FirstTimeNeedHelp

Hi all, Appreciate views from building engineers / water specialists / anyone with similar experiences on this Water Seepage issue observed along my wall (refer to Photo). Upon moving into my newly TOP apartment in mid 2017, I noticed a small 5cm circular water mark on the wall which disappears when it’s sunny. During rainy Seasons of Nov17-Jan18, the water seepage mark grew dramatically. I first reported the issue to my Developer in Nov17 and the joint inspection was conducted in Jan18. Post-inspection, Developer informed that the water seepage was likely the result of my installation of a magnetic mosquito net & its accompanying frame (non-sliding) - refer to photo. Developer informed that this is considered an A&A (Alteration & Addition) caused matter and hence they would not rectify To my family, it appeared as it’s a leakage from the external wall into the interior wall. Furthermore, we never see any water pooling etc along our window frame. This is rather perplexing. Appreciate everyone’s views pls.