Is roof felt actually waterproof

Question

Just wondering how much protection felt really gives under the tiles. Does it stop leaks on its own or is it more of a backup layer?

Robert · Answer

It’s a back up layer in the event of any broken damaged tiles

Liviu Adrian · Answer

Roofing felt (or modern breathable membrane) is not meant to be the main waterproof layer. It is primarily a secondary line of defence.

Its real jobs are:
	1.	Backup protection
If wind-driven rain gets under tiles, the felt catches it and directs it down into the gutter.
	2.	Condensation control
It helps manage moisture from inside the house so it doesn’t rot the timbers.
	3.	Dust and draught barrier
It reduces draughts, dust, and snow being blown into the roof space.
	4.	Temporary weatherproofing
During construction, it protects before tiles go on.

⸻

Can felt stop leaks on its own?

Short answer: No, not reliably.

Felt is not designed to be fully watertight long-term.

Problems with relying on felt alone:
	•	It degrades over time
	•	Old bitumen felt becomes brittle and cracks
	•	Staples and nail holes leak
	•	UV damage if exposed
	•	It can sag and pool water
	•	It can tear in wind

If your roof is leaking, felt should not be the thing keeping water out.

Thomas · Answer

Hello roof felt and insulation is so cheap.

Thomas · Answer

Roof felt (or modern breathable membrane) is water-resistant, not fully waterproof, and it’s designed as a secondary protection layer, not the main barrier.

Its role is to catch wind-driven rain or snow that gets past the tiles and safely direct it down to the eaves and into the gutter. Tiles and slates are the primary weatherproofing; felt alone should not be relied on to stop leaks long-term.

If tiles are missing, slipped, or the felt is torn or perished, water can still enter the roof. Older bitumen felt is especially prone to splitting over time, while modern breathable membranes perform better but still rely on the roof covering being intact.

At Quality Roofing and Guttering Ltd, we often find that leaks blamed on “failed felt” are actually caused by broken tiles, flashing issues, or poor detailing.

Anthony · Answer

It's a backup layer for when you have a broken tile, in the middle of the night for instance, and gives you time to get a repair done before your house and ceilings are damaged.

Ashley · Answer

Yeah it is but I would say use metal as it will last you a lot longer.

Malky · Answer

Yes as long as the membrane is installed correctly and not penetrated my the nails when slating/tiling up then it is waterproof. Without adequate membrane under the slate/tile the roof will susceptible to leaks and further damage. It is there to stop any AWOL water from reaching the main structure and the internal of your house. It is possibly the most crucial layer of your roof.

Tom · Answer

Roofing felt (or modern breathable membrane) is not designed to be the primary waterproof layer. It’s best thought of as a secondary line of defence, not something that should be relied on to stop leaks long-term.

Harvey · Answer

They say a roof could be exposed with new breathable felt for up too 6 months but it is a back up layer as the tiles is the main barrier for water too run off roof

John · Answer

The membrane underneath the tiles should be waterproof, although there is some brands under investigation at the moment as they have been proven not to be.

Having said this water should never penetrate through the roof to reach the membrane anyway, should never be considered as a backup.

If the roof is installed correctly when it comes to water ingress you don’t even need membrane

Is roof felt actually waterproof

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