Tiny home on wheels

[Dokkodo]

Im planning to build a caravan/tiny house/shepherds hut over the summer. Its more in the style of the US 'tiny house' (although theirs are hardly ever anything even approaching tiny) than a shepherds hut, mainly in that I am going to live in it at least half of the time.

Im having a custom trailer chassis made at 2.3 x 6m, which is close to the maximum allowable 2.5 x 7 but hopefully not so huge that on the rare occassion I need to move it it's totally impractical. It will come rated at 2500 kgs which means I can pull it with my van, but if I go over weight on the build I can get it re-plated to 3000 and use something/one else to move it.

So, currently my main concern is weight. It is basically going to be a well insulated shed on wheels, with stud walls, bolted down to the chassis. I would love to know if anyone (hello resident shed experts) has advice on the framing, insulation and cladding side of things, my experience in that sort of construction is limited. heres some questions.

Framing
Can I get away with a 3x2 frame, and how far apart can I go to save weight but retain strength? I guess I will want to put a good number of diagonals to brace it against the forces incurred in transit...

Insulation
Are there different/better sorts of insulation for floor, walls and roof? I suppose the general rules are the same for a shed, in terms of the layers from external to internal cladding?

Any clever ideas for how to build up from the chassis of the trailer to the floor also appreciated.

Roof
I was going to build a rounded, traditional wagon style roof, but I think a single pitch is much more practical as its less work, gives more internal space and is easier to mount solar panels and skylights into. Im not that into the idea of roofing felt though, maybe onduline is a good idea. Any other suggestions welcome.

Cladding
I would really like to clad it externally in larch of maybe cedar, but it will total up to about 40m2 of timber. Would anyone be able to make an educated guess as to whether that's going to take up a huge amount of my final weight allowance?

So, its only all the crucial structural stuff I dont know about! But once that's done then I can do the fun bits inside, trying to be clever with the space. The other day i pulled out of a skip a pair of double glazed patio sliding doors and about a dozen or 15 double glazed wood framed windows in ok condition complete with furniture, and the day before that a family friend gave me a lovely old french wood burner, so thats a few quid saved.

Heres a couple of examples of much larger and more expensive projects and a few related websites for anyone interested:
http://www.jetsongreen.com/2015/11/off-the-grid-trailer-tiny-home.html
http://hiconsumption.com/2015/10/the-50000-diy-woody-trailer-home/
http://www.tinyhouseuk.co.uk/gallery.html
http://www.tinyhousebasics.com/

and ill attach some rough sketchups ive done playing with interior layout and looks, which I will be redrawing now that Ive had some more info from the trailer company and found all my windows, so any advice would be appreciated and worked in soon.

thanks in advance for any thoughts

 

[marcros]

I am watching the thread with interest, because I fancy a garden office. I had initially thought of a shepherds hut along the lines of the construction that you have mentioned. I am keen to avoid a "shed on wheels" look, but am only at the very early thought stage at the moment.

 

[Brandlin]

I've built a shed or two but I wouldn't consider myself an expert like many here. I'm very interested in what you have outlined here so will be following along - great of you to post!

 

[Lons]

Have you thought about buying a cheap twin axle caravan and cladding the outside, modding the inside? Would need to check the weight rating but some of the older ones were heavy unlike mine which is close to maximum size but rated at 1800kg

 

[Dokkodo]

Nice to hear there is interest, ill try and do a thorough WIP and take lots of pictures.

Im not exactly keen for the shed on wheels look either Marcros but its sort of unavoidable, i suppose you could call it a cabin on wheels?

I had considered going down the route of repurposing an existing caravan chassis, but as caravans tend to be made out of rubber bands and cardboard and polystyrene the chassi (plural of chassis?!) apparently dont come with high weight ratings, and it could take me a while to find one close to the right size.

There are other second hand trailers and flatbeds out there but it seems a bit of a minefield, getting the right size and rating and quality, and then second hand ones tend to hold their value if they are in good nick so I figured go new. It will be the foundations of my house after all...

