Using wooden joists for cantilevered rear deck?

[desertfather]

I've seen a few threads about rear decks that extend from the bus frame, and I think it's a great idea, especially as I embark on a shortie build. Even a small space outside the rear door when parked would be really useful. I'm curious: is it possible to build a short rear deck using wood bolted to the frame, and not metal?

The orthodox solution here, I know, would be to bolt metal extensions onto the frame and then cover them with wood decking. But let's say you use treated 2x8 wood joists, bolt 5 or 6 feet of the lumber into the big C-channel beams running underneath the bus, and leave 2 feet extending through the bumper at the rear, and lay your decking on top of that. Let's say, too, that you're not going to put anything heavy on the deck while driving. Would it work?

This tells me that it would be fine for a normal, non-moving deck: https://www.decks.com/how-to/43/deck-joist-cantilever-rules-and-limits

But I'm wondering whether the stresses of driving might somehow cause it to break, although I'd think it would take a huge amount of force to snap a 2x8 joist.

What do y'all think? Terrible or possible?

 

[o1marc]

Yes, it's possible. I would only advise it to someone who has to have it that way and can't afford to weld up a metal frame. Cost wise the difference would only be the labor cost of the welding.

 

[plfking]

What do y'all think? Terrible or possible?

I think you'd be fine. If frame flex worries you, you could always bore your bolt holes a little oversize to allow some movement.

 

[desertfather]

Thanks, guys. I only ask because steel seems to be the "right" answer, but wood is something I know how to get, how to work with, etc. I don't know the first thing about sourcing metal.

Marc, you're saying the labor for welding would be the only difference in cost. You think materials would be about the same price? Would you really need to weld at all, if you just bolted everything to the frame, and then either drilled holes to bolt cross-supports, or used decking to hold it all together laterally?

Again, thanks for the thoughts and ideas!

 

[o1marc]

I would have steel cantilevers bolted to the frame and then extend out to an angle iron perimeter frame with a few supports and decking wood secured to that. It's not a lot of welding and could be done in an hour's worth of labor (around $75). Google "welders" in your area to find one. Any metalfab shop could handle it.

Boring holes larger for movement is the dumbest solution I have heard. If it's allowed to move during flex it will continue to waller out the holes until it falls off.

 

[djdalfaro]

What is the spacing between C-Channels?

I second what o1marc said, basically yeah, it'll be fine, but the cost of welding this small of a job would be pretty small.

Either way it'll be fine. Especially if you're only going out 2 ft.

 

[o1marc]

I think frame spacing is around 31".
I checked locally here and if i used 2-6' 1/8"walled 4"x4" tubing bolted to the frame rail and then made a rectangular box from 1-1/4"-1/8" wall angle into and just welded that onto of the 2-4" cantilevers, and then fill the box with PT 2"x6"s.
Unfortunately my steel yard only sells in 20' lengths, but I can use the leftovers elsewhere. But for this project, $7.20' for the tube is $86.5, the angle at 20' is $13, if going the full width of the us you'll use 14'. So figure just over $100 in steel, $75 for welding labor, and a few bucks for 2x6's. Safe, sturdy, removable.

Put removable plastic caps on the ends of the cantilevers and use them for long pole storage or other items.

 

[plfking]

Boring holes larger for movement is the dumbest solution I have heard. If it's allowed to move during flex it will continue to waller out the holes until it falls off.

Common sense isn't common in your family, is it?

We used to design bariatric recliners with a 3/8" bolt resting in a 1/2" hole in a 1" piece of lumber.....loaded it down with 300 pounds and ran it through 100,000 cycles for BIFMA testing. with no "wallering out" of the hole. So I'm confident a 200 pound deck on a couple of 2" x 8" joists with 3-4 bolts each side will be fine.

 

[Bork-SKO]

As a welder with my own business, and having made two of these now (one for myself and one for a paying customer) I will chime in. First off, yes the wood will work if it will meet your needs for light duty. Just keep in mind that any weight cantilevered over the wood will make it flex repeatedly as you are driving and eventually it will wear out. I recommend using white maple or another good hardwood and not a $3 piece of large ring pressure treated from the local homeless despot. Drilling the holes out larger than the bolts in the wood and the frame will make your life a lot easier when trying to make everything straight and lined up. What really holds things together in these applications is the clamping force and friction of the two materials being squeezed together. With enough bolts nothing should be moving due to the clamping force, therefor the holes will not get rounded out or whatever was mentioned.

As far as the welding labor goes, this is subjective. The only way this would only cost $75 for me to do it would be if you showed up at my shop with everything ground, cut, mounted, prepped and ready to weld. Meaning all I literally have to do is put on my gear, turn on the welder, weld the spots you have ready, and then shut everything off. That means no measuring, no lining up, no squaring, and no grinding or clean up.

If you were to ask me to build the entire thing this is how it would be broken out:

1-2 hours for design and prep/material gather. Lots of emails, photos, and 5 phone calls to figure out how this will be designed.

2-3 hours build time, that is cutting, grinding, welding, finishing.

