"Lowering" a section of my floor?

[musigenesis]

The wheel wells and the floor around it on my bus are tremendously rusted out, to the extent that I need to basically rebuild the entire floor from about two feet behind the wells to three or four feet in front of them. I have discussed this repair with my mechanic (a guy who also does a lot of custom vehicle modification) and we discussed the basic conventional way of rebuilding the floor, which would be to cut out the existing floor, weld in cross-members of some sort (3" high rectangular steel tube or something like that) running side-to-side from chair rail to chair rail and resting atop the chassis rails, and then a layer of 16 ga sheet steel on top of this, creating a replacement floor that is at the same level as the original factory floor (and joined with the existing wheel wells which are themselves OK other than the bottom 2" which is rusted away completely).

However, since I am planning on building a 3" deep insulated subfloor on top of the factory floor (2x4s with a half inch ripped off), I believe that there is a way to rebuild the floor section around the wheel wells so that the new sheet metal would be at the level of the top of the chassis rails (i.e. the bottom of the original floor structure) and the subfloor would be on top of this.

Basically, my idea is to run one cross-member beam behind the wheel wells (about where the fuel tank inlet is) and a second one about three feet in front (where the side exit door starts) and then remove all of the original factory floor in between. The removed flooring bears the weight of the rest of the body, so the two beams would need to be strong enough to bear the weight normally borne by the removed flooring (I'm thinking 3"x2" rectangular tube with 1/4" walls would do the trick, but I dunno).

I would then run two rails (possibly also 3"x2" tube but I think these don't need to be that strong) from the front beam to the rear beam, but these rails would be welded to the undersides of the beams (so that the tops of these longitudinal rails are at the same level as the tops of the chassis rails) and would run next to the chassis rails (on the left and right sides, respectively) in between them and the inside of the wheel wells. The new sheet metal would then be placed on top of these longitudinal rails (and also on top of the chassis rails), so when completed this section would be 3" below the original factory floor.

I would then build the wooden subfloor for this as a separate section on top of the new sheet metal, which would give me a fully-insulated floor section that would only come up to the level of the original factory floor (the front and back of the bus would also have the 3" subfloor but there it would be built on top of the original factory floor and thus be 3" higher). This might seem kind of not worth it, but I'm 6' and if I build a 3" subfloor and insulate the ceiling with furring strips, I'll end up with a ceiling that is an inch or two too low for me to stand up fully. With this "lowered" floor section, I would have an area for my kitchen, bathroom and dressing area that would allow me to stand up fully (these are the only things that I really need to be able to stand up for) and I would achieve this without having to do a roof raise.

Is there some reason this plan would not work?

 

[FAC]

I’m a Fabricator professionally (just for background) I think you could do it,but I wouldn’t recommend it. Just thinking aloud I guess if the sheet metal only had two ribs running parallel with the chassis frame rails I don’t think it would be very ridgid. The span for the sheet metal would allow it to flex, now after you built the insulated subfloor you probably wouldn’t notice it as you walked on it. When driving though it would probably still vibrate and flex which is not great for your welds.

 

[musigenesis]

I’m a Fabricator professionally (just for background) I think you could do it,but I wouldn’t recommend it. Just thinking aloud I guess if the sheet metal only had two ribs running parallel with the chassis frame rails I don’t think it would be very ridgid. The span for the sheet metal would allow it to flex, now after you built the insulated subfloor you probably wouldn’t notice it as you walked on it. When driving though it would probably still vibrate and flex which is not great for your welds.

My thought was that walking-around weight would be borne by the subfloor, which itself would be resting mainly on the chassis rails (with the sheet metal in between). I would also weld four plates onto the chair rails in front and behind the wells that extend down 3" and had a lip (this would support the sheet metal on the outer edge and also support the edges of my wooden subfloor. The joists of my subfloor would have L-clips screwed to the bottom, and these would be welded to the sheet metal.

