A tile roof can look perfect from the street and still let water into the house. That can puzzle owners, because the tiles themselves are hard-wearing. The explanation lies under them. On a tile roof, the tile underlayment does much of the waterproofing, and when water gets past the tiles, the underlayment and flashings are what keep it out. This guide explains how that works, what Florida’s tile installation manual requires, and how a leak under intact tile is traced and fixed.
Why does a tile roof leak when the tiles look fine?
Because tiles shed water rather than seal it out completely. Florida’s tile installation manual describes a tile roof as a water shedding assembly whose performance depends on every component being installed properly. Water that gets past or under the tiles relies on the underlayment and flashings beneath to keep it out of the house.
The Florida High Wind Concrete and Clay Tile Installation Manual, published by the Florida Roofing and Sheet Metal Contractors Association and the Tile Roofing Industry Alliance (FRSA-TRI), puts it this way: tile roofs installed for high wind regions make “a highly-effective water shedding assembly,” and the effectiveness of the system “depends upon the proper installation of the tile roof components.”
That makes a tile roof a two-layer system:
- The tiles shed most of the rain and protect what lies beneath from sun and impact.
- The underlayment and flashings form the barrier that keeps out water that gets past the tiles, at laps, valleys, walls and penetrations.
So a leak under intact tile points beneath the tile: to the underlayment, a flashing, or the details where the roof meets walls, vents and valleys.
What is tile roof underlayment?
Tile roof underlayment is the waterproofing layer laid on the roof deck before the tiles go on. Florida’s tile manual recognises two main approaches: a single-ply system of self-adhered membrane applied directly to the deck, and a two-ply system. The manual sets minimum standards for each.
Single-ply systems
The FRSA-TRI manual describes single-ply, or one-ply, systems as methods where a self-adhered underlayment is applied directly to the deck. It sets a minimum thickness of 40 mil for any self-adhered underlayment, in SBS, APP or an approved equal material.
The manual also sets standards for self-adhered membranes. They must have a minimum thickness of 40 mils, be tested for wind uplift under FM 4474 or UL 1897, and meet a minimum of 90 days of UV exposure according to their product approval. Those details matter because the membrane sits exposed on the deck while the tiles are being laid, and because it bonds directly to the sheathing. Ask your contractor which membrane they intend to use, and for its Florida product approval number, so you can check it against these standards.
Two-ply systems
The manual also covers two-ply systems, built up in two layers with a cap sheet. It includes a matrix showing which one-ply and two-ply underlayments are compatible with which attachment methods and flashing types, and when additional flashings and sealants may be needed.
The point for a homeowner is that underlayment is not one product but a system chosen to match the tile, the attachment method and the flashings. A contractor should be able to tell you which system they are using and why it suits your roof. The manual’s own preface notes that its recommendations aim to improve the long-term performance of tile roofing systems, which is why following it, rather than improvising, matters. A quote that simply says “underlayment” without naming the system is worth questioning.
Underlayment as a secondary water barrier
Some underlayments also serve as a secondary water barrier for insurance purposes. Florida’s wind mitigation form, OIR-B1-1802, credits a secondary water barrier where a self-adhering modified-bitumen underlayment is applied directly to the sheathing, and states that standard underlayments and hot-mopped felts do not qualify.
That means the choice of underlayment at re-roof can affect your wind mitigation report, not only how well the roof keeps out water. Section 553.844(2) also lists a secondary water barrier among the measures to address during re-roofing. If you are replacing a tile roof, ask whether the system quoted would qualify on the form, and ask your insurer what credit it earns.
Where do tile roofs leak?
Where water is concentrated or the roof is interrupted: valleys, the joins at walls and chimneys, around vents and skylights, at the eaves, and anywhere tiles are cracked or displaced so water reaches the underlayment directly. Those are the places a leak trace checks first on a tile roof.
| Area | Why it is checked |
|---|---|
| Valleys | They carry water from two slopes, and the underlayment is laid to overlap through them |
| Wall abutments and chimneys | Flashing must bridge the joint between roof and wall |
| Vents and skylights | Each penetration has its own flashing and seal |
| Eaves | Raised fascia can dam water, so the manual calls for an anti-ponding system |
| Cracked or slipped tiles | Water reaches the underlayment directly beneath |
The FRSA-TRI manual details how valleys and wall flashings are built, including that each course of underlayment overlaps the next at intersecting roof planes, and that raised fascia creates a water dam that needs an anti-ponding system at the eave.
How do you tell if the underlayment has failed?
You usually cannot from the ground. Signs that point to the underlayment include leaks under tiles that look intact, stains that appear during long or wind-driven rain, and water trails on the underside of the deck seen from the attic. Confirming it means lifting tiles in the suspect area, which is a job for a professional.
Useful clues before anyone goes on the roof:
- Where the stain is. Under a valley or near a wall points to flashing and the underlayment laps there.
- When it leaks. A leak that appears only in long or wind-driven storms suggests water is reaching the underlayment and getting past it.
