You can make an early withdrawal of retirement savings to buy a house, and thus increase your equity. This reduces the amount of interest you must pay each month. The amount of savings that you withdraw early is subject to tax and will influence the amount of your pension later.
You can also pledge your retirement savings as collateral to receive a better interest rate for your 2nd mortgage. This hypothecation is a substitute for equity and results in a larger mortgage. On the other hand, the amount that is pledged as collateral is not subject to tax and will not reduce your pension later.