Flooring a roofspace

Homersimpson

One other consideration is what thickness of loft insulation you have/need.

If your existing joists are only 4" then you will only hvae 4" of insulation if you board over them.

What I did at my house was used loft legs from toolstation which added another 7" to the floor so I could have 11" of insulation which was the recommended amount at the time (not sure if this is still the case?).

The loft legs were expensive so when I did the same at my parents I bought some 8" joists and cut them up into blocks around 8" long, screwed these into the ceiling joists and built the floor on top of this with 11" of insulation.

I used chipboard flooring, I think there is a type with a more water resistant glue (maybe called P5?) it used to be green in colour when I bought it from B&Q

Once built it was all nice and stable (and warm).

Homersimpson

These were the loft legs:

https://www.toolstation.com/loft-flooring-legs/p44016

Just one other thing to add, if the electrical cabling in the loft is for anything other than generally lighting you might need to leave it in free air as insulation above power cables for sockets, showers, cookers etc. can cause problems.

A lot of houses only have lighting in the roof but there are a few exceptions.