Loan for large rennovation

silverglider

We are hoping to extend our current falling down barn conversion in to existing brick barns and add outbuildings to the property. We bought the house at £347k and have about 65k equity in it, building works will cost £250k and if our other property sells we would need a loan for 150k of that (if it doesn't sell we will need the full amount). The property should be work about 700k once work is complete. We have combined salaries of 190k.

The initial plan was to start building work with the £100k from selling the other property and then remortgage the house being extended (as it would have gained value) to finance the rest, but for various reasons the other property cannot yet go on the market.

Is there any other option for a loan? Looking on line building loans seem to be for new builds only, extension loans are for up to 25k and we don't have enough equity to remortgage.