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Community and Q&A

Troubleshooting Tiny House on a Budget

NewTinyBuilder | Posted in Plans Review on

Evan here with my first build EVER! Two weeks ago I didn’t know what OSB, flashing, joist hangers, thermal bridging, ISO/XPS/EPS, Rockwool, drainage planes, or really any of the things I learned on this site were. I have read many of the articles and question/responses on GBA and have learned a ton – thank you all, especially Martin Holladay, Dana Dorsett, and others – hopefully you see some of my learning evidenced below. Hoping to get some insight from the GBA community – Im finding it hard to locate information specific to my cabin’s tiny size and location.

Building: Tiny 8×10 foot (80 square feet) insulated cabin. Skillion cathedral roof, slanted 3:12 pitch from 10 feet to 8 feet high over 8 feet.

Zone: Vermont zone 6A

Use: Mostly as a winter cabin while unemployed. Located next to a family home with amenities (bathroom, electric, etc).

Construction: Using mostly used/reclaimed materials. Foundation of skids raised on concrete cap blocks. 2×4 single walls, 2×6 floor joists and rafters.

Goal: Given the size and limited budget my goal is to stay warm and prevent condensation issues. I cannot meet code requirements for R values in my area with my budget and have been advised that I can stay warm with less insulation due to the tiny space, likely with a small wood stove as fuel is free in my area.

Insulation: I currently have several sheets of felt faced ISO and scraps of EPS and XPS. I plan to use fiberglass due to low budget.

I would love ANY advice or feedback you have. This project is super intimidating for me. Example questions: Tips on where I can reduce material costs to preserve my savings? Glaring mistakes or omissions in my assemblies? Should I go with a vented or unvented roof? How do I ensure I have an adequate air barrier? Does Tyvek/tar paper/much-hated-6mil-poly belong in my assemblies? This is my first time constructing a building so all advice will be very appreciated. My floor is almost framed up!

I am working on my assemblies based on what I have learned on this site – if you want to see where I am now, they are listed from inside-out, below:

Floor: Flooring, 1″ XPS, OSB (3/4″ ply if budget allows) subfloor, 2×6 joists with foam board cut and cobble sealed with spray foam, 1/4″ hardware cloth (rodent prevention), 4×4 skids, 10″ of concrete blocks, ground. I know on GBA we prefer to keep foam sheets whole, but most of my sheets are in bits and pieces (2’x2′, 2’x4′, etc) I have been gifted from neighbors.

Walls: Latex paint on drywall or wood planks (likely cedar). Faced R-13 fiberglass batts in between 2×4 studs. 2×6 are beyond my budget and take up more interior space. OSB sheathing taped for air barrier, 1 or 1.5″ XPS taped for drainage plane (about 1:3 or 1:2 ratio), 1x vertical furring strips, siding (reclaimed vinyl or pallet/barn board/wood siding).

Roof (skillion cathedral style): Drywall with latex paint or cedar planks. 3″ of reclaimed felt faced ISO with taped seams (should this be further outside the assembly since it is foam?). 1×3 strips of strapping, then rafters. Rafters potentially filled with kraft faced fiberglass. 2×4 purlins perpendicular to rafters for 1.5″ of airflow (vented roof, air vents along front and back – high and low – roof lines). Roof sheathing (OSB). 30# tar paper. Metal roof. No roof overhang to prevent ice dams (as well as sealing air leaks and … more insulation if you think its needed?)

I plan to use canned spray foam to seal any cracks I can find.

Thank you all SO much! I am learning every hour and I am sure much of my plan above will seem silly based on what I learn in the next day or two.

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Replies

  1. Expert Member
    NICK KEENAN | | #1

    In an 8x10 building it's going to be hard to get a wood stove to put off little enough heat to be bearable. You'll have no choice but to stand right next to it.

    I'd do a gable roof instead of the skillion, the cuts aren't that hard once you figure it out and you get eaves which make it easier to keep the water out. Same amount of materials.

    I built an 8x8 shed from an article in Fine Homebuilding. I think this is it: https://www.finehomebuilding.com/2008/03/05/shortcuts-to-a-shed but it looks like they've taken down the plans.

