Post-frame or steel frame?
Most barndominiums use one of two structures under the metal skin. Both can make a good house. The differences show up in the foundation, the ceilings, insulation details and engineering paperwork.
Post-frame (wood)
The National Frame Building Association describes post-frame as an engineered wood-frame system that meets UBC and IBC standards, using large solid sawn posts or laminated columns instead of wood studs, steel framing or masonry (National Frame Building Association: What is post-frame?). The posts carry loads into the ground or sit on a concrete pier or masonry foundation, sometimes with plastic barriers to protect the wood (National Frame Building Association: What is post-frame?).
A structural engineer at Pinnacle Engineering explains that posts are often set in holes 4 to 5 feet deep on a small precast pad or poured footing, with trusses commonly spaced 48 inches apart and purlins carrying the metal roof (Pinnacle Engineering: a structural engineer's take).
Steel frame (red iron)
Pre-fabricated metal buildings use the same general layout in all metal: steel frames, sometimes called bents, with metal girts, purlins and siding, sitting on a slab-on-ground foundation (Pinnacle Engineering: a structural engineer's take). In Norman, plans for manufactured steel buildings must be signed and sealed by an Oklahoma-licensed engineer (Norman one and two family residential checklist).
Turning a farm building into a house
The same engineer flags changes that add cost to either type (Pinnacle Engineering: a structural engineer's take):
- Drywall ceilings need framing no more than 24 inches apart, so 48-inch trusses need doubling or furring.
- Trusses must be designed for the extra weight of ceilings, lights and ductwork.
- A home needs a foundation wall, which a plain post-frame barn does not have, so a wall or turned-down slab is added.
- Some communities and HOAs require exterior materials other than metal siding.
Questions for any builder
- Which frame do you use, and who stamps the drawings?
- How are posts protected from moisture, or how are steel columns anchored?
- How will the slab edge be insulated?
- Are interior stud walls and ceiling framing in the price?
Price comparisons are on the costs page. Kit sellers often sell either type as a shell only (Turner & Son: kit vs turnkey in Oklahoma).