function of felt

[notaplumber1]

Forgive me for what maybe a stupid question. What is the function of felt in the roof with respect to tiles.?

 

[freddiemercurystwin]

In a new roof two things, firstly to keep the roof dry during re-roofing and secondary as a backup waterproof layer should a tile drop or crack etc or maybe in some periods of extreme weather where water may be blown up the roof between the gaps in the tiles.

But many older roofs do not have any felt or underlay at all.

 

[notaplumber1]

There are traces of felt but has deteriorated. roofer told me that it is more to keep the heat in than to keep water out. I think i am in old roof category , no felting cos when tiles got dislodged by wind i could see inside roof.

 

[terrypin]

Not so, as mentioned felt in a tile/slate roof is a secondary barrier.

That roof will have had felt when roofed, absolutely 100%.

 

[freddiemercurystwin]

Yes as above, the insulation point is rubbish, probably best to avoid that 'roofer'! If the tiles are in OK condition and the roof is not leaking then ignore the fact that the felt has deteriorated. Felt deterioration is not uncommon. That said it does look like a tile/slate has gone awry ......

 

[jontop]

True you don't need felt to have a sound water tight roof but the difference between the temperature in a loft on a cold windy day that doesn't have felt and one that does is huge!

 

[jontop]

Just the draught excluding property of the felt

 

[freddiemercurystwin]

A draughty loft is a healthy loft.

 

[^woody^]

The only purpose of felt, is as a secondary waterproof layer with interlocking tiles. Felt started to be used when interlocking tiles began to be manufactured and the inherent flaw in the interlocking runner, and the porous nature of concrete tiles began to be apparent when the roofs leaked. For some reason, felt then began to be used on all roofs.

Clay bonded tiles or natural slate does not require an underfelt for the roof to be waterproof.

Felt has no insulation value, so it matters not of its there or not, insulation at ceiling level will perform the same

 

[catlad]

Too much air movement in a the loft space and you are going to be losing heat.

 

[^woody^]

There should not be any heat in the loft space

 

[jontop]

To say felt has no insulation value is wrong. EVERYTHING has an 'R' value!
I know a loft with felt will be warmer than a loft without!

 

[jontop]

Local authorities insist that any building for use as a dwelling must have felt because it increases the energy efficiency of the building.
Felt was first used under slates 'sarking' way before concrete tiles

 

[freddiemercurystwin]

Local authorities insist that any building for use as a dwelling must have felt because it increases the energy efficiency of the building.
Felt was first used under slates 'sarking' way before concrete tiles

Haha what a crock!

 

[jontop]

Take a look at thr tyvek website freddy