Framing for trailer with rooftop tent

[ptulli]

Hey guys, I am in the design phase of my squaredrop/back or what ever you wanna call it. It's going to be a 5x8 and I'd like it to be able to carry a rooftop tent if the step son wants to come with the wife and I when we go out. This will be for off-road/overland and also just regular camping when we don't take the pop-up. I have a basic design in mind but no idea how to frame the walls or the roof to be strong enough but yet light enough for my 2dr jk (2K tow rating). I have thought of using a couple 1x1 metal tube in a few spots to carry the extra weight, but not sure it's necessary or too much weight. I tired to search but couldn't find the answers I was really looking for, so thought I'd ask.

Extra's not sure if it's important or not. Looking to have Timbren suspension with 35" tires to match the Jeep when the lift is installed. Galley area 18" deep, interior to be the remainder with the typical cabinets on the interior back to the galley, door on each side, possible skylight or small shelf on front slat wall, possible water tank underneath/underbed storage. I think that's it for the basics, like I said beginning stages trying to get ideas all together but stuck on framing for my designs.

Thanks for your help!

[tony.latham]

If I were tasked with this, I would add stress points to the interior skeleton wall.

Here's an explanation of what my last skeleton was all about:



I don't think you'd have to add a lot of wood. You might bump Tim Curry, aka noseoil a PM about this. He used to design roof trusses.



Tony

[working on it]

* It's perhaps not the way you're planning to build your trailer, but I built a "simple/squareback" variant, using 3/4" plywood, and steel hardware to bolt it together (plus a lot of PL Premium adhesive). There are no trusses used, just Simpson Strongties gusseted angle brackets and steel corner brackets from Home Depot. Stainless 1/4"-20 carriage bolts, fender washers, and either acorn or nylock nuts were used. The roof, a 48" x 72" piece of 3/4" ply was set on the upper edges of the sidewalls, with the rear inner wall as a cross-support(at 22" from rear, defining the galley compartment).

*

measuring the roof size, for support calculations.jpg (291.11 KiB) Viewed 5967 times

* To use the Sagulator http://www.woodbin.com/calcs/sagulator/, I figure that the un-supported area length between the front slope (which has additional support brackets) and the rear bulkhead is 50", while the roof over the galley/storage area is only 22", and the total width is 46.5" (resting atop the 3/4" (x2) sidewalls), so the maximum area of concern is 46.5" x 50". Treating this area as a "shelf", so to speak, the Sagulator shows acceptable support for a 500 lb. (not centered ) load atop the roof.

*

roof weight-bearing calculation.PNG (21.71 KiB) Viewed 5967 times

* If I had been planning to use a roof-top tent, I probably would've put a roof spar under the center of the 46.5" x 50" area, just for extra safety.

[ptulli]

by working on it » Tue Jan 26, 2021 10:42 am

* It's perhaps not the way you're planning to build your trailer, but I built a "simple/squareback" variant, using 3/4" plywood, and steel hardware to bolt it together (plus a lot of PL Premium adhesive). There are no trusses used, just Simpson Strongties gusseted angle brackets and steel corner brackets from Home Depot. Stainless 1/4"-20 carriage bolts, fender washers, and either acorn or nylock nuts were used. The roof, a 48" x 72" piece of 3/4" ply was set on the upper edges of the sidewalls, with the rear inner wall as a cross-support(at 22" from rear, defining the galley compartment).

Your camper is very similar to the build I am looking at doing. The front slope isn't as steep, the front wall would be sloped starting at 3.5' and angled to 1.5' on the roof. The galley I am thinking about 18" for a depth, making that span about 60".

[Tomterrific]

Wood is super strong in compression. You will not need to worry about building light weight and could use 1 x 2 battens on the 1/4" sides to hold the weight. Where problems arise is with the structure racking. A book shelf is a good example. You can build the sides and shelves to hold a ton of books but the merest push on the side and the whole thing collapses. A simple diagonal member turns the weak square into a triangle and the shelf does not rack. The light ply wall does the same up front. The open back is another matter. Gussets top and bottom will triangulate part of the opening. A kitchen design is another way to keep the back from racking.

The 5 foot span of the roof is another problem. You will need a stiff roof and the wood will not be in pure compression so weak. A large gap between the roof and ceiling filled with foam should give the required stiffness. Gussets at every wall batten would also help.

I really think you have a bad idea putting a tent on top. It can't imagine how irritating having someone sleeping 3 feet above my head. Why don't you buy a tent? A 4 man tent gives plenty of room and the cost is low. My buddy bought a cot/tent and we camp together. He loves it.

Tt

[working on it]

1)Wood is super strong in compression....

2)Where problems arise is with the structure racking. A book shelf is a good example. A simple diagonal member turns the weak square into a triangle and the shelf does not rack....

3)The open back is another matter. Gussets top and bottom will triangulate part of the opening....

4)The 5 foot span of the roof is another problem. You will need a stiff roof and the wood will not be in pure compression so weak....

5)Gussets at every wall batten would also help....

6)I can't imagine how irritating having someone sleeping 3 feet above my head....

1)* Whether you use a simple sheet of 3/4" plywood as walls (as in my build), or use thinner ply in a composite sandwich (like tony.latham), laying a similar sheet atop the upright edges of the walls will support up to 875 lbs (uniform loading, at least in my calculations) without appreciable sag.

2)* The diagonal bracing is a good idea for thin plywood, or even one with thin foam core composite, but my trailer's 3/4" solid plywood , and Tony's thicker composite, act as a stressed skin panel. Just as strong.

