OP: you have three problems based on what you said. First, you have inadequate cooling of your upper level. That is in the first instance very likely due to inadequate insulation. Usually, you install the insulation on the floor of the attic, between the ceiling joists/attic floor, and you should optimally aim for at least R-49 (about 14" of blown fiberglass). However, you have a problem in that your A/C air handler is there. I assume you mean your evaporator (where the heat is absorbed and sent to the condensor outside) and the blower unit distributing the air is in this attic, an unconditioned space. That is definitely *not* ideal, although a good HVAC installer would have done meticulous air-sealing and insulating. Some additional problems you may have that contribute to the overheated upstairs, include: 1) you need to meticulously airseal every penetration between the living space and the attic. Every light box, wall seam, anywhere a wire is running up through the stud wall, etc. Insulation is pointless if there is airflow through it. 2) Your HVAC system is working extra hard in that unconditioned space. One way to mitigate that is to make the attic conditioned space (hence, remove the insulation from the attic floor and insulate the underside of the roof (and in doing this, you would need to close off all the air penetrations, etc.)). This is probably not feasible. SO you need to focus on making sure you have adequately insulated and sealed ductwork, a job a good HVAC tech would do. 3) That plywood sitting on the ceiling joists that you stand on and store things on up there? It's compressing your insulation and making it not work properly, Unless you have 2x12 ceiling joists, and you likely only have 2x8s at the most, you need to raise that up. Put 2x4 or 2x6s on top of the joists and then insulate (and airseal penetrations first) and then put the storage plywood down. There's more, but probably worth considering these as the first, obvious issues.

Both

OP: you have three problems based on what you said. First, you have inadequate cooling of your upper level. That is in the first instance very likely due to inadequate insulation. Usually, you install the insulation on the floor of the attic, between the ceiling joists/attic floor, and you should optimally aim for at least R-49 (about 14" of blown fiberglass). However, you have a problem in that your A/C air handler is there. I assume you mean your evaporator (where the heat is absorbed and sent to the condensor outside) and the blower unit distributing the air is in this attic, an unconditioned space. That is definitely ideal, although a good HVAC installer would have done meticulous air-sealing and insulating. Some additional problems you may have that contribute to the overheated upstairs, include: 1) you need to meticulously airseal every penetration between the living space and the attic. Every light box, wall seam, anywhere a wire is running up through the stud wall, etc. Insulation is pointless if there is airflow through it. 2) Your HVAC system is working extra hard in that unconditioned space. One way to mitigate that is to make the attic conditioned space (hence, remove the insulation from the attic floor and insulate the underside of the roof (and in doing this, you would need to close off all the air penetrations, etc.)). This is probably not feasible. SO you need to focus on making sure you have adequately insulated and sealed ductwork, a job a good HVAC tech would do. 3) That plywood sitting on the ceiling joists that you stand on and store things on up there? It's compressing your insulation and making it not work properly, Unless you have 2x12 ceiling joists, and you likely only have 2x8s at the most, you need to raise that up. Put 2x4 or 2x6s on top of the joists and then insulate (and airseal penetrations first) and then put the storage plywood down. There's more, but probably worth considering these as the first, obvious issues.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

You remove insulation in the summer months? Huh? It's about where the cold air meets the house. If the attic is cold, you want insulation on the floor or the attic to keep it from seeping into the rooms below.

And if you have a/c in the rooms and you want to keep the cold air in the room, you need insulation.

Yes, the argument from before was about whether there should be additional insulation above the rafters in the attic, against the roof? I was saying 'no'.

You say some crazy sh*t.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

You remove insulation in the summer months? Huh? It's about where the cold air meets the house. If the attic is cold, you want insulation on the floor or the attic to keep it from seeping into the rooms below.

And if you have a/c in the rooms and you want to keep the cold air in the room, you need insulation.

Yes, the argument from before was about whether there should be additional insulation above the rafters in the attic, against the roof? I was saying 'no'.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

You remove insulation in the summer months? Huh? It's about where the cold air meets the house. If the attic is cold, you want insulation on the floor or the attic to keep it from seeping into the rooms below.

And if you have a/c in the rooms and you want to keep the cold air in the room, you need insulation.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

https://www.energy.gov/energysaver/where-insulate-home

Dept of Energy disagrees with you but you do you.

No, it doesn't. The attic is not a conditioned space and therefore outside the envelope.

your website says "consider." It's not definitive. And if you do that, you'd better have a very robust exhaust system.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

https://www.energy.gov/energysaver/where-insulate-home

Dept of Energy disagrees with you but you do you.

Anonymous wrote:

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

the attic is not a climate-controlled space. it's not intended to be. in the winter, it's just going to be cold up there, and that's OK. The ducts for the air handler are insulated. Remember how cold Chevy Chase was when he gets stuck up there in Christmas Vacation watching old reel-to-reel home movies?

And you definitely do NOT want it insulated in the summer, because it will be 180 degrees if you do.

Anonymous wrote:our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

you want air flow, not air temp. two different things

our upstairs HVAC is in the attic. That said, the attic is designed for free flowing air. That's why we have soffits, and that's why we have attic exhaust fans that activate when the temperature gets above ... something. 90 degrees? Insulation in the attic ceiling (against the roof) would be counterproductive to those goals.

So the insulation goes between the joists, against the ceiling of your upstairs living spaces.

Yes more is always better. The less cold the attic air is, the warmer your top level.

We had someone come add insulation all over and it was well worth the cost.

more is always better op.

I have an attic with a pitched or gable roof. It is storage and also houses the air handler for the AC. I want to add insulation because our upstairs is so cold! Do I put insulation in between the floor joists of the attic or in the rafters? Or both?