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Community and Q&A

Bonus room temperature and humidity

FrankFulton | Posted in General Questions on

We just moved (CZ4, humid) and have a finished bonus room above our unconditioned garage. The insulation is poor. Heat is electric baseboard. AC is currently none. The room is not in regular use. For example, we did not turn on the heat this winter.

If the room were in use, it would be ideal for a minisplit. But, we rarely use the space. Other than a large tub of DampRid, there is nothing up there to protect the space.

What do we need to do to avoid problems from seasonal temperature swings and/or humidity? Can we simply leave it closed and locked, excepting when we have houseguests?

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  1. GBA Editor
    Martin Holladay | | #1

    You can certainly leave things as they are if you want -- that's the cheapest way to go. There is a small risk of funny odors or mold, but these can generally be solved by opening the windows and engaging in ordinary housecleaning methods when needed.

    Or you can install a ductless minisplit and keep the place conditioned. This approach reduces the need for airing and cleaning, but raises your monthly utility bills.

  2. walta100 | | #2

    Mostly the bonus rooms are pretty useless spaces with sloped ceilings and few windows over unheated garages with little or no HVAC. If you a sure you are unlikely use the room for any thing but storage and if your plan is to move in a few years do as little as possible to the room.

    If you see yourself in the house for 20 next years consider moving it outside of the conditioned space by
    1 Block or disable any HVAC systems
    2 Add roof and soffit vents
    3 Replacing the door with an exterior grade one.
    4 Insulating all wall and floors that abut conditioned spaces.
    5 Make sure no water pipes will be put in danger of freezing.
    Understanding you will need to convert it back before you sell the home.


  3. Expert Member

    A digression, but I wonder how Bonus Rooms got their name? They cost the same amount to build as any other room, but because they are situated over the garage and for some reason often left unfinished, they somehow got labelled as though they were a free extra space. Strange.

  4. this_page_left_blank | | #4

    They don't have to be unfinished or ever a garage. I take the term bonus room to mean that it's a room with no specific purpose, and is additional to what you'd expect in the particular style of house. I do however suspect that the term was coined by a real estate agent.

  5. walta100 | | #5

    I suspect it was coined by someone in marketing department a production builder.
    There are multimillion dollar businesses that live or die for one dollar per square foot. Someone noticed they could “finish” the 200 SF space over the garage under 12/12 roof for ½ the price per SF of the rest of the home and lower $/SF number for that home giving them a competitive advantage .


  6. Expert Member
    Dana Dorsett | | #6

    The heating/cooling loads of a typical bonus room is well below that of a ductless mini-split. A half-ton PTHP is probably a cheaper and more appropriately sized solution for an intermittently used space.

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