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Community and Q&A

What’s the best way to optimize attic performance?

stuccofirst | Posted in Green Building Techniques on

I’m working in a 3,500 sq. ft. house that is new construction; however it has many issues. This one as well as every other house in the development has lots of ice damming and cold rooms. There is an air handler in the attic for the 2nd floor zone. It has R-4.3 insulation around the ducts and the main trunk is insulated with the silver stuff (don’t know the R-value).

There is R-30 fiberglass in the floor bays throughout. The house has a few hexagonal raised ceilings built up into the attic space (vaulted ceilings?) They are covered in fiberglass as well, although not continuous on the angles and the rooms are cold.

Along the perimeter, each bay has a flimsy roof vent just kind of hanging there with fiberglass barely reaching the edge. I know the roof vents are not functioning as they should.

First, I feel the roof is overventilated along the soffit. Can I just seal off some these bays to bring it to the 1 sq. ft. per 150 sq ft.?

Also, do you think just covering the vaulted ceilings with rigid foam (after air-sealing) over the fiberglass is a worthwhile improvement?

And should I try to wrap the ductwork with more insulation, or is R-4.3 sufficient? Any product suggestions?

How should I increase the R-30 attic floor without burying the entire attic in loose-fill? Can I use rigid over the fiberglass?

Should build a rigid box around the giant air handler, as it is in the unconditioned space?

Already in the scope is air-sealing all penetrations and improving the perimeter with rigid roof vents and better insulation on the top plate.

Any suggestions are much appreciated!

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  1. Shane C | | #1

    oops, forgot to mention the house is in climate zone 5A.

  2. Kevin Dickson, MSME | | #2

    Yikes. Are there a lot of recessed can lights?

  3. sHANE c | | #3

    No, not alot, maybe 8 total plus bath fan registers. Alot of air-sealing to be done. I'm just wondering how to improve upon the ductwork without doing the attic slope.
    Also, the are two inlet holes on the air handler that are sucking in ambient air from the attic. They are threaded, but nothing is hooked up to these. Anyone know about this?
    The homeowners are working against the current with an air handler in a cold space during the winter and a hot space during the summer. How do I minimize losses?

  4. GBA Editor
    Martin Holladay | | #4

    You have a lot of problems for a new construction house. Are you negotiating with the builder? Is the builder willing to address any of these defects? You might want to see a lawyer.

    The fiberglass batts probably aren't doing much -- especially if the batts are "not continuous." It would be a good idea to blow 12 inches of cellulose on top of all of the fiberglass batts -- unless you end up insulating the sloped roof to bring the attic into the home's conditioned area. Of course, you can't improve the insulation until you have completed all of the needed air sealing work.

    The air handler obviously doesn't belong in an unconditioned attic, so you need to either
    1. Build an insulated room around it, or
    2. Create a conditioned attic.

    The duct system needs to be tested and all seams sealed, if they aren't already. In most areas of the country, R-4 duct insulation no longer meets code.

    What a mess -- this is clearly thousands of dollars worth of work.

  5. sHANE c | | #5

    Thank you. I guess I mis-spoke when saying "new construction" the house is probably 5-8 yrs old. Its into its second owner already (whom I'm working with) so the builder is long gone. I'm BPI building analyst and envelope certified, so I'm working with the homeownere utilizing my knowledge to make improvements. These houses are overpriced energy suckers. They have all the frills, but aren't built to perform. All show and no go so to speak. The way they installed the vents to the roof deck is a joke. they aren't sealed and air just comes in all around them.
    I'd like to just stick to rigid, if I can, as its easier than renting the cellulose blower. However, if cellulose is proper, I'll do it. Probably dense pack the perimeter too.
    Any suggestions on doubling up the duct insulation. what R value should I shoot for? I don't have a duct blaster to do the duct leakage test.
    Do you see any problems with just blocking off some of the roof bays at the perimeter to bring down the ventilation spec of 1 sq ft per 150 sq feet?

  6. wjrobinson | | #6

    Shane, you should think about working with others to gain experience. Maybe you could work with someone on this project via subcontract. Hey, if you do rise to this challenge and succeed, you should do well in the retrofit business.

