The general rule is that you cannot. Sharing ownership of a home with a partner whom you aren't married to is, from a legal perspective, exactly the same as sharing ownership with a person whom you are not romantically involved with.
The problem is this: In Switzerland there are rules which dictate who inherits pension benefits.
If you are married or registered partners, then you generally inherit the property and become its legal owner if your partner dies (and vice versa). This is compatible with Swiss providence rules because it ensures that you or your spouse have a place to live in your old age, which is what the second pillar is for.
But if you are not married and one of you dies, their portion of ownership in the house would normally fall under their estate, and their legal heirs could claim their minimum inheritance shares (Moneyland has a good article on this topic here: https://www.moneyland.ch/en/inheritances-switzerland-rules).
The only way to be able to keep using the property after your partner dies (or vice versa) is for you to give each other usufructuary rights to your home. This legal arrangement allows the other person to use the property even though they do not own it.
Giving usufructuary rights over a property to another person is generally considered to be on par with selling your property. Since you are not allowed to withdraw pension fund benefits to buy a property which you will sell immediately afterwards, you are generally not allowed to use benefits to buy a property with usufructuary rights.
There is an exception to this rule:
If your partner is named as the benefactor of your pension fund in your pension plan agreement, then you can use your pillar 2 assets to buy a home with usufructuary rights. The same applies to your partner.
Buying a home without usufructuary rights
If both you and your partner are able to name each other as the sole heir to the property in your legal wills, then you can generally use pension fund benefits to buy the property because no usufructuary rights are needed.
This could be done, for example if:
- Neither of you has any legal heirs.
- You have enough other assets to be able to satisfy the mandatory inheritance shares of legal heirs without your home being affected. In other words, the home falls under the portion of your assets which are not subject to mandatory inheritance shares.
- All your legal heirs relinquish their inheritance rights.