Dress code to visit Sagrada Familia

Is there a dress code specified for entering Sagrada Familia?

Yes.

The official website clearly spells out the dress code:

"In the space set aside for prayer and reflection in the Chapel of the Eucharist in the ambulatory and throughout the Altar zone, visitors may not enter wearing:

• Trousers, dresses or skirts that don’t fully cover the knees when
  seated or standing
• Shorts
• Sleeveless t-shirts, vests, tank tops, crop tops or other shirts
  exposing the belly or shoulders
• Plunging necklines
• Beachwear
• Transparent clothing

"

Thus dress code is applicable only if you are visiting the religious section of Sagrada Familia.