Chicks at what age can you put them outside

Hi i am new to this forum. I have two welsummers one hen and one cockerel both of which i hatched last year. I seemed to have had better success this year and have 6, three week old chicks, i also have another 11 fertile eggs in the incubator due to hatch in a weeks time.  The 6 are getting very big and i cant seem to find out when the ideal time is to put them outside in the hen house (separate from the others of course). Can any one advise. We live in the Channel Islands south off of  the Uk, we have no foxes, or badgers. 

I do like welsummers, nice birds

Usually growers can be off heat at around 6 weeks or when fully feathered. I have a small shed outside I keep growers in, and have heat in there this time of year just at night from about 3-4 weeks then, at around 5 weeks only at night so by 6 weeks fully off heat as long as the weather is nice and mild.
Would keep them in a well protected covered run as Kate suggests though!