and water shield and have noticed you even went as far as to say cover the entire roof deck before roofing. I have had some experience in this as well it is a good concept. One problem i have found is in Minnesota not all houses are ventalated or insulated properly. and most times homeowners dont want to go through the extra expense of adding insulation or cutting in soffit vents. roof vents are not much of a expence so we can do this. What happens is the roof deck dry rots from excess condensation. instead of forming under the underlayment it forms on the inside of the attic. in which case 15 pound felt will allow condensation to form but absorb it into the felt then dry out. this is what felt paper is made to do.The ridge vent i have had some problems with cottonwood plugging it up after two years so have reverted back to the turtle style vents as well. Grace is the best Ice and water product i have seen and is expensive but still would not recomend covering entire roof. Next thing you know codes will require us to put air exchangers in the attic as well as in the living spaces.
http://www.pfsrf.org/prf/prffaqs.html#4 This is a link i found which may help as far as span ratings go.

Grumpy

Mike no way I am off the hook. I have a ten year warranty. I back up that warranty. In order to back up that warranty I have to make sure the roof meets MY standards. OSB is also to code but I won't use anything less than CDX.

All wood sizes are nominal. a 2"x4" is not really 2"x4" The same goes for plywood. It's just a nominal size.

BTW this is not new construction.



Unregistered, please consider registering I am enjoying reading your posts.

I won't install a roof without proper ventilation, or the home owner has to sign a waiver acknowledging that this is against the manufacturers recomendations and will void the warranty.

Mike Finley

I understand you Grumpy. Makes sense.