Am I over engineering/building?

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Am I over engineering/building?

Postby Bugaboo » Fri Jul 05, 2024 11:58 am

Ok so I am looking to build a 5x12x5 Benroy verry similar to what SCWood built(viewtopic.php?t=66631) thought with a few changes due to my northern latitude. Similar to his it would be a Off road-ish idea to pull behind my Jeep(02 Grand Cherokee lifted w/ built stroker motor, we can get into that later). This would sleep my family of 5 for short 1-3 night trips.

I am thinking of building the floor with 1/2ply, 2x2, 1/2ply so that i can have 1.5" of foam in the floor. I was wondering if i could get away with dropping the 1/2 down to 3/8 without any issue? Then on to the walls, my plan for them is 1/4 outer skin ply, 3/4 skeleton ply frame filled with foam, 1/2 skeleton ply frame filled with foam(giving me a total of 1.5" foam), 1/8 ply inside sheet. The roof would be cross framed with 2x3 boards with 2.5" foam with 1/8 ply inside and out. For the hatch I would change the design to a Fredricks to not have a need to use the aluminum T trim and provide a more positive water seal.

Here is a photo of what i have in mind for the wall/floor attachment, as well as the idea for the hatch design with the integration of the wall as part of the design.

Wall-Floor idea.PNG
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Re: Am I over engineering/building?

Postby RBB » Wed Jul 10, 2024 8:43 am

Bugaboo wrote: I was wondering if i could get away with dropping the 1/2 down to 3/8 without any issue?

My gut tells me that you would be ok using 3/8" for the top and bottom of the floor. With the 2x2 frame internally, as well as 1.5" XPS, you are essentially creating a laminate, and the outer layers of ply are effectively skins at this point. Assuming you are gluing all the layers together, then mounting to a steel frame, you should have more then enough there!

my plan for them is 1/4 outer skin ply, 3/4 skeleton ply frame filled with foam, 1/2 skeleton ply frame filled with foam(giving me a total of 1.5" foam),

I think you might be over doing it on the walls... any reason you are looking at skeleton ply vs 2x2 stick frame construction? If you went with 1/4" outer ply, 2x2 stick frame, 1/8"ply on inside, you will have the same wall thickness, same insulation, and lighter weight. (also easier build, unless you have a CNC for cutting the plywood!)
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Re: Am I over engineering/building?

Postby tony.latham » Wed Jul 10, 2024 10:38 am

I am thinking of building the floor with 1/2ply, 2x2, 1/2ply so that i can have 1.5" of foam in the floor. I was wondering if i could get away with dropping the 1/2 down to 3/8 without any issue? Then on to the walls, my plan for them is 1/4 outer skin ply, 3/4 skeleton ply frame filled with foam, 1/2 skeleton ply frame filled with foam(giving me a total of 1.5" foam), 1/8 ply inside sheet. The roof would be cross framed with 2x3 boards with 2.5" foam with 1/8 ply inside and out. For the hatch I would change the design to a Fredricks to not have a need to use the aluminum T trim and provide a more positive water seal.


You don't need that much insulation in the floor or the walls. 3/4" is fine. (I live in Idaho. Today it'll be pushing 100º and we commonly camp below 32º.)

Fredrick's hatch had issues–-a great concept, but it can be greatly improved. I used his manual for my first build. You don't need the full 1/2" inner wall. 1/4" is fine, and the hatch needs to butt against the rear of the floor, not the top, as his instructions show–-rain gutter puts the water on the floor, not outside.

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Re: Am I over engineering/building?

Postby Tom&Shelly » Wed Jul 10, 2024 11:01 am

We did essentially what Tony did. Four years and no issues. :thumbsup:

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Re: Am I over engineering/building?

Postby TravelJunkie99 » Wed Jul 10, 2024 9:17 pm

Consider checking load-bearing needs before reducing ply thickness. Your integrated foam insulation in the walls and roof should work well for insulation and weight considerations. Excited to see your progress!
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Re: Am I over engineering/building?

