13 May 2019

Heard the one about the Structural Engineer and the Builder?

So an I-Joist, a Glulam and an LVL walk into a bar . . . and the bartender named Simpson says “you know my wife doesn’t like me hanging around with you guys”. Bud a boom. Ok, admittedly engineers are not typically known for their sense of humor and modulus of elasticity is no laughing matter, but how do you get a builder’s attention on a topic like Engineered Wood Products (EWP)? Well, here are several examples that are even less funny:

After the house is dried in, the builder or one of his subs notices a low spot or slope in the floor caused by overloading, or an overly bouncy floor with too much deflection. The house is already taped and bedded, with finish floor laid – no easy fix.

The engineer specified open-web trusses, but layout, approval and/or production lead times shuts down the jobsite for three to four weeks with walls waiting for truss delivery. Switching to I-Joists at this point would take just as long and more engineer review fees.The budget for the 5,000 sq. ft. two-story mirrored the last similar house you built. But with a different architect or floor plan, the structural engineer’s required loading almost doubled the cost of the floor system and blows your budget early in the build.

Highly Engineered or Over Engineered? This has been a challenging area for lumberyards and builders lately. Framers have joked in the Park Cities that builders want wood floors that feel like concrete. That means a very stiff floor (l/600 or higher), even though Code minimum is l/360. Seems the bar gets continually raised by architects’, engineers’ and builders’ natural risk aversion and liability concerns. Sometimes, however, that comes at budget-busting costs! So how do we effectively value-engineer these high-end floor systems to satisfy discerning homeowners with a tighter budget?

I-Joists vs. Open-Web Trusses. The pendulum swings between these competing products over the years, and it seems the current preference with custom builders is open-webs. A nice compromise may be trimmable open-web trusses, but those are not customizable and don’t work in many applications. This floor decision is often made by the architect or engineer before the builder is involved, but here are a few arguments for each:

I-Joist * 25-30% cost savings vs. trimmable open webs * Flexibility in hole placement and sizes for mechanicals * quicker lead times * trim on-site for perfect fit (no call backs or measurement delays) * lower engineering review costs * LVL flanges more dimensionally stable than truss lumber

Open-Web * highly customizable for spans, point loads and duct chases * top chord bearing for shade pockets on contemporaries * fewer beams for ease of mechanicals and ducts *fewer red tags due to other subs’ sawzalls * precisely measured so little waste on job site

Regardless of floor system choice, it is critical that interior design choices are communicated to the floor designer to include unforeseen loads – such as marble, brick or tile on floors, walls, islands or ceilings. Nice to also know about those pool tables, weight machines and water beds (do they still make those?!).

Cost Factor One manufacturer commented that “architects and engineers aren’t designing to save money these days”. With open-webs each professional in the chain seems to build upon his or her predecessor without much collaboration regarding costs – the engineer calculates loads and designs based on the architects’ plans, the truss company builds what the engineer designs, and the framer installs what the truss company lays out. But absent from each step are trade-off discussions that could significantly lower costs. Why is this missing? Is it time-constraints, liability concerns, or something else?

We have observed much more frequent value-engineering from I-joist suppliers. Unless these conversations become more frequent on the open-web truss side, perhaps the pendulum on custom homes will swing back toward I-joists (particularly as housing affordability is a big issue and in the next downturn when costs will be highly scrutinized).

Thanks for jumping into the debate with us (if you read this far!). Please let me know what you think and how we can better serve you with your EWP, lumber and panel needs.


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