Boarding loft rafters

[QuincyME]

Hello everyone. First time poster. About a year and a half ago we bought a 1950s semi-detached house that needed a complete refit. Weve moved in now but to check storage space I ventured in to the loft to see what was available. First thing I noticed was the under-tile roofing felt has split/torn badly in places and is now hanging down. The tiles are visible though the gaps/cracks and a lot of dust has come in from outside and is laying on the insulation. It would also appear that at some point snow has blown underneath the tiles, melted, dripped through the insulation and stained the bedroom ceiling. Going by looking closely at it the "felt" is Kraft paper (even has the Kraft logo on one edge). Its formed of several layers with fibres in between and is brown on one side and dark on the other. It would appear that futher up the tiles have been lifted and another type of felt has been laid which looks like string net encased in a sheet of thick, black plastic (best way I can desribe it).

Speaking to next door they had the same problem and ended up paying £3000 to have a firm come and raise the tiles and relay the felt for the entire loft. We dont have that sort of money and as it is only really the bottom half of the rafters that its coming away I attempted to fix it by using a staple gun and insulating tape. This failed as when a draft came under the tiles it ended up tearing in other places and hang down again.

Now to the advice I need. I have 2 ideas:

1). Put sheets of hardboard over the rafters which would then cover up all of the gaps and stop the draft/dust coming in. I have been advised to leave a gap at the bottom to allow air to circulate in from the eaves.

2). Cut lengths of hardboard the exact width of the space between the rafters and then lay them between the rafters (over the tiles/kraft paper) and attach them to the rafters some how.

Assuming I still left the gap at the bottom would either method work as air would still be able to circulate?

I am also thinking of stapling several lengths of double sided foil/buble insulation over the rafters to give some of the heat in and then boarding over that. Would this be ok (condensation-wise) as there would still be an air gap between the foil layer and then underside of the tiles. What about if I did this with the second method and glued the foil to the underside of the hard board and then laid it between the rafters over the underside of the tiles? Would it still cause condensation between the tiles and the surface of the foil layer and drip down into the loft floor/cavity wall?

Thanks for any advice. If anybody needs further info or clarification give me a shout.
Thanks,
Mike

 

[Burnerman]

Many older properties don't have any underfelt, and from the inside, the slates were sealed - as well as they could be - by lime mortar.
This process is known as 'torching'.
Often the mortar has turned to dust by now, and has fallen in.
So, to prevent dust up there, consider stapling the foil covered bubble wrap insulation on the underside of the rafters, sealing the long joints up with duck tape. Any dust blown in will lie on the top.
Solid slab insulation is good too - but it mustn't touch the underside of the slates.....leave an air gap of at least 50mm if you decide to use this.
On the ceilings, use 300mm of cosywrap type insulation, but don't apply it right in the eaves or soffits. Grants are available for this right now.
One extra point....avoid nailing on the underside of the rafters....you don't want to shake the slates loose!
John

 

[QuincyME]

Thanks for the advice Burnerman John. What you suggested with the foil insulation is pretty much what I had in mind. My concern is that with warm air then being "inside" the loft and the colder, moister air coming through the tiles from outside condensation may form on the outside surface of the foil which would then run down and on to the space between the rafters where the ceiling meets the outer wall (or possibly down in to the wall cavity) and cause obvious damp problems. I did consider the Celotex-type insulation but the concern will still be there regarding condensation forming on the outer foil surface (although is the 50mm recommended gap to allow ventilation and stop the condensation forming?)

Once I lay the foil across the rafters I also want to cover it with hardboard as I have several 500w work lights up there to see what Im doing and I dont want the light to reflect off the foil and blind me! Will this effect it in anyway? The instructions say about what to do if laying plasterboard over but not about any other type of board.

Mike

 

[Burnerman]

Have you considered Celotex PIR board, 25mm thick from the likes of Wickes? I can't see much advantage using a bubble foil and then hardboard too.
I'd put it across the rafters, not in between so you can maximise draught and only lose the minimum headroom.
John