Attic insulation with A/C air handler & ducts

Hello. I have a 110 yo Victorian style home in north NJ with an unfinished attic (tall roof peaks about 10 feet above floor) with vermiculite under attic floorboards above second floor ceilings. I would like to make the attic into a 4 season living space. I also want to install the air handler for the entire house in the attic with the main duct running along the triangular space behind the proposed knee wall and the roof rafters. The individual branch ducts will be run off the main duct between ceiling joists across under the attic floorboards when vermic is removed ( I understand issues with vermic).

My thought is that if the attic is an insulated envelope...if wall and roof rafters are insulated, I should not have to wrap the A/C ducts... Even if I don't actively cool or heat the attic. Is this a reasonable guess?

1. Thinking I would insulate the entire roof rafters- attic floor to peak - sidewalks, and also keep the remaining vermic sealed under floorboards without ducts. I have read about the airflow baffles to place between roof and insulation.

2. Unsure about where or if to install vapor barrier I don't know if the soffits are vented. There is ventilating panels on outside under eaves but don't see light from attic.

I would appreciate tips or pointers to a plan to implement this. Thanks.

If you have knob & tube wiring, you have a lot of "mapping" to do.

The vapor barrier always faces the conditioned side.

Areas behind the knee walls can be insulated with unfaced batts, except ceilings of the 2nd floor.

Rigid ducting insulation is a call out and flex-a-duct has a min. so the area still need climate area insulation.

It is pretty common here to have HVAC ducts in the attic. My second-floor unit is in the attic and my first-floor unit is in my basement. Mine is unconditioned and they used flex duct with *some* insulation built into the duct. Our winters are milder than yours, summers are probably not much hotter, they just last longer.

If you want to go to a conditioned shell I'd probably opt for spray foam on the underside of the roof deck. You can get about an R8 per inch with poly iso. Before you go finishing the space you'll definitely want to make sure any residual knob and tube wiring is gone from the structure. I've heard differing views on whether you need to vent the roof deck with spray foam applied to it. If you want to go for the vent you can apply channels from the soffit vents to close to the peak and spray poly-iso over that.

Here is an article, more suited to my climate than yours on the subject: http://buildingscience.com/documents/reports/rr-9904-unvented-cathedralized-attics-where-we-ve-been-and-where-we-re-going/view

And here is an article on roof venting: http://buildingscience.com/sites/default/files/migrate/pdf/PA_Crash_Course_Roof_Venting_FHB.pdf

Thanks, both, for the replies. I don't understand the last sentence of first reply...but let me look thru the links and will surely get back with some detailed questions. There is no old wiring in place, and the original roof decking was replaced with plywood several decades ago.

Here is the last sentence of the 1st response;"Rigid ducting insulation is a call out and flex-a-duct has a min. so the area still need climate area insulation."

What clarification can I add?

Thanks for taking the time to reprint the sentence, but "call out" , "min." Doesn't have any meaning to me in the context.

Thanks for the article on attic venting. Since I have a 10 foot or so peak in the attic I will leave a sizable channel for cool air flow, though will have to install peak louvers since there is no ridge venting.

Metal ducting is used throughout the industry and depending upon the application is coated with insulation, whose thickness is a "call out", in that , you, say how thick you want that insulation.

As a for instance, have you ever heard the ac system in a movie theatre operating, in the same manner as is normal in a house?

It's because of the system design and the efficiency.

Anybody can throw a length of flex-a-duct across an attic and never wonder why it takes the time, and costs as much as it does to heat and cool the space.

Thanks. Noise, efficiency and condensation are all important issues, though would consider the last two primary. Getting the optimum installation in place, given the constraints of the existing structure, will be a challenge. But I will develop the idea of a conditioned attic space with vented roof deck and use the best duct that will fit under the floor.

fredcapo said:

Thanks. Noise, efficiency and condensation are all important issues, though would consider the last two primary. Getting the optimum installation in place, given the constraints of the existing structure, will be a challenge. But I will develop the idea of a conditioned attic space with vented roof deck and use the best duct that will fit under the floor.

