Disappointed with results of R39 vs R19 blown glass insultion in Atlanta....

[shovel99]

Hi Folks,

A few months ago I used the Owens Atticat system to blow in approx R24 of fiberglass over R15 of existing blown steel. The system works well and blown glass fiber is designed not to fracture into "floaters" and that worked pretty well. Installing the "ducts" to keep air flow open in the eaves was another nasty story in my low pitch hip roof. Had to crawl on my belly and lie on my back to staple them in place.

Two observations: the insulation reduced street and airplane noise an astounding amount, and for us was probably worth the time and effort even if we didn't save a whole lot. We live on a busy street and our house is below grade, already had storm windows, so most of the considerable street noise enters our house from above.

Second, I am suspect that when we tally the results, we are not going to have significant energy savings. The extra insulation is now trapping heat during spring and fall, making the house 5-6 degrees warmer - requiring us to run the AC more now during those periods when in the past the heat escaped through our minimal R15.

I should have suspected this when the "calculate your energy savings" calculator did not make any reference to HVAC "savings."
I literally thought there might be some in that insulation would slow radiant heat down into the house in the summer. Key words: there appear to be additional HVAC cost during shoulder periods.

We won't really know until we have at least a year and better several how this will work out, but as stated earlier, even if this is "a wash": more HVAC cost and less heat, we it was worth it for us for the noise comfort. Also, I really laid on the material at the periphery, and have notably reduced cold spots ... which the original installer did not do well.

Good luck.

Shovel99

[beenthere]

While it may be holding in some heat when you don't want it, it is also keeping the heat from having to come on as soon, or for as long on the slightly cooler nights. Cooling savings will come during the hotter times of the year. A lot less heat from the attic to remove as your attic gets hotter.

You reduced your heat gin from the attic by around 1400 to 1500 BTUs an hour.

[shovel99]

Thanks BT.... that was what I was hoping.

We'll see!

Paul

[heaterman]

Have you identified where your thermal gains are? Reducing gains in these areas would seem a logical step in your weatherization efforts.

[tipsrfine]

For the sake of all the others reading this thread I want to point out that it is important to perform air sealing (when needed) before simply adding insulation.

[motoguy128]

For the sake of all the others reading this thread I want to point out that it is important to perform air sealing (when needed) before simply adding insulation.


Great point. Fiberglass in particular, if you have air movement through it, will dramatically reduce it's installed R value. FIberglass does nothign to stop air leaks. IT just acts like a big air filter. That's why using spray foam with only a nominal R20, can match or outperform R40 fiberglass in overall heat transfer.

[John Culpepper]

A radiant barrier in the attic wouldn't hurt.:.02:

[shovel99]

I suppose an IR gun would be cool, but house is pretty tight, and the obvious need was more insulation, with only 6 inches now compressed down... and several inches of heat conducting joists poking up!

Atticat blown glass was the best compromise I could find..... laid in well on top of the blown rock wool... gave a pretty good continuous layer so there weren't gap problems like batts.

Spray foam in attic just sounds questionable in Hotlanta... especially over the top of spotty blown steel. But complete seal issue is point wall taken.

I was actually given radiant barrier by a supplier to try and demo, but my low 4:12 pitch and near impossible access for attaching barrier made it a non starter. Would definitely do with a higher pitch. But would also have concerns about how it might overheat the roof material, reflecting back the heat through it.

Hoping Beenthere is right with the numbers!

shovel99

[Sbogart40]

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[Sbogart40]

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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Additional infractions may result in loss of posting privileges.

[jpsmith1cm]

Sbogart40

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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Additional infractions may result in loss of posting privileges.

[dan sw fl]

Hi Folks,

Second, I am suspect that when we tally the results, we are not going to have significant energy savings. The extra insulation is now trapping heat during spring and fall, making the house 5-6 degrees warmer - requiring us to run the AC more now during those periods when in the past the heat escaped through our minimal R15.

I should have suspected this when the "calculate your energy savings" calculator did not make any reference to HVAC "savings."
I literally thought there might be some in that insulation would slow radiant heat down into the house in the summer.

