WATER SOAKING INTO SUMMERHOUSE FLOORING

[welshwalnut]

MY FATHER BUILT A WOODEN KIDS SUMMERHOUSE. THE FLOOR IS MADE OUT OF THICK PLY AND THE WALLS OUT OF DECKING. THE SUMMERHOUSE IS SITUATED ON THE GARDEN DECKING AREA. TO AVOID THE FLOOR GOING STRAIGHT ONTO THE GARDEN DECKING HE PUT DOWN INDIVIDUAL WOODEN BLOCKS AND A LAYER OF PLASTIC DOWN. HE THOUGHT THIS WOULD AVOID THE RAIN WATER SOAKING UP FROM THE DECKING INTO THE FLOORING. HOWEVER IT HASN'T WORKED. THE FLOORING ALL AROUND THE OUTSKIRTS IS WET ON THE INSIDE. THE WALLS ARE DRY. THE ROOF DOES EXTEND OUT FURTHER THAN THE HOUSE. SO THE WATER IS COMING IN THROUGH THE FLOORING. THE SIDE OF THE PLY FLOORING ON THE OUTSIDE WHERE IT IS ATTACHED TO THE WALLS IS CONSTANTLY WET WHICH I THINK IS CAUSING THE WATER TO SOAK THROUGH THE PLY AND INTO THE INSIDE OF THE HOUSE. BUT WE CAN'T UNDERSTAND WHY THIS IS GETTING WET WHEN IT IS RAISED OFF THE GROUND AND THE ROOF STOPS THE RAIN FROM DIRECTING GETTING TO IT. ANY SUGGESTIONS?