Teardrops n Tiny Travel Trailers

My first post.

Been on the forums for a while just reading. I've been going through a lot of different build threads for inspiration for my own design and I have noticed two types of internal frames on insulated walls. The first is just the typical straight spars spaced evenly apart and stabilized with horizontal cross members, the second is more of a "Uniframe" of sorts where the entire profile is cut from plywood and then internal sections are routed out for what I assume to be sections for insulation/weight reduction.

I was wondering if I could get some more information on the Uniframe type. Pros and cons, etc?

I tried searching for this but don't really know what to look for.

Thanks

Khughes222 wrote:I have noticed two types of internal frames on insulated walls. The first is just the typical straight spars spaced evenly apart and stabilized with horizontal cross members, the second is more of a "Uniframe" of sorts where the entire profile is cut from plywood and then internal sections are routed out for what I assume to be sections for insulation/weight reduction.

I was wondering if I could get some more information on the Uniframe type. Pros and cons, etc?

I used first approach, straight spars.

If I had to do it over again, I would use the second approach.

The straight spars were not easy to deal with. I had to deal with warpage of the spars, spars with slightly different thicknesses, & difficulty in conecting vertical spars to horizontal spars along the same plane.

With the cutout plywood approach, you will not have any of these problems.

First of all, welcome to the forum. You might pay a visit to the "Newbies" section and tell us a little about yourself. We're all happy you're here!

I am using the "uniframe" method and, all things considered, I am very happy with it. I had concerns about being able to join individual spars well enough to have a good strong stable wall. The cutout plywood eliminates this problem. It takes quite a bit more time than solid wall construction, but I am hoping the sound and temp insulation properties, along with the weight saved, will be worth it.

I will say that I don't think I saved as much weight as someone using a light frame of pine spars would. But I know I saved some. How much is not certain as I haven't even attempted to do any kind of weight calculations, but I only know that before I cut out the insulation holes I could not lift that solid wall by myself. No way Jose`, couldn't even budge it. Now, even with the insulation in and skins on I can actually pick it up and move it by myself. Not saying it's easy, but I can do it. So it's a little bit lighter and I gained some other benefits. There are a lot of steps though, so if you're looking for a fast build keep that in mind.

It will cost you a lot more than a solid wall. Think about it, once you have that solid piece of ply, you can either be done spending money on the wall, or you can commence to cutting away a good 2/3 to 3/4 of it, go out and buy skins (I opted for the more expensive Okoume marine ply), insulation, and glue (epoxy for me) and go on to the next stage.

I am using epoxy to bond everything. So when all is said and done my walls are one solid glued together structure. It should be nice and strong. I will also be covering the entire exterior with a fiberglass cloth skin, and then painting it with one-part polyurethane marine paint.

If I had it to do over....for my first build I think I would have stuck with solid walls. I would probably be near to going camping right now and it would have cost a lot less. Hindsight is 20/20. I think the sandwich wall is a great process and will yeild a really nice result. But considering the overall size and complexity of the project for someone with very basic skills who had never done anything quite like this before, choosing a simpler method for the first build might have been wise. But I know that once it is done we will appreciate and enjoy the benefits gained for many years to come.

I will be posting an update to my build blog tomorrow night (probably late) after I have finished working for the weekend and it will all be about the process of building my walls. You might want to check it Monday.

Good luck with your decision, and with building your teardrop. We will be looking forward to your build journal.

I started building with pine spars and soon scraped the initial attempt. Just got too heavy to early in the build so I did a build made of all framing in a T shape with opposing grains of cedar. The price and the work went up but I believe I can come in sub 800 lbs. with built in heat and air, a 80 watt solar panel, TV and other toys. Cedar stripped the interior with thin (less than 1/8 inch) and 1 1/2 inch insulation in the walls. Should know in a couple of weeks the final weight. I am towing with a VW Jetta TDI so have a need to hold the weight as low as possible and with fuel prices rising so sharply I don't want to tow more than I have to.

Thanks for all the replies.

So am I correct in understanding that your "Uniframe" is the strongest point of the wall and not a combination of the frame and exterior wall? It sounds like your framing with maybe a 3/4" frame with 1/8th" skins on both sides?

My thoughts were to have a 1/2" exterior wall bonded to a 1/2" internal Uniframe insulated and then skinned with 1/8" ply on the interior but this is starting to sound overkill. I need to keep my weight low also as I have a 4cyl with a 1500 lb total towing capacity.

