# Foam Board Insulation on rafter in attic to box in AC system



## sinrich (Jan 27, 2014)

I have 2nd zone AC system ducts running in my attic, before the summer comes, and temps get to 120-130°F up in my attic, I am planning on conditioning the space to enclose in the ac system to keep temps down so it will run more efficiently. I have very good soffit venting, I am planning on running baffles between the rafters, then insulate with unfaced fiberglass, then screw in 2" foam board to enclose fiberglass, basically then creating an enclosed room in which my ac system would operated at lower temps. Anyone do this, I know the closed foam spray contractors do this process to condition the space so ac runs easier, but this is big money, $10K+, and I can do my process for less than $2000... any thoughts, suggestions or recommendations ?
Thanks
Jon, Cherry Hill, NJ


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## joecaption (Nov 30, 2011)

You say you have soffit vents, but how's the rest of the roof vented?
Why would you not insulate all the duct work instead of the whole room?


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## sinrich (Jan 27, 2014)

The roof has ridge vent too, it's not just insulating the main AC trunk, the octopus arms are all over the attic, they are about a 6" dia. insulated flexible arm, and probably a lot harder to box them in instead of putting up foam board on rafters, but now you have me thinking I might use a lot less if I can figure out a way to enclose just the 36" x 36" ac trunk instead of rafters, this is about 30' long, and then cover arms with more fiberglass insulation... hmmm... I'll wait for more replies, but thanks


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## Windows on Wash (Aug 30, 2011)

If you are not addressing the duct leakage at all the flex lines and joints, your efforts will be largely wasted. 

Seal up all those connections and cut the straps on the lines so that they hang on the floor. You can then blow loose fill insulation over the top and that will help insulate the lines. 

You are going to help your system more by insulating all the distribution lines (i.e. more square footage of exposure there) than you will by building an enclosure around the trunk line as well as minimizing duct leakage.


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## sinrich (Jan 27, 2014)

Thanks Joe, I believe the lines of flexible duct are sealed pretty well, my big concern is just getting the main trunk running all that cold air out of 120°F attic heat in summer, I agree blow in loose fill to cover flexible will help too, but my first thought was to enclose the entire attic with 2" foam board, seal seams with great stuff and keep temp of this entire area down under a 100°F and I think this would be helpful too...Thanks


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## Windows on Wash (Aug 30, 2011)

Don't plan on sealing up your attic. 

Where are you located?


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## sinrich (Jan 27, 2014)

i'm in South Jersey ... near Philly... when I say "seal up attic" I still plan on maintaining soffit venting and use of baffles up to ridge vent


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## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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## Windows on Wash (Aug 30, 2011)

I realize what you are trying to do but I haven't seen it done particularly effectively or cost effectively. 

Sealing the duct work, getting the proper insulation value, and sealing any leaks in the plenum will do the trick. 

I realize that the plenum working in a hot attic isn't ideal and putting HVAC in the attic is one of the bigger building science faux pas in the efficiency world. 

Covering your rafters with foam and creating a dedicated vent space is not a proper application in my opinion. If you want to cover the plenum with some foam and create a separated space, that can work and is sensible if you don't spend too much time or money on it. 

Please don't take my remarks personally...this is just my opinion based on what I see out there.


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## sinrich (Jan 27, 2014)

not taking your remarks personally ... I appreciate your input... 

Yes enclosing the maid trunk of the AC with 2" foam board and seal up seams with Great Stuff would be much easier... I'm still considering options.

Gary, thanks for the link !!

Thanks again


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## buck545 (Dec 19, 2008)

what did you ever end up doing? i'm in hamiltion not far from you with the same issues, trying to figure out what to do with my attic


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## sinrich (Jan 27, 2014)

Buck, I have not done anything yet, the foam board project is too extensive, although I am capable of doing, I think I am going to get a roll or two of attic foil and staple to the inside rafters of my roof, this is pretty simple and will reflect a lot of the heat on the south side of my roof. Then I am going to get some of the foam board and box in my main a/c trunk in the attic and this should help a lot, much better than before...


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## Earnie (Jan 24, 2008)

I emailed this company but never received a reply. Anyone know if still selling product?

http://www.linedesignworkshop.com/lab/ultimate-r/


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