Actually, if shorts are banned for male workers then they ought to turn up in kilts. These cannot be banned, especially in the UK, as the ban on wearing kilts, highland dress or clan tartan that came into force after the Highland massacres was repealed ages ago. Nowadays, quite a lot of younger Scotsmen wear kilts in other kinds of cloth than a clan tartan.
Frankly, I wouldn't worry about the builders' underwear if they are in skirts - anything is better than the inelegantly named butt crack displayed by so many men in trousers if they bend over or kneel down.