  7. capnkent | | #7

    Wow- disaster & yikes!
    Know for sure what the ventilation ratio is before reducing it. " Roof vents aren't working properly" -that needs to be addressed too. It's not clear what you mean about the flimsy roof vents hanging there & fiberglass barely reaching the edge...?
    Find out what code requirements are in your area - you may want to permit this job.
    Do a bunch of research before jumping in and possibly making things worse...
    Poor installations need to be fixed correctly if possible.
    Unable to test ducts - It's nice to be able to measure the duct sealing efforts. Duct sealing is usually one of the top priorities.
    Foam over fiberglass? I haven't heard of that before... maybe you mean fiberglass over the foam?

  8. shane c | | #8

    The ductwork is all that 8' flexible tubing that is pre insulated. There are no seams. I think the only places to check for leaks are at the junctions.
    Which is better on the vaulted ceiling: Remove the fiberglass and insert rigid onto the sheetrock, and seal around the rigid and place the fiberglass overtop.
    or just leave the fiberglass and build a rigid shell over the whole monstrosity and seal the seams.
    Should I go for Iso foam with the foil face, eps or xps rigid?

  9. Kevin Dickson, MSME | | #9

    If it were my house, I'd be looking harder at making it a conditioned attic. As others have indicated, it's a tricky business, but the end result ultimately would be better than all those band-aids. There are different ways to make that conversion, and codes to comply with.

  10. wjrobinson | | #10

    Shane, with no heat system in the attic, you would move the glass, seal all the leaks, put the glass back, add vent chutes and cellulose containment barriers at the exterior walls, and then blow a foot or two of cellulose on top.

    With the HVAC in the attic, you are really looking at more expense and doing something closer to the roof. You could get rid of the attic HVAC and add a mini split below the ceiling plane and then do a standard improvement to the attic insulation like I outlined above. For now I see this as the best way to go forward. I also think you will have trouble with selling the cost. Just a guess, $18,500 if your best friend likes to install splits for IPAs in your backyard.

  11. draginfly58 | | #11

    I'm almost afraid to ask this now, but what glass are you talking about removing and putting back?
    You really lost me on this one. I feel really dumb. Sorry

  12. bbSGYnAJUU | | #12

    I assume that he's referring to fiberglass.

  13. Robert H | | #13

    He talks about BPI but what testing is he using. Does he have a blower door, themal camera, duct blaster etc. He should be defining the problem by what the testing is telling him. How much air leakage is there between the house and the attic. How leaky is the duct work. The air is leaking into the attic - where is the make up air coming from.

    Sine there are a number of tray/coffered ceiling areas have the edges been tapped and mudded or short cuts taken and the crown molding covers the unfinished corners.

    Much of air sealing does not require a blower door but rather knowing the places to look for. On the ceiling of the ipper level start by looking at penetrations. Are there soffits in the bathrooms, cieling lights, can lights, or anything else that breaks the drywall. From the top you know all the top plates, plumbing stacks, flues etc will leak,

    Pilling ceuulose over the fiberglass will improve the effectiveness of the fibergalss as well as adding to the total R value.

    With the air handler and ducts in the attic you know there is a lot of area for improvement. If you dont see signs of the duct work being sealed then you know that every connection needs to be sealed. After the all the air sealing figure out how to pile cellulose over the duct work.

    The question becomes is the owner willing to committ to paying to have it done right.

  14. Shane C | | #14

    Thats exactly what I did. I eyeballed the problems without a blower door because I don't have the equipment. Without the test-in and test out, you can't measure the improvements, however just by looking at the attic and the homeowner telling me they have cold rooms, I can surmise the major culprits. The tray ceilings can definitely be sealed from the top at the seams. The attic is huge, so blowing cellulose would be no small task. Thats when you would want to bring in a cost / benefits analysis. But I could make the known improvements for less and its still a win-win because they are wasting less conditioned air to the attic and I'm working for a week or so. The one room is cold because its over the garage. Thats a good opportunity for a dense-pack project.
    I was wondering if anyone has ever heard of wrapping the already insulated ductwork with a wider wrap and, if so, what a good product is.

  15. GBA Editor
    Martin Holladay | | #15

    No one has yet addressed your repeated questions about whether it is a good idea to install rigid foam insulation on top of your fiberglass or instead of your fiberglass.

    The answer is no. If you are insulating the floor of an unconditioned attic, there isn't much call for rigid foam (except for plugging large air leaks at plumbing chases). Once you've finished your air sealing work, the best way to insulate an attic floor is with cellulose, not rigid foam boards.

  16. shane c | | #16

    Thanks for the answer, but can you explain why? Is the R-value just not there? I wouldn't do the whole floor with rigid, just the tray ceilings. They are angled, so walls would have to be built in order for the cellulose to stay.

