Damp and rotten floor

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Hopefully someone can help with some sound advice and what trade to call in to sort out my problem..

I had an extension built in mid 2015. There was an external soil vent pipe (ceramic) on the external wall and originally the builder was going to leave in situ then box in.

looking at some old pics I noticed that the new DPC was placed around the pipe rather than towards the back. I addition there was a previous air brick which will have been covered as part of the work.

The floor was laid then after this the SVP was cut out, sealed and then latexed over.

The external wall is now an internal wall and has been boarded, plastered and painted. However I am now getting small localised damp on the wall with small paint flaking, nothing greater than about 4 or 5cm in the area where the SVP was.

The worst thing is on the other side of the wall (the old internal space) in the other room the floor has rotted, quite severely. I tried to get the floor board up to look, but the jemmy bar just went straight through without any effort and there is mould/fungus on the timber. The floor joists still have some stability but they look like there getting worse.

The patter of "damp" on the floor boards is funnel shaped more or less (give or take 10cm) in the same location as the SVP on the other side of the wall spreading outwards for about 40 to 60cm.

Ive tried to contact the builder, but he's no longer trading or around, so if any one could advise, i would be most grateful.

I live in the Wakefield - West Yorks area and I'm likely to need an expert trades person soon!!

I've attached some pics of the before extension work.
 

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ask the mods to transfer this to building.

that finished level looks well to high.youve bridged the DPC and if the cavity is full of rubble then rising damp is getting across the cav. any air bricks that vent your suspended floor have been blocked. what you describ inside sounds like dry rot due to damp and lack of ventilation. can you show photos of the rotten floor and the inside wall.

you might have to open the cavity for cleaning out and cutting out and treating the rotten floor.
 
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I agree it sounds like dry rot which is a major problem. Google dry rot fungus images and see if yours looks like that.
All affected material including joists must be removed. Unfortunately it sounds like your builder has caused the problem by bridging the dpc and blocking the air brick.

The dry rot needs looking at fast it can spread even through masonry.

Bit of info here ....don't rush in to using a company it's an unregulated industry !

http://www.buildingconservation.com/articles/rot/rot.htm
 
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Was that air vent ducted under the new floor, or if covered up was a replacement provided elsewhere?

Have you got pictures of the situation now? It may well be rot due to lack of ventialtion of the floor void.
 
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Thank you for your responses. I’m going to get a builder in to provide a quote for the work and cover all bases - DPC, venting and new floor, just in case.

thanks again
 
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