×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Design for 2 layers of asphalt shingles?

Design for 2 layers of asphalt shingles?

Design for 2 layers of asphalt shingles?

(OP)
Is there a code requirement that requires an asphalt shingle roof to be designed for 2 layers (original plus one overlay).  I work in California which still uses the 1997 UBC.
Thanks

RE: Design for 2 layers of asphalt shingles?

I don't think there is a code requirement....It would simply be a decision that the owner and engineer would want to discuss up front.

RE: Design for 2 layers of asphalt shingles?

There may not be a Code requirement, but I use about 5 or 6 psf for shingles, anyway.  It seems to be a common belief that a roof can accept re-shingling once, but not twice.

DaveAtkins

RE: Design for 2 layers of asphalt shingles?

I would check with the local building official.  I believe they limit the maximum number of layers of asphalt shingles by building type. You need to design for the maximum number of layers.

RE: Design for 2 layers of asphalt shingles?

Typically - only ONE re-shingle is allowed either by code or shingle manufacturer.  

You buy shingles by their weight - say 220 or 240 which means 220 or 240 lbs per square and a square is 100 sq ft.  Theoretically - the heavier the longer they live......

Therefore - a typical roof has about 2.5 lbs psf for one layer of shingles and add some for felt - like .5 psf

In roof truss design - 10 psf for dead loads if very typical and allows for two layers of shingles.

RE: Design for 2 layers of asphalt shingles?

(OP)
I have always felt that the 10 psf dead load for roofs is low.  Some of the higher end composition roofs can run 400 pounds per square (4 psf).  When you add plywood (1.5 psf), insulation (0.5 psf), 5/8" gyp board (2.8 psf), mech & elect (0.5 psf), misc. (1.5 psf), trusses/girder trusses or 2x12 rafters/beams (3.0 psf) and the slope factor, I usually end up with 15 psf as a minimum design dead load for composition shingle roofs.  That is for one layer of shingles.

RE: Design for 2 layers of asphalt shingles?


I remember reading in one of the codes (can't remember which one) that they limit the number of "reroofs" to one.  Therefore you have the original roof and a reroof.  If the roof requires another reroof down the road, the two existing roofs must be removed prior to the reroof (at least according to code).

RE: Design for 2 layers of asphalt shingles?

Kramer -

I tend to agree in that I was talkling about what most truss guys use - 10 psf dead TOP chord (shingles, plywood, etc.) and 10 psf dead on BOTTOM chord (drywall, insulation, lights, etc.)UNLESS otherwise specified.

If I was doing simple rafters - I would use something in the 20 psf range.

RE: Design for 2 layers of asphalt shingles?

With a gable wood truss roof, I use 10 psf top chord DL, and 7 psf bottom chord DL.  These numbers are used by all of the truss designers around here.

DaveAtkins

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources