2 taxes involved here - stamp duty and, potentially, Capital Acquisitions Tax on the market value of the site.
The site should be formally transferred and details of that registered. The transfer is effective on execution of the deed on an agreed closing date when ownership is to pass. Stamp duty is payable on the deed - on 40K, the rate is 4%. 40K for any site sounds very low - you should make sure you have a formal valuation from a reputable auctioneer to show Revenue if they query it.
If the site is transferred only into the child of the parents transferring ( as opposed into the names of the child plus the spouse) stamp duty will be half the normal rate. However, if you subsequently plan/expect to obtain a mortgage, your then lender may want the property in both names.
There may be a possibility of a site transfer exemption from stamp duty - check revenue website.
The CAT threshold for family is quite high ( about 600K?) so unless there have been very substantial gifts/inheritances, on a transfer from parent to child, it is unlikely that CAT will arise. However, if transfer is to both child and spouse, CAT may apply as rates between non blood related parties have a lower threshold.
And you should take proper legal advice, obviously.
mf