Key words: there appear to be additional HVAC cost during shoulder periods.

Shovel99

You do NOT have additonal heat load from adding insulation unless you are generating Heat within the house.

Clothes dryer would be the only signficant heat source other than the kitchen IMO.
The clother dryer probably doesn't run for significant enough duration to be a real issue.

So, What is the actual INTERNAL heat source that you are noticing?

[energy_rater_La]

I installed rb in my 4/12 kinda like installing baffles in rafter bays..only
you work every bay. moot point now that insulation levels have been increased.
rb won't hurt metal roof. only raises temps 3-5 degrees at shingles.

all insulations allow air movement, except foam insulation (when correctly installed)
fiber glass, rockwool, cellulose none stop air movement.
insulation is to stop thermal gains from exterior to interior.

I'd do my air sealing from inside the house now that you've blown
the attic. prior to blowing insulation was the time to air seal attic.
now you option is to do it from living space.

did you do any duct sealing?

best of luck

[shovel99]

[QUOTE=dan sw fl;14291681]You do NOT have additonal heat load from adding insulation unless you are generating Heat within the house.

You are right that insulation doesn't 'add heat load.'

However, the added insulation reduces the dissipation of the significant heat load that enters the house through the walls, windows and skylights. I don't have the load calc in front of me, but the amount generated inside by appliances and lights is insignificant compared to heat coming through the uninsulated walls (1965 brick ranch) 2 stories facing due south and not many trees, windows with storms, and a huge double pane picture window... full width of the den facing due south. We do have lined curtains, but even when they are closed, we can feel the heat radiating off the inside of the curtains.

My cooling bills, indeed, have not dropped, because the attic insulation is preventing the heat gain ("cooling load") the home already had, from escaping through the attic. The same thing that happens in the winter time, only in the winter, you want to keep the heat in.

As Beenthere noted, there probably is some reduction in heat flow down from the attic.. which, however, raises the temperature in the attic with deleterious effects on the shingles.

But at the same time the trapped heat load... at least 75% of which comes in through windows and walls.... offsets and perhaps exceeds the savings of reduced downradiation.

Paul Davis BSESM 1971
Georgia Institute of Technology
ME342 Heat Flow, 1969

[54regcab]

You could just open a window on the days it's cooler outside than inside instead of turning on the AC.

[shovel99]

You could just open a window on the days it's cooler outside than inside instead of turning on the AC.

Funny guy!:grin2:

[Shophound]

[QUOTE=dan sw fl;14291681]You do NOT have additonal heat load from adding insulation unless you are generating Heat within the house.

You are right that insulation doesn't 'add heat load.'

My cooling bills, indeed, have not dropped, because the attic insulation is preventing the heat gain ("cooling load") the home already had, from escaping through the attic. The same thing that happens in the winter time, only in the winter, you want to keep the heat in.

As Beenthere noted, there probably is some reduction in heat flow down from the attic.. which, however, raises the temperature in the attic with deleterious effects on the shingles.

But at the same time the trapped heat load... at least 75% of which comes in through windows and walls.... offsets and perhaps exceeds the savings of reduced downradiation.

Paul Davis BSESM 1971
Georgia Institute of Technology
ME342 Heat Flow, 1969


You do not have ANY heat escaping the house at all as long as the environment surrounding your house is hotter than the house interior. The heat gain through the walls and windows, on an idenitically hot day prior to and after your added attic insulation, still undergo the same level of heat inflow as before.

As for your increased cooling needs during shoulder seasons, I can see that happening since you said a good portion of the house is below grade. If your shoulder seasons are lengthy, I can see how this might offset some annual savings you may have hoped for. That said, has your peak cooling and heating demands decreased any?

[dan sw fl]

You do NOT have additonal heat load from adding insulation unless you are generating Heat within the house.

You are right that insulation doesn't 'add heat load.'

However, the added insulation reduces the dissipation of the significant heat load that enters the house through the walls, windows and skylights.


My cooling bills, indeed, have not dropped, because the attic insulation is preventing the heat gain ("cooling load") the home already had,from escaping through the attic. The same thing that happens in the winter time, only in the winter, you want to keep the heat in.



