strength of 2 x 6 roof

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Forum topic by jackmo posted 09-27-2015 08:10 PM 861 views 0 times favorited 7 replies Add to Favorites Watch
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2 posts in 1171 days

09-27-2015 08:10 PM

Newbie here, nice site lots of info.

I live in MA.
I have a roof which is 4-12. it is 2×6 16 in. on center, 3/4 plywood sheathing
I just finished adding a second layer of asphalt shingles.
My question is are 2×6’s strong enough?


7 replies so far

View TheTurtleCarpenter's profile


1052 posts in 1264 days

#1 posted 09-27-2015 08:38 PM

That depends on how long the rafter lengths are and how they are braced/proped, or stiffened. The 3/4” ply is a plus. 2 layers of shingles in a Northern climate on a 4/12 pitch are going to give it a stress test for sure.

-- "Tying shoelaces was way harder than learning to Whistle"

View Ghidrah's profile


667 posts in 1420 days

#2 posted 09-27-2015 08:55 PM

Won’t stake my life on it. Ma. has been renovating its regs on roofing for close to 20 yrs, more and more towns are adopting the stricter 1 roof layer because of the older properties with undersized rafters. A 4 pitch is a shallow pitch, shear weight is directed down so if the structure is a ranch instead of a small narrow shed the rafts and ridge are going to see much sag in the near future, (5 to 7 yrs). If the rafts are trussed it’ll take maybe 30% longer but you’ll likely also see the sag transfer into the ceiling below.

You should have checked with your local building dept. before you did the overlay.

-- I meant to do that!

View jackmo's profile


2 posts in 1171 days

#3 posted 09-27-2015 11:29 PM

Thanks for the replies!
The rafter lengths are 11.5 ft.
A few have collar ties.
How about if I sister another 2×6?

View AandCstyle's profile


3177 posts in 2455 days

#4 posted 09-27-2015 11:48 PM

Jack, be sure to check for the snow load in your area; it can be significant.

-- Art

View bondogaposis's profile


5086 posts in 2549 days

#5 posted 09-28-2015 12:57 AM

My question is are 2×6’s strong enough?

Kind of late to ask that after putting the shingles on. From these tables it looks like you will be alright, based on 40 lb/sqft live load. If you get more snow than that, start shoveling.

-- Bondo Gaposis

View BurlyBob's profile


5974 posts in 2463 days

#6 posted 09-28-2015 01:07 AM

Bondo that was a good one. First the common sense, then positive reassurance then more confidence. Totally loved it.

View David Taylor's profile

David Taylor

326 posts in 1285 days

#7 posted 09-28-2015 01:35 AM

I just finished a shop building 20×20, with a 4:12 pitch roof in Southern NH. I saw those same tables, and used 2×8’s, 16 on center. Last winter was the worst on record and it was fine. I think 2×6 might be OK, but only just.

-- Learn Relentlessly

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