Replacing wooden conservatory floor

[DEfusion]

One of the previous owners built a brick & wood framed conservatory from a kit. We recently discovered that all the joists were rotten, some more than others.

The conservatory has no air bricks so my plan is to add air bricks and replace the joists. However between the joists and the chipboard flooring the guy had put down some thin plastic sheeting (which almost looks like cling film) and I was just wondering if it makes sense to do something like this?

 

[pinenot]

Presumably he thought this might stop damp??

But I wouldn't consider this very good practice, normal moisture procedures would be best. A search on Google for "timber floor build up" will do you fine...pinenot

 

[^woody^]

You should not replace the polythene, as part of the ventilation and breathability of the sub floor is via the timber deck

Any air bricks will need to vent across the sub-floor from side to side

Your description of rotting joists sounds like they have rotted at the bearings, in which case you need to take precautions to stop damp getting across from the walls to the joist ends - wrap in polythene or put on hangers. If so, this will have nothing to do with ventilation