    To be cool in the summer and warm in the winter you really want to insulate the ceiling. For about $50 you could put in ten inches of loose cellulose and get R-40. You don't even need to use a blower, just fluff it and pour it in. Make the ceiling a tray to hold the insulation, and then have the space above it well-ventilated. Normally I'd advise trying to make the building as air-tight as possible but with a wood stove in that small space you're going to need ventilation.

    Try to make everything rodent-proof as you build. A mouse can slip into a hole the size of a dime. If there are cracks that allow a draft rodents will sense the moving air and chew there to widen the crack.

    1. NewTinyBuilder | | #5

      Hi DCContrarian! Thank you so much for your advice and the link to the shed article - it is very informative for my build. I was lying out the foundation blocks and kept getting them in the wrong place - took the author's advice, built the floor platform and now I can get the blocks in exactly the right place. Im curious about the LP Corp SmartSide. Home Depot near me has it for $36 per 4x8 sheet. Apparently it can double as sheathing and siding, does that sound right? Did you use that product? Getting both sheathing and siding in one could help save money.

      Im basically trying to make an insulated shed. I will also look into cellulose, I had not considered that. It is definitely cheap! Sounds like it might be a good budget and warm option. I also purchased 1/4" hardware cloth to hopefully keep the rodents at bay, I know mice can be bad especially in fiberglass insulation. I plan to hardware cloth and spray foam gaps as appropriate. Hopefully I can find a tiny wood stove that wont overheat the space!

      1. creativedestruction | | #11

        4x8 LP panel siding is great. It's only about 3/8" thick though so it wouldn't technically qualify as a structural sheathing, but for an 8x10 tiny house it might suffice. You could let-in 1x4 diagonals to the studs for a little more shear strength.

        You still need a weather barrier and a rainscreen gap behind it, which I imagine being tricky to do without structural sheathing.

        1. NewTinyBuilder | | #15

          Oooh thats good to know Jason S. about the LP siding, thank you. Sounds like it wont really save me money but is a good option for siding once I get to that point.

  2. Expert Member
    NICK KEENAN | | #2

    Here's the FH article I was talking about:
    https://redifooting.com/wp-content/uploads/2010/03/redifootingarticle.pdf

    I didn't use RediFootings, I just put it on concrete blocks.

  3. tommay | | #3

    An 8 x 10 room with a wood stove...you shouldn't have to worry about nothing...you'll be opening windows to cool off...

    1. NewTinyBuilder | | #6

      I hope so! That would be fantastic :)

  4. tjanson | | #4

    Wall assembly... If you are on a budget and a new builder, I would skip the exterior foam and use 2x6 24" OC framing with R19 fiberglass. You'll have less thermal bridging with the 24" spacing, the lumber cost is similar, and it's easy to build. If your windows are less that 22.5" in width of the RO then you don't even need any headers. I do understand it would be a bummer to loose that 4" of interior space. 2x4 16" OC framing with r-19 batts alone is probably sufficient given the small space. You could also use 1" foam strips as a thermal break on the interior side of the framing and screw in your drywall with 2 1/4 screws. You'd only loose 2" on the interior that way.

    Cedar planks on the interior will not be airtight to prevent moisture from moving thru it. If you use that you would need at minimum 1.5" of EPS to prevent condensation on the sheathing, or an interior moisture retarding layer such as kraft paper or Membrain. I don't think I would trust the kraft facing of the fiberglass batts to retard enough moisture in combination what would be a very leaky interior layer of planks.

    I would hesitate to use the exterior foam as the sole WRB. Bare minimum of tar paper should be about $50-60 to do your whole cabin. If you haven't read this already: https://www.greenbuildingadvisor.com/article/using-rigid-foam-as-a-water-resistive-barrier

    1. NewTinyBuilder | | #7

      Wow Tim thank you, you gave me some great budget saving ideas! I will price out the 2x6 to make an informed decision - I like your idea to use foam only where its necessary on the studs on the inside that is really smart to help with thermal bridging. That does mean there would be a 1" gap between the backside of the drywall and the fiberglass facing isnt that right? I was worried about the cedar plank air issue too, but drywall intimidates me and I heard it might not be good for tiny homes on trailers (not mine) or on grade cinder block foundations (like mine) that are subject to movement like frost heaves. I will check out that link, thank you - would you wrap the whole exterior, under the siding, with 30# tar paper?

      1. Expert Member
        AKOS TOTH | | #8

        Messing around with foam strips is not worth it for a tiny house. Keep it simple. Provided you can air seal the place, going nuts on the R value is not worth it for such a small space. Stick to simple wall siding/felt/OSB or CDX/studs with batts/vapor barrier/drywall. 2x6 24" OC is a good compromise for cost and R value.

        If you are carful with how you install the vapor barrier and detail it as your air barrier,(caulk all edges and tape all seam and use vapor tight electrical boxes) you can skip the interior drywall and put up either T&G or plywood.

        I would stick to the shed roof as you suggested. Much easier to build. You are over complicating the roof though. The simplest is to insulate on the outside with about 3" of reclaimed polyiso and keep the rafters exposed. You can go right over the polyiso with TPO or EPDM. Down the road you can always add extra insulation in there and drywall over it, but it is also fine to just paint it as is.

        Even the smallest wood stove will overheat a place that small in no time, install enough operable windows in there to be able to let out some of the heat.

        1. NewTinyBuilder | | #9

          Hi Akos! Thank you for this thoughtful response. What would you recommend for the vapor barrier in the stud assembly? Something like poly, or just a vapor retarder like the Kraft facing on the fiberglass batts? Thanks for letting me know, I am prone to overcomplicating. I like the idea of exposed rafters - you think the 3" reclaimed felt/fiberglass faced poly I have is good for this application or would it need to be foil or unfaced? Would your recommendation work as an unvented roof with only the 3" of insulation? Im worried about ice dams primarily. I do have metal sheets of roofing I was planning to use, would that work instead of TPO or EPDM? Not familiar with either of those, I will have to look them up. I just learned about the ZIP system, which is apparently a water and air barrier when taped - too expensive to use for all the sheathing but I could use 2.5 sheets for the roof for an assembly of rafters, 3" felt faced ISO, ZIP, metal roofing if I understand the application correctly? I have 3 windows right now and hoping to find a few more to have at least 1 per wall.

          1. Expert Member
            AKOS TOTH | | #12

            You would have to use poly, the facer on batts is too fragile. You still have to be careful though.

            I didn't realize how small of a place you are building. With such a small footprint, wall thickmess matters. I would save the extra space and go with 2x4 walls.

            In 0F weather, your 8x10 roof with ~R16.5 of polyiso looses around 350BTU (about a 100W light bulb). Insulation is good, but don't need to go nuts for a small space.

            If you have the metal already, the metal roof is much cheaper.

            In case of a metal roof the structure would have to be:
            -rafters
            -sheathing with taped seams (air barrier)
            -rigid insulation
            -underlayment
            -metal roof

            Make sure to protect the edge of the foam from critters. I like to picture frame the foam around the roof with 2x lumber cut to height. Extending the facia board up past the roof deck also works.

            To install the metal roof, you would either have to strap out the foam with 1x4s or install 2x on edge between foam sheets. The 2x on edge works well if you have 2' wide foam.

        2. this_page_left_blank | | #10

          If you don't want to lose the interior space, maybe you could overhang the studs 2" outside the floor. For that size of building, I would think it would still be plenty strong enough. Just curious how you arrived at 8x10. Avoiding building permit? Usually anything smaller than 100 square feet will do that. Will this "house" have any utilities, at least electricity?

          1. NewTinyBuilder | | #16

            Hi Akos and Trevor! Thank you for these replies - I was out leveling the concrete block foundation today! Woo!

