EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Inflight Event / Encounter Other / Unknown
General None Reported / Taken
Environment - Non Weather Related; Procedure
We were cleared into position and hold on Runway XL at ZZZ while downfield a B787 was cleared to cross XL and hold short of XR. We were subsequently cleared to takeoff from XL once the B787 cleared our runway. As we accelerated down the runway we passed behind the B787 as they were cleared to cross XR and increased their thrust. Our fairly light aircraft nearing rotation speed was rocked considerably by this thrust. Had we been going faster or weighed less; we might have had more significant control issues. The cause was the above idle thrust or even just the idle thrust of the large aircraft holding between the runways at or near the rotation point of our smaller aircraft's takeoff run. I don't know if they were cleared to cross XR as we passed behind them and they increased thrust or if this was just the idle thrust; but either way it was more than was appropriate for our operation. Either do not hold large aircraft between runways while clearing subsequent (smaller) aircraft for takeoff while passing behind them; or ensure that they do not increase thrust above idle while an aircraft is taking off behind them.
ERJ-175 Captain reported the aircraft was rocked on the takeoff roll by jet blast from a taxiing B787.