Concerns about garden room wooden base - Cowboy builders.

[aido]

Hi
Ive search in lots of places but cant find a definitive answer to reassure me.

I have some concerns about the base of the new garden room I am having built by some builders. It seems a bit cowboyish to me. The new room sits where the old shed and patio is. So the wooden base half sits on a concrete base and half on a patio. What they did is they placed a layer of dpm on over the existing concrete base and patio. As the concrete base is slightly higher than the patio (about 10mm in places) the perimeter wood sites directly on the dpm on the concrete side. On the patio side to make the floor level the perimeter sits on treated timber and deck boards or is attached to uprights. The floor joists are also sitting directly on the dpm in places and suspended over the patio about 50 -> 100 mm off the dpm.

They then brought the DPM up around the outside perimeter wood and brought it back inside the building. The stud Walls then sit on the DPM. So in affect the base is sealed from the outside.
A layer of eps polystyrene insulation went on top of the dpm between the floor joists and osb boards on top of joists.

The builder said water wont get in. its sealed.
Well water did, a lot got in before roof completed, due to all the rain and snow we got this winter, and not having guttering in place and leaks in roof etc. the volumne of melting snow caused some water to get in over dpm.

Ive had to lift all the floor osb to dry it out. Every morning however the inside of the dpm along the perimieter where it rises up is always wet. Is this condensation. Ive had heaters on inside drying the floor out so the room is warm.

I am concerned that this base will rot due to no external ventilation. However the only way to put in ventilation is to drill holes in perimeter wood and
damage its integrity. Are my concerns valid.

Ill try send some photos to explain better.

 

[Notch7]

Its not the best construction method.

It eouldve been better to put down packers say 25mm thick or similar, ideally plastic. That way theres a gap where water can flow but also it can be ventilated. In an idea world it would 150mm gap but anything helps.

Then put down floor joists insulation in between etc.

What the builders have done, would only work if the concrete base was same size as base with cladding overhanging.

 

[aido]

Thanks for the feedback. Its dried out pretty well during the past week. But last night I ran the hose over the roof and gave it a good soaking. From what I can see water was pooling at the back of the room and must be coming up over the DPM into the room. There wasnt much of a gap left around the room and the fence (about 100 to 200mm max in places). I think the water can't drain away underneath the dpm very quickly as the perimeter is resting on it in places. So it builds up and some comes over the top in my opinion. So some water will enter due to heavy rain. I need to ventilate it better so it dries out. Would dring air holes in perimeter be a bad idea?

Do you have any suggests that could rectify this.

I've attached some photos of his efforts.