DIY Radiant Barrier in attic?

I ran across a big outside vender display for radiant barriers at the Austin Costco yesterday https://mechanicguides.com/best-radiant-barrier/ . After listening to the sales pitch and watching their video I did some googling and found lots of web sites that sell rolls of foil radiant barrier material online.

Doesn't look like that difficult of a job although perhaps a 2 person job. And perhaps something I will wait until mid-winter to tackle so I don't die of heat stroke in my California attic in August.

I was just wondering if anyone else here has attempted a DIY install and what your experience was with (1) the difficulty of the install, and (2) the effect on your cooling bills. Based on my rough calculations I'll probably need about $600 worth of foil to do my whole attic. It's a one-story 3100 sf house house with a 2 car garage and porch and the roof pitch is fairly steep so I'm guessing I need at least 5,0000 ft of foil, probably more. If they are correct and it cuts air conditioning costs by 20% that will probably pay for itself in a couple years.

Someone on here a few years back built an attic fan using a radiator fan from the junkyard and a solar panel to better ventilate their attic and claimed a noticeable difference in temperatures. If the attic is significantly warmer than outside, just getting some better airflow up there is bound to help.

Super easy to install. 

20% AC savings is probably unrealistic. 

If you don’t have good ventilation (continuous ridge vents and soffit vents), it’s effect is gonna be minimal. 

If your attic has an unfinished floor, the installation gets harder. You will need a ladder to reach the high parts with that steep pitched roof, and there is no floor to set it on. 

In reply to Nnetha :I’m not sure of the effects of a radiant barrier on the underside of a roof that has already absorbed heat from the sun.  I do know that on really hot days my attic stays cool even without a radiant barrier because I Use SIP’s ( they are just a solid foam block with plywood on either side as a nailing surface)  

Several houses around here have had a spray foam company come in and spray the ceiling of their attic roof. It’s only a few hours on a typical roof.  First they put up an air chase which is a foam or plastic  chase that’s stapled up to allow the roof deck to vent to the ridge line vent or to roof vents.  

Then they go in and spray about a 1/2 inch or so of foam that expands to 4-5 inches. Pretty much turning  the whole attic ceiling into a big marshmallow.  

What they noticed most of all was they no longer needed ceiling fans  even on really high vaulted ceilings.  

Heat rises, in ordinary homes the ceiling is always a lot hotter than the floor.  With a complete foam barrier heat is no longer escaping out the ceiling and radiating down.  

Instead the whole house stays cooler in the summer, warmer in the winter.  

SVreX said:

Super easy to install. 

20% AC savings is probably unrealistic. 

If you don’t have good ventilation (continuous ridge vents and soffit vents), it’s effect is gonna be minimal. 

Wouldn’t the A/C savings depend on where the outlet is?  I agree that with typical floor outlets blowing cold air up and let it settle after warming in the hot ceiling layer savings would be reduced. 

However with mini splits or mini ducts blowing cold air down into the room  It would seem a greater potential savings would result.  

But you are right 20% does seem arbitrary and there are probably too many variables to make such a flat statement. 

Spray foam?

He asked about a $600 product, and you suggested a $10,000 option. 

I don’t think we are comparing apples to apples. 

In reply to frenchyd :

No. 

AC savings has ZERO to do with register locations. 

Current utilities cost is X. Projected utility cost after installing radiant barrier is X-Y. Register location is completely irrelevant. 

In reply to frenchyd :

We’ve talked about this. Your obsession with register locations is incorrect. It is not relevant in a forced air system. 

SVreX said:

Spray foam?

He asked about a $600 product, and you suggested a $10,000 option. 

I don’t think we are comparing apples to apples. 

$10,000?  My last quote to do the whole  30’x30’ attic was $2300. It was only that high because I still wanted the black walnut timbers exposed. 

In reply to frenchyd :

30x30 is 900 SF. 

He said he needed 5000 SF. 

I can give you a Florida perspective, we did radiant barrier in our 3750 sqft house, two-story so only about half of that was roof but I did do the garage and roof area under the lania. First of all SVreX is right it is all about airflow, we had a continuous soffit vent and off ridge vents up top. The aluminum covered Ovex type material is stapled to the rafters to create air channels from the soffit to the ridge, this gets the hot air moving out the ridge vents, not hanging in the attic. In our house, the AC piping is run through the attic so a reduction in attic temperature improved the efficiency of the ac unit. 

The biggest change I noticed was the temperature in the upstairs was capable of being maintained, without the ac running 100% of the time and we extended the amount of the year we could not run the ac. I did not see at 20% utility bill savings by any stretch and the payback is more like 5 to 7 years, but it was definitely worth it in comfort improvement in living.  What I found was that the DIY approach didn't save enough to warrant doing it myself, shop around a bit and I bet you find a better deal on installing. On my house, installation was about $500 and they were in and out in 6 hours. I know it would have taken me several weekends to complete the same task. 

Radiant barriers are fine, but remember that they don't provide much at all in R value.  Many of the companies selling them will have misleading or outright false R value claims.

Besides the highly variable construction quality, make sure the ones you select will be up to whatever your states fire code is. Many, do not meet it and produce toxic smoke if ignited. Due diligence where your home is concerned. I use it as temporary insulation for a few old drafty windows, and have insulated a van with it, and it works remarkably well for its size. My understanding was that the air-gap between it and the outside surface does more for r-value than the actual material. So correct mounting seems key for such a flexible material. Just some stuff to consider. 

Is the attic insulated? If so is the roof insulated or the ceiling?

I can give you a Florida perspective, we did radiant barrier in our 3750 sqft house, two-story so only about half of that was roof but I did do the garage and roof area under the lania. First of all SVreX is right it is all about airflow, we had a continuous soffit vent and off ridge vents up top. The aluminum covered Ovex type material is stapled to the rafters to create air channels from the soffit to the ridge, this gets the hot air moving out the ridge vents, not hanging in the attic. In our house, the AC piping is run through the attic so a reduction in attic temperature improved the efficiency of the ac unit. 

The biggest change I noticed was the temperature in the upstairs was capable of being maintained, without the ac running 100% of the time and we extended the amount of the year we could not run the ac. I did not see at 20% utility bill savings by any stretch and the payback is more like 5 to 7 years, but it was definitely worth it in comfort improvement in living.  What I found was that the DIY approach didn't save enough to warrant doing it myself, shop around a bit and I bet you find a better deal on installing. On my house, installation was about $500 and they were in and out in 6 hours. I know it would have taken me several weekends to complete the same task.