A
alexpau
G PACK You need 6mm screws to comply with BRE regulations on a 35mm rafter which HILTI sell and are approved under Eurocodes along with item - MSP-RHC-B HILTI ITEM - 435504
The issue is for example if the roof timber is 80mm wide then if you drill into the centre of the timber ie 40mm then the diameter of the drilled hole cannot be bigger than 10mm to comply with building regs this is partly the problem in why you cannot use hanger bolts for fixing slates as they will not allow for compliance with building regs in UK roof timber