Victorian pitched roof insulation

[fornost]

I'm looking for advice on best method of installing some loft insulation into a Victorian period house with rooms within the pitched roof area. These are original with original lath and plaster lining. The roof itself is constructed of slates laid onto a fully wood boarded roof (ie no felt). the supporting boards attached to the outside of the rafters. the access into the roof space is very limited and getting insulation down the gaps between the rafters and the laths is going to be fun. Short of ripping down all the lath & plaster (including some fine Victorian plater mouldings) is there any suitable insulation material I could use. As there is no felt and the slate supporting boarding although close is not fully sealed, could I pour loosefill insulation down into the gaps? Any advice suggestions gratefully received.

Thanks

 

[Freddie]

One hell of a job and i cant think of anything as you will need a couple of inches free so air can travel between the rafters from top to bottom to take away any moisture build up.

All i can think about is replacing the plaster and installing the insulation then anything else would be kind of an insulation bodge

 

[fornost]

Thanks for that, the only thing I can think of if there must be this two inch air gap is using poylsyrene in shhet form that could be cut and slid down between the rafters, only problem being corner areas cos the gaps are narrower at the top than the bottom.

I'm coming to the conclusion that I will have to bite the bullet and rip out all the original plasterwork but if there is someone out there who knows different please let me know..
Cheers

 

[bikerm4]

if you decide to slide polystyrene between the rafters i would suggest you use Kingspan or Celotex.These are more rigid than polstyrene and more thermally efficient. Not an easy task though, ive had to do it on one of my houses in the past but only 1500mm of the roof was sloping and access was from the loft area with room to work.

 

[Freddie]

On new builds you use 80mm kingspan to get the right insulation properties, but then you use 6x2 rafters.

I dont know what you have and you may be wasting your time if the insulation isnt thick enough and you dont have the space for the insulation and through ventilation.

One way round this is to counter batten with 2x2's on your ceiling, not very expensive but that would givw you your space required but of course you will lose 2" in ceiling height.

Dont forget to put plenty of soffitt vents in on both sides for through draft