How did you actually determine the ATTIC temperature is LESS than the room temperature?

[shovel99]

[QUOTE=shovel99;14293351]


You do not have ANY heat escaping the house at all as long as the environment surrounding your house is hotter than the house interior. The heat gain through the walls and windows, on an idenitically hot day prior to and after your added attic insulation, still undergo the same level of heat inflow as before.


As for your increased cooling needs during shoulder seasons, I can see that happening since you said a good portion of the house is below grade. If your shoulder seasons are lengthy, I can see how this might offset some annual savings you may have hoped for. That said, has your peak cooling and heating demands decreased any?

Thanks for your input.

I agree: heat flows downhill, so when T out > T in, then heat is flowing in.

Here's my 24 hour cycle (before):

Brick and roof soak up heat, quite a bit comes in through windows and skylights. Both are screened or curtains, but still some making it in. On a 90 degree day, set temp of 73, AC doesn't run much until 2 - 3 pm when the heat is finally making its way through heat sinking brick and down throught he ceiling.

AC runs heavily till 9 or 10 PM and tails off. With little insulation T out drops below T inside around 7-8 PM and from then on heat is escaping on all sides, especially up because heat rises.

Around 7 - 8 PM, Out T drops below In T, and heat flows quickly out of house through cheesy R15 attic. This helped to reduce overall cooling load.

After:

Same as above except 1. heat flow down from attic reduced by insulation, but part of what would have come into the house stays in the attic, and will dissipate more slowly. 2. When Out T is below In T, the heavy insulation now prevents the heat from escaping during the evening. This is substantial. The house used to drop 4 or 5 degrees overnight when the outside temp dropped dramatically from 70 F at 7 PM to 45 degrees at 7 AM. Yesterday, when that happened our T in dropped exactly one degree!

I believe savings from heat coming down from attic are being offset by heat not exiting through the attic at night when it is cool. I actually believe that the latter may be larger.

I should reap significant benefits during the heating months, but my annoyance is that it is electricity that is skyrocketing and my natural gas heat is dropping like a rock.

Again, I now know why the industry doesn't brag on cooling savings.

Paul

[Shophound]

First of all, "heat" itself is omnidirectional. Air, when its heat content is increased above surrounding air, becomes less dense and will rise.

Secondly, (edit: I just reread your OP where you say you're in Atlanta, Georgia), the wide temp swings between night and day are probably shoulder season and winter time norms, whereas I would expect summer weather in Atlanta to be closer to what I experience here in North Texas (although you guys likely run consistently higher humidity levels).

Third, you need to address the heat gain through the large south facing facade you described above. No insulation in the walls on this elevation is costing you dearly. The windows need exterior shading of some sort, be it awnings, pergolas, external motorized shades, etc. Any brick sitting in full sunlight acts like a "heat capacitor". It stores up heat and then discharges it to whichever area adjacent to it is cooler. Insulation in the wall cavities behind this brick can slow that process.

Also, during hot weather, consider covering the skylights. In the winter, when daylight hours are short and sun angles are low, skylights can brighten the interior and offer some solar gain. The caveat there is at night, if left uncovered, skylights bleed heat like crazy, aided by a direct line of sight on cloudless nights to the universe at large (night radiant cooling).

In hindsight, having your building thermal performance modeled, such as via a heat load calculation, a blower door test, and/or thermal imaging, would have given you a better perspective on where your improvements should have begun in order to realize utility bill savings and better comfort. In the long run, the work performed in the attic is to your benefit, but you need to bring other aspects of your building envelope in line to realize the fullness of the benefit.

[shovel99]

First of all, "heat" itself is omnidirectional. Air, when its heat content is increased above surrounding air, becomes less dense and will rise.

Secondly, (edit: I just reread your OP where you say you're in Atlanta, Georgia), the wide temp swings between night and day are probably shoulder season and winter time norms, whereas I would expect summer weather in Atlanta to be closer to what I experience here in North Texas (although you guys likely run consistently higher humidity levels).

