Two layers of underlayment are required for low-slope roofs. The first course is doubled. Above that, 36-inch wide strips are then applied to the roof in a shingle fashion, starting at the lower roof edge, and overlapping subsequent courses a minimum of 19 inches.
Many flooring manufacturers specifically advise against using more than one layer of underlay, as this can void the product's warranty. The extra cushioning places unnecessary stress on the locking mechanisms and joints of the floor, making it more likely to fail prematurely.
More is not always better, and with underlayment, too much can compromise the integrity of your floor's locking system. Adding additional underlayment under vinyl with an attached pad can create too much cushioning, which causes the floor to come apart through use over time.
You can't double up on underlay.
Doubling up can cause the floor or the underlays beneath to slide, again causing damage to your boards.
Other factors like type, sound ratings, and density matter just as much, if not more than the thickness. With that being said, most underlayments are 2-3mm thick, but are sometimes thicker for carpet or to smooth out an uneven subfloor.
Choosing a thick (10mm+) underlay for your stairs is not a good idea as it can pose a trip hazard. Moreover, thicker carpet underlays tend to compress slightly with heavy use, which can lead to irregular wear and unsightly lumps, particularly in frequently trodden areas.
9-10mm carpet underlays are usually good all-rounders that can be installed in all areas of the home, including stairs and hallways. This thickness is popular with homeowners who want to use the same underlay across their entire home/project, saving the hassle of ordering multiple products and minimising wastage.
Too much padding can make the floor too bouncy, which strains the laminate's locking system. If you are fitting a laminate floor with a pre-attached underlay to concrete though, it's a good idea to install a vapour barrier as well. This will help prevent moisture damage.
In steep-slope conditions -- that is, 4:12 and steeper -- upper courses of felt underlayment should overlap lower courses by at least 2 inches. Here, you can see the difference between the underlayment overlapped 2 inches on the upper roof, and overlapped 19 inches on the lower, less steep roof.
Step 4: Use a flooring underlayment to smooth out any remaining inconsistencies. A flooring underlayment can help to smooth out any remaining peaks and valleys in the subfloor and prevent problems down the line. However, remember that an underlayment can't work miracles, so don't count on it as your only solution.
Calculate the Underlayment Needed
If you go with type #15, you will need one roll per four squares, meaning 3.9 rolls for 15.6 squares. The pitch of the roof can affect how much underlayment you need. If you have a roof with a pitch greater than 4/12, a single layer is enough.
The answer will vary depending on the material used for the floor and the way that the boards are constructed, but, as a general rule, both Laminate and Engineered Timber floating floors do need some form of underlay to have optimal functionality and longevity.
The high cost of synthetic underlayment is due to its superior material strength and long lifespan compared to felt or asphalt paper underlayment. While the initial investment may be higher, synthetic underlayment can save you money in the long run by lasting longer and requiring fewer repairs or replacements.
For added strength and stability, a double-layer subfloor is often recommended. In this configuration, two layers of plywood are installed, with the top layer offset from the seams of the bottom layer. By staggering the seams, the subfloor's overall strength is enhanced, reducing the risk of deflection or squeaks.
No subfloor is perfectly level, but any signs of unevenness and high or low spots must be remedied. Please follow these requirements: Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span. Subfloors must not slope more than ½ inch per 6 feet (25 mm per 1.8 m)
Slopes 2:12 to less than 4:12
On all lower slope applications, cover the deck with two layers of ProArmor® Underlayment.
After all, the smallest mistake can cause the biggest mishaps for your roofing system and yourself as the homeowner. With that in mind, when replacing your roof, one of the things that you should make sure will be done is to completely remove and replace the old underlayment.
Very often, particularly in a below-grade installation on a concrete basement floor, a vapor barrier is recommended in addition to the underlayment. That vapor barrier would go between the subfloor and the underlayment.
If your planks already have a pad-attached underlayment, you most likely won't need an underlayment. However, if your flooring manufacturers installation instructions allow for an extra underlayment, adding an extra underlayment will provide improved sound reduction, insulation, and moisture protection.
Expansion gaps should be left around the perimeter of the floor around 10-12mm.
Underlay can last anywhere between 5 and 20 years. Foam and Felt underlay can last up to 8-12 years. However, if foam underlay isn't properly installed or maintained, it lasts only 5 years. Acoustic and rubber underlay have the longest lifespan, lasting 10-20 years.
Cut underlay into strips and braid them into tug toys, or create crinkly balls for them to chase. Warm and comfy pet beds: Upcycle larger pieces of underlay into snuggly beds for your pets. Add a layer of soft fabric for extra comfort.
Thickness
But as a general rule, the thicker it is, the better. Those around the 3-5mm mark are a great budget-friendly option and they will make a difference to the look and feel of your laminate. But they don't offer the same performance as a thicker underlay.
A 3mm underlay is ideal for flooring less than 18mm thick. This thinner option provides sufficient support without adding unnecessary height. For flooring that is 18mm or thicker, you'll need a 5mm underlay. This added thickness ensures better stability and cushioning for heavier or more robust flooring options.
A high-quality PU foam underlay is an excellent choice, as it offers superior cushioning, creating a soft and luxurious feel underfoot. It also provides brilliant insulation, keeping your living room warm and comfortable, especially during colder months.