Translations:UEFI - Install Guide/86/en

An entry can be added to

/etc/grub.d/40_custom

menuentry 'Windows8 (UEFI)' {
insmod ntfs
set root=(hd0,gpt4)
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
boot
}

In this case (hd0,4) or /dev/sda4 is the EFI System partition where the Windows bootloader is present.