re turfing my lawn

i am going to re turf my lawn and i have been told by a friendly gardener that i can put the new turf on top of the old turf.
will this be o.k some how it does not sound the right way to do it .
i would greatly appreciate any advice.
cheers and many thanks.

 

I wouldn't do that - though the old grass will rot down, it takes time. Also all the weeds of the previous lawn will just grow through. Far better to remove the old turf and prepare the surface properly prior to returfing.