            Akos: Cool. I was reading a lot of bad things about poly but Im glad you think it would be a good solution for my build (tiny 8x10 in zone 6). Wow, I didnt realize it would lose such a small amount of heat! That makes me less worried. I would like to minimize my insulation because Im unemployed and its shaping up to be the most expensive part of my build. I just messaged someone about a ton of free used cellulose from his attic in case I can use that and save some cash. I thought perhaps I could create a cheap cellulose sandwich floor (from interior-exterior: flooring, plywood with taped seams, 2x6 joists with cellulose between cavities, 1" XPS, OSB below joists with taped seams, skids). Would I need a layer of poly in that assembly as well? I do have the metal roof already (free, unused from a barn). I will plan to go with your suggested roof assembly with the strapping between the foam and the underlayment. I didnt realize I would put the sheathing under the foam, I thought it would go on top to protect the foam from any water that by chance gets through the roof, thank you for clearing that up for me.

            Trevor: Oh thats an interesting idea! I chose 8x10 because it felt like the smallest space I could live in for the winter and the largest space I could afford to build (I am unemployed). I am planning to hook up electricity with an extension cord (it will be close to my sister in laws house), but no plumbing - I will use the bathroom in her house thankfully.

  5. Expert Member
    NICK KEENAN | | #13

    It's tempting to make a small building like this even multiples of 4' to economize on materials. Thing is, it never works out, because walls and floors have thickness and roofs have overhangs.

    If you really want the most building for your dollar you have to sketch out the whole thing and make a materials list and price it out. I find the Home Depot website invaluable for this. Then you can fiddle with dimensions and construction techniques and see how the cost moves with different changes. I use Sketchup to do this kind of modeling.

    1. NewTinyBuilder | | #17

      Hi DCContrarian! I was definitely thinking that it would be easier in multiples of 4 with my limited budget, and I am starting to realize what you are saying. Hopefully it will still be cheaper than a larger space, like a 10x10 or something like that. I made a materials list and have been trying to find as much as I can used or free from scrap piles. Im tempted to build using rough cut studs because its so much cheaper in my area but worried everything might not line up right (drywall, etc). I wanted to use sketch up after hearing about it in my research but I have only a few weeks to get the cabin built and was worried the learning curve might be too steep (I want to get into the cabin before snow comes, which is pretty early up here in northern Vermont!) I wanted to thank you for clueing me in on cellulose insulation - I priced it out and its MUCH cheaper! I even found some used locally for free. Im wondering if I can include it in my floor assembly as well as other areas - Im just getting tripped up with vapor barriers/retarders and trying to keep all of the insulation as dry as possible, while anticipating moisture issues in such a small space. What do you think? Thanks! Evan

      1. Expert Member
        NICK KEENAN | | #19

        You can use cellulose pretty much anywhere in a house. For something this small it wouldn't be impractical to gather it in garbage bags and pour it into the cavities.

        1. NewTinyBuilder | | #21

          Hi DCContrarian, that is cool to hear because it's so cheap! Thank you for first mentioning it so I knew to keep an eye out. Now I'll have a lot of free cellulose and scraps of xps, eps, and iso. My floor framing is almost done and I'd love your thoughts on this assembly: flooring, plywood with taped seams, 2x6 joists with cellulose between cavities, 1-2" assorted foam cut and cobbled in the bottom of the cavities with edge gaps spray foamed, OSB or 1/4" hardware cloth below joists to hold everything in and prevent critters, skids). Would I need a layer of poly in that floor assembly as well? I believe with the foam on the bottom I wouldn't want another vapor barrier? Thank you for all your support!

  6. creativedestruction | | #14

    Keep your eye out for houses in the area under construction. Never hurts to ask for scrap materials, especially if you want to avoid dumpster diving. Obviously free stuff on craigslist can be gold.

    Save your money for the door, window(s) and small wood/pellet stove.

    1. NewTinyBuilder | | #18

      Hi Jason! That is a great tip, thank you. I have been dumpster diving a bit (saved me a lot on lumber, even though it was pretty bowed). I would love to find plywood at a construction site cheaper than the hardware store. I just found free cellulose on Craigslist, waiting for the guy to write me back. The wood stove definitely seems to be expensive (the smaller the stove the more they seem to cost). I think I have all my windows and my exterior door, all gotten for free so far.

  7. Deleted | | #20

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