My brother in law has just bought a huge old Manor House (successfull business man) and he has asked my opinion about the loft insulation and I thought I would run it past you lot!. He is having the sash windows repaired and double glazed but there is no other insulation in the place. It will be a cold loft and he is having a new roof installed. He also mentioned the fact they have a rodent problem (its in the middle of woods). What insulation would people recommend for this?

When I did calculations, standard glass wool loft insulation was by far the best value in terms of cost to achieve a certain U-Value.

 

400mm will give you around a 0.11 U-value at a much lower cost than say 200mm of PIR, particularly it is much cheaper to install.

 

If he wanted to make it a warm loft and use the space it might be a different answer, but I would guess that this is by far the easiest/cheapest way to improve the insulation value in an old house.

 

 

Basically I agree with AliG, rolled out loft insulation gives cheapest thermal resistance performance. If the rodent problem could be eliminated then loosefill cellulose with its greater decrement delay is only about 7-8% dearer on a performance basis.

 

https://www.insulationsuperstore.co.uk/product/thermofloc-loose-fill-cellulose-insulation-12kg-bag.html

Loft insulation for value. Keep an eye on Facebook groups, Gumtree etc for even better deals.

 

If he's having the roof done though, possible to consider a warm roof? A lot more thought required but in certain scenarios will be a better result.