Rafter Guard Rail Most suited to houses where the roof has a pitch of between 15 - 32 degrees. Perimeter Guard Rail To be used on steel framed buildings which have exposed purlins. Deck Guard Rail Designed for installation after the roof has been laid. Clamps attach to roof ribs. Bolt on Clamp on Guard Rail Provides additional option of erecting a guard rail to concrete parapets or brickwork.