Bolt-up: fabricated in a shop, bolted on site

A bolt-up building is usually a pre-engineered metal building. The frames are designed for that building's size and loads, then fabricated in a shop. Columns and rafters are often built up from steel plate, and many are tapered. Connection plates are welded on and bolt holes are made before the steel ships.

On site, the crew stands the frames and bolts them together. Columns bolt to anchor bolts set in the foundation. Rafters bolt to the columns and to each other at the ridge. Purlins and girts are usually cold-formed Z or C sections that bolt to clips on the frames.

The welding happens in the shop. The field work is lifting, aligning, bracing and bolting.

Weld-up: stock steel, cut and welded

A weld-up building is often built from standard steel shapes, cut to length and welded together. That welding may be done in a shop, on site, or both.

Purlins and girts may be welded to the frame, and can be tube or channel depending on the design.

The frame

Bolt-up frames are designed member by member for the building, so steel can go where the load is. Weld-up frames are usually built from constant-depth stock shapes, sized for the span and loads.

Either way, the frame has to be engineered for the site's wind, snow and seismic loads, and for whatever hangs from it. Don't size red iron by eye, and don't assume a frame that worked on the last job works on this one. Spans, eave heights and local loads change the answer.

The connections

Bolt-up connections are designed and detailed before fabrication. Plate sizes, bolt sizes, bolt counts and tightening requirements come from the engineering. Most of the connection's quality is set in the shop. The field crew's job is to install the specified bolts and tighten them the way the drawings call for.

Weld-up connections are made by the welder. Their strength depends on the weld size, length and quality, and on the welder's skill. Some jurisdictions require certified welders or inspection for structural welds. Ask your building department before you assume either way.

That difference shows up in scheduling. A bolt-up crew needs a lift, the right tools and the drawings. A weld-up crew needs welders, welding equipment on site and time for the welds.

The material order

This is where the two really split for a dealer.

A bolt-up order is a building package: rigid frames, purlins, girts, bracing, sheeting, trim, fasteners, an anchor bolt plan and erection drawings. The parts arrive made for that building. That makes the order accurate when it's right and expensive when it's wrong, because a fabricated part is hard to change in the field.

A weld-up order covers steel members cut to the design, connection details from the engineering, purlins and girts, sheeting, trim and fasteners. Stock lengths matter here. Cutting members from stock leaves offcuts, so the takeoff has to account for how each member gets cut, not just how long it ends up.

Either way, the order should come from the design, not from square footage. What it takes to get a real material list out of a model.

Which one to quote

A few practical questions settle most jobs:

If you sell both, you need to design and price both without switching tools or rebuilding the takeoff by hand. And when the building might not need red iron at all.

Both in one place

Redline covers red iron in both bolt-up and weld-up, alongside post frame, stick frame, hybrid post frame and tube frame / carports. That's five framing systems on one plan at $250/mo with 2 seats included and $0 setup. Material lists, dimensioned elevations and sheet layouts come from the design, and pricing comes from your supplier price sheet once it's loaded. The 10-day free trial lets you run a red iron job you already know through it.