Building a metal building with C purlins

[Hickey]

Anyone here have experience on building metal buildings? My work is having a small garage/shed built using nothing but c purlins and steel roofing panels. It seems like a simple way to build, but I have a few questions.

They are welding a lot of the c purlins to each other with a mig welder and seemingly no prep work. Do c purlins come coated in a weld thru primer? It doesn't seem to be causing issues with the welding.

What kind of costs versus wood are we talking about here? I sure would like to build a large carport/shelter for my motorhome using the same materials.

 

[Spork]

My dad's done a bunch of metal buildings around his place, I don't think a single one is framed with wood. Typically the biggest issues are you have to have enough support for the steel panels and it's got to be structurally sound enough for your loads. The steel panel can span quite a large distance, the vertical walls typically will have something to screw into about every 4 feet. (attached at floor, 4 feet up, 8 feet up, etc). You can bump that number up a little like if you wanted a 10 foot wall you could put the middle support at 5 foot and then screwed in top and bottom. This probably depends on what gauge paneling you choose also, some google'ing indicated this could be up to 7' span.

A lot of the commercial buildings will use a C purlin or S shaped but usually they are bolted vs welded together, however both are possible. If you go into some of the arch buildings you basically can bypass all the framing and the exterior skin is the support. Example: http://www.archbuildings.com/ The biggest issue with these is if you're looking for shelving against the walls the walls aren't always 90 degrees or the structure doesn't lend itself to shelving because of the in and out pattern of the walls. Typically these don't require the equipment required to lift your walls/trusses into place however they usually will be build with a small trench then cemented in for support to lock them in, if you got partway through building and had a big windstorm come in things could get really exciting without something holding the panels down.

One note, you may want to contact one of the metal building suppliers, if you're not retrofiting an old corn crib like my dad they take a lot of the engineering guesswork out of it and prices can be pretty comparable to DIY.