So basically the sheet metal would not ever have to support any weight, and it would be held rigid because it's welded to the subfloor.

Also: I very much appreciate the opinion of a pro fabricator, since I've never done metal work like this myself. Do you have a rough idea of what this would cost? When looking at materials, there's a place locally where I can get 4'x8' sheets of 16 ga steel for about $40, so my rough estimate for this is that the material might be $500, and then it's just whatever my mechanic guy would charge for labor. I have a feeling my estimate is wildly low.

 

[FAC]

I can see it working well how you are proposing. Basically the sheet metal is a shield and the rest of the framing takes the load. I don’t think I would do it for my own bus, I am planning on going the roof raise route, but if your set on not doing one. We charge 70 an hour plus materials for jobs like this and without seeing it I would guess it would take 6-8 hours $420-$560 for labor. I think your estimate for materials is Close maybe three sheets of 16ga one stick of 2x3 maybe two for the ribs too then odds and ends for the rest

 

[musigenesis]

I can see it working well how you are proposing. Basically the sheet metal is a shield and the rest of the framing takes the load. I don’t think I would do it for my own bus, I am planning on going the roof raise route, but if your set on not doing one. We charge 70 an hour plus materials for jobs like this and without seeing it I would guess it would take 6-8 hours $420-$560 for labor. I think your estimate for materials is Close maybe three sheets of 16ga one stick of 2x3 maybe two for the ribs too then odds and ends for the rest

Cool, glad to know this isn't 100% crazy. This is probably the crazy bit, though: I'm also thinking of keeping open a 2'x2' hole on one side of this section, between the back of the wheel well and the fuel tube (there is just enough room here for an opening this size) and then building a sheeted and insulated box that extends about 10" below the floor. Above this opening I would position a step tub like this one:

https://www.campingworld.com/sit-in-step-tub-right-hand-drain-tu500rh---colonial-white-68806.html

such that the tub part is in the 2x2 hole and projecting below the floor level. This would give me a good bit of extra headroom in my shower (maybe an extra 6" or so) meaning I wouldn't have to position it in the middle of the bus, and then the gray water drain would be at the bottom of this box (the kitchen sink will be right next to the tub and will drain into the same outlet).

One thing that seems advantageous about the tub hole is that it would be a natural low point in this rebuilt section, and if any water got in it would drain down into this box and I could get it out via the tub drain opening.

Crazy idea 2 is to make a similar hole with recessed box on the opposite side of the bus and put a cat litter box in it, with my composting toilet placed above it (so all shitting on the bus would be in one place).

Any chance you're near Philly? I'm not totally sure I trust my mechanic - I took my bus to him because his shop is literally around the corner from my parking spot, and since I don't have the bus registered or insured yet I wouldn't feel good about trying to drive it any farther.

 

[musigenesis]

I can see it working well how you are proposing. Basically the sheet metal is a shield and the rest of the framing takes the load. I don’t think I would do it for my own bus, I am planning on going the roof raise route, but if your set on not doing one. We charge 70 an hour plus materials for jobs like this and without seeing it I would guess it would take 6-8 hours $420-$560 for labor. I think your estimate for materials is Close maybe three sheets of 16ga one stick of 2x3 maybe two for the ribs too then odds and ends for the rest

Sorry, one more question (ok, questions). When butt-welding the sheets for this, is it to be expected that the seams would be water-tight just from the welding? Or would it be necessary to also put seam sealant over the seams? Would this sealant go on the inside or outside? Is it necessary to have a joist over the seam (so that the two pieces break over it) or can it be sort of free-standing?

 

[Native-SKO]

I will answer part of your question(s): When two pieces of metal are welded together, they form one piece of metal. If you have a proper weld along the entire ength of the seam, it will be water-tight ... as if the two pieces were always the same piece of metal and never cut. You will still want to protect the metal by priming and painting, at least on the exposed surface.


