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Green Building Blog

Deep in the Heat of Texas

Insulation, air-sealing, and efficient mechanicals keep this house comfortable in the hot, humid weather

Before.
Image Credit: Image #1: Matt Risinger

You may have heard that here in Central Texas, it gets hot. The average temperature rises above 90°F on more than 100 days out of the year. As you might expect, we turn on the air conditioner more often than the furnace.

Here, as in other parts of the South and West, it’s typical to see houses built with slab-on-grade foundations, which often means that the standard practice is to locate the air-conditioning system in the attic. On a summer day, the air conditioner moves 55°F air through an attic that, if it’s not included within the home’s conditioned envelope, can easily run above 130°F. That doesn’t exactly make sense from an efficiency standpoint.

In addition, the standard ducting often leaks conditioned air into the attic, which depressurizes the house, drawing humid, hot air into the interior through gaps and cracks in the exterior envelope to make up the loss. In this climate, when moist outside air leaks into an air-conditioned structure, moisture condenses on the cooler surfaces, causing mold and rot.

My company recently renovated a 1950s ranch with many of the problems associated with inadequate insulation and detailing. The main goal of Dick Clark Architects, who designed the remodel, was to open the plan up and to modernize the interior and exterior. My firm was hired early in the design phase to consult on how best to achieve a comfortable, efficient, and durable house that would meet the architectural intent and the budget. Our efforts centered on air-sealing and properly insulating the house and on moving the ducts within the conditioned space.

Starting from scratch—almost

To begin the renovation, we gutted the interior down to the studs and stripped the siding from the exterior. We sprayed…

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2 Comments

  1. Aj Builder, Upstate NY Zone 6a | | #1

    Seems like a good design for
    Seems like a good design for the humid south.

    Two questions;
    1- could this home be net zero with PV?
    2- could you redesign this same home same cost and eliminate foam?
    Thank you, great work by the way, worth others taking notice.
    Aj

  2. User avater
    Dana Dorsett | | #2

    Whole-wall R vs. center cavity R
    An R13+ 5 wall is more like R15 whole-wall (unless you use extremely generous estimates for air-film performance in both the rainscreen and interior).

    It's still a pretty good wall for the climate, but using the center-cavity R as shorthand for the wall performance leads to large errors. For instance, R18 could also mean 3" of closed cell in a 2x4 cavity, which would have whole-wall performance closer to R11 whole-wall, (and that's allowing a combined R1 for the air films.)

    AJ: If the site shading & orientation factors were favorable it probably COULD get to Net Zero with an array that fits on the house. But that's a prettty big "if". In Austin TX code requires "Net Zero Ready" for new construction, and they're getting there with air tight 2x6 / R21 construction, better thought-out window size & orientation, and better thought out roof lines & orientation. If you do a web search you come up with multiple examples like this:

    http://www.solaustin.com/net-zero_energy_formula.php

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