When installing a steel roof do you lay a membrane/barrier over the sheathing and screw the steel panels on top of the sheathing, or do you screw rows of 1x4's to the sheathing and attach the steel panels to the 1x4's ? I've seen it done both ways, but not sure which is correct. -Thanks

Always use a membrane. Even if it's 30 wt paper. Then the 1x4's. Metal will build condensation and you will want a barrier with some air flow underneath. Some folks may do it differently, but that's how I do it here in the south. But we don't have the snow load like you get. Sarge

Either way will work. It's nice to provide some ventilation under the metal especially if you have a hot roof. If you have a cold roof, you should already have ventilation in the attic space.

What do you mean by "hot roof/ cold roof " ? I live in northern Indiana so we can get really hot summers and really cold winters. Roof get full sun for most of the day.

The reason I ask , is different people are telling me one way is right and one way is wrong and vise versa. So I'm a little confused, just want it done right and made to last.

Lived in western ny my hole life never seen anybody put a membrane down.. iv never used it also. Not saying it bad or good, just not a west ny thing

I would run tar paper over roof sheathing. Up here, the steel manufacturer would like to see 5/8ths sheeting, if you aren't using purlins, so that the screw sinks into a little more wood, than say, 1/2" of OSB. I see guys run tarpaper over 1/2" sheeting, and go with steel over that, all the time, though.

I might do something like that for myself.

Had a new metal roof put on a couple of years ago and what I was told, was if leaving the shingles, then they would lay 1x4 and install over that. If i had the shingles taken off then they would lay down new tar paper and then the metal. I had them take it down to the wood, so they could make sure that part was good and nothing needed replaced. Last thing I wanted was to have to fix something later.

Over shingles no barrier needed. Over sheeting use barrier. Tar paper works.

I like putting row of purlin over the seam of tar paper so it don't peel up in time.

2 by 4s are vary comparable in price to 1 by 4s and give more holding strength.

How I do my purlin is use ring shank nails through the 2 by 4s into the sheeting. Then use long screws through 2 by 4s into the truss. This gives more strength from wind pull off. Usually when steel roofs get ripped off it takes the purlin with them.

Then screw steel to purlins

The correct way is how the manufacturer recommends.

For mine, 50 yr warrantee (yeah right), to go over new 1x18 hem fir

they said just lay double bubble then install, no purlins needed.
That's what I did. Only thing I forgot was snow catchers as it's 9/12 pitch.

They are on the list to do lol.

I would have used purlins if the deck was old and beat.

After 30 years of contracting and expansion, the rubber wears out on the screw washer anyway. I have watched a metal roofs get replaced now, as I am old enough to see that. They will start to leak in time, and some leak no matter what.

There is nothing wrong with "standing seam" , if I fella wants a nice roof.

There a "little" better now than 30 years ago. Priced a bucket full lately? Yikes.
You are right, It is a very rough environment up there.
Park the truck up there and see how long it lasts is what I told one customer
that was nagging about paint on stop gutters.

30 years is all I need, my best years are behind me lol

is this a house or a garage

House 4/12 pitch, two planes, 16 square. No valleys, dormers, hips, etc.

Installing 1 x 4's over the sheathing won't hurt anything but it's not necessary. Screw the steel right to your plywood over your membrane. I built a new shop last year and did it this way. I used 30 lb tarpaper over 1/2" plywood per the manufacturer's recommendations.

If you plan on installing snow guards and want to mechanically fasten them, run two rows of 2 x 4's between the rafters at the proper locations. Most manufacturers want 1 1/2" penetration. After doing much research, I used glue-on snow guards. So far so good.

30lb felt either way. And make sure it's 30lb. And have them use cap nails, not staples.
Most places don't even carry 30lb anymore
But in my opinion, shingles are better. No chance of condensation, and they look better

I like singles better for looks, but they just don't last as long as steel. I don't want to be reroofing at 70 years old.

I worked construction for nearly a decade, and have roofed several hundred homes, barns, garages, and businesses. We always put down underlayment, be it fan fold, bubble insulation, or felt (only 30# don't bother with the lighter stuff). It's cheap insurance.

They make a good 50 shingle. Elk prestige. One of the better shingles in my opinion
And with a shingle roof, the whole thing will not blow off if the wind gets under one loose piece.
But it's your roof and your discission to make.

Underlayment for either installation but I would only use the purlins if going over shingles(which I wouldn’t do).