As far as the resultant piece being "free-standing", that all depends on the thickness of the metal and the forces applied. In your case, the sheet metal is being used as a cover and the structural support is (mainly) coming from the length-wise and cross-wise 2"x3" rectangular stock you are planning to use to support the flooring.


P.S.: I like your idea of setting the tub down a bit. Please take care to make sure there is enough clearance for the other stuff that is already under the frame ... like your exhaust pipe. I believe there is a college girl (wendysdrivethrudude) that did a complete sunk-in bath tub on this site. The whole thread is a good read. The first post about the sunk-in bath tub is here: http://www.skoolie.net/forums/f11/college-students-skoolie-conversion-17037.html#post199465

 

[FAC]

Native is right on about a proper weld being %100 waterproof and airtight too. Think. Propane tanks air tanks etc The problem is getting that quality of a weld in the environment of the bus, using a 75 25 instead of straight co2 is going to help but there will be a lot of awekward welds to make and I would guess it will be worked on outside which is harder when there is some wind blowing the shielding gas away. My point is that if I was doing it I would not rely on the weld to be waterproof. I would use the welds for the structural part of the job and use an undercoating seam sealer or good paint to do the waterproofing. The welds need to be covered anyways.

I too like the idea of a sunken shower pan, it reminds me of the curbless ADA style showers people have started putting in higher end houses around here. I think it would be pretty easy to build an angle iron frame that fits the pan and sheet it with the same 16ga to protect the pan.

I am all the way over in California so probably a little too far to just get some welding done

 

[musigenesis]

I will answer part of your question(s): When two pieces of metal are welded together, they form one piece of metal. If you have a proper weld along the entire ength of the seam, it will be water-tight ... as if the two pieces were always the same piece of metal and never cut. You will still want to protect the metal by priming and painting, at least on the exposed surface.


As far as the resultant piece being "free-standing", that all depends on the thickness of the metal and the forces applied. In your case, the sheet metal is being used as a cover and the structural support is (mainly) coming from the length-wise and cross-wise 2"x3" rectangular stock you are planning to use to support the flooring.


P.S.: I like your idea of setting the tub down a bit. Please take care to make sure there is enough clearance for the other stuff that is already under the frame ... like your exhaust pipe. I believe there is a college girl (wendysdrivethrudude) that did a complete sunk-in bath tub on this site. The whole thread is a good read. The first post about the sunk-in bath tub is here: http://www.skoolie.net/forums/f11/college-students-skoolie-conversion-17037.html#post199465

Thanks for the link to the sunken shower post. It's reassuring to know that there is at least one other person with the same crazy idea going on.

I'm pretty sure I have sufficient clearance for this - it helps that I already have a big hole in the floor there. Although things will definitely be tight since I want this to be insulated.

 

[musigenesis]

Native is right on about a proper weld being %100 waterproof and airtight too. Think. Propane tanks air tanks etc The problem is getting that quality of a weld in the environment of the bus, using a 75 25 instead of straight co2 is going to help but there will be a lot of awekward welds to make and I would guess it will be worked on outside which is harder when there is some wind blowing the shielding gas away. My point is that if I was doing it I would not rely on the weld to be waterproof. I would use the welds for the structural part of the job and use an undercoating seam sealer or good paint to do the waterproofing. The welds need to be covered anyways.

I too like the idea of a sunken shower pan, it reminds me of the curbless ADA style showers people have started putting in higher end houses around here. I think it would be pretty easy to build an angle iron frame that fits the pan and sheet it with the same 16ga to protect the pan.

I am all the way over in California so probably a little too far to just get some welding done

I'm going to have a local mechanic/fab guy do all the welding for this (I own a MIG welder but I've never used it or any other welder before) and it will be indoors. Is it reasonable for me to assume he can do a waterproof seam?

 

[FAC]

If it’s inside it’s a lot easier to get good welds. The main problem is when wind blows away the shielding gas

 

[EastCoastCB]

If it’s inside it’s a lot easier to get good welds. The main problem is when wind blows away the shielding gas

Yep.
I've been using flux core for a while now since all my welding is out in the breeze.

