Garage ceiling insulation

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Old 05-29-16, 10:46 PM
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Garage ceiling insulation

Hi all I just bought my house in January. I am planning to insulate the garage and add a heat source so I can work in it in the winter. It's a two car attached garage outside of Chicago (brutal winters and hot summers). There are no soffit, ridge, or gable vents. There are only two static roof vents. What is the best way to insulate the ceiling? How do I properly vent it? I plan to insulate the ceiling because I need to use the rafters for storage.
Thanks for the help!
 
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Old 05-30-16, 05:48 AM
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Welcome to the forums! Is the roof structure stick built or trusses? If trusses, the system isn't really made for, nor will it support much in the way of storage. Add to that, you only have 2x4 for a bottom chord limiting you to R13 insulation, which is woefully inadequate. So, it looks as if you have a choice. Floor it for storage with poor insulation, or insulate it properly to about R39 and forego the flooring. Fiberglas insulation is good, but in an open space such as that, blown in insulation would loft up better and give adequate insulative qualities. You can buy your insulation in bales from a box store and they usually will allow you to use the blower for free.

Air must move in and out, so with only the roof vents, you aren't getting the "in" part. If there is a soffit, I would install soffit vents around the garage to allow air in. Hopefully the roof vents will help in evacuating it. Ideally those vents would be history, and ridge venting installed, but you can wait and do that when you re roof the garage.
 
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Old 05-30-16, 10:09 AM
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Im not sure if it is stick or trusses. Ive attached some pictures of it. with regards to the roof vents, if i install the soffit vents do i just need to put them in the same "void" that the roof vents are in? Would i use a baffle system in just those voids to get air from the soffit vent to the roof vent, or would i use baffles for the whole roof?

I'm not looking to keep it 70 degrees in there in the winter, but enough so that it is not bitter cold. Eventually i would put a ridge vent in when the roof is redone, but it is in decent condition, so that will likely not be for a while.
 
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Old 05-30-16, 05:36 PM
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It is stick built, but joists are on 48" centers. From what you are describing, are you planning on insulating the actual roof rafters? This is not the best idea. You need to install more joists if you plan on insulating the joist area, bringing it to at the very least 24" centers, but 16" centers as your rafters are is ideal. You would put baffles all along the soffit look out to capture any and all air it can, and prevent insulation from falling into the cavity.

You can cut a ridge vent at any time. You don't have to wait on a re roof.
 
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Old 05-30-16, 11:05 PM
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Yes I was planning on insulting the rafters so I can keep the joist area open to store wood and other items. So I a wondering what my best options are and how I would properly vent it.
 
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Old 05-31-16, 06:28 AM
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Hi strato.
Several issues in addition to what Chandler posted, I may duplicate. So I'll just list them.
1. Intermittently heated spaces are a problem, especially a garage and especially if you park cars in there with lots of snow or water.
2. I'm judging 2x6 rafters. With an air space for ventilation you are left with 3.5" fiber insulation.
3. Soffit vents and baffles all the way to the ridge and no delay on installing the ridge vent. Moisture from the garage will be looking for a cool surface to condense so that space above needs to be vented.
4. Being an attached garage it is likely that code requirements will kick in and permits will be required. Varies by location so you need to ask.
5. There needs to be a fire barrier between the garage and the house, cloor to rafters and an approved access to the house attic if there is one.
6. Once you build any storage area, even if you only wish to store light things, it becomes a storage place and those who follow you will need it to be strong.
7. You mentioned a heat source but not what type. Wood heaters are usually not accepted.
8. You will need electricity and that will need a permit and inspection.

Bud
 
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Old 05-31-16, 10:40 PM
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It would not be a wood heater. Likely electric or propane. Just something to take the bitter chill out of the air in the winter. There is a fire barrier on the wall shared by the house. So what are my best options?
 
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Old 06-01-16, 06:34 AM
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#4. You start by talking with your local code/building department to see what they want/need for you to move forward. We can't determine that as each local code office can select what codes they wish to follow. My state recently adopted uniform building codes, but they only apply to communities over 2,000 (?). I have one community that takes a magnifying glass to everything and another that would rarely show up at a project. But you need to know from the start to stay on their good side.

Bud
 
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Old 06-01-16, 12:16 PM
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Ok I'll definitely talk with the inspectors office to see what I legally need and if permits are needed. I looked into ridge vents and soffit vents and feel confident in putting them in myself if needed. So now iim just wondering what the best option is for the insulation. I need to know what I am presenting to the inspector to see what changes they would make regarding what I can do.
 
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Old 06-01-16, 02:01 PM
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Bud, I know it is expensive, but I note you have not mentioned spray foam for the rafters. Would that be a viable option, seeing what the OP has for structure?
 
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Old 06-01-16, 02:43 PM
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strato,
There are several insulation options for a traditionally vents roof assembly, but we need to know what the building department wants as a minimum. 2x6 rafters will only give you about r-15 without extra thickness padded to the rafters or a layer of the proper amount of rigid insulation.

Larry, spray foam works well when the space is heated all winter. But I would have concerns with it getting cold while a car covered with snow melts and evaporates from the heat of the vehicle. That moisture will find the colder exterior walls and ceilings and deposit the excess moisture.

Plus the foam would need the required thermal barrier.

The Dow Thermax with an approved foil surface could be cut and fit against the bottom of the roof deck, assuming local codes would approve, but how much falls back to how much is required. And Thermax isn't cheap.

strato, what is on the walls now for insulation?

Bud
 
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Old 06-01-16, 02:55 PM
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There in no insulation in the garage at all right now. Walls or rafters. I plan to do both but the walls are more straight forward than the rafters
 
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Old 06-02-16, 10:47 PM
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What if I ran a dehumidifier in there in the winter?
 
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