3) * There's really no open back to the squareback design, with the front sloped wall closing off that end (mine is also braced with extra brackets and oak boards across and on the sides...tied into the doorframe bracing), and the middle having the rear bulkhead holding upthe roof, while the short 22" overhang (18" in the OP's plan) is negligable (especially if the rear of the trailer is a closed wall...with a hatch opening cut-out). Plus, the angle brackets I used liberally are gusseted, and the corner brackets at every corner, top/bottom, are thick steel with side supports.

4)* Answered in reply 1. Plus, a single beam/spar located midway between front slope and rear bulkhead will make the sag almost nil.

5) * Answered in reply 3; the Simpson StrongTies I used are gusseted and the corner brackets are made with thicker/stronger material to prevent this (the carriage bolts securing these are backed with 1.25" diameter fender washers to prevent pull-thru, while prodigious amounts of PL adhesive further prevent movement on all interfaces).

angle & corner brackets.png (197.71 KiB) Viewed 5892 times

6)* Use a layer (or two) of sound-deadening material, either on the cabin ceiling, or on top, under the rooftop tent. Good at blocking sound/vibration transmission on cars, this stuff is also (most brands) also waterproof and usually self-adhesive. Dynamat here's one type specifically for decking http://www.dynamat.com/automotive-and-transportation/automotive-restoration/dynadeck/#:~:text=As%20DynaDeck%20is%20completely%20weatherproof,so%20no%20adhesive%20is%20needed.is known for effectiveness, and I've used it before. Here's alternatives compared https://aquietrefuge.com/dynamat-alternatives/

[noseoil]

This is the framing I used on our 5x9. It's actually 2 1/4" deep framing members, but if I was doing a tent for the top, I'd add some "hard points" for fasteners & use some oak or another type of hardwood for the framing in that area. Work backward from the tent base. First figure out the framework which holds the tent in place, the fastening points & edges, then figure out how much weight it will take when sleeping & build the roof frame to take that load.

A mock-up of the spars & framing members with the loading applied or attached will let you know if you have enough strength in the system. It could be as simple as a framework of spars sitting on cinder blocks to make sure it's strong enough. I would make sure there's a "shelf" or rabbet joint, which will support the spars as they are bedded in place & fastened at the sides.

Here's the rabbet joint which allows the headliner to go in place first & bend to the contour of the roof, then the spars & framing were set in place with glue. It's plenty strong. Hard points for the solar panel, rear hatch at the hinge & attachments are red oak for holding the fasteners. Most of the frame is 4/4 poplar, which is light & strong.

[ptulli]

I know it's kinda like house building but I have thought of putting metal 1x1s in a few spots to help the extra weight and keep the frame stiff. Here is a rough idea, the dark area is where the metal "studs" would be, the dotted line by door is where I'd like to put another "stud". I think this would take care of the weight of the rooftop tent. Am I going overboard with this idea?

[ptulli]

Sketch with wood frame, 1x2 on flats. I'm not sure how big to make the upper cabinets in the galley. They are 18" deep, not sure how much space I should leave between upper and lowers.

[noseoil]

A standard upper cabinet in a home kitchen is 12" not 18" so I'm not sure you will need the extra depth. The distance between the counter should be for the largest item which will sit there. This could be a coffee maker, microwave, convection oven or a roll of paper towels. That having been said:

[Pmullen503]

Sketch with wood frame, 1x2 on flats. I'm not sure how big to make the upper cabinets in the galley. They are 18" deep, not sure how much space I should leave between upper and lowers.

You really have to have the finished details designed in to make sure the correct framing is in place.

Start with the finished design (including all the details of cabinetry, hard points for mounting accessories, lighting, your wiring runs etc.) and work backwards.

It's not a waste of time to mock up your galley with cheap ply and cardboard boxes for cabinets to make sure there's room for everything.

[ptulli]

A standard upper cabinet in a home kitchen is 12" not 18" so I'm not sure you will need the extra depth. The distance between the counter should be for the largest item which will sit there. This could be a coffee maker, microwave, convection oven or a roll of paper towels. That having been said:

I didn't think to measure the upper cabinets in the kitchen. The depth was figured on the lowers for a Dometic fridge down the road, so I thought of making the uppers match, but again the uppers don't match the lowers in the kitchen either. So definitely will make that adjustment to that. I didn't think of what the largest item would be, guess I gotta work on that.

You really have to have the finished details designed in to make sure the correct framing is in place. Start with the finished design (including all the details of cabinetry, hard points for mounting accessories, lighting, your wiring runs etc.) and work backwards. It's not a waste of time to mock up your galley with cheap ply and cardboard boxes for cabinets to make sure there's room for everything.

I have the outside figured out, it's why I have the door framed in. There will be one on the other side as well. The frame is set for the cabinets for the galley except the uppers as I haven't figured them out. The cabinet in the sleeping quarters is set as well, possibly and upper over the head, but haven't deiced. I gotta a rough mark up of the galley, I will work on getting one and post it up. I'm not worried about the electrical, dad's an electrician and that will help. I know what I want for it, so that part isn't an issue. The biggest is making sure the frame is set, the rest can be worked around. I do like that idea of of the cardboard boxes, never thought of that!

[noseoil]

[ptulli]

That picture freaks me out, I won't lie. LOL! I hate to waste wood, but the weight savings has got to be great! Question I would have, would that hold up off-roading? I'm not doing the Rubicon trail with it, but I want it to be able to take the abuse. I want to go overlanding and be ready for what I might encounter. This is my second concern behind the trailer being able to hold a rooftop tent.

[tony.latham]

That picture freaks me out...

I've seen Tim's teardrop up close. It'll last several generations.

Tony