Replacing/upgrading loft insulation

29 Jul 2019
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United Kingdom
When I bought my house (originally built in the 1930s), the surveyor noted that the loft had polystyrene insulation 'in places'.

I've been looking at properly reinsulating the loft as at present, it looked like most of it was less that 100mm of fibreglass, with a partial chipboard floor screwed direct into the joist.

Now, I know that I should have 270mm of insulation so my plan was take up the floor, stick some loft legs in, and then either put in a base layer along the joists of 100mm insulation, lay over at 90 degree 170mm insulation, and then relay the floors on the loft legs.

Then I made the mistake of poking at the existing fibreglass insulation.

Short version, is it looks like the entire loft has lines of polystyrene tiles between every joint, covered by a small amount of fibreglass. Worse, there are electric cables UNDER the polystyrene...and helpfully, there also appears to be shreds of newspaper everywhere, which to the best of my deductive ability appear to be from the early 1960s. The wiring appears to be in good condition and is sufficiently loose enough that it could be lifted up and have new insulation placed underneath it.

Should I:

a)remove all the existing old fibre insulation, all the polystyrene, and then relay new two new layers (between joists and over joists).
b)lift up all the existing fibre, pull out the polystrene, put the existing fibre back in and just lay one new layer over the joists
c)consider this to be a far more complex job than a standard insulation job and get professionals in
d)something else?
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