Why is my apartment loo always dirty when I return in the evening?

I live in a flat in the fourth floor of an apartment building. In the morning, I flush and clean the water closet (WC) after use. When I come back from work in the evening I find the WC as if someone had used it without flushing and cleaning afterwards. There is nobody in the flat between the time I leave and return. What causes the WC to be dirty as explained above?

There are many potential causes for this phenomenon. These can depend on a number of factors including such things as the arrangement of other apartments above or adjacent to your apartment. You have not given me much information in this regard and therefore I will answer your question in general terms. Hopefully some part of my answer will point you in the right direction towards a solution.

Modern apartments are generally drained via internal “stacks”. These stacks contain waste pipework. These pipes carry waste water from toilets, showers, wash hand basins and sinks vertically downwards and eventually to the public drainage network. The stacks are usually arranged so that they can be accessed from the common areas to allow for routine inspection maintenance and cleaning/unblocking. Each individual apartment will have “branch” pipework discharging into the vertical pipework within the common or shared stacks. Clear guidance is given within EU standards and Part H of the Building Regulations regarding the arrangement and separation of connections to these vertical pipes, to avoid what is termed “crossflow”.

Crossflow relates to the transfer of waste from one branch pipe to another. Crossflow can be more common in a single pipe system. Single pipe systems are more prevalent in modern speculative development. This may be a potential source of the problem you are encountering.

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Regulations

Technical guidance attached to the regulations dictates that there will be a “no connection zone” on the vertical pipe directly opposite and below a branch connection. This zone is usually 110mm - 250mm below a branch connection, depending on the size of the branch and main vertical pipework. This can cause a problem if apartments are arranged “back to back” and at the same floor level. It will be difficult to avoid branch waste pipes from entering the stack at the same level. Therefore, avoidance of opposing connections within the “no connection zone” will be difficult.

Manufacturers have designed products where multiple connections can be arranged via a manifold however, in my experience, these are not commonly used in speculative developments. Regrettably, it is not uncommon to find such internal drainage systems which have been installed contrary to good building practice and building regulations.

My advice therefore is to have the arrangement of the waste pipework serving your apartment assessed by a chartered building surveyor. The arrangement of the apartments above or adjacent to your apartment should be reviewed. Following an assessment of the connections to the vertical drainage system, it should be clear if the problem relates to crossflow. If this is the case, there may be potential for the introduction of a manifold or anti-crossflow valve to alleviate what sounds like a disturbing issue.

Pipework within the stacks are likely to be “common” and therefore remedial works may fall within the remit of the owner’s management company (OMC). Depending on the findings of your surveyor, this matter should be brought to the attention of the OMC, so that adequate corrective measures can be taken.

Noel Larkin, is a Chartered Building Surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie