Suggestions on reinforcing box truck roof?

[WannabeNomad]

Hi all,
New to this site and learning as I go. Apologies if this has been asked and answered before, but I couldn't locate anything in previous threads on it... I'm converting a 14ft box truck and could use some advice on reinforcing the roof. It's got a 20+yo fiberglass ceiling that needs to be replaced.

More importantly, it needs to have some serious reinforcement in the framing, since I would like to ideally have a small roof deck and some solar panels, as well as be able to hang hammocks from several points along the framing on the inside (as traditional sleeping hammocks as well as daytime swinging "chairs" so it needs to be able to handle the stress from different angles). I picked up some ribbed galvanized aluminum roofing sheets to redo the actual roof, since that was much more financially doable than ordering a traditional full sheet, but I have no clue how to go about framing it in a way that will be load bearing from the top and the bottom. The box framing is about 7'7" across side-to-side, with a slight two inch arch at the peak of the roof.

I came across metal web joists that look like they would provide the structural support I'm looking for in the framing, but they're a custom order type thing that's way outside my budget, and the size of them alone would eat up a lot of my already limited ceiling height (for pictures of the joist piece: https://www.donaldsontimberengineeri...-need-to-know/). I'm also not sure how to brace the joists between/against each other from front to back, not just across the width of the truck. Am I even headed in the right direction with the angled/triangular framing joists?

Appreciate any suggestions!

[Unplanned Tourist]

You are going to have to put a good amount of money into your conversion, so don't cheap out on the basics like the roof. Go for it, or find a better rig to start with. Old school buses are great. Well built, cheap and parts reddilly available.

[WannabeNomad]

Originally Posted by Unplanned Tourist

You are going to have to put a good amount of money into your conversion, so don't cheap out on the basics like the roof. Go for it, or find a better rig to start with. Old school buses are great. Well built, cheap and parts reddilly available.

I'm working on a shoestring budget, and since this is my first conversion and I've already got the box truck, I'm really looking for advice for how to work with what I've already got available to me, and specifically how to design the framing in a way that will withstand the kind of stress it'll be under. I don't expect it to be a perfect, state of the art conversion, just sturdy and functional.

[Unplanned Tourist]

Originally Posted by WannabeNomad

I'm working on a shoestring budget, and since this is my first conversion and I've already got the box truck, I'm really looking for advice for how to work with what I've already got available to me, and specifically how to design the framing in a way that will withstand the kind of stress it'll be under. I don't expect it to be a perfect, state of the art conversion, just sturdy and functional.

OK, how are your welding skills? You can make up ceiling supports out of 1X2" tubing. Attach them to the walls with some 2 inch angle iron with the flange against the wall and the other flange down. You will then have room for 2 inches of Styrofoam SM insulation between the cross bars. Space them at 16 inches or less. That will give you a good sturdy roof. A 7 1/2 foot long 1X2 0.083 inch thick tubing will hold most anything you put up there as long as you don't get carried away.

[MechEngrSGH]

Originally Posted by Unplanned Tourist

OK, how are your welding skills? You can make up ceiling supports out of 1X2" tubing. Attach them to the walls with some 2 inch angle iron with the flange against the wall and the other flange down. You will then have room for 2 inches of Styrofoam SM insulation between the cross bars. Space them at 16 inches or less. That will give you a good sturdy roof. A 7 1/2 foot long 1X2 0.083 inch thick tubing will hold most anything you put up there as long as you don't get carried away.

I'm a former RV engineer and custom camper builder so can advise with some more detail.

My first suggestion is to make 'micro laminate trusses' (thin, high-grade veneers with no knots of voids) from 3/4 Baltic birch plywood. This is what Safari Motor coaches use (at least did) for roof trusses (our material was Douglas fir). Cut a 4x8 sheet into 4" strips and taper them from about 2-1/2" on the ends to the 4" height in the center on a table saw jig. Possibly a small flat in the center if you plan to put fans on the centerline, making the flat 14" wide would be best. Fan holes are 14x 14. If you want them rounded, make a pattern and copy them using a 1/2" bottom-bearing router bit.

Making an arched or tapered metal truss (other than by bending a square tube which requires machinery) is problematic from thermal conductivity and cost perspectives.

The sheathing can/should be 1/4 or 3/8 baltic birch plywood. To attach a wood sheathing, use screws. Since the sheathing is wood, why can't the trusses be? R-value of wood is ~1/inch.

DO NOT USE EPS foam (styrofoam) it has only R3.5 per inch. Use XPS (extruded polystyrene) or polyisocyanurate foam. They both have R6/6.5 (respectively) per inch. XPS is more structural. It is used as insulation typically sold in home stores and has a density of 1.5lb/cuft. Denser versions such as to use under concrete slabs are available in a 2.5lb/cuft density. The latter is best for something to be walked on. It is possible to make a roof with 5mm plywood glued to both sides of 2.5lb XPS with a 3/4 wood perimeter. My constructions is different but this may give you some ideas.

https://www.youtube.com/watch?v=A1yOZflKuSY&t=1087s

If you want to use metal,

[Bobertgoes]

Did you do anything? This is old post and you abandon it, you probably joined to aske the question and never came back. I have had the same box van and have done the work, but no use typing if you r gone forever....

[Ollie Rogers]

Subscribing.