Friday, January 21, 2011

Framing sketch and design updates

Tiny house framing in SketchUp
Been messing around with SketchUp a bit more and made the above framing sketch. I'm still not exactly convinced investing time in sketches pays off, I was after all getting by just fine with paper, but it is fun to play with and visualize three dimensionally.

I should also update you on the various design changes made: I've scrapped the staggered stud arrangement. I still like the idea but its needlessly complicated for this project. I'm instead going with run of the mill 2x4 studs at 16" and to prevent thermal bridging, I'l have 1" of rigid foam sheathing over plywood. A side benefit of the foam board is that it will act as a drainage plane so I won't need a Tyvek type building wrap.
Second big change I've made is no more monolithic pour slab on grade. Its great in theory (I love the one step process) but for what we have in mind, it just wasn't the right choice. To make it work for us we would had to have laid foam board around and under the entire foundation. I was particularly concerned with placing foam board directly under the concrete footings supporting the weight of the structure. I was told by a foam board manufacturing company that their stuff is rated for such an application but it still left me feeling shaky about the idea. I just can't help but wonder what if that foam degrades over time? Direct contact with the soil for years could potentially take its toll; moisture and termites and the like. So instead, the foundation will be a standard footing with a stem wall (3 pours instead of 1, ho hum). Then we'll prepare the floor slab by first laying down a vapor barrier, then 2" foam with a beveled edge (the picture below will explain this).

Doing the floor slab this way we'll be able to make our own custom tinted concrete mix with plenty of excavated soil in there (no cost filler and a little extra insulation)

Yesterday I picked up some 20ft 1/2" rebar and had a terrifying ride home in my compact truck with 5ish feet of metal poking out the back with a couple whimpy red flags attached; kept imagining someone getting impaled by my rebar everytime I stopped at a light.
Spent most of today bending, cutting and tying rebar and positioning it in the trench. I've run two lengths around the perimeter and have several L shaped vertical pieces to tie into the stem wall.

Pictures and more coming up after we do the pour!

4 comments:

  1. Wow! What a well written description of what you are doing and the sketches are helpful too! Amazing project and still reminds me of the fort Papa and Uncle Paul built in our backyard on Biona Drive way back when! At least we know where you got the gene from!!! It's definitely a "Brotsky" creative & mechanical gene! I must get Uncle Paul to look at this - he will be so impessed! Have fun!

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  2. I'd reconsider leaving out the Tyvek wrap. I don't think the rigid insulation provides all the benefits of the wrap. For one, the insulation has gaps, so air and moisture can get through it. I'd say use both.

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  3. Thanks for your thoughts Joe; definitely appreciated since I know I am still learning all of this

    I had based my decision off of information from Insulfoam and their PDF about the "total wall system" seen here http://docs.google.com/viewer?url=http://www.insulfoam.com/images/stories/docs/5005_Total_Wall_System.pdf .
    Their system relies on special tape to keep the seams waterproof that I'm not entirely sure I'm comfortable with. How long will that tape last? Who knows. With the housewrap, it's lapped/shingled so there's really no way for water to get in except for at the cuts.

    I'll have to think more about this

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  4. I love your project so much...I'll definitely be following you to see it completed.

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