Posted By bi0hazard on 17 Oct 2011 11:59 PM
Thanks for all responses.

I have noticed a few ridge vents around here. If anyone has new vents (other than the standard), it is usually the turbine. 4/5 companies recommended turbines, and only one wanted to the the ridge vent. The ridge vent's design is seems counterintuitive as far as exhaust is concerned, but I am not a professional. It looks better than a turbine, but it is more expensive (quote $900 for my roof, instead of~ $600 for 4 new turbines). Also, it is very windy in DFW, so I think turbines may actually work It makes sense with foil type radiant barrier, that the heat collected between the roof deck and foil must get out, so I see why I need more ventilation, since I only have about 300 sq in of exhaust for ~3000 sq ft roof area.

My AC and ducts are in the attic, standard here. Only 1/5 companies wanted to mastic seal the ducts ( expensive = $300 for 3 units). Others said the ducts appear OK. I don't know how to know for sure who's right. One company actually took temp readings from my ducts and the guy said it leaks just a tiny amount more than it should but overall it looked good.

As far as insulation goes, nobody does cellulose from the companies I called. They use fiberglass. On person said cellulose is garbage that gets degraded to dust over time and they don't want to install it. What really gets me is that companies are split on whether I need insulation or not. Some say I am at R26 the others R38. How can I figure this out? People charge $600 to add insulation, which is more than I want to pay if I don't need it.

Dana, the solar windows you recommend are popular. My neighbors have them but they are super overpriced and they look awful.

Thanks again for everyone's input.

Very windy + turbine== depressurized attic. Unless you have the worlds-best air-barrier and the tightest house in Texas a turbine is going to suck conditioned space air up into the attic, and hot humid air in wherever it can. DON'T DO IT!! It's an energy-loser.

With rafter mounted RB the heat isn't collected- it's reflected back to the roof deck and keeps it from radiating on your ducts & joist tops, insulation, etc. While this raises the temp of the roof deck & shingles, the higher temp on the exterior allows more of that heat to be radiated back at the sky for a net reduction in collected heat.  Using a more solar-reflective but still highly emmissive CRRC rated roofing material is more effective than interior RB, but I'm assuming you have a lot of life left in whatever is up there.

$300 of duct sealing is CHEAP compared to blowing away 20% off your air-conditioning energy and risking ruining your indoor air quality with fiberglass dust in the process, are you kidding? If you're not going to seal the ducts, at least seal the attic, to keep the pressure differences driven by the duct leakage all within the pressure boundary of the house.

You can't tell how much leakage you have by looking- you have to pressure test it and MEASURE the duct leakage. Visual inspections and temp measurements can sometimes tell when you have a total disaster on your hands, but not much more than that.  Find a specialist with a duct-blaster test setup who can do the job right and verify the result.

Cellulose will only degrade over time via excessive moisture cycling. There are houses with 90 year old cellulose in the walls and attics that are doing just fine.  In high dew-point climates going with an air-tight attic (even if you don't put the insulation at the roof deck) will put the cellulose inside the pressure boundary of the building, and the air-conditioning will keep it from taking on humidity during the cooling season. In DFW there's no good rationale for a vented attic.  The summertime dew points are high enough that higher attic ventilation rates creates higher accumulation of moisture in the structural wood, and more risk of condensation & mold from outdoor air coming in contact with the air conditioned surfaces.  Cellulose crumbing to dust just doesn't happen if applied at proper density and reasonable depths, even under high humidity cycling, but it will settle considerably under humidity cycling. But given that it's more effective during the cooling season at equivalent R than low-density fiberglass, and the fact that it's downright CHEAP, even if you have to top it off with another 6" in 2 decades time, it will have more than paid for itself.   But seriously, if the ducts are in the attic consider adding 6" of open cell foam to the roof deck & rafters, sealing all of the venting at the same time (and VERYIFY the soffit sealing!) Between the air-sealing and additional R the load to the AC will drop, and by containing the duct losses within the pressure boundary of the building the net-efficiency of the system will improve.

