On SketchUp and Why Progress is a Slow Thing

So, one week of early mornings in, what have we been using all that time for here at trtn? Designing our own trailer proved a great opportunity to redo our whole design plan from scratch in order to take best advantage of the trailer’s features. 22 hours and 27 minutes worth of SketchUp modelling later, it’s starting to look like a house. That’s an awful lot of time you say. It sure feels like it. But the end product is (or, at least, will be) an exact model of my tiny house down to the thickness of the housewrap.

This is both the biggest pro and con of planning a build in SketchUp. On the pro side, you get to effectively build the house in virtual reality, running into any little issues where you can more easily fix them rather than after the relevant pieces have been cut, assembled, and half a house built on top of them. For cons, just like building a house in the real world, this takes a looong time. This is partially an issue of patience and wanting to see what your finished house will look like, but also a problem when you decide you want to move a window and have to go back and edit every involved layer of your house’s walls. Hence, why my house has no windows yet – I want to be more sure of where they should go before I build them in.

One solution to this is two models – one for the details and one for the concept. The design you see in the header of trtn is my concept model. It’s got all the windows (plus interior furnishings, appliances, etc) but the structure of the house is just a few big rectangular blocks of about the right thickness for walls and roof. Not great as a plan to build from, but perfect for deciding the kitchen layout.

So, without further ado, here’s the tiny house plan to date:

After building our trailer, time to add some floor insulation.
After designing the trailer from scratch, time to add some floor insulation.

The trailer’s recessed central cavity allows for lots of insulation without losing headroom in the finished house.

And a little more insulation . At least an inch between all exposed metal and the interior.
And a little more insulation. At least an inch between all exposed metal and the interior.

The downside of a recessed insulation style trailer is risking heat loss where the recessed cavity ends and the metal wings of the trailer come into contact with the flooring. We’ve settled on a compromise of 1″ rigid foam insulation (R6) between all exposed metal and the inside of the house. Because this layer sits on top of the main recessed floor insulation, it also offers space to run some of the plumbing where it will be well insulated from freezing. The support for the subfloor is also primarily located over the existing recessed insulation so that we can minimize thermal bridging through the wood from the cold metal frame.

Wood SIP walls reduce thermal bridging and provide an airtight building envelope.
Wood SIP walls reduce thermal bridging and provide an airtight building envelope.

We’re going with SIPs for two main reasons: 1. much better insulation value per inch thickness than almost any other wall type, and 2. they’re much quicker to build with than standard stick framing. The first is due both to the reduced thermal bridging from not having wood 2x4s everywhere and (likely more significantly) the ability to almost completely seal the housing envelope so cold air (or hot in summer) isn’t leaking in through the cracks. The second will let us devote most of our available build time to more exciting things like building our own air-to-air heat exchanger and wind turbines!

Add roofing, interior panelling, flooring, housewrap, and furring strips for the siding.
Add roofing, interior panelling, flooring, housewrap, and furring strips for the siding.

Opted for a rainscreen style siding which means it’s spaced out from the main building envelope with thin furring strips to create a drainage and ventilation plane. This allows any water that gets behind the siding to get out instead of collecting and rotting my lovely SIPs! The metal roof is similarly spaced out from the roof SIPs with the added benefit of preventing ice dams by keeping the roof material the same temperature as the outside air. So many details to consider in designing a house!

Finally with the door and siding installed. Yes, I know, no windows! Haven't had a chance to make and install them. Coming up soon.
Finally with the door and siding installed. Yes, I know, no windows! Haven’t had a chance to make and install them. Coming up soon.

Finally, the door goes in and the siding goes on. The actual siding will be horizontal but I’m having trouble persuading SketchUp to show the material that way.

Now, time for me to go study for my Internal Medicine exam this Friday… There’s a lot to learn so I won’t be working any more on the tiny house until that’s done. In the meantime, if you know anything about building and have thoughts on the house plan thus far, please share them in the comments. We’d love any input we can get!

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