Roof Pitch; 4/12 or 3/12?

[Diggin It]

Cobbling together a shed. Rural area, so no codes or inspections to deal with. No significant snow load to deal with normally, though we have had occasional 10-12" snowfalls over the last 20 years. Wind isn't a major issue either, though gusts of 30MPH or so are not uncommon.

Planning on 24' clear span with overhangs around a foot each side. Most likely 2x6 rafters on 24" centers with 2x4 purlins also on 24" centers, then metal roofing (no wood decking). I'd like to be able to walk on it at least while installing the panels. Hope not to ever need to get on it afterwards.

I can walk around comfortably on a 4/12 shingled roof, less so on metal. Considering 3/12 if there are no real disadvantages.

 

[RNeumann]

Typically 4/12 is the cutoff for “conventional” roofing and “conventional” underpayment- at least from a manufacturer spec. Below 4/12 and they require different underlayment and or won’t stand behind the product. Read the specs on the roofing but, in general, go with 4/12 if either will work for you.

 

[jaxs]

Foam shoe soles and knee pads help. I'm large and old but can walk on my 5 in 12 barn without trouble. To me,less than 3 in 1 doesn't look as good as steeper.
Ok,you know you can't just get answers to questions,we must also meddle. Depending on humidity,metal roofs drip condensation. When car windshields are wet at daybreak,uninsulated metal roof will dip condensation. When I use non-vented propane heat in my uninsulated N Central Tx shop,condensation drips on drywall ceiling.

 

[Birdhunter1]

I have a 6/12 pitch metal on my shop, its nice having that huge overhead space where heat rises to in the summer and vents out, not fun to walk on without tieing off. Snow and ice slides off with force at times with a very low pitched leanto on one side, haven't had any issues in 9 years since I built it.

4/12 metal roof on my horse barn, well vented all around so heat buildup isn't a real issue. Easy to walk on, it was much easier to put up and while snow may stay on it longer it doesn't have an issue draining off. It doesn't slide off is destructive chunks like my shop can do. It can be slick to wk on when its dusty.

3/12 metal on the house, snow sits on it longer but once the sun pops out is drains off, doesn't slide off in chunks. Really no complaints at all. I hope this helps your decision.

 

[joeu235]

4/12 - because its an even number

 

[Diggin It]

On a home brew job, I'm not concerned with whether or not the roof metal maker will back it.

Also not concerned with appearance or aesthetics.

Inside will not be finished in any way, not heated and will be a dirt floor. Cover is to keep the Sun from beating on things and most of the rain/snow off.

While I'm able to walk on 4/12 shingles, my back, hips, knees and ankles hate me for it and punish me for days afterwards. 4/12 metal, I basically have to crawl around on. I'm hoping for someone to convince me that 3/12 won't be the worst mistake I ever made. I've sure made more than my share of them.

 

[3Ts]

My barn is 2/12 pitch. However: I have a steel frame with purlins spaced about 4' apart, roofing steel screwed directly to that and spray foam underneath. No real snow. In last 5 years only a dusting of snow. Light drizzle runs off easily. I don't climb on roofs anymore, but after a hail storm, the insurance guy & roofers walked it without problems.

 

[Birdhunter1]

. I'm hoping for someone to convince me that 3/12 won't be the worst mistake I ever made. I've sure made more than my share of them.

3/12 Won't be the worst mistake you've ever made. I don't think I've seen where you posted your location but you said big snows are not common so I think you will be fine. I've found when it does snow as soon as the sun pops out it tends to go off of a metal rook anyway. To do it over again I would not go with a 6/12 on my shop, maybe a 4/12 because I like the look of it but I would't hesitate to go with a 3/12.

Since you said you are putting them on 24" centers I think you will be more than fine, your truss manufacturer will build them to spec for local snow, ice and wind loads. I'm assuming you will nail in 1x4's flat on top of that to screw to?

 

[s219]

4/12 can be slippery with metal for sure. I did 4/12 on my boat house with PBR metal panels and I do like that pitch for style/looks, but it was about the limit for a metal roof I'd like to walk on. If you do plan to walk on a metal roof, make sure the panel type supports that. I specifically chose 26ga PBR (purlin bearing rib) panels so that I could arbitrarily walk on them. Being a boat house surrounded by water with challenging access, I didn't want to dick around on that roof.

I have done both metal and asphalt shingles on 3/12 (not all asphalt is rated for it so check and be sure to keep the roof clean of pine needles, etc that could cause water intrusion). The math (3/12 = 0.25 tangent ~ 14 degree angle) is very convenient to work with for all your cuts and sizing. 3/12 is about as shallow of an angle as I care to have. I had to do it on my barn lean-to 3/12 in order to get the desired clearance. 4/12 would have made it too low to drive under at the eave end.

I think 2x6 rafters on a 24' span probably won't cut it -- you'll probably need 2x8 (with cross ties every other pair).

 

[4570Man]

I think 2x6 rafters on a 24' span probably won't cut it -- ).

That’s what I thought.