Glulam Building: Start to Finish – Part Two C

Welcome to our “Glulam Building: Start to Finish” series. Our goal is to provide an overview – from idea to completion – of a glulam building, from the perspective of a glulam manufacturer and designer.


Part 2C: Decking & Framing Layout


Last week we briefly mentioned the load path for vertical loads, we’ll take a closer look at that today. This is a very important step in our design process for a building, having major impacts on usability, aesthetics, and cost. We’ll start from the top and follow the loads down to the foundation. 


The first structural component supporting loads needs to cover the entire roof or floor surface, decking or a panel type product is a typical choice. The product chosen will determine spacing requirements for the next step(s) in the load path. Typical options are:

Nominal lumber floor joists with plywood floor sheathing

Plywood – requires support framing every 16″ to 24″. Support framing would typically be dimensional lumber. Plywood is not a typical choice for glulam structures for aesthetic reasons, but is sometimes used in industrial applications or when a ceiling will be installed. Glulam girder spacing, with dimensional lumber running perpendicular, would typically be between 10′ and 20′.

2×6 solid T&G decking spanning beams ~7′ on center

Tongue and Groove (T&G) Decking – requires support spacing between 6′ and 18′ depending on decking thickness. This is very common for glulam structures as it provides a finished wood surface below. The most cost effective combination tends to be 2×6 solid T&G decking on glulam beams spaced approximately 7′ on center with glulam beams spanning to girders from 15′ to 40′ apart. 3×6, 4×6, and 5×6 laminated T&G decking can span progressively further, approximately 10′, 14′, and 17′ respectively (depending on the loads) or be used as floor decking. For roofs, they are commonly used to span directly between glulam girders, eliminating glulam beams for a simplified look.

Laminated T&G decking spanning girder to girder

SIP panels spanning between girders and beams

SIP Panels – required support spacing depends on panel thickness and design, support spacing between 10′ ad 20′ seem to common. Similar to decking, the SIP panels requiring close support spacing can bear on glulam beams, while those with larger span capabilities can span directly to the girders.


















Recently there has been an increased interest in using mass timber CLT or Glulam Panels for floors and roofs, which offer increased spans and increased fire resistance between floors for multi-story structures. These panels can span 12′ to 30′ or more between glulam girders, depending on panel thickness.


The descriptions above all carried loads to glulam girders. (For arch structures simply replace “girder” with “arch”.) Girders can be large glulam beams or various shapes of gluam trusses. Girders or trusses span between columns, and the columns carry vertical loads down to the foundation. Girder, truss, or arch spans can vary greatly, sometimes bumping up against cost or feasibility limits – we’ll cover more on that next time.