A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

"AL_n" wrote in message
...
A layer of bitumous felt immediately under the tiles or slates on a
pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

In Scotland we have solid timber roofs which are covered in slates (with
felt on the wood too). English roofs seem so flimsy.

AL_n wrote:
A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

It's there mainly to stop the wind blowing in and removing all the heat
from the loft area as far as I know. When I had the roof done on one
house I owned, putting felt in reduced heat loss quite a lot. I'd say it
was worth about the same as an inch of rockwool.

The downside is that you need to make sure there's still enough
controlled ventilation to keep things dry, or it encourages rot.

--
Tciao for Now!

John.

"AL_n" writes:

A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

It also reduces movement due to wind. In Scotland wind is more
of a problem and sarking is general wooden boards.

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer?

I think its not uncommon nowadays to use Tyvek sarking, which
might last longer and is semi-permeable so that water wont
collect on the battens.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2010-09-14)

On Sep 13, 8:23*am, "AL_n" wrote:
A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

It was extensively used in days of yore as there was nothing else.
Previous to that, nothing at all was used.
Nowadays there are various man made fibre and plastic sheets used.
However, you need to get read up on the varoius ventilation
requirements.
Very important.

On Sep 13, 8:23*am, "AL_n" wrote:
A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

also acts as a backup in case of tile/slate loss


NT

"NT" wrote in message
...
On Sep 13, 8:23 am, "AL_n" wrote:
A layer of bitumous felt immediately under the tiles or slates on a
pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

also acts as a backup in case of tile/slate loss


NT

I once lived in a house which did not have any felt under the roof tiles. It
was not a problem until it snowed and the snow drove in through the tiles
and laid on the floor.The snow then melted and leaked through the ceiling
making the bedding wet. After the first time we swept up the snow before it
melted. This was not way up north but down south on the Isle of Wight. It
was not our house but came with the job.
Robbie

On Sep 13, 8:23*am, "AL_n" wrote:
A layer of bitumous felt immediately under the tiles or slates on a pitched
roof is normally found in houses.

Is this purely a precaution against rain ingress due to broken tiles or is
there another reason for it?

The felt generally projects a few inches beyond the edge of the lowest
course of tiles and ends within the reach of the guttering. However, this
projecting portion typically perishes and didintegrates within about 20
years. Why don't they use something that lasts longer? Apart from softwood
window frames, it's hard to think of any building material that is so
short-lived.

Al

The bitumen felt is purely a vapour barrier against condensation
ingress from the out roof covering. Bitumen felt replaced touching
morter which was spread on to the back of the roof lath, slates or
tiles this which stopped any ingress of dirt and wind.

There are special units called "over fascia felt support trays" Theses
are fixed on top of the fascia board and under the bottom of the felt,
the bottom of the tray hanges into the gutter. Unfortunatly the are
not suitable on rose mary type tiles.