What was found
CLIMBING THROUGH APPROXIMATELY FL210, RECEIVED AN ECAM ADVISORY FOR CAB VERTICAL SPEED. REDUCED AIRCRAFT CLIMB RATE BUT CABIN ALTITUDE CONTINUED TO CLIMB RAPIDLY. LEVELED OFF AT FL280 TO CONSULT QRH FOR ADVISORY. AROUND SAME TIME RECEIVED AN ECAM EXCESS CAB ALT ADVISORY. DONNED OXYGEN MASKS AND INITIATED A DESCENT. EMERGENCY WAS DECLARED AND CONTINUED DESCENT TO 10,000 FT. CABIN ALTITUDE PEAKED AT AROUND 13,000 FT. RAN ECAM AND QRH. DURING THIS EVENT BOTH OUTFLOW VALVES WERE SHOWING FULLY CLOSED. HEARD A LOUD AIR NOISE FROM THE LOWER RT OF FLIGHT DECK, SUBSIDED ONCE AIRCRAFT LEVELED AT 10,000 FT. DIVERTED. R & R INBD EXTRACT VALVE IAW AMM 21-23-12-04.