Hi, just read your post. You must engage your own independant engineer to do a full bells and whistles survey on your property. The subsidence may be benign or it may be due to a fault with your foundations and if that is the case rectifying it is the responsibility of the building contractor. If you have a problem when the survey is complete you should then approach the builder to fix it under the supervision of your engineer. It is important to note that after six years of the property being signed off over to you the builder's liability ceases (under the statute of limitations act in Irish law) this means you are liable for any costs, so move quickly and get a solicitor involved if you have to.
Subsidence is a serious issue with implications for your services ie gas pipes if you have them and waste pipes, these can become stressed if the subsidence is severe enough and cause leakages! It will also scare away potential buyers who will run a mile if tell-tale cracks are pointed out to them.
I had a subsidence issue with my last house and missed all the signs as I was blind to them and totally green, when we went to sell it the sale fell through and I still own the house today.