Your roof acts the same way.  It can easily reach 150º or hotter on a sunny day.  This heat will then be re-radiated through the attic and will be absorbed by your attic insulation causing high energy bills and comfort issues.

This video illustrates how a radiant barrier works – plain and simple.  Rather than absorbing the radiant heat from the roof, let’s bounce it back and keep the attic insulation cooler. If you keep the insulation cooler, then less heat enters the home and you save money and stay more comfortable.

Think of it this way:  Radiant barrier is your 1st line of defense against radiant heat and your attic insulation is your 2nd line of defense against conductive heat.  They will actually work TOGETHER for maximum efficiency and comfort.

Click here to view the embedded video.

Looking for more videos on this topic? Check out my posts below.

In an attic application, you should ALWAYS use a perforated product. Period.

Perforated Radiant Barrier Foil

Why? Solid products like bubble foil insulation are called “Vapor Barriers”.  A vapor barrier basically stops moisture from moving from point A to point B.  Or, another way to view this is that a vapor barrier will “TRAP” moisture.  I’m not going to get into the technical definition of what defines a vapor barrier (perm rating, etc), but here is an illustration of what IS and IS NOT a vapor barrier.

If you take a wet block of wood and put it inside a bag or an envelope made of perforated radiant barrier attic foil the wood block would eventually dry out.  Therefore, perforated radiant barrier is NOT a vapor barrier.  Moisture ALWAYS goes from wet to dry.  If you did the same test with the wood block inside a plastic bag the wood would still be wet months from now.  If moisture in its vapor form cannot pass through or object won’t “dry” then the product IS a vapor barrier.

Why is this important?

Virtually all (over 70%) of home issues are due to mold, mildew, rot, decay, etc. And moisture is the common theme here.  DRY products don’t grow mold, rot or decay. The bottom line is that moisture in wall and ceiling assemblies is not a good thing.  You want DRY walls and ceilings.

In cooler weather, the moisture INSIDE the home is greater than OUTSIDE.  Think cold and dry.  This is why our lips get chapped in the Winter and not in the Summer.  Since moisture will naturally move from wet (inside) to dry (outside) it will pass through sheetrock, insulation and then into a typical attic.  The LAST thing we want to do is TRAP moisture here.  Moisture, attic insulation and wood do not go well together.  A perforated radiant barrier will allow moisture to pass on through into the attic.  We want our attics to be cool and DRY.

Using a perforated radiant barrier will not change the effectiveness of the reflectivity.  Attic Foil has tiny pinholes about every ½ inch that allow for water in its vapor form to pass through (see picture).  These holes make up a TINY percentage of the surface area and will not change the effectiveness of the radiant barrier.

Solid products like bubble foil insulation are usually not perforated and are a recipe for disaster when installed inside an attic.  Solid (non-perforated) bubble foil is a great product when used correctly in applications like metal buildings.  The problem is that solid bubble foil products are often MISUSED in residential attics. This is especially true if the bubble type reflective foil products are laid directly over the attic insulation.  Moisture will pass through the sheetrock and will get trapped in the insulation below the bubble foil insulation.  This moisture will accumulate until it either condensates (turns to water) or freezes (turns to ice).

This is why it is critical to use a perforated tarp-like radiant barrier product. It will give you all the benefits of reflective insulation without the potential for moisture to get trapped.

I've written several other posts on this that you might be interested in. Check these posts below:

I put together a video to help illustrate how traditional attic insulation and radiant barrier WORK TOGETHER to make a home more comfortable and energy efficient.

Remember, traditional attic insulation – fiberglass or cellulose help to reduce Conductive Heat Loss.  A radiant barrier will help to reduce Radiant Heat Loss.  In cold weather, heat is lost in BOTH ways.

Combining good attic insulation and radiant barrier will give your home the best defense to stay warm in the Winter and cool in the Summer.

Click here to view the embedded video.

I've written several other posts on this that you might be interested in. Check these posts below:

I’m about to reveal the FOUR SILVER BULLETS for making your home more energy efficient in HOT CLIMATES. I’m especially talking about your typical one-story, ranch style home in the South.

Picture yourself sitting in your living room on hot August afternoon. The sun is beating down and it’s about 95º outside. What’s between you and the bazillion degree sun?
Four layers: 1) Roof 2) Attic 3) Leaking Ductwork in the Attic 4) Insulation
If you fix each “layer” between you and the heat from the sun, your home WILL BE MORE EFFICIENT AND COMFORTABLE EVERY TIME!!! Guaranteed. It is not complicated; just follow the recipe for success.

Radiant Barrier Installation

Layer #1 – Roof
Problem: It gets to be about 150º or more and basically acts like a big sponge to absorb heat. This heat is then radiated to the next layer.

Silver Bullet #1 = Radiant Barrier
Installing a radiant barrier is the next best thing to a giant tree instantly landing over your home. Your roof will still absorb the heat, but now rather than that heat being transferred to the home, it will be reflected AWAY.

Layer #2 – Attic

Blocked soffit vent blocks attic ventilation

Problem: Because most attics don’t have enough (or proper) ventilation, the AIR inside the attic basically gets “Clogged” like a drain in a bathtub. The air has nowhere to go and it just heats up and “fills up” the attic. Hot air in the attic will heat up the insulation AND heat up your ductwork that is supposed to have nice cold air running through it.

