If you’re installing laminate flooring, you’ll need to decide if you are going to use a laminate flooring attached underlayment. Here are some things to consider if this is something you need.
The most common reason to add an underlay to your laminate flooring is to reduce noise. Being a "floating" floor, laminate floors can sound hollow when walked upon. It can also creak and squeak in spots. Attaching an underlayment will help to decrease noise.
Most underlayment will offer a moisture barrier. This is great in bathrooms or kitchens where moisture can be an issue. However, most laminate flooring offers some level of moisture protection. A cheap underlayment won’t increase moisture protection by much.
Adding an underlayment can help with any imperfections in the sub floor. If you lay it on a concrete floor, the underlayment will cover some of the cracks and dents that often form in concrete. The underlayment will make a more even surface. However, if your sub-floor has many large dents or cracks, the underlayment will make little difference.
If you choose to use laminate flooring with an attached underlayment, you will be eliminating some minor annoyances. Analyze your sub-flooring to decide if an attached underlayment is worth purchasing.