Loft ventilation
 

Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.
Anyway 2 questions, when is the best time to check for condensation, in
warm damp weather, cold, or when?
Second if I need ventilation I intend to put through air bricks at
either end of the gables, does it matter how high they are placed?
TIA

Loft ventilation
 

Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.

It looks pretty similar. Are you sure you haven't got breathable membrane?

Second if I need ventilation I intend to put through air bricks at either
end of the gables, does it matter how high they are placed?

There no point in insulating the rafters and then putting loads of
ventilation into the warm loft. The loft itself should have as much
ventilation as a habitable room, i.e. a trickle vent, perhaps.

Christian.

Loft ventilation
 

On Wed, 4 Oct 2006 13:22:52 +0100, "Christian McArdle"
wrote:

Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.

It looks pretty similar. Are you sure you haven't got breathable membrane?

Second if I need ventilation I intend to put through air bricks at either
end of the gables, does it matter how high they are placed?

There no point in insulating the rafters and then putting loads of
ventilation into the warm loft. The loft itself should have as much
ventilation as a habitable room, i.e. a trickle vent, perhaps.

Christian.

Doubt he has insulated the rafters.

Loft ventilation
 

On Wed, 04 Oct 2006 11:59:39 +0100, Broadback
wrote:

Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.
Anyway 2 questions, when is the best time to check for condensation, in
warm damp weather, cold, or when?

Cold, any humidity in the loft will condense on the coldest places.

Second if I need ventilation I intend to put through air bricks at
either end of the gables, does it matter how high they are placed?
TIA

I cant think of a reason why it would matter. I put one in lowish as a
trickle vent an am going to see what happens. If I still get
condesation I'll put a tile vent in the other side so I have hot air
leaving at the tiles cold air entering at the air brick convection
thing going.

Loft ventilation
 

Broadback wrote:
Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.

Do you have other reasons to doubt the surveyor?

Anyway 2 questions, when is the best time to check for condensation, in
warm damp weather, cold, or when?

When the roof is cold enough for condensation to form, I found it worse
in the winter.

Second if I need ventilation I intend to put through air bricks at
either end of the gables, does it matter how high they are placed?
TIA

As low as possible but I doubt a few air bricks are sufficient. You
need continuous eaves vents (or equivalent) so that the air enters at a
low level and flows across the roof space.

See
http://www.stockton.gov.uk/resources/environment/BldgControl/BCGuideNotes/condroof.pdf#search=%22roof%20ventilation%20site%3 Agov.uk%22
and many other such pages.

MBQ

Loft ventilation
 

Loft ventilation
 

Broadback wrote:
Recently I have had loft insulation installed, the "surveyor" maintained
that even though there was no obvious form of ventilation it was not
needed because the roof felt was a breathable membrane, looks like
ordinary roof felt to me.
Anyway 2 questions, when is the best time to check for condensation, in
warm damp weather, cold, or when?
Second if I need ventilation I intend to put through air bricks at
either end of the gables, does it matter how high they are placed?
TIA

1/. Condensation will most likley occur on still cold days when hot
steamy air from the bedroom ;-) gets into the loft and condenses on
anything below dew point.

2/. Beware of end gable vents...they do little for rafter ends in the
eave area..the normal recommendation is to vent the eaves, because they
are likely the coldest place, and the ridge, because this is the
warmest. Then a slow convection can draw air from outside into the eaves
and up through the ridge.

Loft ventilation
 

Thanks all for your replies. No the insulation is on the floor of the
loft. It was not that I did not believe the surveyor, just that he was
not a surveyor in the true sense, so thought I would keep an eye on it
myself. I was offered (by a different installer) the option of simple
plastic wedges that hold the roof felt away from the tiles. If I
install the vents the plan was one in both gable ends, which are at
either ends of the rather long and narrow loft. If I need to do that I
cannot complain as I had full loft insulation and cavity wall insulation
installed free!

If you have just had insulation in the loft and the underlay felt is a
breather type, This sound rather quire, as breather underlay felt is a
modern idea. Therefore why have you had to have insulation in a modern
house. Either the property is older and as been re roofed with modern
breather underlay. As regards holding the roof felt away from the tiles,
this comes natural when the lath are fixed and the tiles laid. The underlay
should sag away from the under side of the lath by 10mm to prevent, what is
known as ponding, ponding is condensation that runs and drips of the back
of the outer roof covering either slates or tiles. It as been found that
venting should also be carried out, not only to the roof space, but also
venting between the felt underlay and the roof covering.