 

[Droogs]

Great idea watching with interest. on the design front, personnaly i think the arched roof is more pleasing

 

[CHJ]

Domed Rolled metal profile roof is going to be significantly lighter due to natural stiffness of form requiring less support.

Flat roof using Onduline for instance will need sheeting or close rafter/stringer support to stop it sagging and will be heavier than metal in the first place.

 

[Dokkodo]

Domed Rolled metal profile roof is going to be significantly lighter due to natural stiffness of form requiring less support.

Good thinking, I will look into that as an option. With a domed roof, would one laminate ones curved rafters?

I agree with you also Droogs that a domed roof looks nicer from the outside, but theres not a clear winner to me yet, there are many factors...

 

[MikeG.]

I think I'd at least consider aluminium profiles as used by commercial dry wallers instead of timber in the walls. That will save a hell of a lot of weight. You might also look into the sandwich-products used to wall Tesco vans and the like, which are plastic-insulation-plastic, bonded together to form something extremely light and extremely strong. I hold a patent for something which required strong light base-boards, and used these in the prototype.......they're amazing. Ventilation is critical inside such a structure, and should be designed in at the earliest opportunity or you'll be dripping with damp and suffering mold.

 

[Dokkodo]

I think I'd at least consider aluminium profiles as used by commercial dry wallers instead of timber in the walls. That will save a hell of a lot of weight. You might also look into the sandwich-products used to wall Tesco vans and the like, which are plastic-insulation-plastic, bonded together to form something extremely light and extremely strong. I hold a patent for something which required strong light base-boards, and used these in the prototype.......they're amazing. Ventilation is critical inside such a structure, and should be designed in at the earliest opportunity or you'll be dripping with damp and suffering mold.

I was hoping you would find this thread...

I will look up aluminum profiles, I had sort of discounted them because (I assume) they don't give much structural strength, but maybe a combination would work, some timber framing with ali and plastic in between. Part of me is now imagining an oak timber frame but I think that would end up negating any and all other possible weight saving.

Would certainly like not to be soggy and mouldy so I will work that into the designs. Are plenty of opening windows enough?

thanks!

 

[MikeG.]

No, you'll need an extractor in the bathroom and kitchen.

 

[Rorschach]

Extractor for use in the summer (make sure there is a window on the opposite side to let fresh air in)

In the winter if you trying to keep heat in then you would be best with a dehumidifier, even a small domestic one will be many times overkill for a tiny home and will have no trouble keeping it dry while minimising your heat loss.
If you are using a wood stove or some then this probably won't be necessary.

 

[MusicMan]

For the structure, you are more concerned with stiffness than with strength. As you say, caravans are built with very flimsy walls but still hold the roof up and the contents together. But they are floppy.

The sandwich structures mentioned are really excellent in this respect and can combine good insulation with high stiffness. Oak framing would be very heavy.

For a wood/plywood for internal fittings, poplar ply is about the lightest and comes in good quality. I got some good stuff from Avon Plywood of Bristol, who also have a CNC cut-to-shape service.

You do have a conflict on the roof style/shape if you want to introduce solar panels, which could be a very valuable part of the design. I would consider polycarbonate cellular material, bent into the gentle curved shape, and mount the panels directly beneath them inside the building. You'd lose a bit of efficiency from the absorption in the polycarbonate but not too much (they use them for greenhouses after all), and you would gain some solar thermal as well. Solar panels are about 20% efficient, and the rest emerges as heat. If it gets too hot you have the ventilators.

I freely admit this is armchair design, I haven't built one!

Keith

 

[Lons]

Actually modern caravans are a very different animal from the old ones with walls that were basically built around a jig using 1" square timber staple together and glued to internal hardboard sheet wth the aluminium outer skin being fitted later. ( I worked for ABI Caravans in the 70s ).