"Uniframe" ... I kind of like that description/label ... ... easier to remember than "cookie-cut", but not as descriptive as "stick-frame" ... it'll do 'til something better comes along ... ...! (Maybe we should have a contest to see who can come up with the best name for this construction method ... ...?)

Anyway, what ever you want to call it, I'm a huge proponent of it ... basically been using the method for all my trailers since about 1988. True, it's not as light as a stick-framed body, but it does give you the advantage of the full strength of a sheet of plywood at a fraction of the weight. I figure that on a typical 4'x8' teardrop, I save about 100#, and on a 4'x10' close to 150#, but then, I also use this method to frame out all my cabinetry, too. Obviously, this method relies on some paneling being glued to the inside of the wall and cabinetry, then some sheathing over the outside, and overall weight savings will depend on how thick and what material you use on each. The addition of insulation in the voids will increase the comfort level at almost zero weight gain, depending again on which material you choose. Weight savings also depends on how much material you leave where in the wall framing ... I typically leave 2-1/2" around the perimeter and hinge side of the door & wall, 2" around the door and anywhere cabinetry will attach, 3" where the countertop will attach, and about 1-1/2" for any tie-in framing ... if I know what fenders I'll be using, I'll leave about 2-1/2" material where they will mount. (you can ... and I have ... go/gone with much less and it will turn out just fine, but this is the "comfort level" I've settled on)

For a variety of reasons, I like to keep my walls under 1" thick, so depending on what kind of paneling I want on the inside of the cabin, I'll use either 5/8" plywood for the "core" or 1/2" ... though I have used 3/4" when the outside skin is a "rolled" or "mesa'd" type.

I also build my trailer bodies separate from the frame, forming a kind of monocoque torsional box, then bringing them together only when it's time for door & hatch installation and final molding/trim.

IMHO, the pros of this type of build method are ease of construction, a huge weight-saving over solid plywood, speed of the build, and overall strength, not to mention the advantage of insulation without adding extra width/thickness to the wall ... cons would be that it's a little heavier than a stick-framed trailer and some would say a waste of wood (but, if you have a fireplace or woodstove, then the "waste" becomes additional warmth in the shop or house ... ...!).

My first three teardrops were stick-framed ... the first was a 4x10 that came in at 650# complete with dropped footwell and seating for 4, the second a basic 4x8 that came in at 500#, and the third a 4x8 with a nice galley and another dropped footwell and seating for 2 that came in at 600#. When I switched to the "Uniframe" method, it only added about 100# to the 4x8s and about 125-150# to the 4x10s. Every teardrop I've built up to now has been pulled at one time or another by a 4-cylinder car or pickup without any problems, so I don't think that the slight additional weight disadvantage outweighs the advantages of ease & speed of construction.

The obvious disclaimer here, though, is that others' opinions and experiences will vary ... ...! However you choose to build, Good Luck, and as always ...

CHEERS!

grant whipp wrote:"Uniframe" ... I kind of like that description/label ... ... easier to remember than "cookie-cut", but not as descriptive as "stick-frame" ... it'll do 'til something better comes along ... ...! (Maybe we should have a contest to see who can come up with the best name for this construction method ... ...?)

Anyway, what ever you want to call it, I'm a huge proponent of it ... basically been using the method for all my trailers since about 1988. True, it's not as light as a stick-framed body, but it does give you the advantage of the full strength of a sheet of plywood at a fraction of the weight. I figure that on a typical 4'x8' teardrop, I save about 100#, and on a 4'x10' close to 150#, but then, I also use this method to frame out all my cabinetry, too. Obviously, this method relies on some paneling being glued to the inside of the wall and cabinetry, then some sheathing over the outside, and overall weight savings will depend on how thick and what material you use on each. The addition of insulation in the voids will increase the comfort level at almost zero weight gain, depending again on which material you choose. Weight savings also depends on how much material you leave where in the wall framing ... I typically leave 2-1/2" around the perimeter and hinge side of the door & wall, 2" around the door and anywhere cabinetry will attach, 3" where the countertop will attach, and about 1-1/2" for any tie-in framing ... if I know what fenders I'll be using, I'll leave about 2-1/2" material where they will mount. (you can ... and I have ... go/gone with much less and it will turn out just fine, but this is the "comfort level" I've settled on)

For a variety of reasons, I like to keep my walls under 1" thick, so depending on what kind of paneling I want on the inside of the cabin, I'll use either 5/8" plywood for the "core" or 1/2" ... though I have used 3/4" when the outside skin is a "rolled" or "mesa'd" type.

