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Fireman
Join Date: Sep 2004
Posts: 0 Kansas
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2002-11-02          44562


Which is better, Engineered beams, floor trusses, or dimensional lumber for the floor joists in a house and why. What is the cost difference?

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2002-11-03          44572


I hate loaded questions with complicated answers but here goes.
The answer is it depends.
Normally engineered beams are used with normal dimensional lumber joists or 3" tongue and groove decking. They are used where the span is greater than can normally cut with dimensional lumber or where greater loading is required. This is the most expensive method of construction.
Engineered joists or trusses (there are different designs) are used where longer spans are needed and in replacements to normal joists. They are generally more expensive than regular joists.
Dimensional are the least expensive but you are limited in the span.
These are the costs to get the floor decked. Unfortunately the cost of contruction is something entirely different than the cost of decking.
For example the engineered joists may cost more than regular joists but the deck may have less variation and greater flatness. This effects the rest of construction and may lower the cost of construction. The truss style joist has passages for wiring and plumbing that allows quicker secondary operations.
If you are spanning larger areas then the engineered beams many actually cost less than building support walls or posts in the basement.
Depending on the finish required then the engineered beams and the 3" decking may be less regular joists and tongue and groove.
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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-11-04          44579


I figured there'd be a pretty good answer from Peters on this one and so there is.

I've only worked with regular joists myself. When I talk with our building inspector to see what he'll go for, he hauls out a book and looks up required floor loading for the particular application and then gives me max spans for various joist sizes. If greater spans are needed larger joists might do it or maybe doubled joists.

Larger joists do cost more and reduce headroom if that's a problem and doubled joists complicate working to centers. At any rate, I imagine that acceptable designs for most structures could be made using either type of joist.

The cost answer maybe lies in the amount of labour required for installation. If engineered joists take less work, then commercial projects may have lower overall costs with engineered joists. Do it yourself project costs may be the opposite.

In terms of a structure, I'm not sure there's an easy 'best answer.' I think that codes for the same type structure start off with a required life expectancy. Designs that use different materials are supposed to produce the same life expectancy. The subject is undoubtedly more complex than my grasp of it.
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