Raeding blank cells as zero values

Hi,

I have two cells which I want to add. But one or both cells may be blank. I want the value of any blank cell to be read as zero.

I have attached a simplified attempt to get this to work using =IF(OR(A1="",B1=""),0,A1+B1) but this gives a zero value for the sum if either of the cells being summed is zero.

Any ideas,

Thanks,

Shane