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Old 09-24-2011, 05:06 PM   #1
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Putting a base on the roof for my AC condenser


I'm putting a base on the roof for my AC condenser, sometimes call a "roof jack". See attached photo. It will have a solid top and 18-gauge metal cap, and will be totally sealed. I was just wondering if I should foam the inside of it. There's nothing inside it, and no penetration in the roof. Any thoughts?
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Old 09-24-2011, 05:47 PM   #2
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Putting a base on the roof for my AC condenser


We make the entire unit of metal and call it a "roof curb". We do line the interior with 1" fiberglass duct liner when we make them from metal to keep condensation from becoming a problem.

Even though the wood probably won't sweat I would put fiberglass batting in yours and make sure the metal cap is well insulated. I would glue the insulation to the metal cap just to be sure there are no air pockets. The last thing you want is condensation building up inside the curb and causing structural damage, especially if it gets below freezing where you are.

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Old 09-24-2011, 06:21 PM   #3
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Putting a base on the roof for my AC condenser


I looked closer at your "roof jack" and can't see any pitch. Is your roof flat or is it just me?
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Old 09-25-2011, 12:49 AM   #4
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Putting a base on the roof for my AC condenser


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I looked closer at your "roof jack" and can't see any pitch. Is your roof flat or is it just me?
You're right, there's no pitch in the jack itself. The roof is nearly flat. I haven't actually measured the slope, but it's probably only about 1/8 inch per foot. This type of roof is common around here. We don't get a lot of rain.

BTW, I am putting an extra rubber pad under the anti-vibration pads on one side of the condenser, adding 3/8" to that side to level the condenser, if it really matters (it probably doesn't).
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Old 09-25-2011, 05:27 PM   #5
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Putting a base on the roof for my AC condenser


The top is 7/8 wood (2 sheets of 7/16 sheathing). The metal cap is 18 gauge galvanized. I think I'll just fill it up with some left-over fiberglass insulation I have. That should help with any noise that might get in there.

Oh, and I think the roof slope is closer to 1/4" per foot, not 1/8" like I said earlier.

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Old 09-29-2011, 12:26 PM   #6
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Putting a base on the roof for my AC condenser


How's this look?
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Old 10-01-2011, 08:59 AM   #7
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Putting a base on the roof for my AC condenser


Looks good Gary!

Are the corners of the cap welded to prevent water from wicking under the cap?

We usually bend a 1/2" drip edge on caps like that, but in your situation you'll be fine because of the overhang.
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Old 10-01-2011, 11:05 AM   #8
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Putting a base on the roof for my AC condenser


+1

Looks very well done.
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Old 10-02-2011, 01:08 AM   #9
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Putting a base on the roof for my AC condenser


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Looks good Gary!

Are the corners of the cap welded to prevent water from wicking under the cap?

We usually bend a 1/2" drip edge on caps like that, but in your situation you'll be fine because of the overhang.
My sheet metal guy didn't weld the corners, but the gap at the corner is tight and he put some kind of sealer inside the corner. If it was commercial I'd want the corners welded but it should be OK for what I need.
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Old 10-02-2011, 10:17 AM   #10
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Putting a base on the roof for my AC condenser


Gary,

That looks fabulous!! Great job!!

After looking at this beautiful piece of work, I was thinking towards the future when/if the zinc coating starts to wear off subjecting the cap to rusting. You might want to consider priming and painting. You must treat it with a solvent to get the protective oily film left on from the mill off thus allowing paint to adhere to the surface. Being that the unit is minimally pitched, it would be subjected to elements such as standing water, snow, ice,condensation, that could reduce the life of the original coating. It's easier to put that extra insurance on now rather than later when everything is set up.

Just food for thought!!
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Old 10-02-2011, 06:08 PM   #11
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Putting a base on the roof for my AC condenser


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Gary,

That looks fabulous!! Great job!!

After looking at this beautiful piece of work, I was thinking towards the future when/if the zinc coating starts to wear off subjecting the cap to rusting. You might want to consider priming and painting. You must treat it with a solvent to get the protective oily film left on from the mill off thus allowing paint to adhere to the surface. Being that the unit is minimally pitched, it would be subjected to elements such as standing water, snow, ice,condensation, that could reduce the life of the original coating. It's easier to put that extra insurance on now rather than later when everything is set up.

Just food for thought!!
Thanks for the tip. I had thought about that, but we don't get much rain around here and the humidity is very low most of the year. Galvanized sheet metal seems to hold up for a very long time outside. On swamp cooler ducts the metal will will rust after maybe 20 years or so, but that's another matter.

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