16 inch panels on 24 inch rafters and joists?


#1

I’m replacing a 30 year metal roof with EZ Snap 16 inch metal panels. This is a Gambrell Roof - 7/12 to 18/12 to 5/12 pitch with 7/12 to 5.5/12 pitch transition at the dormers. The old roof was damaged from snow and ice ripping the exposed screws out of the panels. We average 30 feet of snow here plus rain. So it’s important to keep the snow moving. I’m in an isolated community. Supplies are 300 miles away. So I’m trying to work with what I have.

The existing joists and rafters are 24inch centers. The panels are 16 inch. The sheathing is 1/2 CDX. I’m using 1" pancake screws (couldn’t find any shorter). I’ve completed 1/2 of the roof (the carport side).

Pancake screws are set at 12" on center. Quite frankly I didn’t realize the sheathing was 1/2 inch until I started the project. I’m about to replace sheathing on the 5/12 pitch located below two dormers (East Side) as the sheathing is weak and one piece was rotted. This area of the roof is over a living area. Before I place my order I have a couple questions.

I’m beginning to have visions of the panels lifting up in a few years from wind (gable trim should help here, the current roof doesn’t have any) and snow and ice dumping off the dormers to the lower 5/12 pitch roof.

My question:
Will the roof survive with 16 inch panels secured every 12 inches primarily to 1/2 CDX plywood?
If I replace all the sheathing on the East Side with 3/4 or ? what other dimensions are changing that I havent’ thought of i.e. distance between roof and bottom of Dormer window?

Pics of roof are at:
public.fotki.com/akdeepwater/roof-project/

Thanks for your help!


#2

you should have 3/4" on 2’ centers,to hold the weight and keep it from flexing,as far as the snow load on the lower roof,have you ever heard of a snow rake,i highly recommend you get one,and remove excess snow as it builds up ,1/2"ply on 16"centers is rated at 4 lb.s per sq.ft. area,3/4" 0n 2’ centers,slightly more–snow gets very heavy,and you should try and keep it clear—you will probably have problems w/screws ripping out where you have 1/2" on 2’ centers unless you can keep the heat off-also insulate as much as possible to keep the house heat from melting the snow into ice as that will make the situation that much worse-good luck!


#3

Hello,

Judging from your screen name I assume that you live in Alaska. I live in Anchorage and install metal roofing. Send me a pm and I can give you the name of a man who works at Diomede (a metal panel supplier) in Anchorage. He should be able to answer any of your questions.

Keith


#4

Thanks for your thoughts. I wasn’t very clear about the metal I’m laying now. The EZ Snap is hidden screws. The metal I removed was exposed screws.

I’m afraid the impact of the snow and ice coming off the dormers will jar the screws loose (not enough bite into 1/2 inch) and sense the screws are hidden I won’t know they’re loose until the sections of panels finally lift up during a high wind.

So to rephrase the question:
Do I have enough “bite” to hold the panels in place for 30+ years using 1/2 inch plywood, 1 inch pancake screws and 12 inch spacing between screws along the panel edge. No credit for occasionally screwing into a joist.


#5

YOU SHOULD AS TYPICAL IS 1 EVERY 24",W/1ST &LAST W/IN 6 " OF THE TOP OR BOTTOM(W/PROPER THICKNESS PLYWOOD TO CARRY THE WEIGHT OF THE SPAN–MY ONLY CONCERN IS THAT 1/2" IS BELOW SPEC FOR 24" CENTERS,AND THAT ADDED WEIGHT WOULD BOW THE STRUCTURE AND CAUSE SCREW POPPING


#6

Thanks again. I think you’re right. The bowing and flexing of the structure is more problematic than the actual falling snow load. I can find 3/4 CDX locally for $32.99 per sheet. No one inch available.

Is it okay to replace the weak 1/2 that I find and the lay the new 3/4 inch over the all of the existing 1/2 inch?


#7

it shouldnt be a problem as long as you dont cover anything wet,and make sure to nail extra like every 5-6" to make it that much stronger


#8

i would replace any wet sheathing that i cant dry out,so it doesnt warp under the new system