Converted. Windpump - help!!

[RedMill]

I live in a converted wind pump. It has been lime rendered inside and out (done in 2021) and has a flat concrete roof with no insulation on outside (as far as I know) and no insulation on inside either. As the weather has turned very much colder I now have condensation forming on the concrete ceiling and dripping! The room is only 10’ in diameter and is the ‘lounge’. I only have electric heaters so I don’t keep the heater on all the time.
I am currently running a dehumidifier in there and wondered if it would be a problem with the render?
Also could I fix insulation to the underside of the ceiling without leaving a ventilation gap? Wanted to use natural materials but …?
The room is chilly. Warm air doesn’t seem to rise!
Can any one offer suggestions?!

 

[Cubist]

If condensation is forming on the exposed concrete ceiling then warm air is most definitely rising to meet it. Trouble is that ceiling is a large and 'massive' cold spot - zone rather - that will absorb huge amounts of heat despite the perhaps best efforts of your heating system, and in doing so reduce the effectiveness of the convection currents to warm the rooms. In effect isolating the room from that concrete mass with say a false ceiling may be effective be effective but that may not preclude the threat of condensation forming, as it is now, to the affect the false ceilings materials and structure. Are the room heights sufficient to allow such a solution?
Others here have more experience and relevant knowledge concerning typical practices and materials to insulate roofs - but few of them I suspect with experience of your particular situation.

A left field idea - or more properly 'an out of the box thought' if you'll forgive the pun - have you considered the possibility of insulating above the roof? I'm thinking of those subterranean houses that benefit from the insulation of the soil above to help retain the interior heat. Would the building and its concrete roof be capable of supporting a garden?

 

[RedMill]

Thanks. I wondered if we could just stick insulation to the underneath and then add a vapour barrier. Not over bothered at the moment about looks. Wondered if the insulation would stop vapour reaching the cold concrete.
Yes. I have thought of insulating above it. There’s a space of ?2/3 ft and we did think of putting celotex sheets (other insulation is available…) on top and just weighting it down for this winter. It is just getting up there at the moment! A green roof? Hadn’t thought of that!
It’s tricky to reach - possibly a cherry picker but we’d have to wait for summer… and we think there’s a fibreglass top on the concrete…

 

[Cubist]

Frankly I think your best option would be to install a false ceiling with any insulation materials sitting on it and leaving an air gap above the insulation to the concrete. Airflow through that new void could then be established with the installation of a couple of strategically positioned air-bricks in the opposing outer walls to dissipate any warm air and moisture that percolated up into the void from the rooms below. But I still like the green roof concept too.