AC pad same elevation of finish floor

[Jack Wingo]

House under construction, the AC pad has same FF elevation as the living area. The pad is approximate 6'x8' has no slope, will have 3 CB walls and there 2 AC units installed on pad. My concerns include the following:

During a hard rain water will pond against juncture of house wall and slab, which is basically a cold joint, susceptible water penetration.

It is doubtful there will sufficient space for the unit to meet their operating clearance nor service clearance.

I know code addresses operating and service clearance, but does code allow an exterior pad to have same elevation as the house finish floor?

As always appreciate your help.

[Jerry Peck - Codeman]

Jack,

House under construction, the AC pad has same FF elevation as the living area.

That is typically the elevation you should be finding the equipment pads at. Most new construction is done such that the finished slab of the living area is as DFE, which is typically BFE + 1 foot (albeit DFE is sometimes higher than BFE + 1 foot).

Sometimes the garage is a DFE (if the contractor/design professional is smart, or otherwise takes a lower slab into all of its considerations).

All the exterior equipment needs to also be at DFE, which would make it the same elevation as the living space slab if the living space slab is at DFE.

The pad is approximate 6'x8' has no slope, ...

That creates another issue as the slab should be level ... almost ... as it should be able to drain water, but also should be level for the condenser unit. My recollection is that some units allow the surface to be up to a specified maximum slope (less than 2% or 1/4" per foot, I recall having seen some condenser units allowed to be installed on a surface which had surface slope of a maximum of 1 degree (1 degree is 1.7% - as can be seen here: https://www.archtoolbox.com/representat ... slope.html ).

Many manufacturer installation instructions state 'on a level surface'.

... will have 3 CB walls ...

That seldom works out well for the condenser units as it typically does not provide the required clearances and air flow - for that, I would take a photo, measure the area, the heights of the walls, and send those to the manufacturer of the condenser units for their 'okay' or 'not allowed, will void the warranty' comment from the manufacturer.

My concerns include the following:

During a hard rain water will pond against juncture of house wall and slab, which is basically a cold joint, susceptible water penetration.

While that is quite possible, the slab should not be next to the house slab as it will transfer vibration from the condenser unit through the house slab. Ever been in a condo building when work there was floor work being done on another floor or a far away unit? That vibration noise travels through the concrete slab throughout the entire building - that is what the condenser unit vibration will likely sound like - transferring throughout the entire house.

And, yes, there could be water intrusion issues as well.

It also likely intrudes on any termite treatment area around the house slab.

It is doubtful there will sufficient space for the unit to meet their operating clearance nor service clearance.

See above for clearance and air flow and to check with the manufacturer. Service space and access to it (to the unit "in the corner" needs to be provided - code required.

That condenser unit 'stuck back in that 3 walled in corner' rarely, if ever, meets the requirements for service access, clearances, or air flow (it is simply sucking in already heated air and trying to put more heat from inside into that already hot air - efficiency drops quite a bit, that is a manufacturer warranty voiding condition (at least from my past experience of those installations) - at the very least, the manufacturer cannot come back and refuse a warranty claim later because they were made aware of it upfront).

Water intrusion would be the easiest to correct - saw cut some drainage grooves into the top of the slab and knock out a concrete block or two on the side walls/end wall.

Service access and air flow will be the ones which may need those walls to come down or the area to be made much larger, although a 6' x 8' area is pretty good sized area and it may depend on how high the walls are - which gets back to what the manufacturer says about it.

[Jack Wingo]

Jack,

House under construction, the AC pad has same FF elevation as the living area.

That is typically the elevation you should be finding the equipment pads at. Most new construction is done such that the finished slab of the living area is as DFE, which is typically BFE + 1 foot (albeit DFE is sometimes higher than BFE + 1 foot).

Sometimes the garage is a DFE (if the contractor/design professional is smart, or otherwise takes a lower slab into all of its considerations).

All the exterior equipment needs to also be at DFE, which would make it the same elevation as the living space slab if the living space slab is at DFE.

The pad is approximate 6'x8' has no slope, ...

That creates another issue as the slab should be level ... almost ... as it should be able to drain water, but also should be level for the condenser unit. My recollection is that some units allow the surface to be up to a specified maximum slope (less than 2% or 1/4" per foot, I recall having seen some condenser units allowed to be installed on a surface which had surface slope of a maximum of 1 degree (1 degree is 1.7% - as can be seen here: https://www.archtoolbox.com/representat ... slope.html ).

Many manufacturer installation instructions state 'on a level surface'.

... will have 3 CB walls ...

That seldom works out well for the condenser units as it typically does not provide the required clearances and air flow - for that, I would take a photo, measure the area, the heights of the walls, and send those to the manufacturer of the condenser units for their 'okay' or 'not allowed, will void the warranty' comment from the manufacturer.

My concerns include the following:

During a hard rain water will pond against juncture of house wall and slab, which is basically a cold joint, susceptible water penetration.

While that is quite possible, the slab should not be next to the house slab as it will transfer vibration from the condenser unit through the house slab. Ever been in a condo building when work there was floor work being done on another floor or a far away unit? That vibration noise travels through the concrete slab throughout the entire building - that is what the condenser unit vibration will likely sound like - transferring throughout the entire house.

And, yes, there could be water intrusion issues as well.

It also likely intrudes on any termite treatment area around the house slab.

It is doubtful there will sufficient space for the unit to meet their operating clearance nor service clearance.

See above for clearance and air flow and to check with the manufacturer. Service space and access to it (to the unit "in the corner" needs to be provided - code required.

That condenser unit 'stuck back in that 3 walled in corner' rarely, if ever, meets the requirements for service access, clearances, or air flow (it is simply sucking in already heated air and trying to put more heat from inside into that already hot air - efficiency drops quite a bit, that is a manufacturer warranty voiding condition (at least from my past experience of those installations) - at the very least, the manufacturer cannot come back and refuse a warranty claim later because they were made aware of it upfront).

Water intrusion would be the easiest to correct - saw cut some drainage grooves into the top of the slab and knock out a concrete block or two on the side walls/end wall.

Service access and air flow will be the ones which may need those walls to come down or the area to be made much larger, although a 6' x 8' area is pretty good sized area and it may depend on how high the walls are - which gets back to what the manufacturer says about it.

I've already requested AC manufacturing information, I know there is not sufficient space to meet operating or servicing clearance.

As always great information, thank you Jerry