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Old 07-08-2016, 04:02 PM   #1
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100 degree inside attached garage. 145 degree in attic. Where to begin?


Our single story attached two car garage is consistently reading 100 degrees temps inside. The attic space above is reading 143 degrees. Current outside temp is 97 degrees here in Bham, Al. Since this is not a conditioned space, I'm not certain of how impactful insulation could be so I'm looking for suggestions.

Here are a few pics of the space:










The automatic garage door is an insulated model, and there is insulation in the one exterior wall. The other two walls are connected to the house.

There is no insulation in the attic above the garage. The roof is a very low pitch, but I have ready access to get to it for blowing insulation.

I'm thinking that my best low cost option may be to rent a blower unit and a few bags of cellulose and blow some over the garage attic.

I may also consider installing a solar attic fan in the attic here. Perhaps a radiant barrier.

I may also consider a small mini-split unit once I get the insulation in place.

Any suggestions?

Last edited by homeimproverjoe; 07-08-2016 at 04:22 PM.
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Old 07-08-2016, 04:36 PM   #2
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Is there a firewall in the attic between house and garage? If so, get some attic venting going on. Two windows in the garage on opposite sides would allow air to flow, making it the same temp as outside. Insulation in the walls/attic would make the garage hold the temp it is for a longer period of time compared to the outside temp. So if it's cold inside the garage, it will heat up slower and vice versa in winter. The issue is dropping/raising the temp initially. Naturally, it would cool off at night and stay cooler into the day but would peak and stay warmer in the night while outside air cools off faster. Just my two cents.
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Old 07-08-2016, 04:46 PM   #3
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Thanks for the info. There is no firewall in the attic space between the house and the garage. There is a single solar powered attic vent fan in the center of the house appx 50-60 feet from where the garage space begins.

There is only a single set of windows in the garage. They are the ones you can see in the picture behind the car. Its not possible to get cross ventilation with windows here since the only other outside wall is the garage door.

If I were to get a sub $1k mini split system here, I'd have to get an extra long line set of about 30 feet to reach through the utility room adjacent to the garage and out to the back yard - installing it over my workbench area at the back of the garage opposite the garage door. Or I could possibly install it over the garage door and run the line-set out to the side of the house next to the garage door where I keep my trash cans.
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Old 07-08-2016, 04:50 PM   #4
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


What are thoughts on an portable evaporative air cooler vs a mini split?

How about a whole house attic fan installed into the garage ceiling to vent hot air out of the garage?

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Old 07-08-2016, 05:20 PM   #5
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Sounds like you have the right idea. Insulation and a mini split. I've been in a few of those 140 degree attics today. They are tuff.
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Old 07-08-2016, 06:38 PM   #6
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Any soffit vents for make up air for roof venting.
A ridge vent will vent the whole roof not just a circle with air trapped in the rafter bays.
With no insulation in that attic the whole ceiling is acting like a radiator.
Not having 5/8 fire code sheet rock seperating the garage from the house all the way from the wall to the roof is a big code infraction.
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Last edited by joecaption; 07-08-2016 at 06:41 PM.
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Old 07-08-2016, 07:40 PM   #7
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


"I'm thinking that my best low cost option may be to rent a blower unit and a few bags of cellulose and blow some over the garage attic."

Yes, this should be step one, made a huge difference for me. Careful not to block eave vents. Go for at least 12". Do that and then reevaluate temperatures and what might be a next step.

What is your objective, a place to store the car that's not so hot or do you want it comfortable enough to work on the car?
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Old 07-08-2016, 07:47 PM   #8
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Why rent anything? Buy 10 bags at any Lowe's or HD and the rental is free.
Improper roof and soffit venting and there's not going to be a big change in temp.
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Old 07-08-2016, 10:28 PM   #9
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


It is common for older houses to have insuffiient attic ventilation. It's not always the end of the world, but it can make things less efficient in terms of climate control. I would check to see if you have more than the solar vent for your whole attic. Any passive vents on your soffit, or ridge?

If the garage isn't insulated, is the house attic portion at least insulated?

