Closet over garage insulation question


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Old 08-30-14, 06:28 AM
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Closet over garage insulation question

Hi everyone. I have a 20' closet over my garage. It gets cold in the winter and warm in the summer. I have two access panels on either side. I popped them open and I see that they basically built an insulted boxed (the room) using batting and ridged foam to surround it. The room is insulated on all sides, but only the size of the room. The rest of the space above the garage is not insulated. Further, the soffits are open with only mesh screening to prevent birds from coming in. So basically in the winter, outside air is freely allowed to come into the space surrounding the insulated room making the air against the room the same temperature as the outside. It seems that the floor of the room is the coldest part. I am wondering if the joists are acting like a heat sink since they would get as cold as the outside and bringing this cold through to the floor of the insulated room.

I am wondering if I can put in insulation batting between the joists and then over the joists to help keep them warm. I've included some pictures.

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Old 08-30-14, 07:13 AM
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If all of that floor space is over an unconditioned garage then insulating those joists will do only a little good.

Where those walls rest on the floor joists you need an air block to prevent circulation under the floor. Air moves right through fiberglass insulation, so add something rigid and sealed in place. Some use rigid insulation, but I prefer plywood to be sure critters can't chew through, and they will.

In any unheated space the floor will always be the coldest. Even with extreme insulation in the garage ceiling (that floor) the cold air will always flow down. If one gable end wall is facing the heated house, that is the only source of heat. But you can't open that space to moist heated air without other considerations.

How much insulation is surrounding that room and where?

Bud
 
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Old 08-30-14, 07:26 AM
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Hi Bud. Thanks for the response. It appears that the walls are 2X4's. The are filled with batting and then foam board is nailed to the sides. Under the floor of the room is just batting, which looks to be 8" thick or so. This ends at the walls of the room (see picture 3).

So should I seal each joist location at the start of the walls with pieces of rigid foam and then seal with say silicon chalking? I am wondering if I will create a vapor problem if I seal it?
 
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Old 08-30-14, 08:08 AM
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If you are parking snow covered vehicles in the garage then that moisture will need to be considered. Otherwise winter air is relatively dry. Key word is relative.

In the summer, as long as that space is not air conditioned there should be no moisture issues. Cold surfaces have to be isolated from warm humid air.

Along with the 8" of insulation in the floor, is there a vapor barrier, be it kraft or plastic and where is it installed. Since the 8" does not fill the cavity, is it pushed to the top or located at the bottom?

The storage area itself has similar concerns as any closed space in that it needs a bit of ventilation. In winter, allowing cold dry air in and out is good. In summer the warm outside air can hold more moisture so if the space is ventilated it needs to be allowed to be a bit warmer than the outside, which is basically what it is doing now.

Bud
 
 

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