 

[musigenesis]

Yep.
I've been using flux core for a while now since all my welding is out in the breeze.

Interesting, is that generally what flux core is used for (welding outside)? My welder does flux core apparently, and I have the same amount of experience with that as with MIG (none). I think I'm going to let a pro do this job, however.

 

[alpine44]

I like your idea of modifying the floor structure to your needs if you have to replace it anyway and am planning to do the same on my box truck conversion.

A couple of things to keep in mind:

Rust grows out of control where moisture is trapped. I would use open profiles like I, T, or L instead of rectangular tubing unless a lot of torsional loads have to be carried. (How great closed profiles are for torsional loads -twisting the profile along its axis- can be easily demonstrated with a PVC pipe that you try to twist in the original state and then with a lengthwise slit cut through the wall. The difference is huge.) Unfortunately, closed profiles are rust traps unless seamlessly welded on the ends or properly coated inside and drained.

Another common rust trap is a piece of sheet metal laying on top of a beam. Water gets into the thin gap between the sheet and the beam and major rust is the result. Welding sheet metal seamlessly to a beam of much larger material thickness is prohibitively difficult and expensive. A better and commonly used way is to join floor plates on top of the beams with many spot welds and then run a bead of a quality sealer along the corner between the beam and the sheets.

Whether the original metal floor in your bus contributed significantly to supporting the loads from the walls depends on whether this floor was part of a stressed skin structure or just a "cover". To act as a stressed skin, the floor metal would have to be rigidly(!) attached to the joists and to the structural members at the wall by the factory. Then, it would greatly enhance the bending stiffness of the entire floor system. (The thousands of rivets you see on airplanes connect the skin to the internal structural members not just to cover them but also to carry a substantial amount of tension loads through the skin). OTOH, if the skoolie builder just tacked the floor down to keep the road spray off the wood, I would not worry about modifying that section like you proposed.

I will be in Delaware from mid April until at least June and could meet you in Philly to take a look at your project and to exchange ideas. My box truck to off-road RV conversion is my first "bus" project but I am a mechanical engineer who has build several motorcycles, cars, airplanes, etc. and is still alive and well to tell the story.

 

[musigenesis]

I like your idea of modifying the floor structure to your needs if you have to replace it anyway and am planning to do the same on my box truck conversion.

A couple of things to keep in mind:

Rust grows out of control where moisture is trapped. I would use open profiles like I, T, or L instead of rectangular tubing unless a lot of torsional loads have to be carried. (How great closed profiles are for torsional loads -twisting the profile along its axis- can be easily demonstrated with a PVC pipe that you try to twist in the original state and then with a lengthwise slit cut through the wall. The difference is huge.) Unfortunately, closed profiles are rust traps unless seamlessly welded on the ends or properly coated inside and drained.

Another common rust trap is a piece of sheet metal laying on top of a beam. Water gets into the thin gap between the sheet and the beam and major rust is the result. Welding sheet metal seamlessly to a beam of much larger material thickness is prohibitively difficult and expensive. A better and commonly used way is to join floor plates on top of the beams with many spot welds and then run a bead of a quality sealer along the corner between the beam and the sheets.

Whether the original metal floor in your bus contributed significantly to supporting the loads from the walls depends on whether this floor was part of a stressed skin structure or just a "cover". To act as a stressed skin, the floor metal would have to be rigidly(!) attached to the joists and to the structural members at the wall by the factory. Then, it would greatly enhance the bending stiffness of the entire floor system. (The thousands of rivets you see on airplanes connect the skin to the internal structural members not just to cover them but also to carry a substantial amount of tension loads through the skin). OTOH, if the skoolie builder just tacked the floor down to keep the road spray off the wood, I would not worry about modifying that section like you proposed.

