Building an elevated AC concrete pad??

[00lightning]

I'm having the outside unit for the AC system installed soon and need to pour a 3' x 3' foundation. I want to have the pad 18" above grade, about a foot below the top of the workshop floor. I plan on removing what little topsoil there is (rocky soil) and laying a 4" base. I'm using 8"*16" concrete block in a 4 x 4 grid in the center. I'll build a osb form and fill with concrete. Any thoughts?

[Wild Turkey]

When we built our house they put the concrete pad for the AC too close and it catches lots of leaves between it and the house so consider maintenance while you're moving dirt.

They also just poured a 4" thick pad on top of the fill and it settled on one edge. When we added on we poured a new pad and just shifted the old unit over.

Sounds like you'll have a good thick pad. Are you planning any mesh/rebar in it?

Do you need to anchor it to the foundation of the shop?

[00lightning]

I'll be leaving about a foot in between the shop foundation and the new pad so no need to anchor. Yes I'll be using rebar. Thanks.

[blackhat]

Overkill by a factor of 10. If you are 18" above grade, you could use angle iron brackets screwed to the wall. Pretty common method here to keep the condenser up out of the way for mowing and to obviate soil movement.

[J-W-P]

blackhat said:

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, you could use angle iron brackets screwed to the wall. Pretty common method here

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When we moved to Ohio, we noticed all the houses use two support brackets or pipes mounted in the foundation and the A/C unit rests on that. That was new to me. When I had one of the units replaced last year, the guys took out the pipes and put it on a thick synthetic pad. They said when new homes are built they often use the brackets so they don't have to worry about the ground settling after back filling. With the house now 20+ years old, the pad would be fine. It looks better too.

[blackhat]

A pad 18" thick is going to move.

[Robert Adams]

Unless there is a need for it to be that high ie flooding or up north they are usually in a platform or wall mounted above the average snow depth... I'd just put down a pad and call it good. Like mentioned an 18" slab is going to move.


Also make sure to have a gutter over the condenser as rain off he roof is bad for the condenser fan and the ecm motors used now are very expensive to replace.
I have to do the same but since we don't have menards I don't know where to get gutters as depot and lowes only carry white and poop brown which no one uses either color anymore. Leaf guard wanted $56 a linear foot....

[daddo]

I prefer slabs not connected directly to the homes slab or structure to prevent noise from being transferred to the structure.

Servicing some of the taller units lifted 18" higher when not necessary can make working on it more difficult.

[Robert Adams]

daddo said:

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I prefer slabs not connected directly to the homes slab or structure to prevent noise from being transferred to the structure.

Servicing some of the taller units lifted 18" higher when not necessary can make working on it more difficult.

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They like to hang them off the side of houses up north. I don't like it either for the vibration and noise transfer you mentioned. I'd rather do a freestanding support.

But being up high makes repair easier but makes replacement of units a bear and condensers are getting heavier every day. Well higher everything is better for me anyway as the ground gets harder and harder to get to every day.

[srv52761]

Cut high compression insulation board, stack to the appropriate height.
Build an attractive enclosure/form.
Pour your 3'x3' pad.

Realize that any gap between the form and insulation will make the bottom have the same pressure as if there was no insulation board until it sets.