loft condensation, at a loss!

[kitch]

Hi all, moved into our 4 bed detached 2 1/2 years ago and first winter i topped up the insulation in the loft and had new facias and soffits etc done.
When the temp really dropped i noticed condensation on the underside of the felt (non breathable) so doubled up the soffit vents as the installer only fitted 4 front and back and put the dehumidifier up there and all dried out fine.
This year i again topped up the loft insulation (now about 400mm thick) and checked for condensation when the temp dropped and it had returned-i squeezed in a couple more soffit vents and made sure the insulation was not blocking the vents and also fitted 2 tile vents (tiles are redland regent) to the rear on the house 4 rows down from the ridge and let loose with the dehumidifier and again all dried out fine!
Now 2 weeks later i checked again and its starting to return-the ensuite and bathroom both are vented and my other half only dries the odd item on a radiator-im now at a loss, do i fit 2 more tile vents to the front to match the back? the loft is freezing so insulation is doing it job and i also fitted some pipes as makeshift felt lap vents-what else can i do as there are no signs of the roof leaking!
By the way the house also has cavity wall insulation and the area over the 3rd and 4th bedroom is free from condensation!
Our bedroom had 10 spotlights and i even removed these to help!
Thanks for your replies!

 

[^woody^]

You wont stop condensation in lofts.

The idea of vents, is that condensation is allowed to evaporate and the loft does not become humid for any length of time so as to allow mould growth

 

[SurreyRoofingEstimator]

Yup, near impossible to stop condensation in lofts, the best you can do is to try to stop moisture getting up there in the first place by putting a vapour control layer below the loft insulation over the ceiling. Vapour will find a way seemingly no matter what you do

 

[kitch]

So a small amount is ok?
The odd 1 or 2 rafters has damp patches is this ok too?

 

[SurreyRoofingEstimator]

As long as it dries out again after the cold weather it should be fine

The last two years have been exceptionally cold so exacerbates the problem, I spoke to Celotex last year when we had a similar problem on a large commercial roof and they are experiencing the same issues due to the cold even on buildings that are very well insulated

 

[smashngrab]

Like you said stick two more in,or even go three front three back.I always say do both sides.

Maybe the soffit vents just arn't doing it! Go mad stick 3 low and 3 just down from ridge on front and rear.If that dont work move.