The Oak Ridge Nat'l Labs data is unequivocal about the effectiveness & economic value of more insulation than R26 (which doesn't even meet current code-min).  And you're looking for the most cost-effective route to COMFORT, not mere net-present-value on energy savings. Going to R50 using cellulose or high-density Optima or Spider on the attic floor would be a huge improvement in comfort, as would 6" of open cell at the roof deck and sealing the attic. See the table on pages 5 & 6:

  http://www.ornl.gov/sci/ees/etsd/bt...et2010.pdf

DFW's cooling season is somewhere between Austin's and Atlanta's, you're only going to get big dollar savings out of RB if your ducts are un-insulated and located in the attic.  If you're at code-min on the insulation it'll save some, but the money is better spent on improving the ducts.   If the ducts are insulated or located inside of conditioned space, RB buys you squat.  But going 1.5-2x code min on the insulation isn't hugely more expensive than bringing your R26ish up to R30-R38 you'll be able to feel the difference, at least as much as with rafter mounted RB, and with higher net annual savings.  Open cell foam on the roof + air sealing will be more expensive than a cellulose blast or RB, but it will be the better performer, particularly if the ducts are in the attic.

To figure out your nomimal R value, get up there with a tape measure and measure the depth of the (presumably blown-fiberglass) insulation, and multiply inches by 3.2. If it's only ~8", that's R26.  IIRC dode min in DFW is R30, which is more like 10".  But if it's not covering the joist tops/truss chords by at least 3" you're getting a huge amount of thermal bridging through the timbers, so any retrofit insulation needs to be at less joist-depth + 3".  If those are 2x10s (9.25"), topping the joists by 3" would mean 14-15", or R45-50. But those last 3" add quite a bit more performance than would be accounted for by center-bay R, since it's raising the R-value of the ~R8 thermal bridge of the joists to ~R20.  If you insulate right up to the joist tops with 9.25" of blown fiber you'll meet your R30 code min, but with R8 joists most of the heat transfer is being conducted through the joists. With a 10% framing fraction (it's probably more), you end up at ~ R26-R27 for whole-assembly performance.  But for 3" more the center-bay value becomes ~R40 but the whole assembly R rises to ~R38- a 50% performance improvement for 33% more material.  Even if you do it with low-performance fiberglass, insulate over the joist tops.

Exterior shades are a trade-off between comfort and visual aesthetics, and not everyone will make the same choices, eh?

bi0hazard-

You said: "Dana, I think windows are a big problem on the west side of the house. Temps are 105-110 until 8-9 PM in the summer so I think this is letting in a lot of heat. My neighbors have solar screens on their windows. They look horrible (cheap) and they are super expensive (2K installation) . Do you think this is a good way to go instead of RB? "
If you have west, south, or east windows with no interior or exterior shades or solar screens, then you likely have passive solar heating that must be dealt with. The cheapest solution ($10? per window) is simple roll up shades that have a white finish, preferably shiny toward the outside, to keep the majority of the solar heating out of the room to begin with. Other more expensive options are cellular shades, again with a white surface facing outward. Room darkening cellular shades have some reflective material within them that will really reduce the solar heating, but you may or may not want that much darkening. (Sounds like the room is unusable currently anyway.) You need to limit direct solar heating as a first step if you have not already. You did not define the window situation very completely, but if you have a window(s) that is uncovered or has fairly transparent curtains, think of it as a big solar panel that is letting in large amounts of direct radiant heating.

The exterior shades are more effective than interior shades, but he hates the look (and expense) of them. Getting the heat back out through a low-E double-pane window isn't as simple as a cellular shade with a reflective exterior, but it'll cut down some.

I agree afternoon solar gains through windows are probably at least as big a factor in the ability of the AC to keep up as the accumulated gain through the attic (unless he has huge duct leakage and duct gains in the attic, which he might.) While it's better to close all the barn doors, slamming just one of the bigger ones tight might be enough to tip the balance to where the AC keeps up with the load, even if it's not the ultimate in energy-efficient design.

In one of my posts I asked if he had cathedral ceilings and he response was yes. Depending on how much of the space has a cathedral ceiling will affect how difficult it will be to control heat gain. Short of tearing into the ceiling their is not much that can be done. Building codes can have a lower r value for cathedral ceilings. IT is not uncommon to see R30/38 with the R30 applying to cathedral ceilings and R38 for attics.


