D and ,
This is not the case.
I realise this is a detailed technical discussion in relation to principles, but a few rules can be distilled.
Here is the link to Part F again http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1647,en.pdf
10mm is not a good practice airgap within the roofspace - you couldn't maintain a 10mm air gap with quilted insulation, it will creep, sag and bunch up.
A 300-400mm passage from eaves gap to attic of only 10mm depth would restrict airflow - its a long tunnel as opposed to a 10mm gap at the eaves through a 19mm board .
10mm is the eaves air gap required for a roof without dormer conversion or restrictions in flow.
Good practice and Part F compliance requires installing a 50mm eaves air gap to serve such a roofspace.
Condensation can also occur on the roofing felt above any insulation - the 50mm gap encourages good venting.
In fact any roof type, anywhere within the roof requires the 50mm gap - look at the dormer roof requirements in Part F.
The eaves gap is now 25mm but the clear air gap within the roofspace requires to be 50mm - this is the dimension to work to.
Its also important that you don't block airflow above insulation that extends across the wall plate.
You may have have either frozen the wall plate out of it or else enclosed it completely
Hard to say and in fact this is the hardest detail to get right with quilted insulation.
The aim is to insulate over it but leave a 50mm gap above the insulation.
You can form the 50mm gap by fixing "solid" insulation [not quilt] appropriately.
Snugly cut it to fit between the rafters and mechanically fix it if required.
Slide the cut sections down the rafter gap but it must be a snug fit.
If using quilt, you need to fix a thin board between the rafters to leave 50mm above it.
Don't install from a 200mm roll and then compress it by 100mm to leave 50mm.
This halves the trapped air and doubles the glass fibre - doesn't work well.
That why I advice HD "solid" insulation between the rafters.
Fixing with a board stops the quilted insulation bunching up and restricting the gap.
As I've noted before, insulating anfd venting detailing like this benefits from the advice of a professional.
Professionals deal with such matters on every building and are able to offer competent advice.
More importantly, they have gained experience of several different methods of compliance.
thus most situations can be competently addressed avoiding condensation build up.
D and , one final word in relation to "wet" insulation:
Depending on your insulation type, you may need to wholy remove and renew your installations.
Some insulation types absorb water and holds it, while other types can be dried by venting.
In severe instances the insulation will actually get wet and become very hard to dry.
Working remotely and not being familiar with the type I cannot say more on this.
Wet insulation can be even worse than no insulation, BTW.
It will conduct heat and evaporation is a cooling process.
Plus the water in it will move around and land elsewhere.
It can badly effect gypsum based materials and timber.
That is why wet insulation usually should be removed.
Remember.
1. Vapour check - restrict the passage of water vapour into the attic - attic hatches, downlights, ceilings without visqueen above or foil-backed plasterboard all allow passage.
2. Ventilate - ensure its equivalent to 10mm continuous eaves vent for an unconverted attic and 25mm eaves and 5mm ridge for converted/restricted attic space.
3. Insulate - after you've vapour checked and ensured adequate ventilation, insulate - review services, and insulate pipes and tanks [but not under tanks].
BTW , I cannot see how you can properly insulate water tanks using blown fill insulation.
You need to take the insulation from "floor" level in the attic, up the sides of the tank, leaving none below it.
You can do this by fixing quilted insulation or HD insulation boards around the tank, but blown fill will just slump away.
Its also a good idea to check all sides of the tanks, not just the ones you can see by looking from the attic access hatch.
And be very careful in an insulated attic - its very difficult so see where to place your feet properly and its easy hurt yourself.
Personally I never investigate attics alone if I can avoid it - always attend with someone to hold hte ladder and stay within earshot.
I hope this gives a little clarity.
FWIW
ONQ.
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