Recommended answer
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.