Common area exclusive use sewer lines

Our community has had similar problems because we also have a lot of trees. Our CCRs state homeowners are responsible for the line once it enters the unit and the association is responsible from the point it leaves to the point it reaches the main line (after which the water company is responsible)l.

Our trees were also causing a lot of problems and I imagine their care falls under the association, so the board might not be able to completely turn over responsibility to the homeowner - as you said the homeowner doesn't know if or when tree roots will cause the problem. If you're on the board, you may want to discuss the current rule with your association attorney and the master insurance company to see if you can do this.

In our community, what we've done in the last three years is to cut down trees that were half dead anyway and whose roots were causing sewer damage, roof damage (and foundation issues in at least one unit). When I was on the board, we also walked the community to see how many townhomes had visible and accessible sewer line cleanouts (half of them, including mine didn't). The idea was to compel the homeowners to ensure they remained that way because some people had put in shrubs and/or flower beds over the cleanouts that were flush to the ground and in a few cases installed their air conditioner units over it.

With available cleanouts, we considered hiring a plumber to come out once a year to clean out the lines - better to pay $5K or $6K for that (we have 156 units) instead of two or three $4K or $5K repairs a year. Your board may want to consider a similar approach - why not hire an arborist to survey the community to see what you have?