condenstaion in loft post celotex insulation

[unclebob1]

Good Morning,

Was looking to tidy up wiring in the loft over xmas/new Years, but got stopped in my tracks once i noticed a fair amount of condensation on the felt layer and wetness on the roof joists.
Time line is as follows:

Pre Nov 2015:
loft insulated with two layers of fiber glass compressed into 100mm space between ceiling of room and floor boards in loft.
roof was straight tile (and lots of daylight).

Nov 2015 - had internal chimney removed, and roof re-tiled (many of the tiles were crumbling or already broken). Flet layer introduced, and new tiles, sofits attached to existing boards.

Oct 2016 had ground floor rendered and plastered, and upstairs landing, Heating system switched off and replaced - occupants moved out.
Nov 2016, some heating turned back on to assist drying of plaster, fiber glass insulation removed and celotex installed over 3 weekends. Note the rear of the property was done first but not sealed with foam. front of the house done next, and was sealed, followed by the center also foamed (loft is roughly divided into three sections based on joists).

16th Dec 2016 heating back up and running, and occupants moved back in.
30th Dec 2016 went up to tidy wiring, noticed large amounts of condensation to the rear part of the roof, some along the side and a bit at the front. Note it had been foggy outside for about 4 days prior to this nearly constantly not just in the mornings.
2nd Jan 2017 foam sealed the remaining part of celotex (back of the house).

Some other notes re the house:
The rear of the house backs to a park.
The side has a shared alley way followed by another property - approx 5-6m distance.
The front is to a road, with houses on the other side - approx 15m distance.
The bathroom is to the rear of the property, and currently the extractor fan is not functioning. - Prior to new heating system water wasn't hot enough to create loads of steam, plus door was left open while showering. Since moving back in on the 16th lots more steam when showering, plus door is now closed. And i am looking to find out whats wrong with the fan and get it changed/fixed asap.

There is also condensation around the edges of the roof, where the joists meet the outside walls, where there is currently NOT any insulation (cutting celotex to fit the gaps is time consuming!) and also where there is existing fiber glass.

There are no vents as far as i can see, both in the roof tiles, and in sofits (didn't need it prior to reroofing as i could see daylight in more places then i can count in my fingers and toes!)


So what are my steps going forward to reduce/remove the condensation:

Can i just foam fill the gaps where joists meet the outside wall (on top of the sofits)?

Foaming the remaining areas i hope will reduce a fair amount of the heat getting into the loft so reduce condensation. (done yesterday 2nd)

Fix Fan (in progress)

 

[JohnD]

What you need is proper ventilation of the loft space.

It sounds like your foam fill is going to block it.

And a powerful and effective extractor in the bathroom

//www.diynot.com/diy/threads/condensation-in-loft-answers.160032/

 

[unclebob1]

Thanks John,
I'd seen that link already, and loosely following it, just wanted to see if anything i did with the insulation was done incorrectly or not complete. It didnt apear to be a problem last dec/jan, so could it be as a result of the plaster drying, heating not being on and insulation being changed that caused it?

Hopefully will be looking to fix the fan (and wiring) this week, fan not working at all so prob need to replace - 12v job going out of the wall, not sure if the transformer dead or fan.

 

[garyo]

When you re-roofed in 2015 did you use felt or breather membrane? Is it a dry (vented) ridge, or bedded on mortar? Did you change any of the soffit or over-facsia vent arrangements at that point?

 

[unclebob1]

Sorry it was a breather membrane, and vented ridge (i assume that using clips to hold ridge tiles down rather then mortar are vented?) previously was bedded on mortar.
Soffit was wood, and is now covered in plastic, there were no vents prior, and still are none.

 

[unclebob1]

With the celotex sealed around the edges, the amount of condensation seen has reduced a lot (as it its almost not visible) however joist are still wet at the top edge.
Fan has been fixed on Sunday, so will see what happens over this week. However weather is warmer now so not as much condensation.

Looking to add two tile vents to the front, and two to the back, anyone suggest a decent place to get tile vents for redland 49 rustic red tiles? (Don't want to be paying £50 per vent!) Also thinking of sticking a fan on one of the vents, with a humidistat so if it does get overly condensation then the fan will help keep air moving. Sound like a decent plan?

 

[JohnD]

water vapour is lighter than air, so if you give it a chance it will rise up out of any holes or vents you provide. It is usual to provide vents on at least two sides, so that any trace of wind will tend to flow in one side and out the other. The loft should be cold and draughty.

Hot air will do the same, so it will reduce excessive heat on sunny summer days.

It would be very strange to need a fan in an ordinary house loft.

Condensation is water, so you just need to reduce the water vapour that can get in, or increase the amount that can get out. Any holes in the ceilings (e.g. for pipes, and especially downlighters), or round the loft hatch, will allow warm moist air up from the house, and it can diffuse through the ceiling.

 

[unclebob1]

Thanks for the response Johns, I guess I had lots of condensation when the insulation wasn't sealed, as it was over bathroom area.

At the moment the loft is cold, with a light draft (though that's is with the hatch open so need to see when it's closed) fan was more as a just in case, the joists have started getting mould in then month or so it's been like that even with me wiping it down! Don't want it to get worse.... But also want to board up loft to start storing things... Sooner rather then later along with alarm panel!