large window in a tiny house

erin85 · June 16, 2013, 11:17:42 PM

Hi everyone! My husband and I want to build a tiny house on a trailer about a year from now (8.5'x20'). We've never built anything significant before, so we want to make sure we know what we're doing! I was happy to find this forum; there is a lot of helpful information!

We'd like to have a large picture window along one long side of the house -- hopefully something about 8' long, maybe 4' high. There would be 2' to the end of the wall on one side, and 7' on the other (total 17' long, there's a little porch to get to the full 20'). I know this is a pretty substantial portion of the area of the wall. Can this be done without losing structural integrity? I have been reading a little about framing, and I guess we would need a header and lots of cripple studs. We would go with tempered glass also.

Since this is on a trailer, I don't have to adhere to building codes, but I obviously don't want the house to fall down!

Thanks for your help!

flyingvan · June 17, 2013, 12:07:26 AM

Sounds more like a terrarium than a house. Are you thinking fixed window or sliders? It's going to get pricey to buy an 8-0 x 4-0 window, especially one that doesn't turn the place into a solar cooker.
I've helped folks get big windows in. They were difficult for many reasons, and when I go to visit I notice they are covered in curtains. Bigger windows don't really help you see out much, especially in a tiny home (think of how you can see the world through a pinhole if it's right against your eye) all they do is make it easier for people to see in. You're also losing valuable wall space for lighting, storage, entertainment centers, etc. But if you're set on a big window---
Structurally, the header will help with the compression load. Extra cripples won't really do much unless you're using the window as a load bearing member (not a good idea) The real structural challenge is the shear strength in the wall. There won't be much to keep that wall from turning iteslf from a rectangle to a parallelogram. This is a job for an engineer--especially if you're hoping to actually make this a road worthy structure.
My last build, I cashed in all my window area on the high side of the house where the view was. I had to deal with a significant wind load. There are some things you can do to make the most of the wall to add shear strength---sheet it with oversized OSB or ply, inside and out, and stagger the joints so the inside ones don't line up with the outside ones. Increase the nail schedule to 4" on center edges and 6" field nailing. Metal strapping can help transfer shear also.
Again---these are just ideas on how to make up for the shear strength lost, and not replacement for an engineer's stamp

June 17, 2013, 01:39:56 AM

Thanks for the input. We would like the windows to open, but I haven't determined exactly how yet. We originally wanted a sliding glass door actually, but with the wheel wells of the trailer, it's going to be too hard to deal with. I've been working a lot of floorplans, and we won't be giving up space that's needed for shelving or anything else with this plan -- the main draw of this big window is that you'd be looking out (hopefully on some lovely landscape) when working at the desk (which is combined with the kitchen counter), but several feet back; there's a hallway between the window and the desk. I will post an image from my sketchup model later, when I get home from work, to make this more clear.

You make a good point about privacy... I guess I can see this being an issue sometimes. We don't know where we will be building this yet, but we definitely do plan to take it on the road part time, boondocking on BLM land, etc. Hopefully we will get a higher percentage of nice views, rather than creepy neighbors. I just love windows so much. I have something like 10 of them built into the plan total.

I am an engineer, just the wrong kind (nuclear, not civil), but I have a couple friends that might be able to help me as I get closer to finalizing the plans... just wanted to see what was in the realm of possibility! I could live with breaking it up into 2 smaller windows, so we'd have a stud in the center.

Don_P · June 17, 2013, 05:28:10 AM

For something that is travel worthy and poked full of holes you should probably go to a welded steel frame. Aluminum is lighter but more expensive, harder to weld, and more apt to metal fatigue. If you size the "header" beam out of square tubing sufficient to handle the largest opening, 8', and run square post tubes up to it with gusset plates wherever possible it will form a rigid box. The trailer frame rails need to be sufficient to take the point loads from the frame posts above and the frame rigid enough to not twist. You can weld clips to the steel frame to accept wood or metal subframing if needed and then screw plywood, steel or fiberglass to the frame. If you use ply, use exterior or marine grade, the skin can be thinner if the frame is a grid. Fiberglassing over a plywood shell works pretty well. Sprayfoam the voids before applying interior finishes. With thinner walls and a small tight box, condensation is a problem to be dealt with. Flat roofs will end up ponding at some point, put some camber in it and minimize roof penetrations. The '72 motorhome is failing but it started as just a bare chassis and a milk crate for a seat, done as above.

cbc58 · June 17, 2013, 07:02:21 AM

have you checked with the DOT about having a window that size? i know they want tempered glass but maybe there is a thickness requirement based on window area.. just a thought.

June 17, 2013, 07:31:04 AM

erin85 have you considered a travel trailer. We live in one full time now. (Fifthwheel) Will not go into why we do. We will be building soon I hope

but you can not beat the pricing on a lot of the well made used units and some of the new units are not that bad priced either. Though we do not intend to be full time RVers many - many are. I guess what I am saying is with all the units out there and the pricing as it is. I would bet you could not cost it out for what you can buy a well made, well kept used unit for. They are very tow-able where with what you make very well may not be......

Many are a snap to hook solar to for 'boondocking'. Many we met down south last winter use them. Most were not mounted permanently but some are permanently mounted to roofs and some raised and lowered. The portable types folded up and either went in the back of the tow vehicle or strapped to the rear of the unit. If you get down around the fabled Quartzite RV Show and the pricing and competition for solar is crazy. (Whole place is for that matter.)

As far as windows in them if you are going to any where colder you will find they are your worst enemy. Our fifth wheel is a cold weather model and windows are smaller and fewer than on some. It is a trade for where you are going and what you are doing. We have lived in this down to single digits and we found that it was uncomfortable but doable and the unit never froze up but I was sort of the heat tape wizard here and there and around the RV park. Then we pulled up stakes and went south.

People I know of that have tried to build it themselves have had a lot of trouble with towing issues and fuel mileage. There was a sort of Tumble Weed type home being built over in Oregon that they were hoping to be a lot more portable. 50 mph was like tops with a ton pick up and they were all over the road. They really never got that issue straightened out at least I have heard about. I do know the owner of the company was never well pleased with road ability.

erin85 · June 17, 2013, 07:49:58 AM

Thanks for all the suggestions! rick91351, we have considered a travel trailer -- it makes a lot more sense than a towable house for many reasons, but tiny house has a few good points going for it. First, we really want to build it ourselves, from scratch! My husband and I haven't had a good project to work on together for a while, and I want to learn the new skills... buying a trailer isn't as fun. And admittedly, I like the look of tiny houses a lot better -- there is something just so cute about them. So yes, I realize we could probably do a trailer for a lot less, and get better gas mileage, but I just can't get excited about it like I can with a tiny house. I get really into making all the plans. Anyway, we might do both eventually, as I do realize I'm a bit overly-optimistic about the portability of the thing

We're only in our late 20s, so we don't quite have the luxury of being full time RVers yet. We'd probably buy a little land to live on most of the time, but I like the option of just moving and taking your fully-paid-for house with you.

cbc58, good point... I will look into that. Hadn't thought about it.

Don_P, I like the idea of metal, but I'm not too sure that we're up to it... it's definitely something that we'd have to get professionally done, and again, I want to build it! I've also heard that metal framing is tough to insulate, but I will look at your idea a bit more too. Thanks!

Don_P · June 17, 2013, 08:04:35 AM

Ditto on what Rick said, our motorhome was built by a hard headed dutch mechanical engineer with a number of boats and a kit car under his belt before that project, who I cussed and discussed back and forth with from wherever the latest fire or breakdown was happening for many years... her Dad

It did survive negative double digits but none of us were happy. I think he came out cheaper than new but a used trailer would have been a bargain. I think the entire JC Whitney catalog is in there somewhere. I suspect CBC is right, but it would need to be not just tempered but laminated tempered glass, Kaching!

I was typing while you posted... metal is a good conductor, lousy insulator, it is heck for stout in the joinery which is what you need here, wood wallows out quickly under repeated cyclic loading like road use. It is a good skill to have, taught at many community colleges and the equipment is not expensive...

rick91351 · June 17, 2013, 08:09:44 AM

Please do keep us up dated as to your progress. Though I am admittedly not a fan of what you are planing. I'm still interested in seeing how it comes together and wish you-all the best.

erin85 · June 17, 2013, 09:43:01 AM

I'll definitely keep y'all up-to-date. But, we won't actually start building for a year or more, so don't hold your breath! I'm sure I'll be asking plenty of questions between now and then

I am really interested in the metal framing... I had imagined that it was for professionals only, who knew lots of welding, but after a little googling, I'm intrigued; maybe we could do it. I think it would have a lot of advantages for the road-worthy house. I don't know too much about insulation yet, but I do know that I hate cold weather, so we won't be spending too much time in sub-zeroes.