teeing into cold water feed?

[doityourselfer]

Hi all, i have a quick question, i hope its not too stupid! I want to install a garden tap and washing machine from an extension. However only cold water pipework avalible in extension is the cold water feed leading directly into combi boiler. Can i tee into this pipework, or will it affect pressure? and if i can tee into for outside tap and washing machine, is there a minimum distance from boiler before i can make first connection? any advice would be appreciated. Thanks

 

[kevplumb]

turn the water off first then do it
dont forget the double check valve on the os tap