def find_y_overlap(rect1, rect2):
	"""
	Return bottom_y and height of overlapping y of two rects
	"""
	r1bottom = rect1['bottom_y']
	r1top = r1bottom + rect1['height']
	r2bottom = rect2['bottom_y']
	r2top = r2bottom + rect2['height']

	highest_start_point = r1bottom if r1bottom >= r2bottom else r2bottom
	lowest_end_point = r1top if r1top <= r2top else r2top

	if highest_start_point < lowest_end_point:
		return highest_start_point, lowest_end_point - highest_start_point
	else:
		return None