Builder whay hours

I don't know if they are governed by legislation but they tend to start early ( 08.00 ) before it gets too hot, most I have used or seen work hard all day long although they might take a long lunch and then work until it is dark, they will work all year round but are busier in the cooler months.

Used to the heat. Sure others will tell. Villas

A lot of builders work all year round as they need to make a living!  many don't have the luxury of having time of in the summer.

As Willy correctly points out, for many will work out of the siesta times, but in general & in answer to the OP, especially mid-afternoon, and the traditional reason for the siesta is for the workers in the fields to shelter from the heat. They would then feel refreshed after their sleep and would work until quite late in the evening, longer than they would have been able to without the siesta.

While people do still work outside in Spain, this reason doesn't account for why shops and businesses in big cities should close down today. Indeed, offices can get hot too, but the invention of air conditioning has helped in this department. So why do they still do it? Answer, it´s traditional for obvious work hours including shops, car mechanics, etc. My female partner (in her 50´s) worked all day in the campo since 13 years of age. Her son´s (in construction) will testify the reason for the siesta, although I saw him only yesterday above a house laying concrete (in order to finish off) at 2pm (shouting down that he was hungry!)

       Desayuno (Breakfast): 7 a.m. to 9 a.m. ...

Almuerzo (Mid-morning snack): 10:30 a.m. to 11 a.m. ...

La Comida (Lunch): 2 p.m. to 3:30 p.m. ...

merienda (Mid-afternoon snack): 5:30 p.m. to 7:30 p.m. ...

La hora del aperitivo (Tapas Hour): 8:30 p.m. to 10 p.m. ...

La Cena (Dinner): 9 p.m. to 11 p.m

As a basic answer, therefore…...that is why.

Villas

Well explained nice one.