Tilt fillet or proprietary eaves ventilator?

On a tiled roof, all the tiles are fixed onto battens with the bottom (lower end) of each tile resting on the top of tile in the row below. At eaves level the last row of tiles (that ends above the gutter) doesn’t have a tile or batten to rest on. Without support this causes the last row to hang 20mm or 30mm lower than the rest of the roof, the tile cantilevers and pushes the tile above up.

To prevent this, a piece of timber triangular in section is fixed to the rafter and goes beneath the roof membrane, rather than on top like a roofing batten and lifts the tile parallel to the tiles above. This is known as a tilting or tilt fillet.

A preformed under tile eaves ventilation system is fitted in the same way beneath the roof membrane and also lifts and supports the tile throughout the length of the eaves.

Why do we need this support at the eaves?

Aside from looking unsightly, this is a crucial part of the roof where any water discharges into guttering. A roof membrane...

• acts as secondary protection to the roof tile
• collects any condensation that forms on the underside of roof tiles and prevents it dripping back into the roof
• prevents wind driven rain and snow from being blown into the roof
• keeps the building dry until the last ridge tile is fixed during construction.

In each case the water that collects on the membrane drains down to the lowest point, which should be the gutters, unless something prevents its progress.

Because the membrane is flexible there is potential for it to sag under its own weight unless it’s supported. Even if the membrane is pulled tight during installation, in practice it stretches and shrinks with temperature changes and wind movement, creating slack.

The only way to ensure that water does not collect in the sag of the membrane and runs into the gutter is to support it with a rigid timber or plywood board between the top of the fascia board and the first tile batten for the full length of the fascia board.

The use of a preformed plastic support tray, either as part of an eaves ventilation system or as a direct replacement for the tilt fillet, will provide some support. Any support needs to be both deep and capable of spanning up to 600mm between rafters. The tiles shouldn’t be just rested on the fascia board as that is not what it is for, it’s bad practice, and makes replacement fascia work harder.

The tell-tale signs of lack of support to the membrane or a back fall away from the fascia at the eaves are water coming through the soffit, especially under valleys, hips and any side laps in the membrane.

So tilt fillet or proprietary eaves ventilator? It doesn’t really matter as long as either is present and preventing a latent defect from occurring.

Disclaimer:  

Every care has been taken to ensure that the above content is correct at the time of publication.  Any reliance on the content should be verified by the dutyholder(s) and their professional advisers.  It is the responsibility of the dutyholder(s) and/or person carrying out the work to ensure compliance with the relevant building regulations and associated legislation.

This content is given in good faith by LABC.  It is not definitive, and compliance will be a matter for the relevant building control authority to decide as the enforcing body for the building regulations, and ultimately for the appropriate tribunal or court to determine.  

LABC – Application and use of Member Guidance Notes   LABC is a membership organisation, providing guidance and support to its member local authorities around England and Wales. LABC is unable to comment on the application and enforcement of the Building Regulations or other building safety related legislation to a particular proposal, as this is a matter for the local authority in whose jurisdiction the building work is being carried out or, in the case of High-Risk Buildings (HRBs), the Building Safety Regulator (BSR) and for the courts to rule upon.  

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