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Flooring for a passive solar

user-304075 | Posted in GBA Pro Help on

I am building a home that will use a combination of a mini-split and passive solar in the Pacific Northwest. For thermal mass it has a concrete slab floor with insulation underneath.

My question is about flooring. I was planning on an engineered wood floor but my builder pointed out that this would prevent the sun from heating the slab. He suggests a stained concrete floor or tile. I really do not like either of these options.

How bad is a wood floor? Would a Terrazzo type floor using recycled glass such as Enviroglass be a good option?

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  1. GBA Editor
    Martin Holladay | | #1

    Your builder is right; traditional passive solar design calls for a concrete slab or tile floor. Terrazzo would work too, but it is likely to be expensive.

    However, there are lots of reasons to question the traditional wisdom. First of all, an insulated concrete floor can only store solar heat efficiently if sunlight strikes it directly. In most homes, furniture and rugs prevent more than a small percentage of the floor from seeing direct sunlight.

    Second, the Pacific Northwest sees much less sunlight during the heating season than Arizona or Colorado, undermining the importance of passive solar principles in your climate.

    Third, if your home was built with attention to air tightness and above-code levels of insulation, an investment in passive solar principles is unlikely to result in much of an improvement in energy performance. (See Top-of-the-Line Windows are a Waste of Money for a discussion of this issue.) Trying to quantify the performance difference between a concrete slab and engineered wood flooring would be a complicated calculation, but my guess is that the difference between the two types of flooring is trivial.

    Fourth, it's your home -- so you should choose the flooring that you really want, not a type of flooring that you think is required for passive solar principles.

  2. Expert Member
    ARMANDO COBO | | #2

    Clay, stone or ceramic tiles are good options to stained concrete or terrazzo. There are unbelievable tile floors in the market today; just in case you haven’t been at a tile store lately.

  3. user-304075 | | #3


    Thanks for the feedback. Since starting this design two years ago using the latest state of the art "green" technology such as ground sourced heat pumps I have radically simplified my approach. I have done this mainly by taking guidance from Martin's blog and the GreenBuildingAdvisor site in general.

    I agree with you about not spending too much money on high end windows. I am planning on using Intus windows which I feel offer a good cost/performance compromise.

    I suspect I will end up with wood floors in the living area and tiles in the kitchen area.

  4. user-304075 | | #4


    The design of my house uses a shed roof with the high side pointing south. This allows for a second set of windows above the main level windows. In the heating season most of the sunlight falls on the back wall of the main room or on the ceiling.

    Would it make sense to beef up the thermal mass using thicker dry wall. This way I don't need to worry so much about covering the concrete floor.

    Does anyone have experience with Phase Change drywall that is coming onto the market?


  5. wjrobinson | | #5

    Drywall. Two layers of 5/8" and your favorite dark color. But as Martin says superinsulation with a minisplit seems to be the best bang for the buck idea of late. Unless you have a view, go easy on windows for heat gain.

  6. chuck77 | | #6


    Interesting. I too am about to build a house with 2.5/12 shed roof, high side south, celestory windows, slab floor. Stained concrete. It's a horse property and has to be easy to clean (Roomba style) and low maintenace (steel siding, roof, facia) since the horses are pretty high maintenance. Curious about your design. I went with 26' wide with 29" tall parallel chord trusses. 29" to avoid interior access hole in ceiling.

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