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Community and Q&A

Zone 2A insulation

Seth Vose | Posted in General Questions on

I’m very appreciative of the resources here. I’ve read through many, many postings and while I followed along I became a little stumped with the northern to southern variances in requirements/techniques. I’m in the very early stages of planning an owner-builder home under contractor supervision.

I’m in zone 2A outside of Austin, Texas and prefer to have the majority of my ducks in a row before seeking out an architect/contractor and avoid being persuaded into something I don’t know about or wouldn’t want.

My end goal is to insulate a 600sqft Tudor style home to balance out central cooling and radiant slab heating needs. I want to be independent on solar energy if at possible so it will scale with the finality of insulation. Passive heating doesn’t really fit within the design aesthetic I’m looking to create. Though, triple glaze windows are absolutely in the plan for cooling needs with landscape and light color roofing to assist.

After everything I looked at with all the different techniques I realized some might not be suitable for my climate zone (2A). So far I’ve noted to keep the cooling system within the living space. Insulate the slab for radiant heating. Seal the walls and roof very well and properly vent. I image the attic would remain unconditioned with some deep depths of cellulose. Being in an attic in a Texas summer is not on my bucket list of adventures so access can remain outside the living space.

Where is the balance between insulation thickness and the various types while conserving as much living space as possible for zone 2A? I’m not cost sensitive but I also don’t want to waste money for a negligible gain. Nor am I sensitive to perceived toxicity of building materials. I really just want what works; but I think a 16-inch wall of rigid foam would look a little on the “chubby” side for such a small space. I apologize if this has already been answered, I missed it. Thank you!

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, can you tell us your name?

    I'm summarize what you have told us. Basically, you are building a tiny house in a mild climate. That puts you in an excellent position. Your house will be easy to heat and cool.

    If you are a green builder, you will realize that it doesn't make environmental sense to buy expensive materials if those expensive materials aren't needed.

    Your tiny house in Austin does not need triple-glazed windows. All you need is double-glazed windows with a low SHGC. Design your house so that your windows are shaded, and so that the area of the east-facing windows and west-facing windows is minimized.

    You don't need radiant heating in your slab. Compared to those of us who live up north, you barely need any heating at all. Your 600-square-foot tiny house can be easily heated and cooled by a single ductless minisplit. Using simple HVAC equipment is much more green than investing thousands of dollars in unnecessary heating and cooling equipment.

    If you want R-value advice, I suggest that you read this article: R-Value Advice from Building Science Corporation. In that article, you'll learn that good targets for your climate zone are the following:
    R-15 walls, R-50 vented attic, R-5 slab edge (with no horizontal insulation under the slab).
    Windows should have a maximum U-factor of 0.35 and a maximum SHGC of 0.25.

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