Ventilation in roof space?

Good morning.

I have a sloping roof on an extension, ready for me to put in the insulation and plasterboard. I plan to use Celotex or Kingspan between the rafters. (Thanks to those who advised me on that here, a few weeks ago.)

There is a continuous strip of ventilation along the eaves, and two chimney-type vents further up, one for each room in the extension. (Are these called tile vents?) The roof space is divided by a wall also, so there is a space and a "chimney" vent above each room, but no air flow between the rooms in the roof space.

When I insert the insulation boards, leaving the statutory

50 mm gap below the sarking, air (and moisture) will be able to move along the spaces (i.e. parallel to the rafters) and through the breathable sarking and roof. Then each chimney-vent will only be connected to one inter-rafter space. This seems a bit odd to me. If those vents are required, should they not each vent a large area of roof space? Otherwise, what is the point of them?

Or is there sufficient across-the-rafters air flow in the little space between the rafters and the tiles?

And another thing: assuming this is all OK for ventilation, can I put lighting junction boxes in the

50 mm gap?

Thanks for any advice.

-David Pearson (a bit groggy in Taunton)

Reply to
David Pearson
Loading thread data ...

If you are using breathable felt, do you really need the 50mm gap? Hve a look at the kingspan website, or the seconds site.

It looks like seconds are no longer available. ODPM strikes again!

Reply to
<me9

Why put vent tiles in when you have already used breather underlay felt.. If you've used this type of felt, its designed to let the air carrying vapour through. Any condensation runs down the outer side of the underlay felt, down the 10mm sag between the felt and back of lath, down to the eave and out into the guttering, providing that you've used an over fascia support tray. If not it will just collect in the trough at back of the fascia.

Reply to
keith_765

If you want to vent all the way across every spar, providing its a lean-to roof with an top abutment with a Lead apron, you should used an abutment vent system. All the major tile manufactures supply them.

Reply to
keith_765

Try

formatting link
?

Are these companies connected, competitors or is one trying a fast one?

-- Adrian

Reply to
Adrian C

They seem to be different:

formatting link
?domain=secondsandco.co.uk-David P.

Reply to
David Pearson

I've never come across this in venting a roof.. Still ones never to old to learn.

Reply to
keith_765

I think you meant

formatting link
who have plenty. I've heard the message on the
formatting link
is because Kingspan won't supply them with 'second' stock any more.

Reply to
Mike

Hard one that. I think I would class it as inaccessable so really it should be crimped if there as to get to it to tighten a loose screw you'd have to both cut the plasterboard ceiling which is easy to repair but then cut through the insulation which isn't.

Reply to
Mike

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.