Hi Peno, welcome to the rollercoaster of negative trade ups! My expeirience so far has been this..
Put apt up for sale in May and received close to asking from cash buyer of €121,500. Saw a house for €200,000. We had the 10% deposit for the mortgage so NE of €45k. When we were close to closing sale of apt it emerged the house contracts would not be ready in time so the bank agreed after much negotiation to let us proceed with the sale and release the deeds to new buyer. We sold apt in Oct. We were allowed sell on certain conditions mainly being that we had 12 weeks to complete purchase of house. We also had to lodge €15k into a deposit account which they can absorb back into the NE if we do not go ahead with the purchase, so it's used as collateral. If we do not complete the purchase the remaining €30 will be converted into a personal loan and we will not be in a position to apply for a mortgage for a long time again.
We approached the banks and asked for the 12 weeks timeline and offered €20k collateral, it went to a credit forum in the bank and our solicitor also had to give an undertaking to the bank that he understood the implications of all this.
We are now in the process of drawing down the mortgage, our deadline is up in 3 weeks.. We began that process 2 weeks ago but they lost some of our paperwork and it was only sorted yest! We are with BOI.
Hope this helps