Picture this: 30’X56′ living area spanning crawl space with 16 vertical inches to work with. The plan right now is to install a beam running lengthwise (supported as needed by piers over a lengthwise footing), then run the floor joist crossways over the beam.
What is the best, least expensive way do construct this? Engineered joists? Split the difference with 8″ beam and 8″ joists, or some other configuration? How often to support the beam?
Discuss please?
Replies
How dry a crawl space?
A lot is going to depend on how dry this crawl space is going to be.
Unless this space is well sealed and or conditioned space you run a strong risk of moisture and maybe mold development.
Unless you were going with floor trusses (tall ones at that), you will need one or more beams.
Using a steel beam will at least keep any wood further away from the ground - but rust would still be a possibility.
I have a local inspector that will demand any framing within 16" be treated material. If you did use treated, I would look for material KDAT (kiln-dried after treating) to help control shrinkage.
Have you considered either deepening the crawl space or even filling it in with sand and pouring a concrete floor?
You are looking at about 80 yds of fill and another 25 yds of concrete
Terry
Steel bar joists can easily accommodate your 30' clear span. Something as light as a 16K2 (16" depth) will allow 161 psf/lineal ft total load at only 165 lbs each. Powder-actuated fasteners make fast work of attaching decking to the bar joists. You don't have enough depth to run bar joists in the other direction, which might be cheaper.
My roof's a bit heavier, 200 tons total with a 30' clear span. My bar joists are heavier, with a 24" depth. These structural members are ubiquitous in commercial construction. Low cost, including installation, is the reason for that.
Call your local steel company to get a nice surprise about cost and help with installation instructions. .
Ooooops, I believe I misled you. The crawl space will actually be 4'. I wanted to keep 32" of "head room". Or thereabouts. It will be conditioned space also with insulation and vapor barrier everywhere.
Proceed.
BTW, steel joists are REALLY way more expensive than engineered or regular construction lumber. :)
"BTW, steel joists are REALLY
"BTW, steel joists are REALLY way more expensive than engineered or regular construction lumber."
Not in ANY jurisdiction where houses like mine have been built. I've heard this misinformation before, from people who never bothered to get a quote. As I mentioned, go into a commercial building and look up. You think steel is used because it is "REALLY way more expensive"?
I'm in a really rural area, so we don't have any close steel companies. I do understand the idea of less material = less labor, and I will get specifics. As far as cost recovery along the line of disposal of waste product, I heat with wood, so as long as wood isn't treated, I burn it. My insurance company shows no difference on my policy regard wood vs steel floor trusses/joists. I found this article well done, you may scroll down to Table 10.4 for the summary.
http://www.huduser.org/portal//Publications/pdf/steel_vs_wood1.pdf
double 2x10 beam with piers at 8' spans allowing for ijoist or dimensional lumber as floor joist.
There's one suggestion... Thank you.
What's best or least expensive is very much open to debate.
Regular lumber (like 2x10s) is the lest expensive option for materials, but has the highest labor cost. Readily available pretty much anywhere.
I-joists have higher material cost, but arguably less labor. There is usually a short wait to get them, unless you're near a place that stocks them. They allow for a very flat floor.
Floor trusses have the highest material cost, but the least labor. Lots of room to run mechanicals in the trusses. (depending on the depth)
Consider open web floor trusses or I joist
You should consider open web 16" deep floor trusses and span 15' with a beam down the middle. Could also place them at 24" o.c. and use 1 1/4" plywood. The end of the trusses over the central beam could be top chord bearing - this would allow the beam to be be located within the height of the trusses. The central "beam" could also be a truss to allow plumbing and ducting to get thru if necessary.
Or better yet, instead of a central beam, consider an unsheathed stud wall with studs at 24" o.c on a continous footing. This would allow you to order 30' I joist or open web trusses with bearing point at the center of the span.
Ok, I can picture that too. Meeting with salesman from building supply place at noon today to price options including steel.