For heavy infestations like this we use a cob web duster on an extension pole first. Make sure you do NOT get the duster wet, I mean not even a drop of water on it. Also make sure that you very lightly run the duster over the surface. Don't use pressure like a broom, but just lightly skim over the surface. If you use to much pressure, you can mash the bugs/eggs and cause the bugs/eggs to smear on the surface. If you do this the stain will come out but just adds more work to it so use very light pressure. You will need a good stiff hand brush to keep the the duster clean and remove the build up from it. Once done with the duster, put it way out of the way, along with the cleaning brush, so that it has no chance of getting water on it cause you'll need again later. My guys know to take it off the pole and put it inside the truck with the cleaning brush till we need it later. They also know to NEVER lay it on the ground. We keep about a 1/2 dozen of these on hand.
On the top ceiling, when using the duster, run it from the wall out towards the street...this will help in getting the stuff out of the gaps of the siding...when doing the wall, go side to side for the same reason...
Once you have gotten most of the stuff off with the duster, use a combination of Roof Snot and just water. On something that big I work in small sections, say like column to column at a time. The Roof Snot makes the webs and nests very slippery and easy to move even without bleach. What your doing here is saving on using a lot of bleach when you really don't have to. Apply generously to the surface, I downstream it, and allow to dwell a couple minutes. (You don't want to let it dwell too long so it doesn't dry out. If it does fry out, sometimes even a little, just reapply and rinse quickly. You want everything wet for easier removal.) My feeling is the Snot is actually helping to pull everything away from the surface. Once you have done this then rinse using a high flow nozzle in small sections at a time, (you don't want a lot of pressure)and rinse down towards the floor, staying on top of all the stuff. The higher the GPM of you machine the easier this will be and faster it will go. Once you have removed as much as you can this way, go back and and add your bleach to the mix for a final clean. Then once everything is TOTALLY DRY, go back over with your duster and get any little strands that did not come off, and yes you will have some that you didn't. DO NOT promise the customer 100% removal. We tell them we can get anywhere from 85% to %100 removal. It just all depends on the surface. This being what looks like vinyl or aluminum siding you will get close to %100 removal. But under promise and over deliver.
Take plenty of before and after pics, put on the ipad, and go door to door, since this house is on a river, just about every home will have this problem.
Get this customer and all the neighbors set up on 6 month maintenance....we have many homes on lakes/rivers that we do this for as well as their docks. Tell this customer that for ones she refer's to you, she will get a discount on her 6 month maintenance cleaning.