Third, you need to address the heat gain through the large south facing facade you described above. No insulation in the walls on this elevation is costing you dearly. The windows need exterior shading of some sort, be it awnings, pergolas, external motorized shades, etc. Any brick sitting in full sunlight acts like a "heat capacitor". It stores up heat and then discharges it to whichever area adjacent to it is cooler. Insulation in the wall cavities behind this brick can slow that process.

Also, during hot weather, consider covering the skylights. In the winter, when daylight hours are short and sun angles are low, skylights can brighten the interior and offer some solar gain. The caveat there is at night, if left uncovered, skylights bleed heat like crazy, aided by a direct line of sight on cloudless nights to the universe at large (night radiant cooling).

In hindsight, having your building thermal performance modeled, such as via a heat load calculation, a blower door test, and/or thermal imaging, would have given you a better perspective on where your improvements should have begun in order to realize utility bill savings and better comfort. In the long run, the work performed in the attic is to your benefit, but you need to bring other aspects of your building envelope in line to realize the fullness of the benefit.

Thanks for the insights. We actually do have more of a swing ... lower night temps here than you guys get. I remember my first trip to Dallas... flew in at 11 PM for an interview the following day, and being met with a wall of heat when the door opened from the DFW terminal.

Had 3 bids for HVAC replacement... all "reputable guys" and none even offered "load calc".. so thinking about a higher grade analysis than that wasn't in the picture.

We are probably going to be moving outside the city limits of coming taxes to cover the collapse of ATL finances and fat retirement system, so not spending much more on this house.

What kind of cover for the skylights are you thinking about? We do have levalor blinds inside the skylights, and use them extensively to block sun, and in winter at least slow the pouring of our heat out into the sky!

I like the "heat capacitor" analog. If this were our retirement home, exterior insulation might be in the cards, but really messy and can't be cheap.

Paul

[54regcab]

Solution: Open windows at night when it's cool. Natural free cooling instead of running AC at all. 40years ago a thing call an "whole house fan" was very popular to pull in the cool night air. In the day you would close the house up for trap the cool until the next evening. Worked pretty well until temps go into the 90's in the day.

[jtrammel]

Thanks for the insights. We actually do have more of a swing ... lower night temps here than you guys get. I remember my first trip to Dallas... flew in at 11 PM for an interview the following day, and being met with a wall of heat when the door opened from the DFW terminal.

Had 3 bids for HVAC replacement... all "reputable guys" and none even offered "load calc".. so thinking about a higher grade analysis than that wasn't in the picture.

We are probably going to be moving outside the city limits of coming taxes to cover the collapse of ATL finances and fat retirement system, so not spending much more on this house.

What kind of cover for the skylights are you thinking about? We do have levalor blinds inside the skylights, and use them extensively to block sun, and in winter at least slow the pouring of our heat out into the sky!

I like the "heat capacitor" analog. If this were our retirement home, exterior insulation might be in the cards, but really messy and can't be cheap.

Paul

Did you try Estes heating and air

[shovel99]

Solution: Open windows at night when it's cool. Natural free cooling instead of running AC at all. 40years ago a thing call an "whole house fan" was very popular to pull in the cool night air. In the day you would close the house up for trap the cool until the next evening. Worked pretty well until temps go into the 90's in the day.

Here in the A T L it gets into the 90's about half the year, and humidity is awful. We are also on a dusty street. As a bachelor, it worked for me, but not with the bride and the expensive trappings ;-).

Actually had one and used it, but........ that was years ago.

[54regcab]

Since you are destin to live in a house where the windows might as well be sealed shut.. let it be known that AC units put out a LOT more BTU per watt as ambient conditions get cooler.

[dan sw fl]

Here in the A T L it gets into the 90's about half the year, and
humidity is awful.

We are also on a dusty street. As a bachelor, it worked for me, but not with the bride and the expensive trappings ;-).

Actually had one and used it, but........ that was years ago.

So Pay me NOW
AND Pay me Later.

I work in HVAC
AND the Utility.

Of course, one option is to set the t-stat at 79'F.

[dan sw fl]

How did you actually determine the ATTIC temperature is LESS than the room temperature?

Apparently, NO attempt was made.