Silver Bullet #2 = Attic Ventilation
Attic ventilation is real simple. All you need is holes in the top and holes in the bottom. The more holes, the more outside (relatively cool) air moves through the attic and the cooler the attic air. The lowest the air inside the attic can go is near ambient (outside) temperature. The overlooked key to fixing attic ventilation is usually more soffit vents.

Leaking ducts in the attic

Layer #3 – Leaking Ductwork In The Attic
Problem: Putting Ductwork in the attic is about a dumb as making ice cream in the oven. Since you can’t move the ductwork, at least keep it from leaking. Most homes have duct leakage ranging from 15-50%. Older homes and homes with old metal ductwork usually have the highest leakage. What this means is that probably 25% or more of the cold air you are buying is being blown into the attic OR Hot dirty attic air is being SUCKED into your home if the leaks are on the return side of the AC system.

Silver Bullet #3 = Seal Ducts In Attic
If 30% of your water from your sprinkler were spraying into the street, you would fix it today. Why not do the same for your ductwork? Have your ductwork sealed or replaced. A tight duct system will save energy and increase comfort. Plus, indoor air quality will improve by reducing humidity and dust from being pulled into the home.

Attic Insulation being blown in

Layer #4 – Attic Insulation
Problem: Most homes do not have enough attic insulation to create a good thermal barrier between either the heat in the summer and the cold in the winter.

Silver Bullet #4 = Attic Insulation
Increase your attic insulation to the recommend level for your area. Check the DOE (Department Of Energy) for recommendations.

There you go. Four silver bullets for fixing your summer electric bill. Your attic is waiting.

I've written several other posts on this that you might be interested in. Check these posts below:

Click here to view the embedded video.

Looking for more videos on this topic? Check out my posts below.

Foil Under Shingles Will Not Work Unless There Is An Airspace On One Side Of The Foil.

At first it sounds reasonable.  You are getting a new roof, so why not scrape off the shingles, put down roofing felt, THEN radiant barrier foil and THEN shingles right on top.  What an easy way to install a radiant barrier, right? I also get asked if eShield, SolarGuard or Bubble Foil Insulation will work.

Unfortunately you just wasted time and money for NO additional benefit.

Radiant Heat by DEFINITION is electromagnetic radiation that travels in a waveform ACROSS a void, either an air space (or gas) or a vacuum.  Without this space you CANNOT have RADIANT HEAT.  Therefore, if NO radiant heat exists you CANNOT have a radiant barrier.

If you have items “sandwiched” together, you will get conductive heat. It is usually impossible to have radiant heat through solids. (some exceptions are transparent solids like glass, water etc.)

I keep hearing of some roofers starting to push products like Polaralum® and other types of foil coated roofing underlayments as radiant barriers.  This following quote is from the manufacturer’s website:  “During Summer Months Polaralum® acts as a radiant barrier on walls, and thermal barrier on roofing areas”.

Excerpt From a Manufacturer of Polaralum

Notice how they say “THERMAL Barrier” not “RADIANT BARRIER” under the roofing. Yes, this product is a thermal barrier.  In fact, a sheet of notebook paper is a thermal barrier to some extent.  The manufacturer states it correctly. It is NOT a radiant barrier if installed under (normal) roofing shingles.  Somehow roofing companies are misinterpreting this and selling it as a “Radiant Barrier” for this application.

If you are getting a new roof, beware of roofing companies who are selling radiant barriers under shingles.  Radiant barriers without an air space don’t exist, they can’t exist, and they will never exist.  They laws of physics always apply.  Remember:  No Air Space = No Radiant Heat = No Radiant Barrier.

Attention roofing companies: If you wrote on your invoice that you installed a “Radiant Barrier” in this method you should get ready. Customers & lawyers will be calling you soon starting with my neighbor who just got scammed.

If you are a roofing company who knowingly has been doing this – Shame on you. I hope you get sued and you go out of business.

If you are a roofing company and have done this by mistake – Contact the homeowners, and make good on your mistakes.

If you are a lawyer, feel free to go after the first group of roofers – it should be like shooting fish in a barrel and send me a referral fee.  It will be impossible for them to find a lawyer who can defend them since the definition of radiant heat is pretty indisputable.

Radiant Barrier Under Tiles with Required Air Space

What do you do if you are re-roofing and STILL want a radiant barrier? There is a way to incorporate radiant barrier foil into a re-roofing application.  The ONLY way is if you can create an air space on one side of the foil.  There are several types of roofs that have an air space between the roofing material and the roof deck.  Barrel-type tiles, or roofs installed over wood battens, which create the needed air space.

With these types of roofing systems, a radiant barrier can be incorporated easily and economically.  Simply roll out the low-cost roofing felt, roll out perforated radiant barrier foil, install battens as per manufacture instructions and attach roofing product.  It is also recommended to “notch” the battens or leave spaces between the battens to allow for more airflow between the roof deck and the roofing material.

This method of installing a radiant barrier is low cost, and very effective in reducing heat gain into the home.  Plus, it is profitable for the roofing contractor.  Homeowners will appreciate saving money and having a radiant barrier installed the right way.

Foil Installed Before Installing Standing Seam Metal Roof

Foil Installed Under Roof Using Battens To Create Air Space

Foil Installed Before Metal Shingles With Air Space

I've written several other posts on this that you might be interested in. Check these posts below: