Dear Simran,
No need to transfer the plot of land in son's name as he still be eligible to get the benefit of loan for construction of house.
Answer is in the charging section itself - Sec 22 -
The annual value of property consisting of any buildings or lands appurtenant thereto of which the assessee is the owner, other than such portions of such property as he may occupy for the purposes of any business or profession carried on by him the profits of which are chargeable to income-tax, shall be chargeable to income-tax under the head “Income from house property”.
For computing income underhead house property - it is not necessary that assessee should also be the owner of Land since the "conjunction" used between the two words is "OR"
Now if you think that the same way "land" alone can also be computed under House property then I am afraid the answer would be "NO" - since the word "land" is used in a context i:e appurtenant to building.