My 2017 Elddis Crusader Zephyr has walls which are very rigid and supplied to the manufacturer in a laminated sheet form which they cut on cnc machines in the factory. This sandwich of Aluminium / foam / ply is bonded and I recently examined some of them at the Elddis factory so it's an informed opinion.

I don't know if these or similar sheets are available outside the industry but if they can be found, could well offer the strength and lightweight desirable for this type of project. Strong, insulated and waterproof with very few fixings to rust or allow leaks.

No problem fixing cabinets to these walls !

 

[Dokkodo]

Appreciate all the advice everyone, feels like cheating getting all these pearls of wisdom for free.

In terms of heating and ventilation, I'm going to have lots of windows and a double sliding patio door and a barn door, so i dont imagine itll be much of a problem in the summer. In winter I will have a wood burner going some of the time, but presumably that'll steam everything up, especially if im cooking on it (getting one with an oven and backboiler which is exciting) so a dehumidifier sounds good. Its going to be pretty open plan and cabiney, kitchen at one end, no toilet (compost WC cabin outside), so maybe an extra vent at the kitchen end.

Really great to hear about those specialist materials, ill do a bit of research and see if I can find anything. Id still like the timber cladding really, though having had a look at this:http://www.metalline.co.uk/product/ultima-insulated-aluminium-composite-panels, maybe a silvery finish might be quite cool, like an airstream, or a spaceship....

The roof is still a tossup. Im yet to find a product thats suitably enticing.

thanks again

 

[Rorschach]

Woodburners produce a nice dry heat and a in a small space a large surplus of it so you will likely have a vent or window open most of the time for cooling and of course for a fresh air for the fire. You may well find you don't need the dehumidifier but I would still allow a good spot for it in your plans just in case.

 

[Dokkodo]

Me again, dredging this one up because I have commissioned and received a shiny new trailer chassis, been hoarding special bits and pieces, I have made a bit more progress on the design and am hoping to start and get the outer shell done over the spring months, any more thoughts much appreciated as i am still improvising somewhat...

its no longer so traditional, in fact quite boaty now, i rejected curves and instead went with angles. simpler and more space efficient. these are old layouts and ive made brought the roof down a foot, but you get the idea:

I did a bit of research into the various composite panels mentioned but I struggled to find just the right thing, or in sensible quantities, and think I might have come up with a method that should be relatively quick, light and robust, and be more efficient because of the weird shapes.

My plan is to use reclaimed roofing 2x4s, i have a good source and they can look nice with a bit of TLC, bit of character, to provide a main framework, incorporating apertures for doors and windows. These will be oriented so that they protrude internally.

Then im thinking ill frame between 2x4 sections with 2x1 treated batten, and have these spaces spray-insulated once the exterior cladding is on. a couple i know who have been travelling and living in a beautifully converted truck for a few years recently had their insulation redone this way and strongly recommended it, wonder whether anyone else has experience? apparently it negates the need for a membrane but i cant remember if this is correct.

this layer of batten and insulation will be 50mm thick ish, so the 2x4s will still produce a couple of inches, giving an exposed-frame feeling inside, which I like. I will then clad the internal spaces with thin birch/other nice ply.

I have three main areas of contention:

the floor: my trailer chassis is just the bare frame currently. Im not sure of the best way to fix the main frame down around the edges, which is obviously a pretty major thing! A treated timber floor plate going all the way along, fixed up into the posts before being bolted down?

Then there is the order to layer the flooring in. I have guessed at something like this:

the outer cladding: what, if anything needs to go between the internal wooden framing and the outer cladding. Should I have a sheet layer, batten out and leave an air gap, which sounds like it would cause a bit of a pain around doors and windows. Or maybe a sheet and layer of membrane. It seems incorrect that the other cladding would be fixed directly to the main 2x4s with nothing in between. Also, whatever this first layer of exterior cladding is, will be what the interior spray insulation is gettting sprayed up against.

The roof: Havent really got this far, but I think Ill be going with corrugated steel sheet to keep weight down. however, im not sure how heavy duty the roof frame would need to be, or how to layer this up at all really, and I would love to be able to have a big skylight and decent solar rig.

Also, Im slightly worried that so far there isnt much bracing across the width of the structure, which will have to be done at the top, though im pretty sure lengthways once its all built up and clad it should be plenty rigid.

Sorry, thats a lot of questions, but any insights here and there much appreciated.

heres a more developed but still rough idea of what im going for, still playing with furniture etc... all rights reserved

the four gaps in the framework are timber double glazed window units ive already got, a barn door by the kitchen and double glazed patio doors opposite the sofa. im hoping itll end up somewhere with nice rural views.

NB - I have about 1900 kgs of weight allowance on top of the chassis weight of 600 kgs before i can no longer tow it with my current vehicle, so thats something im trying to bear in mind...

 

[MikeG.]

4x2s are going to be very heavy. I would certainly not be going that route. I'd use this stuff if framing rather than building a monocoque.

 

[Lons]

What Mike said.

What is the maximum permitted gross weight of your chassis? Remember that includes the chassis weight itself also and that you need to allow a reasonable allowance for personal items, gas, water etc., you might be surprised how they add up unless you're an experienced caravanner in which case my apologies for stating the obvious. The wheels / tyres will also have a maximum loading.
You've probably already looked up the legal requirements and regs regarding MTPLM and GVW

All this assuming you're actually going to tow it in which case you need to go to a weighbridge and have it officially plated. You will also need to plan your construction very carefully to achieve an acceptable noseweight. Too low ( tail heavy ) is almost not towable and too high will be dangerous also and almost certainly void your tow vehicle warranty and insurance.

You may in any event have difficulty insuring it and your tow vehicle insurers will require some sort of professional certification.

Not trying to pour cold water on the project which looks great, I'd love to do it myself tbh.

 

[Dokkodo]

I had thought that about the 2x4s, but couldn't imagine them adding more than a 150/200kg overall and thought the structural and aesthetic benefits were worth it... But I will do some maths and consider my options.

If I were to follow the same construction method without them then can I infer a monocoque version would be rigid enough? By guesstimation it would seem so, as this is what mass produced caravans are essentially...

Max permitted gross weight of chassis is 3500kg. Chassis weighs about 650kg. Max tow capacity of my vehicle is 2500kg, so id like to keep it below that and get it plated as such if possible, but if that isn't possible its not the end of the world, I just wont be able to move it without paying someone else to do it, but that will be infrequent. It isnt going to be moving regularly or going touring or anything, the idea is to move every year or few years depending on what nice living situations arise. Got a network of off grid friends and connections, might end up in wales for instance in a few years, where all that is much easier.

The director of the company who made the chassis was very helpful, having made a few tiny home chassis already. He offered to get it plated as it came, but advised that I take it away, build the main structure and then get it plated as a box trailer at the ideal weight bracket (2500kg), to avoid any future confusion if I were ever to be pulled over and it was listed as 3500kg flatbed. So currently, as it is a work in progress, its a bit of a grey area, though I need to get my towing license if I am to be able to move it myself (much more) with my van.

During my initial phase of research a few months ago I did indeed totally bend my mind with all the rules and regulations and laws and outdated conflicting opinions online. I think I have boiled it down to <2500kg total = I can tow it, with license extension.

As I do a costing spreadsheet I am also keeping tabs on component weights as they add up so that will hopefully give me a rough idea.

I didnt know about nose and tail weight though, so thanks for that. Kitchen was going up the front end with bed and living space at the back, relatively little actually in the middle section. So I will perhaps try and plan to keep battery banks/water storage etc in this area to balance things out.

I also recently got a real bargain on a load of oak parquet flooring from a local 1920s house that was being renovated, twice the amount id need. Snapped it because it was going so cheap, and was going to worry about weight later. If i decide against I can always sell it but im aiming for a high end (though homely) interior so i'm up for making concessions in some places to facilitate other luxuries like a really really nice floor! If I have empty the whole thing of anything not screwed down each time it comes to moving, so be it!