Woodshed #2 is nearly complete, just need to put on a few galvanized panels to finish it up. I've never laid metal roofing, and have read two schools of thought on properly attaching corrugated metal roofing.. One side says screws in the valley, one says screws in the peak. Screws in the peak is supposed to yield fewer leaks by virtue of being out of the flow of water (makes sense.) Screws in the valley is supposed to make shedding snow easier. We get plenty of snow and rain here in the hills of Berkshire County. I'd love to hear a few of you smart FHC members share your wisdom! My current thought is that the tighter bond will be had by screwing in the valley. I'm more concerned with wind than a little leakage, really. The roofing will be attached straight to purlins, no sheathing. Woodshed on the cheap is the plan here.
The screws should have a rubber seal, which will seal better in the valley, there isn't enough flat space in the profile of the metal to allow the rubber seal to seal well at the peak, also if your pitch is low and the snow doesn't shed well by itself, the screws on the peaks will get in the way of roof raking. You might find you have to drill at the peaks too, the screws will self start a lot easier in the valley. My wood shed is non traditional construction, I didn't use purlins, screwed the metal at the peaks directly to the "rafters". It leaks a little, but it's "just a woodshed"...
I've never seen "5 rib" metal screwed on the ridge, or nailed in the flat. I've never seen corrugated screwed, always nailed in the ridge. But I haven't seen corrugated that's been installed recently enough that screws were in common use. I've done a few houses, shops, buildings, ect with 5 rib. All screwed in the flat, no leaks.
My barn is screwed in flat.. 25 years from now when it needs to be painted because rubber gaskets are drying out. Easier to seal flats then ridges.,
in the shingle world you didn't nail in valley's you stayed at least 7 inches out from it. While the neoprene screw may not lay flat on the peak, you can always dab them with a tri-polymer sealant. (I would use geocell) That will stop water penetration for quite some time. Snow lays in valley's longer than on the peak. If you really want to play it safe, grab a roll of ice and water shield and lay it down in the valley before putting the metal on. Way overkill for a woodshed though and more $$
valley unless you have the matching closure strips that may/may not provide support for the rubber washer under the screw head used on the peak. Once you have a couple inches of snow it likely doesn't matter where the screw heads are. Don't squish the rubber much.
Went with screws in the valleys - thanks all for the input! Will have to get some pics up shortly.. Mine is similar to yours, DaveGunter, in that I didn't really follow "Framing 101." Pallets and dimensional lumber, built to hold wood rather than people. It's not pretty, but hopefully it keeps wood dry and doesn't blow away. These two little pallet sheds should hold most of the season's hardwood. I'd be comfortable with one more, but that will have to wait until spring. Then I'd like to build one for shoulder season wood. But now 'til we get buried, I've got wood to process and move!
I did it at the peak on mine since the water will run off the peak more than running straight down the valley and eventually through the nail/screw hole causing leaks. As the roof ages there is a lot of micro movement over the years due to wind and weather that works it up and down/back and forth making the hole bigger. Even if the screws nails have rubber grommets/ washers it makes sense to me to do it at the peak to minimize channeling all the water right over those holes. Though all in all, there is probably not a huge difference. But you have to pick one or the other.
