GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Roofing question: Do I NEED 5/8″ plywood decking under a 50-year steel roof?

Mai Tai | Posted in GBA Pro Help on

Specs:

House 6:12 pitch, garage 3.5:12 pitch

Trusses 24″ OC, 2X6 top cord (solar ready). Climate zone 6A, mid to low snow load.

I’ve already moved off the 7/16″ OSB decking that is on the plans, and have temporarily settled on 1/2″ plywood decking for the roof. Roofing contractor said this would be much better for the screw holding power (using click-lock standing seam panels, 26 gauge, 16″ wide). Now the question is would I see any benefit over time going to a 5/8″ plywood roof decking? The cost is incremental vs 1/2″ ply (let’s call it 1k), but it all adds up, and if 1/2″ is plenty i am content leaving it at that. Will 1/2″ ply sag over time on 24″ OC trusses, and if so will 5/8″ provide any benefit for this over a 50 year life span? Assume venting will be more than adequate (full length ridge vent gable roof, full vented soffits).

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Malcolm Taylor | | #1

    Mai Tai,
    No you don't need 5/8" plywood. It's better but not necessary. The most noticeable difference between 1/2" and 5/8" is when you walk the deck before installing the metal and feel the flex if you stand on a horizontal seam. Once the roofing is on this disappears. There is no reason to believe the plywood will sag over time.

    Having said that, I've suggested and used 5/8" on two houses, and liked the feel of both the deck and the way it held fasteners. But I think it falls in the category of upgrades which are nice, but over time makes no discernible difference.

  2. KEVIN ZORSKI | | #2

    Mai Tai - use plywood clips between the 1/2" sheets in between the trusses. Good stiffener for edges, though may not matter once metal roof is on.

  3. Malcolm Taylor | | #3

    Kevin,
    I wouldn't use H-clips under metal. Too great a chance they get slightly misaligned and telegraph through. The metal roofing fasteners end up doing the same stiffening of the plywood edge.

    Using H-clips really slows down the sheathing. Do you use them where you build? I haven't seen them here on a house for years.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |