Just dreaming -- what is the design envelope

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Just dreaming -- what is the design envelope

Postby Karina » Sat Aug 15, 2015 2:28 pm

Hi all.

I've been reading avidly on and off for several years. Had a teardrop planned and got a dead popup camper off craigslist to use as the base, and then life intervened. It's been sitting in my driveway for 3? years waiting for me to get to it. Meanwhile I am also dreaming about tiny houses and think I want to build one to retire into in 10 years time.

I'm playing around with ideas for clever use of space but I need a better sense of the hard limits. Headroom in the loft on a tiny house can be such an issue. I'm considering something like 8 x 20 with loft and a single-slope "shed" roof with metal roofing. I am trying to understand the practical interior volume so I can figure out what will work.

+ I think I read that trailer height at that size runs about 22". Does that sound right? Can I guesstimate 2ft for trailer and be OK?
+ Do you think at that size the floor can be framed with 2x4s or do I need bigger joists? 2x6?
+ How many inches do I need to allow for roofing? Would the trusses likely be 6"? More? Plus a couple of inches for sheathing and metal roof? More?
+ Depending on the above, I think the interior volume on the high side maxes out at about 10'3" and a couple feet lower on the low side, depending on roof pitch? (I am in snow land so will have to do some studying to find the best angle.)

Similarly, with the 8'6" max highway width I am thinking 8' wide trailer frame.
+ Framed up with 2x4s and some kind of interior wall covering do you lose about 4.5" on each side to give a 7' 3" interior?

I have some thoughts but I don't know if any of them are practical until I get the design envelope a little clearer. Of course once I get the design envelope clearer I will start from there and wonder if there are better, thinner, lighter ways to accomplish the same thing, but the tiny house world so far seems to be all stick built.

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Re: Just dreaming -- what is the design envelope

Postby bobhenry » Sun Aug 16, 2015 4:22 pm

8-6 by 13-6 are the "on the highway day to day" maximums. There are accommodations for oversize loads. I you are building to by moved ever so seldom you can exceed these by asking for moving permits when relocating the home.

However you are headed right, by staying 8' outside of raw framing by 13' to max of roof framing. By the time you add decking , siding, and trim features you will be at or very close to the day to day max sizes.

There are ways to reduce the depth of the sleeping loft joists, and the top chord of the trusses by utilizing stronger lumber. Ditch the SPF #2 for a Douglas fir. There is also even stronger machine stress rated lumber or perhaps rough sawn hardwoods which would be even stronger yet. I would have no fear of a 2x4 top chord truss spanning 8' even in spf, as long as the center splice plate was glued and screwed and only slightly deeper and at least 3 ply 1/2 plywood. Simpson metal brackets may add even more strength in lieu of the plywood gussets.
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Re: Just dreaming -- what is the design envelope

Postby Karina » Sun Aug 16, 2015 7:00 pm

bobhenry,

Thanks for the reply. I've enjoyed reading your build threads. So If I start fiddling with ideas for 10'3 max headroom on one side and more like 8' on the other and 7'3" interior width I'll be more or less OK? It's so much easier to expand a few inches than to figure out where to cut them.

I can see already that the main issue will be headroom under the loft. I can make do in 5'6" but I have a brother and a nephew who need 6'3" clearance. I will have to decide how nice I want to be to guests. I have some ideas about how to do loft access, but the max height is the max height and I don't like hitting my head in bed or sleeping on a thin mattress. I'd like to have a minimum (low side) of 3.5' clearance on top of the loft floor to allow a 6" mattress and comfortable headroom. My impression is that to achieve that with 6'3" underneath I will have to shave trailer height, floor assembly, loft assembly and roof assembly pretty tight. Or decide It's not possible and lower the loft. I am thinking the loft will only be a shelf for the mattress (with maybe some cabinetry on the low side to use up any extra space, but that can hang off the studs.) So maybe I can get away with building the loft floor out of 1x1s with .5" ply on top? I don't want it to sag and it could have 2 people + several dogs so I don't want to underbuild it either.

The question of how much height is needed to get a strong assembly within the 13'6" limit is clearly going to be my big crisis for the next year or so. By my math I'm wrong by 1-2 feet at the moment. When I watch Tiny House Nation it looks like they are fitting in sitting headroom in a loft framed with 2x4s over at least 6' of headroom below, so I guess I need more real-life measurements.

I was originally wondering if I could have a sizeable deck that pulled out from under the trailer frame. It would be really cool. But looking at clearance issues I need the height inside the house a lot more. I probably wouldn't be moving a tiny house a lot, but I feel that if it is "mobile" it needs to be able to be towed normally upon occasion with no special permits and no crazy low clearance underneath.
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Re: Just dreaming -- what is the design envelope

Postby loaderman » Mon Aug 17, 2015 12:58 am

Loft height can be an issue. Design it so the maximum loft height is where you come up the stairs or ladder.
Loft floor if it is really only a bed can be 1.5" angle iron back to back with plywood in-between. Really all you are making is a bed bottom.
You could go with a 2x6 rafter for R20 then 4" rafters with styrofoam insulation to gain 2" height over the loft.
Make your trailer as low as possible, torsion axles are good for this.
Here is a design I did that shows some of these principles.
Image
This design allows one to stand beside the loft bed.
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Re: Just dreaming -- what is the design envelope

Postby M C Toyer » Mon Aug 17, 2015 2:46 am

Karina -

I am not an architect or engineer and I do not know what temperature extremes you might face in Wisconsin but my general observation of most tiny houses is the designers/builders tend to mimic standard home construction techniques and materials and that is neither necessary nor does it accomplish the goal of maximizing space.

The floor joists for example - why do you need any at all? The trailer frame itself will provide the strength to support a 1 inch tongue and groove plywood subfloor and if there are heavy traffic areas that needed stiffened short lengths of 2x4 could be placed in between the steel frame members. An 8 x 20 trailer would likely have at least a 4" deep frame and insulation could be placed within the rails.

2x4 wall studs are also overkill if used in the normal method but turned on edge would require less than 1/2 the space and if fully sheathed on the outside using adhesive and a similar application of interior paneling would provide the strength to support your roof - after all you will not have to bear the weight of ceiling joists or any mechanical equipment.

The rafters do not need to be 2x6 or 2x4 or wood at all and since you are planning a single slope, i.e., shed, roof no trusses are involved. You may need some lateral bracing in a couple places in addition for the front and rear walls but that could be incorporated into the loft framing, The sloped metal roofs for barns and commercial buildings are supported by steel purlins and for a 10 foot span would be less than 2" thick.

You can compensate for the thinner walls and roof by using higher performance rigid polyurethane insulation. There are also reflective membranes that can augment the wall and roof insulation.

Just my thoughts on what has worked for me.
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Re: Just dreaming -- what is the design envelope

Postby bobhenry » Mon Aug 17, 2015 7:07 am

M C Toyer wrote:Karina -

I am not an architect or engineer and I do not know what temperature extremes you might face in Wisconsin but my general observation of most tiny houses is the designers/builders tend to mimic standard home construction techniques and materials and that is neither necessary nor does it accomplish the goal of maximizing space.

The floor joists for example - why do you need any at all? The trailer frame itself will provide the strength to support a 1 inch tongue and groove plywood subfloor and if there are heavy traffic areas that needed stiffened short lengths of 2x4 could be placed in between the steel frame members. An 8 x 20 trailer would likely have at least a 4" deep frame and insulation could be placed within the rails.

2x4 wall studs are also overkill if used in the normal method but turned on edge would require less than 1/2 the space and if fully sheathed on the outside using adhesive and a similar application of interior paneling would provide the strength to support your roof - after all you will not have to bear the weight of ceiling joists or any mechanical equipment.

The rafters do not need to be 2x6 or 2x4 or wood at all and since you are planning a single slope, i.e., shed, roof no trusses are involved. You may need some lateral bracing in a couple places in addition for the front and rear walls but that could be incorporated into the loft framing, The sloped metal roofs for barns and commercial buildings are supported by steel purlins and for a 10 foot span would be less than 2" thick.

You can compensate for the thinner walls and roof by using higher performance rigid polyurethane insulation. There are also reflective membranes that can augment the wall and roof insulation.

Just my thoughts on what has worked for me.



Whoa! whoa! whoa! cowboy........ Denton Texas doesn't see -13 temps with wind chills in the -35+/- range. The wall thickness is not just for strength you need "R" value to be able to heat the box. I built mine (right or wrong) with 2x6 walls for insulation value only.
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Re: Just dreaming -- what is the design envelope

Postby bobhenry » Mon Aug 17, 2015 7:08 am

M C Toyer wrote:Karina -

I am not an architect or engineer and I do not know what temperature extremes you might face in Wisconsin but my general observation of most tiny houses is the designers/builders tend to mimic standard home construction techniques and materials and that is neither necessary nor does it accomplish the goal of maximizing space.

The floor joists for example - why do you need any at all? The trailer frame itself will provide the strength to support a 1 inch tongue and groove plywood subfloor and if there are heavy traffic areas that needed stiffened short lengths of 2x4 could be placed in between the steel frame members. An 8 x 20 trailer would likely have at least a 4" deep frame and insulation could be placed within the rails.

2x4 wall studs are also overkill if used in the normal method but turned on edge would require less than 1/2 the space and if fully sheathed on the outside using adhesive and a similar application of interior paneling would provide the strength to support your roof - after all you will not have to bear the weight of ceiling joists or any mechanical equipment.

The rafters do not need to be 2x6 or 2x4 or wood at all and since you are planning a single slope, i.e., shed, roof no trusses are involved. You may need some lateral bracing in a couple places in addition for the front and rear walls but that could be incorporated into the loft framing, The sloped metal roofs for barns and commercial buildings are supported by steel purlins and for a 10 foot span would be less than 2" thick.

You can compensate for the thinner walls and roof by using higher performance rigid polyurethane insulation. There are also reflective membranes that can augment the wall and roof insulation.

Just my thoughts on what has worked for me.



Whoa! whoa! whoa! cowboy........ Denton Texas doesn't see -13 temps with wind chills in the -35+/- range. The wall thickness is not just for strength you need "R" value to be able to heat the box. I built mine (right or wrong) with 2x6 walls for insulation value only.
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Re: Just dreaming -- what is the design envelope

Postby bobhenry » Mon Aug 17, 2015 7:15 am

Karina.......

You really do not want to cheat the main floor below 7'6" you will hate yourself later if you do.

Let's think a bit........

I have seen mobile / modular homes where the roof is actually hinged and is lifted into position upon arrival.
Since you are planning a single slope roof it would be simple to lift it into place and flip up a hinged section of stud wall to support the high side of the roof.
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Re: Just dreaming -- what is the design envelope

Postby Karina » Mon Aug 17, 2015 1:32 pm

M C Toyer,

Thanks for the repy. I loved your log cabin. Your sketchup is something like what I am thinking about. I'm just trying to refine the degree of "overbuilt" needed to be solid and well insulated while still saving an inch where I can. It looks like refining this will be a multi-year process. I probably have to build a couple of the smaller trailers I've dreamed up to get a better sense of the tradeoffs. (Not to mention to bring my skills up to snuff. I haven't really built anything in years and know nothing about residential framing.)

I spent years intending to build or renovate a boat, so many of the trade-offs in your log cabin were familiar. Tiny houses have an advantage over boats in not needing the pointy end or cockpit or entry down a ladder. They have a disadvantage in needing insulation below counter height.

Bobhenry,

I want the weather-tightness of all fixed walls and ceiling on this one. I am only 5'5" and not claustrophobic so I am perfectly happy limiting headroom below the loft to 6'3". My only question is whether I need to take it lower, which would be fine for me but involve some social trade-offs. The loft will be primarily for me and will be small enough I might need a shoehorn on a bad day. When I am alone I will have the whole house to spread out in. When I have visitors the loft will give me some privacy. I am planning stairs up one side of the trailer with a landing about 2.5 feet below the bed platform so with a 6" mattress I will have a 3' bed height and standing room to dress. The "loft" will thus be a 5' wide platform for a mattress running along one long wall, supported on one side by the exterior wall studs and on the other side by an interior wall. I think I can fit that with 6'3" clearance below but if not I will lower the loft because I get to be comfortable in my own house even if tall guests aren't. That's what the porch is for, right? Entertaining tall people. :)

As to the R factors needed, I don't have a clue at the moment. I am watching out for all the info I can get on temperature maintenance and fuel use. I'm assuming at this point I will have a Dickinson diesel heater because they are the norm, but that could change. I think the biggest concern is researching the roof slope needed. There is no way in heck I will be shoveling that roof.

I am, by the way, one of those crazy older ladies who likes to keep the house at 50 in the winter and 68 in the summer, so insulation will be as much for cooling as for heating.

I really appreciate everyone's input. I'm in the very early stages of thinking, but trying to figure out if my general ideas are doable. For instance, I have no idea how thick you actually need to floor an 8' wide frame to get a sag-free floor. If I can do it with 2x4s and insulation between, that's great. If I can do it in even less that's even better -- but I want to be able to treat this as a house and have a party with lots of people and dogs wandering around without worrying if my floor is up to it.
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Re: Just dreaming -- what is the design envelope

Postby kriellian » Fri Aug 28, 2015 9:25 am

Karina -
Two quick questions come to mind: 1) Looking at retirement 10 yrs down the road is quite a time span....have you considered any health issues that may or may not evolve that would make getting into and out of a loft bedroom difficult, and 2) is your plan to "stay put" or follow the sun on a seasonal basis, which may influence your decision on wall thickness...which influences the overall weight of your TH.
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Re: Just dreaming -- what is the design envelope

Postby s60088 » Sat Jun 18, 2016 5:38 pm

Hi. This seems to be a thread closest to my subject of concern. I have materials in my garage ready for application to my 1,720# bearing trailer bed. I have pressure-treated lumber to carry the cantilevers beyond the steel frame and 3/4" regular plywood. I've counted my base lumber to be about 400#! I intend to make the walls using steel framing (1-5/8" studs & track using hurricane straps at the roof eaves, rigid insulation, marine-grade 1/2" ply outside w/building wrap and metal sheeting, 1/4" beaded waitscot inside).

Am I making huge mistake adding this much load in framing and flooring? I like the idea of the weight and security at bottom with lighter above. I read that steel studs weigh 2/3 that of wood... not so great a savings comsidering their being more timely to construct.

This won't be a travel TinyHouse. Just has to make it down 200 miles to my land where I intend to move.

Would love ideas....comments on this because I really want to start this week and wonder if I should exchange my wood for thinner ply and maybe go with all metal framing.
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Re: Just dreaming -- what is the design envelope

Postby bobhenry » Tue Jun 21, 2016 9:22 am

One time 200 mile trip :roll:

Build a good quality yard barn in the size you want and call a wrecker service with a roll back unit and simply pay to move it. One question is why can you not build it on site?

Better yet purchase a barn shell and utilize the supplies you have acquired to finish off inside and around the property.

If you want an on line coach PM me with a phone number and we can one on one long distance.
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Re: Just dreaming -- what is the design envelope

Postby Andrew Herrick » Wed Sep 21, 2016 4:50 pm

Karina wrote:Hi all.
+ I think I read that trailer height at that size runs about 22". Does that sound right? Can I guesstimate 2ft for trailer and be OK?
+ Do you think at that size the floor can be framed with 2x4s or do I need bigger joists? 2x6?
+ How many inches do I need to allow for roofing? Would the trusses likely be 6"? More? Plus a couple of inches for sheathing and metal roof? More?
+ Depending on the above, I think the interior volume on the high side maxes out at about 10'3" and a couple feet lower on the low side, depending on roof pitch? (I am in snow land so will have to do some studying to find the best angle.)

