In WA, unless the carpet becomes a health or safety hazard, there is no law that requires that the landlord replaces carpets after any specified time.
The questions are not whether the carpet was new when you moved in but what the fair market value of the carpet (including the cost of installation) was right before you moved in and whether you caused damages to the carpet beyond normal wear and tear.
Most landlords do not put in very expensive carpets in their rentals. Some carpets are not very high quality to begin with. How long ago the carpet was installed may not be a reliable indicator of its fair market value.
You likely are not liable for the entire cost of replacement even if you damaged the carpet beyond normal wear and tear. At most, you are liable for the fair market value of the carpet that it had right before you moved in.
What is normal wear and tear is not clearly defined. Normal wear and tear likely does not include your pets soiling the carpet or you exercising by dragging weights across the carpet or your children playing with water guns over the carpet.
There likely is some room in negotiating with the landlord if you agree that you did cause damages to the carpet beyond normal wear and tear.
You can review the specific facts with your attorney to find out your legal options.
The market dictates when the carpet looks so awful that new incoming tenants refuse to rent until the landlord replaces the carpet. That is usually what motivates the landlord to replace it. This can happen with absolutely no damage to the carpet at all, but if it was a cheap carpet to begin with, it could look awful after five years with no damage at all.
The UCC says that chattel goods have a useful life of 12 years. This is a place to start anyway; what you can argue is that you could, if you destroyed the carpet by damaging it, be held responsible for four years use out of twelve. I am not saying this is a great argument, but it might work for you. It is called amortization.
What landlords will try to say is that you damaged the carpet. If you damaged the carpet then yes, they can make you pay at least a portion of the replacement cost. If you did not damage the carpet, but used it normally and it is only showing normal wear and tear, then be prepared to show the Court there is no damage, it was a cheap carpet to begin with, and looks awful even though you cared for it.
Hope this helps. Elizabeth Powell
Using Avvo does not form an attorney client relationship.
In agreement with and in addition to the comments above, most carpets have a "useful life" rating of 5-20 years. This rating is available from manufacturers and retailers - if you can identify the particulars, which are sometimes tagged underneath the carpet itself. You may also ask the landlord to identify this from the installation records/invoices, if available. Also, carpet replacement does not always require replacing the pad, underlining, tacks, etc., which can add noticeably to material and labor costs. Charges related to Kilz or other undercoating may also be spurious.