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Community and Q&A

Zone 1 (Oahu) uninsulated house, but don’t want to use A/C – DIY

73Greencorvette | Posted in GBA Pro Help on

Hello, I’m in a Zone 1 climate, leeward (west) Oahu, Hawaii. My house is a mid 1980’s construction, double-wall but with no insulation, anywhere. AC is via window units, installed in either windows or wall, but I really don’t like using them as even if it’s just one AC, room closed up while habitated, say the bedroom, it will raise the bill by $~70 for the month and is not pleasant anyways (noise, cycling etc). I’ve looked at several sites and this and green building talk seem the most professional in their engagement, and have some of the same posters it appears.

I’m curious as to how much of an impact ceiling temperature has on the room, and the effectiveness of insulation of various types for my specific situation (warm to hot, intense sun, relatively dry compared to the windward side).

I took temperature readings (IR hand tool) of multiple rooms throughout the day and even early in the summer on a partially cloudy days there appears to be significant radiant heating (yes.. I’m going there).

Friday 82. 84. 85. 88 88 84 88
8am. 11am. 12 . 2pm 4pm. 6pm. 8pm 10pm
Kitchen. 81.2. 92.9. 93.5. 98 96.5 94 92
Hall. 78.9. 90.5. 94. 98.7 96 95 94
Office. 78.8. 90.6. 94. 100 99 96 95
Bedroom. 81.4. 94.6. 96. 100.4 98.5 95 95 94
Bed closet. 80. 95. 96.6. 101.2 100 99 98 96
RB spot bedroom. 90.4. 89.5. 93. 93.4 93.4 92 91 91

Kitchen is south end, hall oriented N to S, bedroom on NE office is on NW

Todays after-work numbers so far are very similar.

I’m considering a whole house fan for when the trade winds aren’t doing their job and to target rooms that I might be inhabiting (bedroom, office) instead of just the hallway that benefits most from the breeze. I am also looking at some degree of insulation for the attic, 100% sun exposure roof with 0 lot lines and no shade cover. Roof is a standard composite shingle in a light to medium tan color, it was unfortunately replaced within the last 5 years (prior to purchase). Is this a case where radiant barrier might actually be applicable as there is currently no other existing insulation and there is an airspace for either installation method? Naturally, one of the whole-house fan companies also sells a specific brand of radiant barrier (e-guard or similar) and suggests that ‘blown in isn’t the only option’. As there is absolutely no need for cold weather consideration here, my concern is only keeping heat out, and not causing problems with condensation if that is a thing in hot, sometimes humid environments. House does not use gas for any appliances etc. The ‘RB Spot bedroom’ data point is a 5’x2′ piece of the e-guard placed on the attic ‘floor’ as if install between joists (4″ air gap below)

Furthermore, Lowes doesn’t do site estimates locally like they do mainland for DIY or installation, so it’s either contract it or DIY with regards to blown and roll insulation. Other options would be radiant barrier (standard Lowes/HD products or more expensive online and ‘authorized dealer’ options like e-guard), and perhaps the solid boards but that might be tough getting into the attic. I have 1 access to my attic currently, it is a 2’x2.5′ access point in my master bedroom closet.

This is going to be a DIY job for me as labor is pretty high here. Cost is a factor, and comfort is important (the only reason I’m doing this, rather than just cranking up the AC and shelling out $100’s a month…)

I have attempted to attach a picture of my attic – its very empty, and has some wiring (in good shape) and recessed lights (half are IC rated, the other half… are not…) all are LED. The center is about 4′ vertical, and it’s probably 24’x60′ dimensions, including the garage and lanai overhangs. Finished/living portion of the house is around 1220 sq ft.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Green Corvette,
    Q. "Is this a case where radiant barrier might actually be applicable as there is currently no other existing insulation and there is an airspace for either installation method?"

    A. Yes. An attic radiant barrier and a whole-house fan might make a significant difference in your case. Good luck.

  2. Expert Member
    Dana Dorsett | | #2

    Painting the underside of the roof deck with a low-E paint (silvery stuff, not some magic nanosphere voodoo products need apply) AND an alumninized fabric type radiant barrier should do better than either alone.

    Even though it's more material and harder to install, putting the radiant barrier on the underside of the top chords ( the rafter-like elements of the truss) will be better than putting it on the attic floor, since it'll stay cleaner longer. Using a perforated type RB (not any more expensive than smooth types) keeps it from forming a moisture trap on unvented rafter bays, and reduces or eliminates the potential for nighttime condensation at the roof deck.

    Shading the roof deck with a PV solar array will also reduce the attic temperature, and more cover the cost of the power use of the whole house fan, no matter which reumuneration option you use for the PV, self supply vs. grid supply. (It's more complicated in Oahu than most places.)

    While window shaker AC is pretty noisy, whole house fans aren't very quiet either- considerably noisier than mini-split heat pumps, which ar quieter than your refrigerator when operating at low speed. If you take the self-supply no-export rates option for rooftop PV, a mini-split provides a handy load for the peak PV output, since the cooling load roughly tracks the insolation over the course of a day. This is even more true if the array faces the southwest or west. An electric water heater controlled as a power dump for the array can deal with the the rest without curtailing the output. PV with self supply gets preferred treatment by the utility and on the approvals queue, and at HECO prices for electricity it's really worth looking into before spending the money on a whole house fan (which does far more good after dark than during the day when PV is producing power.)

