Avoiding condensation on joist ends

[CharlieB1981]

1920's solid brick house, insulating internal walls while renovating and taking this chance to insulate between floor joists, but is there a danger of condensation on the joist ends and any advice on how to stop this.

Many thanks

 

[tony1851]

Risk of that is minimal; but why insulate between the floor joists anyway?

 

[CharlieB1981]

This is between ground and first floor, I may have missed something but as far as I know it's now good practice to insulate this to reduce heat loss to unused rooms.

 

[tony1851]

In reducing heat loss to unused upstairs rooms, you will increase the likelyhood of condensation in those rooms.

 

[CharlieB1981]

Surely that's if those rooms are kept really cold and no ventilation. Bit confused here if your saying not to yet I'm doing this on advice from many others

 

[tony1851]

Whether you heat the upstairs rooms or not, water vapour from the lower part of the house will still find it's way into the (unheated) rooms.
As they will be a little colder than before, there will be an increased tendency for condensation to form, other things being equal.
But if many others say that won't happen, then the majority must be right

 

[Blagard]

Surely that's if those rooms are kept really cold and no ventilation. Bit confused here if your saying not to yet I'm doing this on advice from many others

I think you miss the point. A cold surface such as the walls of an old house in an unheated room are likely to get condensation. The remedy to avoid or reduce that is both heating and ventilation not either.

The rooms not heated are not hermetically sealed from the rest of the house so water vapour will get in there and it will condensate out on a cold enough surface.

The situation would be a bit different in a modern house. With better wall insulation the room even unheated would have warmer walls than an old house so the risk of condensation would be less. However it would still increase the risk by leaving the room unheated.

So the bottom line is save energy by what you are trying to do but at the risk of condensation elsewhere in the unheated parts of the house and in the knowledge the risk is very much higher in an old house.

 

[CharlieB1981]

Thanks for the replies, understand what your saying and that it needs heating and ventilation, this has been considered. My original point I was after advice on is exactly the situation you described.

The walls are being internally insulated in accordance with building regs meaning the middle section will be inside where it's warm yet the ends will be set in brickwork outside the insulation so colder, it's hear I'm worried about.

The unused room will have ventilation and lower heat to avoid damp and condensation

 

[CharlieB1981]

Prob worth noting If I decide to not insulate between floors this question will still stand