With the majorit of the images I take, any section of the image that is slightly underexposed turns to the red grain as you can see on the bottom of the balconies in the image above. Is there a setting I can change or is it just what the Canon 70D does?
It was bright sunlight with no clouds, I was standing in the shade.
And, the building face is not in direct sunlight. The sky is totally washed out.
I think your shot just might have too much dynamic range. Are you familiar with HDR captures?
Here is one. Exposing for the background was too dim to capture the foreground. Exposing for the foreground was too bright for the background. I took three shots -2, 0, 2 Ev.
The DR of that shot is not extreme. It is drastically underexposed. Try the shot again with a more correct exposure and see if it helps. But first reset your camera to default settings. Otherwise call Canon and schedule a C&C. Tell them the problem you are seeing.
HDR, "..but dont know how to take them in camera"
Very simple and any camera can do it. Some cameras can do it automatically. Check your manual. Essentially you take three or more shots each with a slightly different exposure. For instance take a 1 stop underexposed, correct exposure and a 1 stop over exposed. I prefer to use Lightromm or Photoshop to merge the three, or more, shots together.
I hope your sensor is not failing.
This is really not a whole lot of post processing. All I did was click [AUTO].
My guess is that 70D reads out 4 columns at a time and one of them is defect. Search for Weird stripes on 5D mark II raw. The sky has a maze pattern same as some 7D and 5D II. Green Equilibration in RawTherapee solves that.
Bayer pattern from your 70D below:
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