Condensation in roof space

Timbo29

I have a house built by persimmon around 20 years ago. I'm was well aware of the standard of building however it was in a good location and within our budget. 

I work in the construction industry but still interested in your thoughts on the following. 

The roof is trussed rafters, and traditional non breathable felt has been used, and a bedded ridge (no ventilation). There is spacers at the eaves but upon inspection of the roof there is condensation building up on the underside of the felt, staining/mould on the timber members, and evidence of dripping on the loft wool insulation.  
I've checked all extract fans are not leaking. 
I do have a young family so have regular baths, and there is an open plan layout so all kitchen steam can quickly go up to the first floor. 
The houses isn't that warm in winter, and very hot in summer.

Would you:
1) leave as it is

2) use dehumidifier
3) strip off ridge tiles and replace with dry fix type with ventilation 
4) as above but also strip 2 rows of tiles off and replace bitumen felt with a breathable felt

5) install tile vent tiles only

The cost to scaffold the property is around £550, and option 3 is going to cost around £450. 

ashe

Common issue atm 

solutions (pick some)

install a PIV system
put loft lids on any gu10 lights and seal with sealant 
purchase 20 or so lap vents and insert between where the felt overlaps, or put some pipe lagging inbetween to hold it open , do this in each side of the roof so that there is ventilation and air flow 
install ventilation tiles 

I did 25 lap vents, loft lids on all gu10's and at some point may do a PIV to draw air into loft while circulating air below 

ThisIsWeird

Hi Timbo.

In-laws had (I'm pretty sure) a Persimmons bungalow, bought new around 25 years ago. I have to say, there were only the most minor quality issues, easily solvable, and it looked as good as new when they sold it about 5 years ago.

Anyhoo, they stored lots of cardboard boxes of stuff in their loft, and I usually had the job of bringing the stuff up/down the shoogly aluminium loft ladder. What I found up in the loft was that it was very draughty, and I could see specks of light along the eaves. Outside, the soffits had continuous vent strips in them - the source of the wind.

The result was that it was bludy cold up there, but bone dry. Not a single sign of damp in the boxes and contents.

Are your eaves ventilated like this? If not, what alternative have they used? Round vents can usually be installed easily - a hole saw, and screw then in at the suggested intervals (lots). Ensure the eaves are then kept clear inside - not blocked by insulation.

Then, as said above, check the obvious for limiting moist air getting up from the house below; a well-sealed and insulated loft hatch, fire hoods on any downlighters (change lamps to LED types of risk of overheating) and you can replace the loft insulation over them, and increase loft insulation levels to current standard if needed.

Keep eaves clear - I think there are flat trims available in order to ensure this - they ensure the loft insulation is kept sloping down at the eaves to leave an air passage above?

Some moisture will percolate up through the ceilings - that's natural, I understand - but this can be minimised by a good layer of insulation above.

Finally, some visible condensation up there at certain times of the year - cold weather coupled with still days - is, I understand, quite normal and not an issue as it will always dry away before long. I'd be concerned if the timbers showed signs of staining, tho', but don't panic. Yet.