I will be in Delaware from mid April until at least June and could meet you in Philly to take a look at your project and to exchange ideas. My box truck to off-road RV conversion is my first "bus" project but I am a mechanical engineer who has build several motorcycles, cars, airplanes, etc. and is still alive and well to tell the story.

I would love to meet and talk with you about these projects. It would be nice to talk to someone in person who does not think I'm insane with the bus thing.

I was thinking that rectangular tubing was overkill for these beams since they won't be twisted, but I didn't think about the water trapping issue. I think they should only be subject to bending loads so I guess an I-beam would be better.

That's good to know about the spot-welding and sealing approach. It's almost enough to tempt me to try doing this all myself, but fortunately not quite enough. One other thing I'm not sure about: the "beams" of the existing floor (which are actually formed from two ends of sheet bent into opposite-facing C shapes and welded together) rest on top of the chassis rails, but there is a pad of some sort of material between the beam and the rail (about half an inch thick), and at this spot the beam is clamped to the chassis. As I understand it, this pad/clamp combination is meant to slide in a head-on collision so that the body does not stop as abruptly as the chassis. I can't reproduce the clamp with my structure (although I'm not sure there's actually one in this region, I need to check that) but I think I would need some kind of pad material between the chassis rail and the new sheet metal, and I'm not sure what I would use here.

It's encouraging that people who have done fabrication think that this floor-lowering approach is feasible. Thanks for your interest in this.

 

[Mountain Gnome]

(How great closed profiles are for torsional loads -twisting the profile along its axis- can be easily demonstrated with a PVC pipe that you try to twist in the original state and then with a lengthwise slit cut through the wall. The difference is huge.)



(The thousands of rivets you see on airplanes connect the skin to the internal structural members not just to cover them but also to carry a substantial amount of tension loads through the skin).

It is the combination of the physics described in this post that explains why I don't want to remove the inner metal "skin" on the inside of my roof (and I am not - but also because it is a pain, and my bus IS rust free). There are rivets every 3 or so inches (by memory, not measured), and they add so much strength and rigidity to the overall body. If the inner ceiling panels were not structural, they would only need 12 or so rivets per panel, not over 100. The fiberglass end-caps for the exterior roof are riveted to the roof's rib-beams with like 5 rivets. The front one especially has to deal with enormous wind pressure Along that same seam, the metal panel has over 50, yet it is relatively shielded from the wind.



I read once Ferdinand Porsche said to make a vehicle light weight, but stronger at the same time, curve the metal panels. I believe that is why buses are built with round roofs, and the roof itself is built like a giant box-frame - or more like corrugated cardboard. Strip one side of that cardboard off, and it is no longer rigid; it becomes floppy like a piece of paper.


I've rolled a truck before, and I had no warning or control to prevent or stop it. I want my bus to survive that if it should ever come down to it again.

 

[musigenesis]

It is the combination of the physics described in this post that explains why I don't want to remove the inner metal "skin" on the inside of my roof (and I am not - but also because it is a pain, and my bus IS rust free). There are rivets every 3 or so inches (by memory, not measured), and they add so much strength and rigidity to the overall body. If the inner ceiling panels were not structural, they would only need 12 or so rivets per panel, not over 100. The fiberglass end-caps for the exterior roof are riveted to the roof's rib-beams with like 5 rivets. The front one especially has to deal with enormous wind pressure Along that same seam, the metal panel has over 50, yet it is relatively shielded from the wind.



I read once Ferdinand Porsche said to make a vehicle light weight, but stronger at the same time, curve the metal panels. I believe that is why buses are built with round roofs, and the roof itself is built like a giant box-frame - or more like corrugated cardboard. Strip one side of that cardboard off, and it is no longer rigid; it becomes floppy like a piece of paper.


I've rolled a truck before, and I had no warning or control to prevent or stop it. I want my bus to survive that if it should ever come down to it again.

Buses have rounded roofs because that allows the walls and ceiling to be formed from a single rib made from a gradually-bent channel. Buses with flat roofs (like Continentals) need the ceiling beam to be welded to the wall beams, creating potential weak spots in the corners that can fail in a rollover (like Continentals actually did just a few years ago).

