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)

"David Pearson" wrote in message
...
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)


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.

wrote in message ...
On 5 Jun,
"David Pearson" wrote:


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.


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

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


--
B Thumbs
Change lycos to yahoo to reply
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.

wrote:

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

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


Try http://www.secondsandco.co.uk/ ?

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

--
Adrian

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

They seem to be different:

http://www.uk-cheap-domains.co.uk/wh...=seconds.co.uk

http://www.uk-cheap-domains.co.uk/wh...ndsandco.co.uk


-David P.

"David Pearson" wrote in message
...
Are these companies connected, competitors or is one trying a fast one?

They seem to be different:

http://www.uk-cheap-domains.co.uk/wh...=seconds.co.uk

http://www.uk-cheap-domains.co.uk/wh...ndsandco.co.uk


-David P.



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

wrote in message ...

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

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

I think you meant www.secondsandco.co.uk who have plenty. I've heard the
message on the www.seconds.co.uk is because Kingspan won't supply them with
'second' stock any more.

"David Pearson" wrote in message
...

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

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.