Dana - I dont know if duct testing is necessary in an attic with the ducts exposed and accessible . If a person gets up there and seals all the joints and after the first round of sealing close the vents and then turns the blower on. Now check for leaks with your hand, smoke pencil, fog machine etc and seal what was missed the first time. You will not have a before and after number but you can do the same level of sealing.

I dont know much about window films but could it be worth while to have window film installed.

I will go up there and check the depth of the insulation.
As far as ducts are concerned, I'm not sure if they are sealed or not, don't know what it means. For the most part, roof companies seem to be impressed with it. It's all aluminum hung throughout the attick. Im pretty sure it's standard where I live based on observation. Only one person offered the extra sealing around joints and ac units and I might do that based on responses here. Also, based on what I've learned here, I am considering putting a limited number of solar screens on the upstairs windows.

Thanks to all.

If the ducts are sealed there's usually some mastic or FSK tape at every joint & seam. Even 99%-tight aluminum ducts that are not insulated are a huge efficiency problem from a conducted-heat point of view in an unconditioned attic. Highly reflective aluminum might take the edge of the direct radiated gain from the roof deck, but even R6-8 is a huge improvement. Insulating the ducts with air-permeable fiber insulation in a VENTED attic in DFW is likely to result in condensation/corrosion on the ducts during the cooling season, since the dew point of the attic air would then be the same as the outdoor air, and the temp of the insulated supply duct will be below the average midsummer dew points in that area. In some instances sealing & insulating with 1-2" of closed cell spray foam is possible, and being air-impermeable would not have that problem. In a sealed attic (even if not fully conditioned) the dew point of the attic air is about the same as that of the conditioned space air, pretty much eliminating the condensation issue.

In an attic with no insulation at the roof deck, insulating both the supply & return ducts need to R8 is cost effective, but in a sealed semi-conditioned attic with half or more of the total R is at the roof deck, R6 on the supply-ducts-only is fine.

Roberth- All ducts should be pressure tested, even if they look good and are clearly mastic or FSK tape sealed. The visual inspection can only tell between a true disaster "energy emergencies" and "maybe OK". Typical new construction has on the order of 20% duct leakage, give or take 5% unless it's be mastic-sealed and pressure tested.) With a duct-blaster and remediation getting that down to low-single-digit losses is usually possible. Where duct pass through the sealing need to be sealed to the gypsum too, as it's otherwise a high pressure-difference point in the building's pressure envelope driving massive air infiltration whenever the air-handler is running.

Dana

What I see around here is metal trunk lines with interior insualtion. The ducts are mostly flex but sometimes metal. I should add that the interior insulation is for trunks running through unconditioned spaces. I was picturing something like that.

Now I have seen pictures of some crazy attic duct work in southern climates with has a shiny foil appearance , I assume it is a fiberglass insualtion with a reflective barrier attached. If that is what he has then I would agree duct testing should be performed.

If the trunk lines are are not wrapped on the exterior then I dont think duct testing is necessary. A person should be able to identify all the joints and seal them.

In looking back on it he should have been told to get an energy audit although I think the owner would baulk at spending the money based on his comments about not wanting to pay $600 to add insualtion to the attic. As it is the owner is relying on salesmen to solve his problem.

I don't think you understand. I don't balk at spending money. The problem is that I do not trust roofing companies, and there is not even consensus in this thread! For example, everyone I spoke with here, recommends turbines, which is not what I am getting here. So why -waste- money? I want to do the right thing before I make a decision, that's all. I have 10-12 inches of pink fiberglass, I just checked. Thanks.

When you post on a site like this people can throw out ideas but it really takes someone to look at the house and see where your problem lies. You said that you had cathedral ceilings. I have no idea how much of the top floor cieling is cathedral. When you look at code for cielings you will see something like R30/38. The lower number will apply to the cathedral cieling and the higher the open attic. The cathedral ceiling portion is much hard to deal with and there may not be much you can do without greatr expense. Stanard attics leave you more options.

Anytime you call a tradesman he is going to try to either solve you problem with what he sales or sell you something you dont need. In the first case it may not be the optimum solution.