A bus is not really anything like corrugated cardboard, because the channels are much stronger than the sheets (in cardboard the inner parts are the same material as the outer skins). I think a bus is much more like an airplane's semi-monocoque fuselage, with strong ribs and an outer skin that stiffens the overall structure (airplanes do not generally have an inner skin that is in any way structural).

But it's not quite like an airplane, because in an airplane the entire tubular structure is kept rigid (prevented from bending) by the stiffness provided by the outer skin. In a bus, such resistance to bending does not have to be provided by the skin - the body resists bending because it is clamped to the chassis. I think the purpose of the outer skin in a bus is just to keep the channels perpendicular to the floor in case of a rollover; if the bus were just the channels without any skin (inner or outer) and the bus rolled, the channels would just flatten forward or backward and the occupants would be crushed.

This is probably why the outer skin panels (and the inner skin panels) are only riveted to every other channel. If they were really structural in the same sense as an airplane skin, the panels would be riveted to every rib.

Additionally, the ceiling panels in my bus all had a bunch of tiny holes drilled in them, making them basically a mesh rather than a solid sheet. This is apparently done for acoustics (reducing the echoes) but it's not something that would ever be considered for a structural material.

FWIW, the fact that the ceiling panels are so damned thick and heavy anyway is the main thing that makes me think they are actually structural in some way. It seems like you could do a basic ceiling panel of much lighter material like plastic or fiberglass. It could well be the case that both outer and inner panels provide stiffening in equal measure, in which case you're probably throwing away your safety margin by removing the ceiling but not necessarily dooming your bus to a crushing (I need to check my bus - maybe the ceiling and roof panels are staggered such that they're not riveted to the same channels?). But to be fair, this whole problem can be avoided by just never having anyone ride in the back of your skoolie (assuming you left the front ceiling panels in place like I did) which they shouldn't without proper seats and shoulder restraints.

 

[EastCoastCB]

It is the combination of the physics described in this post that explains why I don't want to remove the inner metal "skin" on the inside of my roof (and I am not - but also because it is a pain, and my bus IS rust free). There are rivets every 3 or so inches (by memory, not measured), and they add so much strength and rigidity to the overall body. If the inner ceiling panels were not structural, they would only need 12 or so rivets per panel, not over 100. The fiberglass end-caps for the exterior roof are riveted to the roof's rib-beams with like 5 rivets. The front one especially has to deal with enormous wind pressure Along that same seam, the metal panel has over 50, yet it is relatively shielded from the wind.



I read once Ferdinand Porsche said to make a vehicle light weight, but stronger at the same time, curve the metal panels. I believe that is why buses are built with round roofs, and the roof itself is built like a giant box-frame - or more like corrugated cardboard. Strip one side of that cardboard off, and it is no longer rigid; it becomes floppy like a piece of paper.


I've rolled a truck before, and I had no warning or control to prevent or stop it. I want my bus to survive that if it should ever come down to it again.

Wanderlodges (BB factory conversion) didn't come with a metal headliner, AND they have half the ribs.
These aren't unibody vehicles. They're body on frame.

 

[Sleddgracer]

Wanderlodges (BB factory conversion) didn't come with a metal headliner, AND they have half the ribs.
These aren't unibody vehicles. They're body on frame.

the arch is the strongest construction - even an egg will hold a tremendous weight when applied end to end - ( .'Chicken eggs were found to have a compressive strength of 100 lbs' ) - bracing ( skinning ) the arches on both sides gives great strength fore and aft and side to side - using ply wood to make side to side connective walls would reduce damage in a roll over or from a downward force - without the use of heavier material, I doubt a vehicle could be stronger or safer than a school bus

 

[EastCoastCB]

The wanderlodge is a school bus body with less ribs and no interior skins... Its just cardboard clipped to the ribs.