Reroofing with a new roof over an older roof is becoming more of a common practice, especially if you have an asphalt shingle roof and you're adding a different type of roof (like metal or tile) over it. This is also the time to make sure your new roof is going to perform at its optimum capacity and you'll likely only get one chance to get it right. That's why using single-sided RoofingFoil™ during this process is useful, it will give all the benefits of a traditional underlayment, but it has an additional benefit of being a radiant barrier too.
If you have an existing shingle roof and you're planning on adding a metal roof on top of the shingles without doing a tear off of the old roof, then this is how you should do it.
- Perforated, single-sided RoofingFoil™ radiant barrier
- Wooden battens/furring strips (1x's or 2x's) - not pressure treated
- Roofing cap nails (nails with a plastic washer attached)
- Corrugated metal roofing panels
- Metal fasteners for metal roofing
Step 1: Step 1: Apply Radiant Barrier Over the Old Shingles
Considering the cost alone of a new roof, the radiant barrier is a no-brainer add-on. When you are adding radiant barrier foil over an existing roof, you need to use the perforated foil. The perforations allow the foil to breathe and they prevent moisture from getting trapped between the old roof and the foil layer. The perforations are tiny little holes that will allow the moisture to pass through, yet they are still small enough to provide a secondary waterproof layer against liquid water.
The foil side always has to face an air space in order to work; if the new roof will be on a batten system, the battens will create the necessary air space (we recommend no less than a 1/2" air gap). Unroll the single-sided RoofingFoil™ with the foil side facing up, toward the sun. Use roofing cap nails to secure the foil edges to the old roof. Since the battens will go on next, you don't have to worry about securing the foil too much, the battens will really hold it in place. Start at the bottom of the roof and work your way up to the peak with the foil, overlapping seams a couple of inches along the way (no need to tape the seams).
If the roof will not use battens, then you will want to secure the foil a littler better than if it were using them.
Once all the foil is in place, your'e ready for the next step.
Step 2: Step 2: Install the Battens/Furring Strips (if Using) Over the Foil
After the roof is covered with the RoofingFoil™, it's time to install the spacers (furring strips/battens) to the roof. How you install battens can affect the how well the roof drains and cools, so make sure you consider that when you're adding them. Additionally, the battens will create the air space that is required for the foil to work to reflect radiant heat back. A simple batten system where the strips are staggered horizontally or spaced apart will work too. The main idea is that you want a system where air can easily flow and water can easily drain.
The RoofingFoil™ is strong and will not rip or tear. So you can walk on it as you're installing the battens without worrying about destroying the product. Get the battens in place and then you're ready for the final step!
Step 3: Step 3: Add Metal Roofing Panels
Now that you have covered the old shingles with the RoofingFoil™ and secured the battens on top, you're ready to add the roof on!
Secure the metal panels using the fasteners and finish the roof installation.
With the addition of a radiant barrier ABOVE the roof deck, the bottom of the roof deck should be close to ambient temperature (this assumes you have decent attic ventilation). This means you will eliminate virtually ALL the radiant heat that would come off the deck with traditional black felt underlayments.
Watch the 1 min video below to see how RoofingFoil™ works to block the radiant heat from getting in to your attic and, ultimately, your home:
The result is a high-performance roofing system that reduces radiant heat gain by 97%! That means no matter what type of metal or tile you choose (including color) the radiant barrier will block 97% of the radiant heat from the sun from getting through the roof and into your home. Your home will have immediate energy savings, and be more comfortable year round.