You use pipe brackets. These brackets are made to order and space the awning brackets off the wall the depth required to miss the downpipes.. There are however 2 options generally..
Your first option, if the downpipe is only partially in the way of the awning by a small amount is to get the downpipe redirected to the side at higher level leaving a clear space where the awning cassette is to go.
The second option is to use a pipe bracket spacer system. These are very sturdy box section brackets made to order and fitted to space out the awning the required depth which varies from different pipes in Upvc, aluminium or older cast iron types. They can also be used for other obstructions such as chimney breast protrusions, fan outlets and other items.
We ensure there is a bracket fitted at every required key point depending on the size and model of awning ordered. Once installed there will obviously be a larger gap down the back than normal and this is sorted with most higher end awning manufacturers using an aluminium profile section fitted to the top of the awning cassette and sealed back against the wall to make sure all the rainwater is directed to the front.
Brackets and top cover profiles are always matched to the same colour as the awning cassette chosen.
See in the images below the use of quite large gutter brackets to get this very large Markilux 5010 awning installed. The awning is actually a coupled system (larger than 7 metres wide) with the optional drop down front valance so is a very heavy awning indeed.
The brackets have made the awning cassette forward of the downpipes and then sealed from above.
See underneath the awning a sealed awning back to the house wall