I settled on about a foot of depth enough to keep it well buried but obviously it will still freeze in winter.
How deep to bury gutters.
Dig a trench along the desired route of the drain pipe.
Along the entire area where you plan to install the drain pipes dig a trench around 12 to 14 inches deep.
Dig a trench about 6 inches wider than the drain pipe you plan to bury and dig the hole deep enough so that the drainpipe sits 3 inches below grade.
If your yard is flat or doesn t naturally have the desired slope dig the trench deeper as it extends away from the house to create the slope.
Create a fall of 1 8 inch per foot of drain line.
The deeper the trench you can dig the better.
Lay the downspout drain pipe in the trench.
Make the trench the same width as the downspout pipe and about 12 inches deep.
We found that the trench needs to be 10 12 inches deep with about a 2 inch slope.
And the length is how long you want it but far enough away from the building we decided we did not want less than 5 feet.
First thing first dig a trench.
Dig the trench 15 inches wide down the entire length.
Step 1 dig a sloping trench from your downspout to a point 8 feet away.
The end of the trench next to the house will be 18 inches deep and the far end will be 30 inches deep.
As a consequence the pipe trench will be quite shallow at the beginning and much deeper at the end.
I live in minnesota and the frost depth last year was 7 way deeper than i could ever dig my trench.