You might be wondering what radiant barrier is. It is a reflective material that bounces back radiant heat, aka infrared heat. You may have seen movies in which people are wrapped in a silvery plastic sheet in emergencies. That's a radiant barrier that reflects body heat back to the person wrapped in it. It doesn't warm you, but it reflects your body heat back at you to keep you from losing heat.
In the case of an attic, you can buy rolls of the reflective material that you can then staple to the roof rafters. This reflects heat from the roof back to the roof. This prevents that radiant heat from penetrating the insulation and other materials in your ceiling. Once your ceiling gets radiant heat, it warms up and transfers into your home through heat conduction, another way for heat to travel. Therefore, by installing the radiant barrier, it reduces the amount of heat that your ceiling conducts into your home.
I don't have any images of the radiant barrier installation as it was installed in winter. With summer, even using radiant barrier, it's still quite hot in the attic. However, it's not as hot as it has been in prior years.
Here is an image of improperly installed radiant barrier by Grok. It should be stapled to the rafters, leaving an air gap between the roof deck and the barrier.
Here is an affiliate link for radiant barrier from Amazon: click here
Last year, I installed radiant barrier on the attic rafters, but I ran out of the material and only got a portion installed. We experienced less heat than in previous years. But it was still warm on hot summer days. This winter, I ordered more radiant barrier and finished the job. But more than that, I lay another layer of the radiant barrier on the floor of the attic to keep the insulation and ceiling materials from absorbing any other radiant heat from the attic.
One thing to remember is that an air gap is essential. Radiant barrier is great at reflecting infrared heat. But it is not very good at stopping conducted heat, which is how pots and pans heat your food. If the radiant barrier is hot, it will also emit radiant heat. The air gap prevents the radiant barrier from becoming hot through conduction.
When you lay down the radiant barrier on the ceiling floor, it is important to first have something that will create space for the air gap. The radiant barrier will "float" on the spacers, therefore avoiding any heat conduction. You should try to minimize contact between the barrier and attic floor.
So far, the results have been great. The house is much cooler, even on the hottest days. Our window air conditioners are able to keep the house cool much better than in past years when the house would heat up to almost 90 F, even with air conditioners running.
At first, after this final installation, the house temperature always hovered at 81 F. I thought perhaps it had failed. But I think that the items in the house were still warm (latent heat). Now that we have had the air conditioner running and everything in the house has also cooled. The temperature has lowered to 76 F.
We do experience higher temperatures in the house when we use the oven. That is to be expected. Otherwise, the house is pleasantly cooler than it ever was before completion of the radiant barrier installation.
I suspect that the cost of buying the material will be more than offset by the energy savings over the coming years. Last year, with a partial radiant barrier, our summer electricity bill was as high as $200 from a base cost of $88 when we don't run the air conditioners. Before that, we had electricity bills as high as $280. However, some of our savings is the result of also installing solar panels to offset our usage. Since the solar panels, our highest bill last year was $202. But we mostly were in the $180 range. This year should give us new baseline data on our energy usage.