(I searched for this topic and didn't quite find an answer, or I'm too ignorant to understand what was said).

I don't have enough insulation in the attic of the home we bought almost two years ago (DFW area) and in the summer my AC unit (which is two years old and is working fine) can't keep up. I had two quotes on adding insulation, and the third company that came out recommended adding a foil radiant barrier to reduce the attic temperature (said that would be more beneficial). It almost looks like a foil tent. https://energyattic.com/radiant-barrier-dallas-fort-worth/ The temperature in my attic was already over 120 today, with the weather reaching 90.

I can't decide which option I should go with, added insulation or the barrier (I don't really want to drop the cash for both, as I have other repairs I need to take care of as well). If any of you have any insight or knowledge to share, I would greatly appreciate it.

Lots of factors at play here. In terms of the attic, I would say that insulation and ventilation are key components 1 and 2. If you don't have sufficient soffit vents or sufficient escape (i.e. ridge vent or whirly birds), then the hot air has nowhere to go. In addition, if you have 4" of cellulose which is common in older homes, then you don't have sufficient insulation. The next issue I would consider is windows. If you have original windows or old windows, then you have in inefficiency in your house. Our house faces west and has the original windows from 1985. Those rooms that face west get hot in the summer and our north facing windows get cold in the winter. Also if your HVAC units are 10+ years old and in the attic, they're going to struggle to keep up with the heat. I'd say first address ventilation, then insulation. Radiant barrier can be great, but solving those 2 things and maybe updating windows and/or HVAC will make a massive difference.

I have no idea which is best but we have a radiant barrier(installed by previous owner) and it does make a difference. Not sure how much as I've never attempted to quantify,

Thank you for the reply. The guy said my ventilation was good, (and that I might benenfit from a solar fan, but said it would be the last thing he would add) and my AC unit is only 2 years old. The windows were replaced by the previous home owner a few years and my home faces north. As far as current insulation, it's as low as 5" in some places, and has as much as 9-10" of blown in fiberglass in others. Definitely under insulated all around. The house is 50 years old.

I did both on my 130 year old house with no previous insulation. I did them a couple of years apart with no other changes made to the home or with the lack of shade on the house.

I installed the radiant first since it was cheap and easy with my attic roof height. I would suggest a power stapler and a second set of hands.

It knocked the house down about a degree… maybe. I would do it again because it was a cheap easy day for me.

I had insulation blown in the next year and it knocked things down inside my house by about 4 or 5 degrees in the summer.

The best money I have spent on making the house comfortable for me have been rolling blackout blinds on the south and west 6' windows.

Had our house renovated years ago that included revising the roof configuration to enclose the patio area under the roof. During the roof reno, they had to replace the decking and roofing so I went with radiant barrier decking and it made a significant difference as the attic temps are about 30-45 degrees lower than before. Used to sweat up a storm working in the attic and now it's not an issue.

And to top it off, I still have two entire bedrooms some other areas that have zero insulation above them and the temps in those rooms/areas are equal to the rest of the house. I will eventually get them insulated to get the full improved effect!

I was fully intending to DYI blown insulation in this past spring but I got busy with other crap and just looked at it this weekend to assess. It's actually better than I remember and I might just buy some rolls to supplement. Good whirlybirds and movement. I can move around easy enough in most of it so that seems better bang for the buck than the barrier.

I have a small house that had minimal, poorly distributed blown in fiberglass insulation and the AC could hardly keep up. I bought 10 bags of fiberglass from HD, used their machine and brought it up to about R50. It made a huge difference. Took about 4 hours. It already had the radiant barrier under the roof.

I could really bend you ear on all this but after reading your deal, the solution is a simple DIY one that could be done a little at a time.

http://rb.gy/bk1wu

http://rb.gy/4ix2s

or you could get a free rental blower buying enough bag insulation THEN
throw foil faced "radiant" sheets/blankets over all that

You really don't have to throw money at this, buy a tent, send the saleman's kids to college, etc.

I'd suggest both insulation and radiant barrier. However, if you have to pick one , insulation is the way to go, assuming you have some but not much. If you already have 14" of insulation then you aren't going to notice a huge difference. There is a diminishing return here. The other things you can do in the future are increase attic ventilation and change the color of your roof. If you want to shoot me your address, I'll rough calc the roof footage and give you your two current standards for adequate ventilation amounts. It's not that your guy doesn't know, but I'm a science kind of guy and like to validate claims or at least get consistent advice. I'm happy to do that and discuss what you have. Maybe it is enough and In that case you can stop wasting thought on that. Lol. The next thing you can do, if you want to push the envelope of your neighbors and HOA is change the color of your roof to an Energy Star rated color. Generally, that color is going be dang near white, but I can attest to first hand experience that going from a black roof or a dirty brown roof to a white roof makes an immediate and noticeable difference. Plus, those shingles are designed to reflect energy, so you can snag a little benefit of a radiant barrier and get away with not doing that too.

Energy efficiency is not always about one thing, or even two things. It's all the small things that add up. Roof color, radiant barrier, insulation, ventilation, thermal envelope tightness, etc etc.

As stated above, the 1 degree difference from the barrier isn't much but it's measurable and worthwhile as a part of the system even if it's negligible on its own.

Is the diminishing return you are talking about with 14+ inches of insulation that you just aren't getting any appreciable savings in electrical costs versus the amount of insulation you buy or could you literally have too much insulation?

14" is just an example number. A pro can tell you want it actually is but it's somewhere around R38. You just don't realize a benefit. You can't really have too much I don't think.

You spend the same money for extra insulation but it isn't gaining you much additional benefit or energy savings. Think of it like buying a Yeti cooler and comparing it to a yeti cooler that costs twice as much because it's twice as thick. Does it insulate more? Of course. Does that matter from a practical sense? Probably not and you spent more on it.

When our house was being built 17 years ago, I had our builder install CoolPly instad of plywood for the roof, CoolPly is chipboard with a factory-applied radiant barrier on one side (think aluminum foil). The radiant barrier, combined with soffit vents, made a huge impact on our electric bills. Radiant barriers help keep the heat out of the attic and soffit vents are the most effective means of allowing heat to escape your attic. Both of these reduce the heat load in your attic, which may allow your exsting insulation to do its job.

Perhaps also consider a thermostatically controlled roof and/or gable fan (or two?) depending on size?

Insulation and air flow are the best impact. Barrier is third.

I wanted to report back and thank all of you for your input/advice, after a summer of evaluation. I ended up starting with insulation and the radiant barrier and noticed a sizeable decrease in attic temperature, but not as large I was promised. The company I used was great about delivering on what they said they could accomplish, and ended up adding ten soffit vents (to increase air intake) and a solar attic fan. On the days when we were hitting 106-108 degrees, my attic was between 124-130 degrees and on the "cooler" 98-100 days, the attic is around 112-116. As a reference point, before I did anything, my attic was getting up to (and over) 140 degrees on the 95 degree days before I did anything.

If was to do it again, I would most likely go with HDeathstar's suggestion of insulation and airflow first, if I had to choose. A down side to that would be the insulation getting disturbed and moved around if I had to go back and have a radiant barrier installed. Thanks again for everyone's suggestions and experiences.

The foil or the spray? I did the foil from Atticfoil over 10 years ago and the attic is about ambient +5. 2 turbines and 20 soffits. It's a large (and high) cathedral type attic, so I created a false ceiling with the foil at about 7.5 feet. Insulation is still the crap from 1990.