Floor disaster..How can I prevent this happening again?

[petek001]

So I have an outbuilding built 5 years ago at the back of my garden. I could smell damp inside and the floorboards were very bouncy. The building has a concrete base with suspended wooden joists. This is followed by plywood panels then laminate flooring vinyl then laminate floor itself. There was a source of moisture near the door and the laminate vinyl was in contact with this and I suspect over years the damp has spread and turned into mould. All the plywood panels have rotten. The concrete base underneath has been dry and the joists have been a tad bit damp due to the strikethrough from the plywood. I have put a pic of the mould under the vinyl and on the plywood panel. All this is getting removed. To prevent this I was going to seal off the source of the water drip near the door, put a breathable membrane in between the joists and then placing insulation in between the joists and then putting a damp proof membrane nder the new timber panel floorboards.

 

[big-all]

general comments
you need through airflow to the outside above the concrete off perhaps 20-25mm
a breathable membrane then insulation in the void thats left supported to maintain the air gap
no air gap think off off taking your washing up basin with a few dripps off water in it topped with membrane and insulation the water has no choice but to circulate where its not wanted
if you choose to omit the airgap the insulation sits in the water

 

[petek001]

As the concrete is completely dry on the base there has been no moisture there at all in 5 years from what I can see. Do I still need to ventilate the gap at the bottom? If so how do I do it because the builders didn't do anything in that regard and the building is rendered on the outside AND there is a 2 block thickness wall separated by insulation.

 

[robinbanks]

Can you do us a sketch of how it is now?

 

[petek001]

Sure. I can attach a file, the pic is of the current floor as it is, i know i dont have much room between the bottom of the joist and concrete base.

 

[robinbanks]

I don't, personally, think I would go to particular efforts to ventilate that space. The leak is repaired, and I'd insulate between the timbers and close up as you propose

 

[Deluks]

Sure. I can attach a file, the pic is of the current floor as it is, i know i dont have much room between the bottom of the joist and concrete base.

Where is the 2 block wall and insulation in relation to all this?

 

[petek001]

the two block wall is the wall u see on the roight, it goes right around the outbuilding. ONe thing I ahve noticed is that after a lot of rain the past 5 years, the concrete base in the outbuilding is completely dry. so as per 'robinbanks' advice, i dont think ventilation is needed, i could be wrong, however.
so, i was thikning of the following
a breathable membrane in between and over the joists and then insulation laid on top of this in between the joist spaces, then on top of that laying a damp proof membrane, then the plywood floor etc. Is that a bit overkill?