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Most pitched roofs covered with tiles rely upon the ability to easily nail or screw components such as gutter brackets, snow guards, telephone cables, television aerials, soffit boards, over fascia ventilation systems and interlocking tile eaves clips to a structural or semi structural piece of the roof. A fascia board, whilst not as structurally important in a roof as a rafter or a purlin, should be considered as a semi structural member. If timber fascia boards are replaced with another material, such as UPVC, there can be compatibility problems.

UPVC fascia boards can cope with heavy components, such as overhead telephone cables, when they are fixed through the material and into the roof structure behind. Light weight components can be fixed into the rigid UPVC outer skin to give an acceptable fixing. Where tensile loads such as wind forces on interlocking eaves tile clips are fixed into the top edge of the fascia board where there is no rigid plastic skin, the foam core is likely to be inadequate. 

Foam core
The open foam core on the top edge of the fascia board provides less resistance to nail or screw pull-out than with softwood, even with the best high-density foam. To my knowledge no UPVC fascia board manufacturer provides pull out tables for nails and screws into their products to allow designers to decide if the resistance is adequate, or to compare it with the nail or screw pullout resistances quoted in BS 5268.

Grill fixing
Where 9mm thick fascia board is used to over clad existing timber fascia boards, some over fascia ventilation grills, designed to lip over the front edge of the fascia and nail into the middle of a 19mm timber fascia, may be compromised.

With a 9mm thick UPVC section the nail fixing designed to pass into the centre of

The eaves clip is nailed through the over fascia grill into the UPVC fascia board. The ability of the eaves clip to hold the eaves tile down is directly related to the grip of the foam core on the nail. (Fascia board supplied by Project Plastics)

 a 19mm timber fascia board will inevitably pass down the back face of the UPVC fascia and provide no fixing at all.

To overcome the majority of the structural and dimensional problems, the fixing of a traditional solid timber tilting fillet, as used with open rafter eaves details, should be employed, making allowance on the tile overhang for the fascia board thickness. Tile the roof as normal and ensure the plastic fascia board is put up afterwards. This has the advantage of ensuring a good mechanical fixing, allows you to determine the correct tilt fillet height, ensures you are not delayed by other trades, and ensures the self finish of the UPVC is not damaged during the roofing works. 

However, putting the plastic fascia up after an over fascia vent grill system has been installed requires the top of the fascia board to be chamfered, or kept clear, to ensure that the air volume into the grille is not restricted.


Compiled by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove, Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774
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