Pitched Roof Ventilation - Barn Conversion

[tren]

I am working on converting a small agricultural barn made of granite stone into a dwelling with vaulted ceiling (for the head height upstairs).

The pitched roof is in a very good state as it was redone 15 years ago. It's made of slate, bitumen membrane and rafters are every 400mm. Ridge is traditional clay tiles bedded in mortar.

My plan is to insulate the roof in between and below the rafters leaving a 50mm gap but I am concerned with the ventilation gap at the facias (and ridge).

On one side there is a 12-15mm gap between the wall plate the membrane but on the other side they left no gaps at all. The last row of tiles meets the corner of the wall plate and pinch the membrane. See picture attached/below.

My questions are:

- What's my solution here? How can I achieve adequate roof ventilation at the facia?
- Do I need a dry ridge (or vents) to ventilate at the top or a continuous gap all across will suffice?
- Would 12-15mm gap at the facia with a 50mm gap above insulation be enough?
- Will a VLC not stop condensation or at least help if the vent not as good as it should be?

 

[alexander]

three in one felt support trays at the eaves will allow ventilation from the eaves, depends really what type of membrane you have on the roof under the tiles as to whether a dry ridge would be of benefit,

 

[tren]

three in one felt support trays at the eaves will allow ventilation from the eaves, depends really what type of membrane you have on the roof under the tiles as to whether a dry ridge would be of benefit,

it's bitumen membrane so it's non breathable

 

[alexander]

sorry read it wrong, ventilation strip under the first tile felt support trays over the top of the vent strip then felt over the trays, dry ridge will make no difference what so ever in ventilating the roof as your current membrane is non breathable all it will achieve is holes in your secondary protection [your felt ] in reality a dry ridge system is only really useful if its an air permeable membrane on your roof, what your proposing will stop heat escaping from below but will not stop major dampness issues being caused by mother nature creating condensation in your roof area above the insulation & you can only really solve that from above which would require at least some removal of the current roof covering

 

[aockenden]

Tough one when there’s no overhang and not true trusses. Maybe as an alternative you could install some kind of mechanical ventilation system in the loft? Aren’t there passive, wind-driven vent-pipes that sortof look like stove pipes which you could install through the roof?

 

[tren]

Tough one when there’s no overhang and not true trusses. Maybe as an alternative you could install some kind of mechanical ventilation system in the loft? Aren’t there passive, wind-driven vent-pipes that sortof look like stove pipes which you could install through the roof?

There is but realistically I would need it in between each rafters which is not realistic

 

[jamest]

I may be missing something, but do you object to using vent-pipes because having one between every pair of rafters would be not merely inconvenient, but aesthetically detrimental? If so, could you use vent tiles instead? You could even have two between each rafter pair - one near the ridge and one near the wall plate (second row of tiles up). I assume there is probably some reason for not doing this, but I'm not sure what it is.

 

[tren]

I may be missing something, but do you object to using vent-pipes because having one between every pair of rafters would be not merely inconvenient, but aesthetically detrimental? If so, could you use vent tiles instead? You could even have two between each rafter pair - one near the ridge and one near the wall plate (second row of tiles up). I assume there is probably some reason for not doing this, but I'm not sure what it is.

Yes vent tiles are an option I think. They are not cheap though and since my rafters are every 400mm it will be rather a few of them.

My question is do I need it to vent at the ridge too? Or a 50mm continuous gap from one eave to the other is enough or a pitched roof?

 

[alexander]

the more vent tiles you put in a roof the bigger the chance of leaks, underfelt or membranes is your secondary protecting against water getting under your roof tiles, before it was lime mortar that caught any drips getting under the roof tiles, you cannot stop roofs tiles leaking a little bit that's what your membrane catches and directs to your gutter to put lots of holes in it to vent your insulation will only create leaks & damp,
good luck

 

[alexander]

you need air flow between the underfelt & the insulation throughout the entire roof area to prevent mother nature creating a condensation issue & ultimately rot & damp