Think of roof underlayment as a second line of defence for your home, sitting directly beneath your roof tiles or slates. It's a protective layer, usually a membrane or felt, that's installed over the roof decking before the visible roofing material goes on. Why is it needed? Well, even the best tiles can sometimes let in a bit of moisture due to wind-driven rain or snow, or even just condensation. Underlayment is there to catch any of this and channel it safely down to your gutters, preventing it from reaching the timbers of your roof structure and causing rot, damp, and costly damage. For homes across Kent and the South East, with our variable weather, underlayment is absolutely essential for a long-lasting, healthy roof.

While your roof covering – whether it's tiles, slates, or another material – is designed to be the primary weather barrier, it's not always completely impenetrable. Think about those strong winds we get in areas like Crawley or Tunbridge Wells. They can drive rain up and under tiles. Also, tiles can crack or slip over time, creating gaps. Underlayment provides that crucial backup. Skipping underlayment to save a bit of money is a false economy. It's like not having building insurance – you might be okay for a while, but when problems strike, they can be far more expensive to fix in the long run. For peace of mind and long-term protection, underlayment is a must-have component of any properly installed roof.

There are a few main types of roof underlayment, and the best choice for your home in areas like Sevenoaks or Ashford will depend on factors like your roof type and budget. The most common types we use at Century Roofing and Building include:

• Breathable Membranes (Modern Underlayment): These are increasingly popular and for good reason. They are ‘breathable’, meaning they allow moisture vapour from inside your loft space to escape outwards, which helps to prevent condensation build-up within the roof structure. At the same time, they are completely waterproof from the outside, offering excellent protection against rain and snow. Breathable membranes are a fantastic choice for most modern roofs and offer superior performance.
• Traditional Roofing Felt (Non-Breathable): This is a more traditional, bitumen-based felt. While still offering a waterproof layer, it's not breathable. This means proper ventilation of the loft space is even more critical when using non-breathable felt to avoid condensation issues. Felt is generally a more budget-friendly option, but breathable membranes often offer better long-term value due to their enhanced performance and condensation control.
  We can advise you on the best type of underlayment for your specific needs when we provide your free, no-obligation quote.

Good quality roof underlayment is designed to last for a very long time, often matching or exceeding the lifespan of your roof covering itself (tiles or slates). Modern breathable membranes, in particular, are very durable. However, like any material exposed to the elements, underlayment can degrade over decades. If you're having a new roof installed, you can expect the underlayment to last as long as the new roof covering – typically 50-60 years for tiles or slates, and sometimes even longer.
When we carry out roof repairs in places like Rochester or Gillingham, we always inspect the condition of the underlayment. If it's damaged or deteriorated, we'll recommend replacing it, especially if it's nearing the end of its expected lifespan. Replacing underlayment is much easier and more cost-effective when the roof covering is already being worked on, rather than having to remove tiles later just to access and replace the underlayment.

It depends on the extent and location of the roof repairs. If we are only replacing a few tiles or slates in a small area, and the underlayment underneath is in good condition, it might not need replacing. However, if the repair work is more extensive, or if we find that the underlayment is damaged, torn, or has deteriorated in the area being repaired, then yes, we would recommend replacing it at the same time. It's best practice to ensure the entire roof system is in good working order, and replacing damaged underlayment during repairs in towns like Redhill or Reigate is a sensible way to ensure long-term roof health.