  17. wjrobinson | | #17

    Shane, No one puts foam board on top of fiberglass. If you don't know that, I don't know how you can do any work on your project. You want to do what you can without tools. Sounds like you have never been in this type of business. Join up with a blower door BPI and an insulation contractor that does all types of insulation and has experience improving attics.

    -Find all air leaks and seal
    -Fit fiberglass back perfectly
    -Vent chutes and cellulose containment around perimeter
    -Blow cellulose but according to Martin you can't blow on flex ducts as they will sweat in the summer and wet the cellulose, leave ducts above cellulose.
    -Big project if you think you are going to enclose HVAC and you can cause issues.
    -The cold room above garage, you could add sheet foam to garage side sheetrock and then resheetrock over it for proper type x fire barrier. You will never make it much warmer, rooms over cold garages have cold floors. Dense packing cellulose is a possibility, are you saying that there is NO insulation now?

    What have you done and what is the budget for this project?

  18. Shane C | | #18

    Anyone ever use the Ultimate R system for the ducts? As for the air handler, I'm going to build an insulated box around it. The attic remains unconditioned, but it won't cost the homeowner $15,000 to spray foam the attic slopes either.

  19. Danny Kelly | | #19

    Shane - you do not need a duct blaster to check for leaks in the ducts. You should have learned how to use a pressure pan in your BPI Envelope Professional training. In some cases, the pressure pan is a better test anyway - can tell you which duct runs to pay particular attention to.

    I build in zone 3 so cannot comment for sure in your zone but I do not think that a vented attic can really be "over ventilated" and would not advise blockig off any of the cents unless you decide to make the entire attic unvented altogether. Also keep in mind that a typical 2" soffit vent only has a net free area of about 9 sq. in. per foot not 24 sq. in. as some often miscalculate.

  20. Danny Kelly | | #20

    To post 18 - "You will never make it much warmer"
    This is incorrect - we take very cold bonus rooms over garages and have them performing perfectly and do not even need to use foam.

    Shane - some free advice - do not write AJ any checks (Post #22)

  21. GBA Editor
    Martin Holladay | | #21

    In order for rigid foam insulation to work, the seams need to be airtight, and the rigid foam needs to be secured to the structure of the house. This is not possible if you lay loose rigid foam sheets on top of existing fiberglass batts.

  22. Shane C | | #22

    I am aware of that. What about on the tray ceilings built up into the attic. They are especially cold because the fiberglass was cut for the angles, and thus not continuous. I can
    a) Remove the glass, caulk the seams of the drywall, replace glass, build a sealed rigid box over it and attach it to the framing that is built around it.
    b) Same as a accept just build high cardboard walls (with vapor barrier?) and fill it with 18" of celluose.
    or c) remove the fiberglass, seal the drywall gaps, place rigid in between the bays, place fiberglass over the rigid.
    I'm planning on using an Ultimate R type system for the ducts. Ideally, I'll spray foam the soffet perimeter with rigid blockers added. Seal the attic hatch with rigid and weatherstripping. Mastic all duct junctions. Tape and mastic the air handler. Build a closet around air-handler. Double insulate the hot water copper pipes leading across the whole attic to the handler. Wish I could quatify the savings. I think this is a good alternative to spray-foaming the attic slopes.

  23. wjrobinson | | #23

    Shane, I just chatted with the owner of the Ultimate R idea.

    He is going to email me reports that supposedly state ductwork buried in cellulose is OK and not a problem with sweating.

    Martin, Help out with this since you are the one that alerted me to the idea of sweating ducts. Would be nice to start a topic just to do with what can be safely done to attic ducts and in what climates.

    By the way, Ultimate R products are not available at this time. They hope to be in the future.

    Lastly, if reports somewhere find that Ultimate R works then one could just as easily bury the entire attic in cellulose instead of buying the moisture resistant cardboard boxes from Ultimate R.

    Back to the drawing board it seems Shane

  24. GBA Editor
    Martin Holladay | | #24

    I'm not a fan of fiberglass batts. If you remove them from the tray ceiling, put them in the dumpster. Then proceed with cellulose or rigid foam plus cellulose.

  25. wjrobinson | | #25
  26. Shane C | | #26

    The house I'm referring to doesn't have tray ceilings, it has quadrangle vaulted ceilings that go up into the attic.
    Here is a nifty link:

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