"IKA is the largest Social Security Organisation in Greece. (...)  IKA covers those in dependent employment in Greece or abroad for an employer who is based in Greece, as well as those who offer full-time or part-time personal labour on commissioned work agreements and are not insured with any other Main Insurance agency."

Your engineer will prepare the estimate for the minimum number of NI stamps required for the construction of your house and along with other documents and plans that will be submitted to the Town Planning Authority (to obtain the Building License) he/she will also submit the NI stamp budget to I.K.A. This budget is based on specific legislation and is decided by the sq.m/surface of the various house sections and also the method of construction used (i.e. stone house, conventional house with bricks and mortar, prefabricated house etc).

How we estimate the IKA stamps
For conventional constructions the NI stamps are calculated according to the sqm of surface of your house multiplied by the following coefficients:

Free area PILOTIS: 0.62
Underground utility areas: 0.86
Covered ground floor parking areas:0.59
Semi-covered areas:1.03
Swimming Pool: 0.89
Open(uncovered) areas:0.06
Other surfaces MAIN AREAS:1.35

All you need to do is to multiply the aforementioned coefficients by the relevant sq.m to produce an estimate of the minimum IKA stamps that you will need to pay to IKA up to the completion of the house cosntruction.

For example:
We have a 500sqm plot with building coeffient=0.05 and ground coverage coeffient=0.25. We intend to have 2 floors of 125sqm each and additionally 50sqm of semi-covered areas and a100sqm basement. We do not intend to have a pilotis or a pool. The garage will be in the basement and our construction will be conventional.

0.8X100(Basement) + 1.03X50(Semi-covered areas) + 0.06X375 (open areas) + 1.35X250 (Main areas) = 421 stamps

If you calculate on average 61.93€ for each stamp that will give you 421 stamps X 61.93€/stamp=26.072,53€