Geneva has a law, the loi sur les démolitions, transformations et rénovations (LDTR), which fixes rents after a significant renovation for three years, ie the rent has to remain the same as before the renovation for a period of three years after the renovation.  This means that if the owner of the apartment has to retroactively apply for building permission because they did not do so at the time, the difference between the original rent and the current rent (assuming this is higher than the previous rent before the renovation) needs to be reimbursed to the tenant who has been paying the higher rent, for the whole period from when the new contract started until three years (or until the date the tenant moved out, whichever happens first). 

I first heard about this at ASLOCA and after just over two years received that reimbursement from my régie.  If your apartment was renovated just before you moved in and the green sheet of your contract indicates that the previous rent was lower than the new rent in your contract, you can check on the http://etat.geneve.ch/sadconsult/ database (click on Connecter to enter without a password.  Use the drop down menus in the lower section for your Commune and street) if there is an entry against your address. Note that the permit could have been applied for months before the actual building works, so go back a year or so.  If there is none, chances are that there was also no application for a building permit. 

You then need to write to https://www.ge.ch/construction/demarches-prealables/autorisations-construire.asp, providing a copy of the contract (very important: the green sheet that shows the previous rent and the current rent, photos, any evidence of renovation works – eg I had photos of the building works going on when I had visited the flat before renting it). 

After the letter I had to follow up with the council by phone as I initially received no response, but then a case worker came to see my flat and took photos.  The process then continued directly between the council and the owner (actually the régie as their legal representatives) and I was not involved beyond the first letter.  I basically presented my letter to the council as an enquiry into wanting to know the reason for allowing a rent increase as I thought my apartment would be subject to LDTR (this was a subtle difference that allowed me to respond the régie´s aggressive phonecall after they had been contacted by the council by saying that I was just asking and I had not “denounced” them with the council as the lady suggested). 

The council tells the régie/owner that they retroactively need to apply for building permission and need to supply all paperwork.  The process is described somewhere on this page https://www.ge.ch/construction/demarches-prealables/autorisations-construire.asp.  It is legally a case between the council and the flat owner (in my case through the régie), not the tenant ,and the tenant no longer needs to provide anything, nor testify, etc.

Once the building authorisation has been issued retroactively by the council, the owner can appeal the decision (which apparently they usually do to try to get out of paying the reimbursements, and usually lose the case if it is obvious that there were significant renovations).  The owner then has to reimburse the tenant the difference between the old rent and the new rent for the period they were in the flat, up to three years. I was told the last instance of control is the council confirming with the owner that they have actually reimbursed the rent difference.

The process does not have a time limitation (that´s what I understood at least, as I sent my first letter a year after moving in), but it takes time: I sent the letter in March 2012 and only got confirmation letter from the régie that a reimbursement was due in December 2013 and I had to follow up with a polite reminder to the regie a few months later. However, the council worker was happy to keep me informed on the process when I called a couple of times to follow up; they see this as another means of keeping rents under control and not jumping every time a contract changes, which then allows general upward “market value” adjustments in rents. 

I had moved out before the first three years were up and got reimbursed for the period I was in the flat. Technically after three years they can raise the rent I think (check with Asloca if you can then contest the rent increase – I don´t know as this did not apply to me).

Luckily beyond the first phonecall from the régie I was not bothered again. I´m surprised my régie was renovating without permission as otherwise they were extremely professional and any other issues were immediately resolved. And even at the time of moving out and finding a replacement tenant they were always very helpful.  

You might want to check with ASLOCA about your rights if your régie starts bullying you, and also if you are on a fixed contract that is up for renewal it might make sense to wait until your contract becomes a rolling contract or has just started a new period (ASLOCA: http://www.asloca.ch/asloca-gen%C3%A8ve). 

I understand this law applies to Geneva, but maybe Vaud has something similar.  In any case, there is not an equivalent law in other cantons (your local tenant´s association and the internet are your friends…).

A good description and examples are at  https://www.ge.ch/construction/pdf/formulaires/notice_ldtr.pdf

Note that I am not a lawyer and accept no responsibility for anything you do based my post – it is just a piece of information that you can use to see if this applies to your flat.  

If you might be in this situation, good luck, be patient and trust the system to get a bit of money back at the end.  It can compensate for the excessive rents in Geneva.  I did it all in French, but my French is far from fluent, so don´t let that discourage you!