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Community and Q&A

High end shed: sealed envelope or open to roof?

QBe9upShRb | Posted in Energy Efficiency and Durability on

Building a 12×15 multipurpose shed, most of the time just storing stuff unattended in Central Texas heat (and very rare freeze). Framed brick construction (light colored brick) with white metal roof, one window and french doors. Roof on top of radiant barrier. Attempting to beat the heat (9 mo/year and sometimes beyond 110 degrees), and condensation after fast temperature drops (sometimes >10 degrees/hour). No use of grid power (eventual plan is small solar system for lighting, fan, and radio). 3 months of the year there can be cold weather also, occasionally freezing.

Should a shed like this optimally be wide open and unfinished inside from side vents to ridge vent? That’s typical commercial shed design. Or optimally should roof system be self-venting and sealed from rest of shed with soffit vents providing airflow around roofing system radiant barrier? In former case, I’m not sure if it’s even useful to finish interior walls inside structural wall and framing. In latter case, all finished walls and ceiling could give sealed envelope if I go that way; I’m thinking that would necessitate upper and lower side vents with dampers, optimally motorized and humidistat controlled, to prevent condensation internally when there are large temperature swings. It seems to me like that sealed envelope would be the best approach, but not sure if it actually accomplishes much since frequent or continuous venting is still required anyway. I’ve never seen anyone else go sealed interior envelope in shed situation. Won’t energy flows (including convection through venting) eventually bring interior to outside temperature, then perhaps best that can be done is prevent exceeding outside temperature and humidity with continuous ventilation?

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  1. GBA Editor
    Martin Holladay | | #1

    I don't think there is any way to prevent condensation problems in an unconditioned building.

    During the winter, the temperature of the items being stored will drop. Let's say you have some steel tools. They'll get cold. Then, the weather warms up, and suddenly you have a warm, humid, spring day. That air will enter the building and the moisture in the air will condense on your steel tools.

  2. QBe9upShRb | | #2

    Thank you. However I am not aiming for perfection. The question is which approach would work better in keeping out temperature extremes and condensation in an unconditioned building. If I were to condition this building significantly I would be creating a huge energy sink. I keep tools in my garage (which is moderated somewhat by attachment to house) and they are fine. I do avoid putting boxes on the garage floor, that leads to immediate rot for various reasons. Actually much of what I will be storing in the shed is factory boxes for collectable hifi equipment. The equipment itself stays in house. The boxes will on a ledge 6.5 feet off the concrete floor, also somewhat above the coldest heaviest air.

    I'm still thinking fully insulating and sealing the shed will moderate the temperature/humidity the most, Putting in upper and lower cross vents with dampers allows for situations where venting might prove to be preferable. But I'm also wondering if all the additional expense of full insulation vs. unfinished would be worth much. And maybe insulating self-ventilating roof system is the single most important part, then no venting in the room itself is regularly required.

    I was als thinking a 200w solar collector with a few kwhr storage could also power a tiny heat source: 100 watt light bulb say, and/or fans for internal circulation for when needed most. I'm not sure that would make much difference even in well sealed small room.

    I'm avoiding windows on south side because actually I think heat may be one of the bigger problems, and I'm not sure a mere 2' overhang (maximum I can do) would be enough to shield such a window from summer sun, well maybe if window is very high, or with window shade just above window. I'm unsure how to calculate needed angles to catch sun november through february only...and it can get hot then sometimes too. However the solid brick wall will help somewhat, I hope.

  3. homedesign | | #3

    I live Near Dallas. My climate is just a little bit cooler than central Texas...not much
    My Garden Shed/Shop is 12 x 20 ... slab foundation...the roof is light colored comp. shingles
    The shed is unfinished on the inside... no venting or insulation.

    I store cardboard boxes and tools and "stuff" ... no rust, no moist problems
    Heck, I even store drywall mud !

    the Overhead door faces south
    The photo was taken after an extremely rare snow

  4. 4RT9yHJNbp | | #4

    Seems like a this maybe overkill for a storage building. But I understand how you want your things to be dry and not have to worry about them. I would say that the reason most people do not go with a sealed shed interior is due to the expense of doing it. Since most people do not heat or cool the interiors, the temperature differences are not that drastic. I doubt that condensation will be a big issue. Finishing out the interior is also something you could do later if you decide later that it needs it.

    Tim Hicks

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