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What is heating the floor in one room of my stilt home?

hojgard | Posted in Energy Efficiency and Durability on

I live in the Florida Keys, in a frame home on concrete posts and beams. There is a carport with concrete pad on each side of a storage room at ground level, then two stories of living space. Double hip roofed. The house faces west. Every day in the summer, BEFORE THE SUN REACHES THE FRONT OF THE HOUSE, the floor in the room above the north-side carport heats up — not the whole floor but eight feet or so nearest the front of the house. I measured the temperature rise and it is about 5 degrees – noticeable to a bare foot. The double window at the front is covered by a Bahama shutter. The room above the other carport does not have this problem. Most of that side of the house is shaded by trees, back to front. The carports are not particularly hot, and there is usually a breeze going through. The rim joist is not insulated, nor is any of the flooring above the carports. I would understand right away if this heating issue occurred after the sun hits the front of the house, but that is not the case. Can you suggest a reason, and perhaps a fix?

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  1. user-2310254 | | #1

    Do use air conditioning or not in the evening?

  2. hojgard | | #2


  3. user-2310254 | | #3

    Are the Bahama shutters on the inside or the outside of the windows? You say the room heats up before the sun reaches the house. But the sun is above the horizon, correct?

  4. hojgard | | #4

    Shutters are outside, covering most of the windows, with just a gap of a couple of feet at the bottom. Ref the sun, yes very much above horizon. It comes up over a bay. The sun shines on the back of the house as soon as it rises and continues to hit the house throughout the day. In the mornings the sun is on the back of the house and the front is shaded. At mid day the sun reaches the apex of the house, at which point the front begins to get the full blast of western exposure and the back ends up in progressing shade. In my tests, the floor heated up before the sun began hitting the front of the house. Also, in case it is relevant, the roof is metal.

  5. GBA Editor
    Martin Holladay | | #5

    Your description is a little hard to follow, since you switch between references to the "north" and references to the "front." I'm guessing that the front of your house faces west, but you never made that explicit (unless I missed it).

    There are a limited number of ways that subflooring or finish flooring can heat up. These range from (a) solar gain, (b) conduction from below (which can be solved by insulating the joist cavity), or (c) heat transmission from mechanical equipment or a hot-water pipe. It's hard to diagnose this problem over the internet, but you can probably figure it out with a little investigation.

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