3-? hours install time. This is the most difficult thing to judge because it might be as simple as drilling 8 holes with a mag drill, it might be me taking lots of brackets off and re supporting things from the new steel. It might be me having to cut holes in existing steel and prepping everything for welding. If I have to bring out all of my mobile welding gear to meet you someplace other than my shop that typically cost about $100-$150 per hour.

So on the high side, this could be 10ish hours of my time. Shop rate is $50 per hour. If half of this time is someplace with my mobile setup that brings it to $750 or more.

I know it sounds like a lot and I am just throwing out what would be necessary for me to complete a job that would be up to my standards professionally. I do have a name to uphold and this is something that could impact the safety of you and others driving on the road so it is not something taken lightly. Please also remember that I have insurance to pay for that covers all of this work and I would need to use thousands of dollars of tools and special equipment to get it done properly.

Here is what I would do. Look up a steel surplus store in your area, even junk yards sometimes keep good steel to the side and you can just buy that back for the weight of the steel. Get what you need, drill holes in the frame of the bus, clamp the steel up to the frame, mark the holes in the steel, drill those, bolt it together. Now you have a frame sticking out the back of the bus. Bolt on brackets for the wood you want to hold up, or find a neighbor, or cousin, or friend of a friend with a welder and buy him/her a 30 pack to come over and burn some metal together. There are always other options, just keep in mind that professional work has a value to it that needs to cover a lot more than just the workers time.

 

[desertfather]

This is all great info -- gets exactly at the questions/issues I was wondering about. Thanks, everyone.

Bork, I much appreciate your thorough explanation of the time and effort involved in something like this. Now I can count the costs a little more accurately, and if I do work with a welder, I won't show up with unrealistic expectations.

I'm leaning toward doing it with wood now, not only because I think I can do it cheaper, but also because I can do it myself. When I hire things out, I tend to mentally disengage, you know, as if the finished product belongs to someone else. When I do something myself, there might be limitations, but at least I know exactly what those limitations are, and then I'm much more likely to maintain what I built. Maybe that's human nature, or maybe it's just me.

If I build a cantilever deck with wood, you'd better believe I'll be underneath the bus pretty often, checking and double-checking the integrity of the thing, keeping it all clean so the wood doesn't rot, etc. I'd try to do that with a deck someone welded for me too, but I probably wouldn't be as conscientious afterward. :shrug:

 

[Drew Bru]

First off, yes the wood will work if it will meet your needs for light duty. Just keep in mind that any weight cantilevered over the wood will make it flex repeatedly as you are driving and eventually it will wear out. I recommend using white maple or another good hardwood and not a $3 piece of large ring pressure treated from the local homeless despot. Drilling the holes out larger than the bolts in the wood and the frame will make your life a lot easier when trying to make everything straight and lined up. What really holds things together in these applications is the clamping force and friction of the two materials being squeezed together. With enough bolts nothing should be moving due to the clamping force, therefor the holes will not get rounded out or whatever was mentioned.

100% great advice here

If it were me (and as someone more familiar with woodworking than metal work, I very well may steal this idea), I'd use 8/4 hardwood for the joists....not construction lumber. White oak is fairly rot resistant, but expensive. There are sawmills in unexpected places, you just need to poke around a little to find them. Prices will be much better than retail big-box store. Another source of hardwood is old doors, especially for beefy hardwood that you would need for joists. Our local Habitat for Humanity RESTORE has old frame-and-panel doors for like 20 bucks. 2 of those should give you some material to work with.

I'd also protect the wood with several coats paint. No sense in spending the money and time and have it rot away from all of the road grime and rain/snow or road salt.

Just some thoughts from the peanut gallery here.

 

[desertfather]

100% great advice here

If it were me (and as someone more familiar with woodworking than metal work, I very well may steal this idea), I'd use 8/4 hardwood for the joists....not construction lumber. White oak is fairly rot resistant, but expensive. There are sawmills in unexpected places, you just need to poke around a little to find them. Prices will be much better than retail big-box store. Another source of hardwood is old doors, especially for beefy hardwood that you would need for joists. Our local Habitat for Humanity RESTORE has old frame-and-panel doors for like 20 bucks. 2 of those should give you some material to work with.

I'd also protect the wood with several coats paint. No sense in spending the money and time and have it rot away from all of the road grime and rain/snow or road salt.

Just some thoughts from the peanut gallery here.

Good call, Drew -- there are plenty of sawmills around here, and using some good local white oak would give the project a lot more personality. I think I'd paint the part that's down under the bus, and stain/varnish the part that's visible out past the bumper to show the character of the materials. Plfking's "woody" truck and bus accents on his build thread are inspiring.

 

[Drew Bru]

I think I'd paint the part that's down under the bus, and stain/varnish the part that's visible out past the bumper to show the character of the materials. Plfking's "woody" truck and bus accents on his build thread are inspiring.

Exactly! I can't wait to see the finish product, it's gonna look sharp

 

[plfking]

Just some thoughts from the peanut gallery here.

And just one more.

Desertfather, this might be another option for you to avoid cutting holes in your bumper. I think it would work great for a deck that's not going to carry a lot of weight.....I'm thinking of taking it one step further, and bolting the framework together instead of welding....would still be strong enough for a couple hundred pounds, plus I could easily disassemble and store it if need be.