Hi,
I am having the inadequate 100mm of insulation increased to somewhere nearer 300mm in my loft. and want to retain the storage space.
I have considered increasing the insulation with celotex but the cost of this is prohibitive and so I am left looking at adding new joists around 20cm above the existing ones.. The span is 4.6m which I guess is too much for a suspended floor to be a viable option.
I see from previous threads that there is some concern about the weight of adding new joists (at 40cm centre to centre) to the loft, with this in mind I would like to keep the size of the perpendicular joists down and plan to use the off cuts to make spacers to raise the new joists off the old ones.
My two questions are firstly are 40cm centres excessive or can I use 60cm centres for the new joists. I will be using something similar to B&Qs 18mm loft flooring packs which are already installed.
Secondly what size of joist would be recommended I am considering either 38x75mm or 38x100mm but not sure if this will be strong enough (I guess this partly depends on the distance between joists)?
The existing joists are 37mm x 138mm (1.5"x5.5")
I am having the inadequate 100mm of insulation increased to somewhere nearer 300mm in my loft. and want to retain the storage space.
I have considered increasing the insulation with celotex but the cost of this is prohibitive and so I am left looking at adding new joists around 20cm above the existing ones.. The span is 4.6m which I guess is too much for a suspended floor to be a viable option.
I see from previous threads that there is some concern about the weight of adding new joists (at 40cm centre to centre) to the loft, with this in mind I would like to keep the size of the perpendicular joists down and plan to use the off cuts to make spacers to raise the new joists off the old ones.
My two questions are firstly are 40cm centres excessive or can I use 60cm centres for the new joists. I will be using something similar to B&Qs 18mm loft flooring packs which are already installed.
Secondly what size of joist would be recommended I am considering either 38x75mm or 38x100mm but not sure if this will be strong enough (I guess this partly depends on the distance between joists)?
The existing joists are 37mm x 138mm (1.5"x5.5")