Regularisation of Loft Conversion - Fascia Vents

[Woody3]

Bought a house where the loft conversion (dormer) had no building certificate (built in 1990).

Externally it is clad in slate, with a asphalt flat roof.

I've stripped it back to the studwork and planning on re-insulating etc (with Building Control involved).

The (cold) roof currently has 100mm of fibreglass insulation under the deck. I'm replacing this with 120mm PIR allowing for a 50mm air gap above. The loft space to the front of the property is still a loft, so I can get ventilation flow from this side, however, the dormer eave detail proves a bit of a sticking point. See drawing detail below:




How can I ventilate this through the fascia board that is overlapped with lead? Is there a vent that is at 90deg, but fairly slim, so I can pull the lead out a little as I really don't want to penetrate the roof covering.

[Equus]

You shouldn't be venting through the fascia board, anyway: normal practice is to overhang the eaves a bit, then ventilate the soffit behind the fascia board (though the overhang doesn't need to be as large as suggested by the following):



Google 'soffit ventilators'

[Eddieslofart]

As above, although i prefer the soffit board with continuous vent.

Ensure vents are insect proof.

[Woody3]

That's the problem - I've got no soffit to work with...

My drawing is as existing I'm afraid.

Hmm...

ETA: I was hoping there was some sort of vent that acts as the dashed arrow in your drawing Equus. (The actual timber fascia board isn't on show - it's hidden behind the lead.


EATA: I was hoping that someone made something similar to a telescopic underfloor vent, but obviously reduced in size and a "7" shape as opposed to a "Z"

Edited by Woody3 on Thursday 3rd August 14:38

[wolfracesonic]

Would it be possible to remove the existing facia, reduce it in height and then fit an over facia vent?

[Equus]

Or you might be able to replace the existing fascia board with an abutment ventilator like this one, with the lead dressed over the upper edge of it.

[Eddieslofart]

wolfracesonic said:

Would it be possible to remove the existing facia, reduce it in height and then fit an over facia vent?

Because he has a lead drip that needs to drip into a gutter i would guess.

You can always mushroom vent it, but you'll need to do every rafter run.

[Equus]

Eddieslofart said:

You can always mushroom vent it, but you'll need to do every rafter run.

...which would look an utter bugger! I'm just doing a flat roof garage conversion this way, because the owner is insisting on it in an attempt to save money, despite both myself and the BCO having made clear to him that it's highly inadvisable.

You might persuade the BCO that you don't need to ventilate at all, if you can provide a well enough sealed vapour barrier and no void above the insulation. It's not good practice, but I've done so before where there is genuinely no other solution: at the end of the day, it's really not much different in principle to a SIP panel, which has a high vapour resistance skin on both sides.