Adding more insualtion may not do any good if you have a lot of air leaks. There may be hidden large "attic bypasses" that some insulation guys will not attempt to discover. Some insualtion installers will want to top off in the insulation as quickly as posible and move on to the next job. It takes someone that knows what they are doing and pays attention to details.

I think you should get an energy audit. Get someone who can recommend installers that do things the right way. Why pay an auditor? First off an auditor is not trying to sell you and he is not tied to certain products that can limit your solutions. An auditor is bringing in diagnostic tools that the saleman arent. An auditor can give you a gameplan that shows what needs to be done in what order. You dont want anyone in the attic after insualtion is installed. Air sealing must be done pryor to insulating. If a radian barrier and/or duct sealing is recomended then that needs to be done before insualting.

I read an interesting study about the uniformity of insulation. If the insualtion has lots of peaks and valleys the insualtion performs closer to the R value of the low spots rather than r value of the average depth. What it is telling us is that when somone distrubs the insualtion it has a big impact on the total R value for the attic.

Roberts,

You are absolutely right! That's exactly what I need to do.

Thanks.

b

Greetings,

Adding any more bulk insulation to the existing would be throwing money away.

Here is a chart that will tell you the increase of your insulation eff. not counting effects of moisture.

From your info you have about "R" (?) 26. Going to a "R" 38 would increase the sys eff by about 3.6 %.
To "R" 50, about 5.6 %. Hardly worth the cost, and would have no effect on the ac run time. Adding cel could cause the ceiling to cave. Since FG is such a poor insulator against RH your best bet is a Perforated RB laid on top of the existing. That will decrease the ac run time about 50%.

THIS CHART WAS DISTRIBUTED BY FOILPLEAT WHICH MERGED WITH ANOTTHER COMPANY


The chart below gives the rate of depreciating returns for each added R-l through a given area beginning with averages for uninsulated areas. This same information is available through architects, engineers, power companies, etc.

To find the approximate amount that you would save on your bill, use the following example. Please keep in mind these figures are best results as they do not figure in reduced performance due to moisture from condensation and other factors.

1. Present R factor (2.3 blown or 3.3 batts per inch)
2. Desired R factor (R 30 is recommended; most builders install R 22)
3. Add up numbers in "B Improvement" column from present R to desired R rating
4. Figure average a/c costs. (Figure base 0perating cost for average of 4 people 120O sq.ft. all electric house at about *$8O/mo*. Balance Is a/c costs.)
5. Since heat gain is greatest through ceiling and due to heat retention, figure
60% of a/c cost (60% x Fig. 4 result).
6. Line 5 result X line 3 result gives the approx. cost saving with rock or glass wools. **Cel approx 12% better than FG and foam about 12% better than cel.**
COMPARE THIS TO A SAVINGS OF UP TO 30% FOR THE SUPER RB SYS' SAVINGS.

THE FOLLOWIG A thru C HEADINGS ARE FOR THE 3 DIGIT LIST BELOW

(A)R-Opaque Area (B)U Opaque Area (C) %Improvement over previous R based on original’s area

3 .3333 - EXAMPLE A=3 B=.3333 C= -
4 .25 25
5 .20 l5
6 .1667 10
7 .1429 7+
8 .125 5+
9 . 1111 4+
10 .10 3.3
11 .0909 2.7
12 .0833 2.3
13 .0769 1.9
14 .0714 1.6
15 .0667 1.4
16 .0625 1.3
17 .0588 1.1
18 .0556 1.0
19 .0526 .9
20 .05 .8
21 .0476 .7
22 .0455 .6
23 .043s .6
24 .0417 .5
25 .04 .5
26 .0385 .5
27 .0370 .4
28 .0357 .4
29 .034s .4
30 .0333 .4
31 .0323 .3
32 .0313 .3
37 .027 .2
38 .0263 .2
39 .0256 .2
40 .025 .2
41 .0244 .2
42 .0238 .2
43 .0233 .2
44 .0227 .2
45 .0222 .2
46 .0217 .2
47 .0213 .1
48 .0208 .1
49 .0204 .1
50 .02 .1

* Used original costs reference for dating of document (probably mid ‘80’s).

** NOTE added