Dear Friend,
I have a low slope roof that is approx. 20 ft by 30 ft rectangular.
The asphalt roll roof material has deteriorated, so I want to have
this low slope section replaced. The following is an estimate that
was given to me. Can you tell me is this is acceptable. I am
especially worried about osb. Why should this be an issue,
since plywood is cheap and has always been used in the past.

Here is the write-up:

1. Remove entire rolled roof (approx. 20ft x 30ft) and haul away all debri.
2 Inspect roof decking and structural components of flat roof (he means low slope).
3. Replace all deteriorated raftes and/or roof decking.
4. Apply 4x8 sheets of 7/16 o.s.b. plywood over entire roof deck.
5. Apply liberty sbs self-adhering roofing system to entire flat roof area (he means low-slope)
6. Install new custom bent galvanized steel counter flashing to base of single
flue brick chimney.
end of write-up, total cost $2,978.00

Why do they install o.s.b. instead of traditional plywood?

Thanks, Paul Hoskins

 

I just purchased a 4x8 piece of 7/16" OSB and it cost me $5.34 each. The last piece of 1/2" sanded plywood I bought was $19.50 each. 1/2" CDX plywood is closer to 15.00.

He is probably trying to save you some money.

You will probably find more OSB being used today than plywood in roofing applications.

 

Yes, the OSB is being used because it is cheaper.

You need to get a couple more bids and compare.

Also, don't be afraid to ask the contactors these questions - if they can't give you a good answer, you should think twice about following their advice.

 

I just recieved this email from a professional group.

Paul,

The estimate has "osb plywood", which is a contradiction. It sounds
like you believe they meant OSB. OSB is used quite frequently, because
it is typically less expensive than plywood.

NRCA is concerned with potential fastener-holding problems and
dimensional stability because of the effects of moisture where OSB and
other nonveneer products are used as roof decking.

Thank you for contacting NRCA.

Joan P. Crowe, AIA
Director of Technical Services
National Roofing Contractors Association
10255 W. Higgins Road, Suite 600
Rosemont, IL 60018
800/323-9545




----- Original Message -----

Sent: Sat May 17 11:27:27 2008
Subject: this is an estimate that was given to me (please advise me)

Dear Friend,
I have a low slope roof that is approx. 20 ft by 30 ft rectangular.
The asphalt roll roof material has deteriorated, so I want to have this
low slope section replaced. The following is an estimate that was given
to me. Can you tell me is this is acceptable. I am especially worried
about osb. Why should this be an issue, since plywood is cheap and has
always been used in the past.

Here is the write-up:

1. Remove entire rolled roof (approx. 20ft x 30ft) and haul away all
debri.
2 Inspect roof decking and structural components of flat roof (he means
low slope).
3. Replace all deteriorated raftes and/or roof decking.
4. Apply 4x8 sheets of 7/16 o.s.b. plywood over entire roof deck.
5. Apply liberty sbs self-adhering roofing system to entire flat roof
area (he means low-slope) 6. Install new custom bent galvanized steel
counter flashing to base of single
flue brick chimney.
end of write-up, total cost $2,978.00

Why do they install o.s.b. instead of traditional plywood?

Thanks, Paul Hoskins

 

I've seen that OSB does puff more than plywood when water damaged. And it warps at least as much.

The NRCA comment about fasteners is interesting. Because I've noticed that when OSB swells the flakes kinda rip off the screw threads, by their own pressure. Plywood maintains a grip even when the plies are separating.