Adding values from two rasters

[DanielHenn]

Hello,

I'm having trouble to add values contained in two overlying rasters of different sizes. 

A simplified example of what I mean:

Raster 1                              Raster 2                                             Result

1 1 1 1 1                                                                                       1 1 1 1 1

1 1 1 1 1                                3 3 3                                               1 4 4 4 1

1 1 1 1 1                                                                                       1 1 1 1 1

So I would like to maintain the size of the larger raster set and basically just add the values contained in Raster 2 where they are present.

I tried a few things but it seemed like the biggest problem was that size was always adjusted to the smaller raster.

I'm not quite sure which GIS operations can be applied for this case (I'm quite new to the program).

Thanks in advance!