Similarly, with the 8'6" max highway width I am thinking 8' wide trailer frame.
+ Framed up with 2x4s and some kind of interior wall covering do you lose about 4.5" on each side to give a 7' 3" interior?

I have some thoughts but I don't know if any of them are practical until I get the design envelope a little clearer. Of course once I get the design envelope clearer I will start from there and wonder if there are better, thinner, lighter ways to accomplish the same thing, but the tiny house world so far seems to be all stick built.


Hmmm .... lot to answer here!

First of all, if you want a decent understanding of how beams (rafters, trusses, spans, joists, etc.) work, visit this link: http://www.finehomebuilding.com/2016/03 ... wood-beams

Technically, as one commenter mentioned, if you custom-build your trailer chassis with cross members spaced every 16 inches, you may be able to nix the floor joists. Then you run into the problem of how to attach your subfloor. Do you bolt the whole thing to the trailer? What if the trailer breaks? How do you hide the bolt heads? How will you insulate the floor?? I can imagine ways to make both designs work, but I have a feeling you'll have an easier time using a traditional 2x4 subframe with joists spaced 16OC (assuming you have 3/4-inch subflooring minimum).

If you're set on a single-pitch roof, yeah, you can build the roof with 2x4 ceiling joists ... but you'll have to space them REALLY closely. Not sure how you close. If you're mathematically minded, you can use the calculators here (http://www.engineersedge.com/beam_calc_menu.shtml) to figure it out. Otherwise ... make friends with an engineer :) Personally, I'd recommend a simple gable roof. Much easier to build with 2x4's. And +1 on someone's comment on Simpson Strong-Tie's. Can't use enough of those.

One quick note on your last comment about "better, thinner, lighter" ways. Remember: this is a Tiny House. If you plan to relocate often, build an RV, and then slap some cool-looking wooden siding and a gable roof on top. Well, it's a little more complicated than that, but you get what I mean. If you try to do something in the middle - half RV, half house - you may find yourself unable to use the standard fixtures and appliances designed for one or the other.
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Re: Just dreaming -- what is the design envelope

Postby Andrew Herrick » Wed Sep 21, 2016 5:02 pm

M C Toyer wrote:Karina -
The rafters do not need to be 2x6 or 2x4 or wood at all and since you are planning a single slope, i.e., shed, roof no trusses are involved. You may need some lateral bracing in a couple places in addition for the front and rear walls but that could be incorporated into the loft framing, The sloped metal roofs for barns and commercial buildings are supported by steel purlins and for a 10 foot span would be less than 2" thick.


Not sure if I understand exactly what he's saying ... but if he's recommending framing your Tiny House the same way as a pole barn or commercial metal storage building (which I used to sell), then I have to disagree :/ For lots of reasons. Most importantly, those roofs have a 20-30 psf load rating. That's not a safe roof to walk on. Not even close to code. It's also lightweight enough that enough snow or a falling tree limb could collapse it.

Now, you can certainly frame your roof out of metal box beams, and it will much thinner than a wooden one for the same strength! So the principle is sound. But you'll need more or beefier framing members than what you'll find on a normal pole barn.
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Re: Just dreaming -- what is the design envelope

Postby yrock87 » Wed Sep 21, 2016 5:52 pm

If you will leave it at your property forever, I would suggest building in place. or if you would rather build locally due to facilities, time, ext... then don't be so concerned about the size. Go with a 40ft gooseneck trailer that will give you almost double the SQFT to work with. you may also consider a trailer with a drop floor behind the axle, which would give you space to add your loft. lastly, maybe consider a different roof line.
Tiny houses are cool, the ability to move as often as you like is an intriguing idea. But I never did understand why most are limited to 20ft trailers. especially when it appears that many people hire a professional to move them.
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