  3. user-6258531 | | #3

    I'd consider the Quiet Cool whole house fans. They seem like they would be quieter than the whole house fan usually recommended on this site.
    https://quietcoolsystems.com/products/energy-saver/

  4. 73Greencorvette | | #4

    Thanks folks - I think I got the responses from the individuals I was hoping I would, and got answers which confirmed both my hopes and my fears. My hopes that RB could help due to the limitations on access, and fear of installing on the top-chords (fortunately, my wife is short, so maybe she'll volunteer to help!). The Quiet Cool fan is the one I'm looking at for that exact reason; it appears more in keeping with the volume and tone that isn't as disruptive to my sleep.

    Dana - I hadn't thought about the other cooling routes; to be honest I'm in the tricky spot of 'I could see myself living here long term' but I'll be moving in about 2-3 years regardless and probably not be back for a decade. If it makes sense financially with the multitude of considerations (non-resident penalties, taxes, lower locality pay when I move), I'd like to rent the house out and have the option as it will probably be only more cost prohibitive to buy in HI again in the future.

    I considered PV, but blew most of my budget on DIY renovation projects indoors; see above for the financial considerations making me second guess installation of PV now and not really being able to consider the leased route. I think this by itself limits ability to consider other active cooling options. If nothing else, my experience here has really sparked an interest in green building/living (excluding my '73!) and is providing significant input to my approach at future home renovation and building considerations. If nothing else, it's like the even more adult version of classic car restoration...that actually has some measurable ROI.

    I thought it would show my email, not just SN, so it's Josh by the way.

  5. Expert Member
    Dana Dorsett | | #5

    The radiant barrier on the top chords doesn't necessarily have to reach all the way down to the apex at the soffits to have a measurable effect, and spray-applied or roller applied low-E paint can give you full coverage of the roof deck without crawling in there.

    Then installing the top chord RB as low as can be done comfortably for non-contortionists gives nearly full double-RB cover. Rolling out RB over the bottom chords along the low-headroom area not covered by the top chord RB still works. The flat applied goods will collect dirt more quickly than the sloped stuff on the top chords, but it'll still be doing something.

    Start with the low-E paint + RB, see how much active cooling you end up doing. Then mull over the mini-split option before pulling the trigger on a Quiet Cool.

    Three-quarter ton and 1-ton DIY (pre-charged refrigerant lines) cooling-only or cooling + heating heat pump (for those 6 hours per decade you might need to heat your place in paradise) mini-splits run about the same or even less money as a Quiet Cool Classic, but may not have the same long-term low-maintenance reliability as a high efficiency fan.

    As more PV goes onto the grid in Oahu the number of hours of negative wholesale electricity pricing mid-day is going to rise, and if they implement time of use rates to encourage more mid-day power use it might end up being cheaper to run a mini-split during the day than a Quiet Cool at night. This is highly speculative- right now residential time of use rates apply at night, but the rate structures are in a state of flux. At Oahu's PV installation levels the mid-day distributed PV is evolving from a local-grid back feeding problem in a few neighborhoods into a wider scale overall overgeneration/curtailment problem.

    At only 2x the current installed base of PV it would make sense for the time of use rates to have a mid-day off-peak period to soak up the excess, with peak rates only during the 5-9PM hours to tame the "Nessie" or "Duck" curve. Currently residential TOU rates go to off-peak starting at 9PM, which would be the projected peak hour once there is a lot more PV on the grid- I'm pretty sure that TOU schedule will change! See:

    https://www.greentechmedia.com/articles/read/hawaiis-solar-grid-landscape-and-the-nessie-curve

    https://www.hawaiianelectric.com/Documents/my_account/rates/hawaiian_electric_rates/heco_rates_tou_r.pdf

  6. 73Greencorvette | | #6

    Thank you gentlemen. Embarrassingly enough, while conducting another search I found an old 2016 post where someone (me....) asked the same question. This time, I was more detailed, and so were the answers; and they were the same answers. So I guess it's further confirmation (that I need a better memory).

    Dana, your post has inspired me to legitimately learn more about solar here in Hi; it definitely is a microcosm, but I don't think it a stretch that many prime solar regions will eventually face similar tipping points at some time.

  7. walta100 | | #7

    Given only 3 year the plan that takes the fewest dollars out of your pocket is to run the window unit.

    If your roof is not vented I think ridge and soffit vents will provide the most comfort per dollar.

    Walta

  8. Expert Member
    Dana Dorsett | | #8

    Given that he's seeing 95-100F ceiling temperatures well into the evening, low-E paint + RB is going to be "worth it" from a comfort point of view, even if it might not "pay off" financially in three years, though at HECO's nation's highest residential rates it might.

    The only place electricity is more expensive than Oahu are small island grids disconnected from the transmission grids, and similarly isolated micro grids, such as those found in parts of Alaska. Cutting the monthly cooling bill by even $20 month for 36 months buys quite a bit of RB and silvery paint.

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