Roof construction

[slangivar]

MY roof has 3 layers between the loft and outside, first a layer of felt which would not take any water outside the house, then a layer of polystyrene insulation followed by an air gap and then concrete tiles. Can anyone tell me what the purpose of the felt is as it only seems to channel the water as far as the inside of the external wall?

My other question is about adding additional insulation in side the loft. As the only venting appears to be directly under the tiles will it cause an issue to put additional insulation right up to the inside of the felt?

If it helps the house was built in the 1970s.

Thanks

 

[noseall]

The purpose of roofing membrane is to weather the structure until the tiles are ready to be fitted.

Once the tiles are fitted they become the primary weathering material.

However, just like the tiles, the membrane should be laid so that it discharges any rainwater into the gutter, just the same as the tiles.

I get the feeling that someone has retrospectively fitted felt and insulation from the INSIDE of your loft without actually realising what they were doing.

If you are not sure of the processes involved regards insulation, venting and felting then i suggest you get some professional help as doing it badly can do more harm than good.

 

[slangivar]

The felt and are on top of the trusses and are the same in every house in the street so definately not a retrospective fitting.

I've been trying to get roofers in to take a look since May. The first one has done about 3 days work in the meantime and achieved nothing, The other 2 have so far been no shows. It sounds like the construction of our roof is sufficiently unusual that even the professionals have no idea.

 

[Alastairreid]

Your roof is a typical construction except north of hadrians wall there would normally be sarkin or ply on top of the rafters.

The way you worded your original post sounded like the felt was inside the attic below the rafters.

The felt should continue into the gutter or above the eave trays.

The polystyrene sounds like it has been retro fitted though.