Spray foamed attic and duct work question.

[rob air]

1800's old House total remodel. Third floor attic is all new spray foamed roof, soffit , walls. NO ROOF VENTS at all now.
Large staircase leading to this attic space. There will be a horizontal 95% gas furnace and ac system up there.
Does duct need to be insulated ? The ceilings below will not be insulated just drywall.
The staircase door leading to this area will be undercut. Builder wants a return in attic duct to draw air from under cut door up into attic for air change.

[doc havoc]

I can't answer with 100% certainty, but I would think that if you had a supply on one end and return on the other end the space would be conditioned enough to prevent sweating during cooling season. Technically, the attic is now inside the building envelope. It shouldn't be a whole lot different than a unit in a basement.

[sui generis]

Usually, at least an R-4 is required in an encapsulated attic.

[mogy]

you will need to verify with residential & energy codes for your climate region. Most are minimum of R6 within the building envelope. I am in the southern region, R4 maybe suitable for up north

To get air changes a small tap for both supply and return will work. Make sure that there is a balancing damper on the supply collar if you are not using a grill with adjustable louvers. That is code. On the return I use a small 4"x4" or 6"x6" louver with screen.

[chrisevansac]

Minimum r-6 is code on any duct other that vented attic r-8

[jason12000]

Duct work should still be insulated. As doc havoc said it's now in the envelope. Is the combustion air piped from outside? Does undercutting the door give you enough free space for air changes?

[rob air]

yes two pipe vented. Combustion from outside. Well the undercut door will be around 3 inches. One supply and one return in attic would be a better air change.

[motoguy128]

Closed cell or open? drywall under foam? If open and no vapor barrier, it could end up being very humid in the
attic. Even with r20, itf can still be almost 90f up there in mid summer on a sunny day. I know from experience. I added a small register in the attic to dehumidify it a little.

Be sure to have line the supply plenum to reduce condensation.



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[jeremyr325]

Just finished a job like this spray foam on attic on rafters. 1 in of foam is R-8 no insulation in ceiling the Sheetrock will have enough infiltation to keep the attic within a four to five degree difference from the downstairs. The walls are foam and blown in we had to add a outside air damper that takes air samples every 2 hours. Equipment is 90 % dual fuel and the duct is insulated it is working better than great. Anxious to see about this summer with our high humidy here in west tn

[wicat3]

We do alot of jobs like this and most of the areas dont bust on us for using unwrapped duct. There is a town that requires the duct to be wrapped no mater where your putting it but thats about it.

[davidj001]

here in north carolina it's not required (yet) to insulate duct installed in that manner but we do because to offen it does sweat if the system is running for a period of time longer than a "normal" cycle