Zonal Fixing Method

The Zonal Fixing Method is designed to provide a first-estimate method for obtaining a fixing specification for single-lap and double-lap tiles.

It first came about at the request of members of the NFRC who fit commodity products. Their concern was that each manufacturer seemed to have a different fixing specification for a similar tile on the same house types in the same area . The NHBC also requested a common fixing approach so it could easily check the fixing specification for similar manufacturer's products on similar house types in similar areas without retrospectively having to contact the manufacturer. Zurich wanted it so they had a datum to check an insurance claim for storm damage.

To reduce the numbers of variables that need to be considered a number of conservative simplifying assumptions are made:-

• The highest local roof area Cpt value from Table 6 of BS 5534:2003 is used. This assumes the lowest pitch recommendations as follows: 12.5º for single lap tiles; and, 35º for double-lap tiles.
• A site gradient of up to 10% and that the building will be at the top of the gradient.
• Counterbattens are not be used for the uplift values given in the approved tables, however,
• Where counterbattens are required then the uplift values have been increased by a factor of 1.25. 

These assumptions together with the resultant wind uplift requirements and the related spreadsheet calculations are calculated in accordance with BS 5534:2003.  

All manufacturers of roof tiles will provide tables of fixing specifications for their products to meet the wind uplift requirements given in this document.

Included in the scope of this guide are single-lapped and double-lapped clay and concrete roof tiles including ridges, hips, verges and valley junctions.

The Zonal Method does not apply:-

• For buildings where the site altitude is greater than 300m.
• For buildings on sites where the maximum gradient of the land within 200 m of the building is greater than 10%.
• Where the building is within 6 kilometres of an airport and is plus or minus 10 degrees each side of the runway centre line measured from the touchdown point.
• Where the ridge height of the building is greater than 15m.
• Where the roof pitch is greater than 54º for single lap tiles and 59º for double lap tiles.
• For buildings where the roof substructure does not provide a shielding factor of 1 as defined in BS 5534 e.g. the roof does not have an underlay or sub-roof system such as liner trays or sandwich panels.
• For tiles or slates not made of concrete or clay.
• Heritage, listed or historic buildings requiring restoration using traditional skills.
• For buildings on sites located in wind zones where the wind speed is greater than 25m/s i.e. Zone 3.

The fixing specification for the roof covering of any excluded site or building must be determined by calculation in accordance with the methods described in BS 5534 and BS 6399-2. 

Should you require a full fixing specification for your project, please download the form below and send to our Technical Department.