Do I need a carpet underlay?
If your new carpet is of a secondary backed, jute backed or ‘action back’ type, the answer is probably yes. These carpets are intended for use with a separate underlay, except in certain commercial installations where the carpet can be glued directly to the sub floor. If your new carpet has a textile or felt backing, these can be laid directly to the sub floor, so saving on cost, this option will however give you less comfort and energy efficiency, the latter due to increased heat loss through the floor. Another downside to laying these carpets without an underlay is that carpet gripper cannot be used to stretch the carpet to the shape of the room, often giving a less precise finish to the installation.
Can I re-use my old underlay?
Re-use of old underlay is generally not recommended; it may look fine at this stage, but could fail during the lifetime of the carpet, rendering any guarantee on the carpet as invalid.
How much should I pay for underlay?
The answer to this one is “As much as you can afford to.” Underlays do vary in quality and suitability, but generally speaking, when comparing ranges, the more you pay for the underlay, the better the quality it will be, giving extended life to your carpet. That said, before you spend out on that new underlay, do compare prices, as the internet based companies are often just a third of the price that you would pay to one of the ‘big’ carpet stores.