I know you're probably losing your mind with all these posts

I wouldn't justify buying a minisplit if you're just cooling the place. I'd just buy a window air or a portable ac unit. Window air can be installed into the wall if you cut a hole for her and flash it right, then you just replace the window air unit every 10 years or so. A mini-split is $$$$. You would get better bang for your buck buying a portable AC unit (they just have a fresh air intake) and insulating the attic with leftover funds. You should probably shoot for the most passive cooling possible which as you can tell from the posts is ventilation, physics will say warm air rises, and when cool air enters with warm air, the cool air can push the warm air out if it has a higher vent point than the cool air coming in. Just like the indians did with their teepees. They rolled the bottoms up a few inches and had the top point open to have a natural convection current going in.
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Old 07-09-2016, 06:55 AM   #10
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Quote:
Originally Posted by joecaption View Post
Any soffit vents for make up air for roof venting.
Yes. Soffit vents running the entire length of the eaves adjacent the garage.

Quote:
Not having 5/8 fire code sheet rock seperating the garage from the house all the way from the wall to the roof is a big code infraction.
Interesting. The home was built in 1961. I'll need to learn more about that. I could do the sheetrock as part of this job.
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Old 07-09-2016, 06:58 AM   #11
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Quote:
Originally Posted by ChuckF. View Post
What is your objective, a place to store the car that's not so hot or do you want it comfortable enough to work on the car?
Both. We currently park both of our vehicles in there. Fortunately, the garage is large enough for two cars and room left over for a second refrigerator, my John Deer lawn tractor, and a sizable workbench. The main goal is to make it comfortable enough to use the workbench area for projects for extended periods of time.
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Old 07-09-2016, 07:09 AM   #12
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


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Originally Posted by CTSNicholas View Post
I would check to see if you have more than the solar vent for your whole attic. Any passive vents on your soffit, or ridge?
Yes. I replaced an inoperable powered roof mounted vent fan with a 20 watt Durabuild solar attic fan rated for 1850 sf. I also have eave venting at both sides of the house.

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If the garage isn't insulated, is the house attic portion at least insulated?
Yes, most of the house has loose blown insulation.

Quote:
I wouldn't justify buying a minisplit if you're just cooling the place. I'd just buy a window air or a portable ac unit. Window air can be installed into the wall if you cut a hole for her and flash it right, then you just replace the window air unit every 10 years or so.
Good suggestion. I actually hadn't thought of cutting a hole for a window unit vs having a window. Thanks for that.

Quote:
You should probably shoot for the most passive cooling possible which as you can tell from the posts is ventilation, physics will say warm air rises, and when cool air enters with warm air, the cool air can push the warm air out if it has a higher vent point than the cool air coming in. Just like the indians did with their teepees. They rolled the bottoms up a few inches and had the top point open to have a natural convection current going in.
Valid points. Thanks.
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Old 07-12-2016, 03:50 PM   #13
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


The 5/8" drywall on the ceiling is your firewall, no other is needed, do not cut any ceiling holes compromising the firewall ceiling, check local AHJ. Add a radiant barrier to the roof rafter bottoms (leave 6" spaces at top/bottom), then insulate with cellulose leaving air channel open to soffits. The old FHA code required openings in side walls of garages for venting fumes- check AHJ before cutting any holes.

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 07-12-2016, 04:44 PM   #14
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Gary, thanks for the information. That sounds like a good suggestion.

Radiant barrier should be a pretty simple retrofit. I may just try that first to see what kind of impact it has.

Do you have a suggestion for a specific brand or type?

Curious what your thoughts are for or against an attic fan or passive venting in the attic gable to go along with your suggestions?

Last edited by homeimproverjoe; 07-12-2016 at 04:51 PM.
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Old 07-16-2016, 04:00 PM   #15
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Re: 100 degree inside attached garage. 145 degree in attic. Where to begin?


Don't use RB's around here... do some research first, eg; http://www.reflectixinc.com/basepage.asp?PageIndex=730

http://www.energyideas.org/documents...atTransfer.pdf

You really need the insulation first and foremost -to stop the heat gain from roof; http://www.rfoil.com/pdf/8-Effect-of...erformance.pdf

Fans usually use more energy than they save... and may draw from furnace pilots, etc. Make sure the inlet vents are clean- big affect on performance; http://www.blocktheheat.com/ventproblems.htm

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