I also build my trailer bodies separate from the frame, forming a kind of monocoque torsional box, then bringing them together only when it's time for door & hatch installation and final molding/trim.

IMHO, the pros of this type of build method are ease of construction, a huge weight-saving over solid plywood, speed of the build, and overall strength, not to mention the advantage of insulation without adding extra width/thickness to the wall ... cons would be that it's a little heavier than a stick-framed trailer and some would say a waste of wood (but, if you have a fireplace or woodstove, then the "waste" becomes additional warmth in the shop or house ... ...!).

My first three teardrops were stick-framed ... the first was a 4x10 that came in at 650# complete with dropped footwell and seating for 4, the second a basic 4x8 that came in at 500#, and the third a 4x8 with a nice galley and another dropped footwell and seating for 2 that came in at 600#. When I switched to the "Uniframe" method, it only added about 100# to the 4x8s and about 125-150# to the 4x10s. Every teardrop I've built up to now has been pulled at one time or another by a 4-cylinder car or pickup without any problems, so I don't think that the slight additional weight disadvantage outweighs the advantages of ease & speed of construction.

The obvious disclaimer here, though, is that others' opinions and experiences will vary ... ...! However you choose to build, Good Luck, and as always ...

CHEERS!

Thanks for the detail.

Khughes222 wrote:Thanks for all the replies.

So am I correct in understanding that your "Uniframe" is the strongest point of the wall and not a combination of the frame and exterior wall? It sounds like your framing with maybe a 3/4" frame with 1/8th" skins on both sides?

My thoughts were to have a 1/2" exterior wall bonded to a 1/2" internal Uniframe insulated and then skinned with 1/8" ply on the interior but this is starting to sound overkill. I need to keep my weight low also as I have a 4cyl with a 1500 lb total towing capacity.

Because my wall is basically one solid panel by the time I have bonded everything together, I think that it all works together for strength. But as Grant said, you basically get the structural strength of a solid piece of plywood with much less weight by using the plywood core. I used 3/4" birch ply for the core, and 3mm Okoume marine ply on both sides for the skin. 3mm is a hair less than 1/8 inch so by the time I add the fiberglass cloth on the outside, my walls are about 1 inch thick total. I do think that 1/2" external wall is overkill with a core construction. By the time you add the weight of that, plus your 1/2" ply core and your interior skin, you will probably be over the weight of a solid 3/4" piece. Your skins alone total 5/8" in solid plywood. I think you could go 1/4" for the exterior skin easily. Any of you pros disagree with that? I have seen some people say they used a 1/2" solid piece by itself for their wall construction and feel that is was very adequate.

Oldragbaggers wrote:
Because my wall is basically one solid panel by the time I have bonded everything together, I think that it all works together for strength. But as Grant said, you basically get the structural strength of a solid piece of plywood with much less weight by using the plywood core. I used 3/4" birch ply for the core, and 3mm Okoume marine ply on both sides for the skin. 3mm is a hair less than 1/8 inch so by the time I add the fiberglass cloth on the outside, my walls are about 1 inch thick total. I do think that 1/2" external wall is overkill with a core construction. By the time you add the weight of that, plus your 1/2" ply core and your interior skin, you will probably be over the weight of a solid 3/4" piece. Your skins alone total 5/8" in solid plywood. I think you could go 1/4" for the exterior skin easily. Any of you pros disagree with that? I have seen some people say they used a 1/2" solid piece by itself for their wall construction and feel that is was very adequate.

This may be a dumb question but, how do you drill a countersink hole and screw down a board that's only 1/8" thick without drilling right through it?

Khughes222 wrote:

Oldragbaggers wrote:
Because my wall is basically one solid panel by the time I have bonded everything together, I think that it all works together for strength. But as Grant said, you basically get the structural strength of a solid piece of plywood with much less weight by using the plywood core. I used 3/4" birch ply for the core, and 3mm Okoume marine ply on both sides for the skin. 3mm is a hair less than 1/8 inch so by the time I add the fiberglass cloth on the outside, my walls are about 1 inch thick total. I do think that 1/2" external wall is overkill with a core construction. By the time you add the weight of that, plus your 1/2" ply core and your interior skin, you will probably be over the weight of a solid 3/4" piece. Your skins alone total 5/8" in solid plywood. I think you could go 1/4" for the exterior skin easily. Any of you pros disagree with that? I have seen some people say they used a 1/2" solid piece by itself for their wall construction and feel that is was very adequate.

