Vaulted ceiling / insulation / Air flow?

[macc365]

I am currently up to roof level on my single storey small extension (1.7x3.3m) with a few issues and was after some guidance before BC come and intergate me!!

I originally allowed for a vaulted ceiling with a 50mm vented air space. make up 100mm K7 with 50+12.5 K18 board /Breathable felt/battens and slate. (this is fixed to the existing 9 inch solid wall).
Now heres the issue, i have a catnic lintel above the door/window but with height restrictions and trying to gain as much pitch as possible (22') i'm left with one brick between lintel and bottom of joist. With barely any soffit and the facia having guttering in front how can you get an airflow into the roof space?

Now i've come across this problem it seems a bit much for myself to get right and as a DIY job was wondering if i should go down the full fill unvented option with the use of sarking board or (if i read it correctly) a breathable sarking membrane?

Was wondering on peoples thoughts and do i have to consider any other aspects?

Thanks

 

[r896neo]

I can't quite envisage what your on about but a pretty common option is over fascia vents like this http://www.manthorpe.co.uk/Building/Products/Roof-Ventilation/Over-Fascia-Vent.html.

 

[freddiemercurystwin]

I was reading this and wondering why on earth you aren't using a breathable membrane. I doubt there are many rooves built nowadays with trad felt.

 

[macc365]

I have tried these threads before but never seem to get the description right so apologies. I looked at the fascia vents but would the guttering not cover these and be potentially open to the elements as in rain, thats why i thought vents were to the underside of the soffits? if i have vents allowing air in do i have to have vents allowing air out as a through flow?

yes, your correct it is breathable membrane, i keep calling it felt ofr some unknown reason and has caused others to look at me funny, lesson learnt!

 

[freddiemercurystwin]

So have you used a breathable membrane or felt?

Is the roof battened/tiled yet?

 

[macc365]

hi,

No no tiles/felt laid yet. I have only fixed the beginnings of the roof so far the wall plate / roof plate and fixed 2 joists either end to get the gable profile.

 

[freddiemercurystwin]

So just use a breathable membrane and forget about ventilation. You only need a 25mm gap between a breathable membrane and the insulation BTW to allow for a bit of sag in the membrane.

 

[macc365]

Thanks very much. Reason a bit flustered on this is building regs were signed off with a ventilated design. If i was to deviate from this would they be ok as long as it stood up to modern regs or would i have to submit a revised spec? Anyway i'll have the first meeting with my appointed BC officer this week as he's been on leave so my 4 previous inspections have been carried out by others, never the same face.

 

[freddiemercurystwin]

They won't care, same result.