Click to expand...

There are some downfalls with conditioning the whole attic space, you can consider a room to put the unit in that will be conditioned.

i intended to say that the attic space will be an insulated, integral space and appropriately vented. Will not necessarily be cooling it but the intent is to keep the peak summer tempos at a minimum.

fredcapo said:

i intended to say that the attic space will be an insulated, integral space and appropriately vented. Will not necessarily be cooling it but the intent is to keep the peak summer tempos at a minimum.

Click to expand...

Around here we typically add a separate unit for the attic when finishing it. I have two units in my 2500 square foot house. I can tap into the first-floor unit for my basement, but if I try to tap into my second-floor unit to finish my walk-up attic it would likely overwork the unit. The heat load on the attic is much higher than the second floor so keeping both happy with one unit can be a challenge. A lot of people use thru the wall units like you see in hotels for their attics, I prefer to use a mini-split system instead. That gets the noisy part away from the living space.

Adding a separate unit for attic is a good and doable suggestion.

So just to clarify...if the attic is insulated and roof deck is properly insulated and vented, to what extent do I need to additionally wrap/insulate the AC air handler ducts and chilled air supply ducts that will be on and under the attic flooring? ...and need for drip pan for air handler? I understand the return does not to be insulated. Thanks.

I can't help with much about AC but about the drainage I can give you some pointers.
Under the air handler you install a pan to catch any overflow which should never get any water in it to the drain for that should come out of the house above a door or window so it gets your attention right away, telling you that you have a problem.
The air handler as two drains on each sides both should be hooked up. One is slightly higher than the other so if the first plugs up the second one takes over.
HVAC people put traps on the line from the handler, make sure they can be taken apart for cleaning.

And the last addition is a piece of expanded aluminum laying in the the drain pan inside the air handler, this allows the water to pass but the crud that gets in there will get hung up before it gets to drain outlets.

Clean this stuff yourself once a year at the end of the season so the crud does not dry out and becomes lumps. Service people do not always think a full inspection of the drain system is needed.

Thanks for the previous comments.

I now have the attic floor removed, the vermiculite removed and the cavities encapsulated. I can now begin to install my ductwork in between the floor beam cavities. Since I will be installing insulation in the roof rafters above the attic, does it make sense to also insulate the attic floor where there will be no ducts? I don't plan to keep the attic conditioned and heated all the time. My objective was for the attic to be a buffer of sorts and to protect the AC handler and ducts from temperature extremes. Thanks.

Did you confirm that you have a path for air to travel from the soffit area to the peak and escape. If you are insulating roof you consider the attic conditioned space so insulation in the floor would be for sound only.

Neal, thanks. That is the next issue to solve. The roof is plywood that replaced the original shingle/shake roof. The plywood is nailed to a series of horizontal 1x2's, spaced appx 3 inches apart, that are nailed to the rafters. So the spaces are horizontal, parallel to the floor...so no air flow from soffit to peak...but side to side.

So, thinking if I cut sections out of the 1x3's I will create a vertical channel for air flow. Just not sure how large a section and if it will affect the roof integrity.

Otherwise, leave them and add the pink rafter mate but will be giving up an inch of depth.

Is that understandable? Thanks

Just run the chute behind the insulation all the way up to the collar ties and insulate at the level of the collar ties so you have a cavity on the top, Soffit vents box vents ridge vent?

Neal, the house has soffit vents ( Aluminum grid under soffit ) though I don't feel much air or see light looking from attic.
I plan to insulate from floor to the collar and across the collar tie. Will be knee walls and plan to leave some insulated and some insulated behind knee wall in rafter. Will leave the peak gable uninsulated. Wondering if I should install gable vents? Thanks

They may have blocked the soffit so the loose insulation would stay in place, Have a close look at and see what is there.
I don't know how gable vents work compared to box vents, but we seldom see gable vents any more if that says anything.