This may be a dumb question but, how do you drill a countersink hole and screw down a board that's only 1/8" thick without drilling right through it?

There are no screws involved in putting the skin on the frame. After I apply the adhesive thickened epoxy, I lay the skin on, add a few staples around the edges to keep it from slipping out of position. then I put sheets of plywood on top of it with everything in the garage piled on top of them to weigh it down. As far a screwing into it when I start adding cabinetry, as I said, it is bonded to the 3/4" plywood core so that it is one solid piece now. I have left core plywood in all the places where I will be attaching things so I will be drilling through solid wood in all those places. I will countersink the screws and then, because my walls are skinned with fiberglass cloth, I will be using epoxy filler to fill the holes. Then I will sand it all down smooth and paint it. There will not be any occassion, unless I plan really badly and miss my mark somehow, where I will be drilling and screwing just into skin material.

Oldragbaggers wrote:There are no screws involved in putting the skin on the frame. After I apply the adhesive thickened epoxy, I lay the skin on, add a few staples around the edges to keep it from slipping out of position. then I put sheets of plywood on top of it with everything in the garage piled on top of them to weigh it down. As far a screwing into it when I start adding cabinetry, as I said, it is bonded to the 3/4" plywood core so that it is one solid piece now. I have left core plywood in all the places where I will be attaching things so I will be drilling through solid wood in all those places. I will countersink the screws and then, because my walls are skinned with fiberglass cloth, I will be using epoxy filler to fill the holes. Then I will sand it all down smooth and paint it. There will not be any occassion, unless I plan really badly and miss my mark somehow, where I will be drilling and screwing just into skin material.

That totally makes sense. I am now looking at the photo in your signature and I can almost entirely visualize what your interior is going to look like.

So are you planning on fiberglassing the entire exterior?

Khughes222 wrote:

Oldragbaggers wrote:There are no screws involved in putting the skin on the frame. After I apply the adhesive thickened epoxy, I lay the skin on, add a few staples around the edges to keep it from slipping out of position. then I put sheets of plywood on top of it with everything in the garage piled on top of them to weigh it down. As far a screwing into it when I start adding cabinetry, as I said, it is bonded to the 3/4" plywood core so that it is one solid piece now. I have left core plywood in all the places where I will be attaching things so I will be drilling through solid wood in all those places. I will countersink the screws and then, because my walls are skinned with fiberglass cloth, I will be using epoxy filler to fill the holes. Then I will sand it all down smooth and paint it. There will not be any occassion, unless I plan really badly and miss my mark somehow, where I will be drilling and screwing just into skin material.

That totally makes sense. I am now looking at the photo in your signature and I can almost entirely visualize what your interior is going to look like.

So are you planning on fiberglassing the entire exterior?

Yes, I am. I'm glassing the side walls now and I am doing them laying horizontal (much easier). When the roof is on I will add a layer of cloth to the roof and lap it over a couple of inches onto the side wall so there will be no open seams to leak where the roof joins the walls. No need for trim or sealers at that joint!!

I am going back and forth between my blog and the forum right now. I am putting up a lot of new pictures there, and if I can copy them easily to the forum I will put them on my build journal as well.

I had considered glassing the whole exterior mainly for painting reasons. I don't know if I'm missing something but every trailer that I see that's painted directly to the wood looks like it has an orange peeled texture. I am looking for that smooth glossy texture.

I thought if I glassed over the wood, I could sand it so smooth that I could achieve the look I want. I have never glassed anything before and YouTube makes it look like somewhat of a complex process. I am hesitant to try it but thought if I did I would just glass the edges sealing them up like what you are trying to achieve.

I just posted my blog update. Some glassing details included!!
http://www.sagwagonteardrop.com/2012/04/15/wall-construction-almost-complete/
Have a great week!!

I used the "uni-frame" method too.

Before cutting expensive plywood, I made a template out of 1/4" MDF. Then I traced the outline on top of the plywood, rough cut it with a jig saw, and finished cutting it with a router.





As far as attaching the 1/8" plywood sides, I used temporary screws through scraps of plywood to apply pressure to glue joints. Later, the holes were filled.





Take care,
Tom