- What the attic shows. Wet decking or water trails beneath an area of intact tile point below the tile.
- The roof’s history. An older tile roof that has not had its underlayment replaced is a natural suspect.
Does ventilation matter on a tile roof?
Yes. Florida’s tile manual says proper ventilation is recommended on all tile applications, and tells installers to verify ventilation requirements in the governing building code. Ventilation helps the attic and the underside of the deck dry out, which matters in a humid climate where moisture can build up beneath the roof.
The manual’s own inspection step reflects the same concern with moisture: before underlayment goes down, installers are to verify that the surfaces receiving it are uniform, smooth, clean and dry. Underlayment laid over a wet or uneven deck starts at a disadvantage.
When a tile roof is replaced, ask the contractor how the attic is ventilated and whether the existing vents meet the current code. Blocked soffit vents, missing ridge or off-ridge vents, and attic spaces that stay hot and damp are all worth fixing while the roof is open. Ventilation is set by the building code rather than by the tile manual, so the contractor should be able to point you to the requirement they are following.
Is it safe to walk on a tile roof to check it?
No. Tiles crack underfoot, and a cracked tile can let water reach the underlayment. The FRSA-TRI manual itself says installers should caution everyone against traffic of any kind on a finished tile roof, because damage to roof tiles and the sub-roof may result. Leave inspection to a professional.
Inspectors and roofers who have to move across a tile roof know where to step and how to spread their weight. Even so, every visit carries some risk of breakage, which is one more reason not to have the roof walked unnecessarily. From the ground, binoculars and photos are a safer way to spot slipped or broken tiles.
How is tile roof underlayment replaced?
By lifting the tiles, replacing the underlayment and any damaged decking or flashings, and relaying the tiles. Tiles that are sound may be reused, while broken ones need matching replacements. The new underlayment and flashings should follow the FRSA-TRI manual and carry product approvals.
The order of work, in outline:
- Remove the tiles carefully, and set aside those that can be reused.
- Remove the old underlayment and inspect the deck.
- Repair the deck where panels are rotted or damaged.
- Install the new underlayment and flashings to the manual.
- Relay the tiles with the attachment method the system requires, replacing broken tiles.
Ask each contractor what happens to tiles that break or cannot be matched, and to state it in writing. If your roof predates the 2007 Florida Building Code, also ask how Florida’s repair rules apply. Under section 553.844(5), only roofs built to the 2007 code or later get the exception that limits code work to the repaired part.
How long does a tile roof last?
The National Roofing Contractors Association says most roofs are designed for about 20 years of useful service and that clay tile can last longer, depending on climate, installation and maintenance. No source we can verify gives a fixed life for tile underlayment, so judge it by condition, not age alone.
For insurance, Citizens’ March 2023 bulletin describes roofs older than 50 years for tile, slate, concrete or metal, and requires five years of remaining useful life for roofs over the maximum age. It also bases roof age on the oldest part of the roof. A tile roof can therefore stay insurable for a long time on paper, while its underlayment still needs watching.
Does a leaking tile roof affect insurance inspections?
It can. Citizens’ sample 4-point inspection form asks for photos of each roof slope, the roof’s age and remaining useful life, visible damage such as cracked or missing tiles, and any visible signs of leaks in the attic, on the underside of the decking or on interior ceilings.
The 4-point form lists missing, loose or cracked tabs or tiles and soft spots in decking among the damage items an inspector records. A leak under intact tile can still show up through stained decking or ceilings. Fixing the leak and keeping the invoice helps if your insurer asks about it later.
In Orange County, Census figures show 82.9% of housing units were built before 2010, so many tile roofs in the area have been in service for a long time. If your tile roof is leaking, Residential Roofing Orlando can trace the leak and explain whether the underlayment, a flashing or the tiles themselves need attention. See our tile roofing service or call (407) 305-0865.
Frequently asked questions
These are short answers to questions homeowners search about tile roof underlayment. Each points back to a fuller section above. Do not walk on a tile roof to check it; Florida’s tile manual cautions against traffic of any kind on a finished tile roof.
Does a tile roof need underlayment?
Yes. Tiles shed water but do not seal it out on their own. Florida’s tile manual sets out single-ply and two-ply underlayment systems, and the underlayment and flashings keep out water that gets past the tiles.
What is the best type of underlayment for a tile roof?
The one that fits the tile, the attachment method and the flashings, chosen from the systems in Florida’s tile manual and carrying a product approval. A self-adhered membrane applied to the deck may also qualify as a secondary water barrier on the wind mitigation form.
What do roofers put under tiles?
Underlayment on the deck, flashings at valleys, walls and penetrations, and the attachment needed for the tile system, such as battens, fasteners or adhesive, as set out in Florida’s tile installation manual.
How do you replace the underlayment on a tile roof?
By lifting the tiles, removing the old underlayment, repairing any damaged decking, installing new underlayment and flashings to the manual, and relaying the tiles. It is professional work, because walking on tiles can break them.