Postby tony.latham » Wed Jul 10, 2024 9:55 pm

Consider checking load-bearing needs before reducing ply thickness.


I just looked at your seven posts. Have you built a camper? :thinking:

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Re: Am I over engineering/building?

Postby Pmullen503 » Wed Jul 10, 2024 10:00 pm

You get to the point of diminishing returns pretty quickly with a small camper because of the ventilation requirements. I think you could get away with 3/4" insulation in the walls and never feel a difference. The ceiling and floor benefit from being thicker due to beam strength. Just do a good job during assembly with glue on the foam too.
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Re: Am I over engineering/building?

Postby reaver » Thu Jul 11, 2024 1:36 pm

My floor consists of a 1/2" ply bottom layer, with 2x2 internal spars and 1.5in foam, with a 1/4 in plywood top layer. With my mattress on top, it's plenty sturdy enough. Even without the mattress, I could walk on it with minimal flex.
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Re: Am I over engineering/building?

Postby tony.latham » Thu Jul 11, 2024 3:07 pm

building the floor with 1/2ply, 2x2, 1/2ply so that i can have 1.5" of foam in the floor.


My floor is a 3/4" framework with 1/4" plywood top and bottom with the voids filled with foam board–-which is more for structural reasons than insulation. Our 8" mattress works well for that issue.

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Re: Am I over engineering/building?

Postby Tom&Shelly » Tue Jul 16, 2024 6:55 am

XXX
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Re: Am I over engineering/building?

Postby tony.latham » Tue Jul 16, 2024 1:09 pm

Think he just proved you right this morning Tony.


So does that make me a narcissist? :? And do these yahoos actually make money off of this stuff?

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Re: Am I over engineering/building?

Postby Tom&Shelly » Tue Jul 16, 2024 4:02 pm

XXX

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Re: Am I over engineering/building?

Postby Bugaboo » Wed Jul 17, 2024 4:16 am

tony.latham wrote:Fredrick's hatch had issues–-a great concept, but it can be greatly improved. I used his manual for my first build. You don't need the full 1/2" inner wall. 1/4" is fine, and the hatch needs to butt against the rear of the floor, not the top, as his instructions show–-rain gutter puts the water on the floor, not outside.

Tony, My plan was to use your adjustment to the design. I have been lurking for a while, just working my through the planning stage and design. I actually just ordered your book to read through. I just reference the Fredrick's as the overall idea of the hatch doing the sealing wrapping the sides vs having a more traditional hatch with trim doing the sealing like most tend to build.

RBB wrote:I think you might be over doing it on the walls... any reason you are looking at skeleton ply vs 2x2 stick frame construction? If you went with 1/4" outer ply, 2x2 stick frame, 1/8"ply on inside, you will have the same wall thickness, same insulation, and lighter weight. (also easier build, unless you have a CNC for cutting the plywood!)

I was planing on this to alow continous framing and for me it is easier to remove sections than add. Im sure im not explaning it well but it makes sense in my head. Additionally it would allow me to have a thermal brake between inside and out in areas that i remove if I don't need support on the inner vs outer ply.

Tom&Shelly wrote:We did essentially what Tony did. Four years and no issues.

tony.latham wrote:You don't need that much insulation in the floor or the walls. 3/4" is fine. (I live in Idaho. Today it'll be pushing 100º and we commonly camp below 32º.)

It sounds like I am going over kill with the walls/insulation. Once I get the books I just ordered and have a chance to read through it may change some design ideas.

Regardless, I have plenty of time to plan and adjust the designs before I get home to be able to start working on the build (currently working for Uncle Sam). I appreciate all the input from those that have already built. I plan to start a build thread after I get home to cornicle the build and keep up with progress.
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Re: Am I over engineering/building?

Postby tony.latham » Wed Jul 17, 2024 10:57 am

I plan to start a build thread after I get home to chronicle the build and keep up with progress.


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