Condensation in well ventiated loft

[radsik]

I'm a bit confused as have a problem I can't identify with a loft. Property built in the 90's with full length soffit ventilation and vents in gable front and back . Can feel the that their is air circulating in there. No sign of any hot water being vented back into the storage tank, both cws and header tank have tight lids yet there is quite a lot of condensation building up in the loft. Manthorpe hatch fitted which seals nicely and is insulated. No sign of condensation throughout rest of property. The loft has 100mm insulation in which I know needs topping up but could this lack of insulation lead to the condensation?

Any ideas?

 

[mointainwalker]

Not if you have a functioning vapour-barrier under the insulation. If you do the amount of insulation is irrelevant ( for moisture purposes) as the moist air simply cannot get through.
There was a oood comment on an earlier post about sun on one side of the roof whilst other in shadow. The poster said that this was enough to cause condensation when warmed air met cool air.

Stupidly though , I can't remember what he said he did . Sorry

 

[lordgoata]

Surely if you have a vapor barrier under the insulation, when the warm moist air rises, it will be trapped between the ceiling (plasterboard) and the underside of the vapor barrier, leading to further problems (damp plasterboard etc) ??

I've seen this mentioned a few times now, but its confusing me for the above reason! ?

 

[stuart45]

Surely if you have a vapor barrier under the insulation, when the warm moist air rises, it will be trapped between the ceiling (plasterboard) and the underside of the vapor barrier, leading to further problems (damp plasterboard etc) ??

I've seen this mentioned a few times now, but its confusing me for the above reason! ?

The moisture won't condense there because it is on the warm side of the insulation, therefore the temperature should be above the dew point. In the loft the temperature is much lower because the insulation prevents most of the heat from below getting to it. You need to check the R/H and temp in the loft, and the surface temp where the condensation is occuring.

 

[lordgoata]

Ahhh! Ok, that makes sense now - thanks!

Sorry for hijacking the thread, been meaning to ask that a few times and it came to me when reading this one.

 

[masona]

A good investment would be to put in ridge tile vents at the top so as heat mositure rises the fresh air coming in from the bottom soffit will push the moisture out to the top vents giving you a good air flow circulating, I have continuous soffit vents and 4 ridge tile vents at the top, I never get condensation problem even now in this cold weather

 

[stuart45]

A good investment would be to put in ridge tile vents at the top so as heat mositure rises the fresh air coming in from the bottom soffit will push the moisture out to the top vents giving you a good air flow circulating, I have continuous soffit vents and 4 ridge tile vents at the top, I never get condensation problem even now in this cold weather

That's a good method, but to get the full benefit you will need to take out the lower level gable vents, or the air will circulate below the ridge.