Already have R-38 in 2nd floor ceiling but want to condition the attic. Need advice please.

Shoorik17
| Posted in General Questions on
I’m buying a home in NJ from a builder who was essentially going to do a builder flip but has allowed us to customize a lot of things along the way, and it’s overall been a very positive experience, though with some drawbacks of decisions he made to essentially maximize profit.
The original plan called for an unconditioned, vented attic, with R-38 batt in the ceiling of the 2nd floor. I ended up going with a Mitsubishi ducted heat pump system, with the 2nd floor’s air handler, ERV, and ductwork being setup in the attic. They wrapped the ductwork in the attic with R-8 insulation, but it’s been pointed out to me recently that NJ’s weather will cause extreme temperatures in the attic in winter and summer, causing the HVAC system to run inefficiently, making my bills higher than they could/should be (electricity in NJ is quite expensive) and the equipment possibly breaking down sooner.
I’ve done a bunch of research and have come to understand:
– If I get R-49 from closed cell spray foam in the attic rafters, there’s risk of moisture being trapped in the attic.
– I have an option to remove the R-38 in the 2nd floor ceiling (the sheetrock isn’t up yet) which may potentially reduce the risk of moisture, but it would still be better to have some sort of mechanical solution to removing moisture and circulating air in the attic, so I’m probably better off keeping the R-38, and asking the HVAC guys to create a small supply and return from the ductwork in the attic. The R-38 may in fact help with some soundproofing from the attic.
Does that sound about right, or am I missing any important considerations?
I’ve been quoted ~$16k by a few companies to put the close cell spray foam in the attic (it’s quite large, and vaulted) so definitely a big expense but this is planned to be our forever home and over the period of decades, I’d like to make sure I’m doing the right thing. Any feedback or advice is appreciated.
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Replies
Shoorik17,
Your approach sounds like a good one to me. Conditioning just means supplying heat and limiting humidity to keep the attic at the same levels as the rest of the living spaces. The ceiling insulation only becomes a problem if you don't do that as it will keep the attic cooler and as a result more susceptible to moisture issues.
Thank you Malcolm, I appreciate the feedback.
Closed cell spray foam won't cause you any moisture problems IF you condition the attic, which just needs some air movement from the HVAC system as you described. Batts can be used too, but they you need a VENTED assembly. As long as you have 1" minimum vent channels in EVERY rafter bay running all the way from the soffit (intake) vents to the ridge (exhaust) vents, batts can work fine too. You could put some polyiso under the rafters to both get some more R value and to provide a vapor barrier (assuming foil faced polyiso with taped seams), which will help to ensure you never have any moisture problems in the roof assembly. The polyiso will also help to cut down on the thermal briding from the rafters. 1/2" polyiso is fine if you just want the extra insurance, up to about 1" will also get you more R value while not significantly increasing the difficulty of securing the drywall underneath.
Bill
Thank you very much, Bill! This is very helpful.
Instead of spending 16k to insulate the roofline with a lower than optimal R value that has a larger surface area than the ceiling making it lose more heat than the current ceiling would. Consider spending a similar amount to undo the very poor choice of installing your HVAC equipment in the attic.
My guess is the current HVAC in the vented attic will require about 25-50% more fuel than moving the HVAC inside the current conditioned space.
Expanding the conditioned space to include the attic and HVAC will require 10-25% more fuel than moving the HVAC inside the current conditioned space.
Another option is to test the ductwork in the vented attic with a “Duct Blaster” seal the leaks below 2% and bury the ducts in insulation. Does not help with the equipment losses.
https://www.energyvanguard.com/blog/buried-ducts-allowed-2018-building-code/
Walta
Thank you Walta.