Loft insulation and cabling...

[Adam-the-Kiwi]

Hi there uk.d-i-y,

Both we and our neighbours have loft conversions, and there is a small (1-2m wide) shared space between us that is generally used for storage. This area has never had any type of insulation, and it is noticeable in the winter that while frost forms on our roof and our neighbour's, there is always a frost-free spot over this shared area. We have offered to insulate and floor this area (partly because I think we suffer more from thermal loss, partly because we want to run a toilet extractor system through this area) but, because of the age of the properties, it is a maze of difficult to identify pipes and cables. I know we should run cables over the top of any insulation we put in but it appears that most of the cables (some of which, I think, belong to our neighbour) do not have enough slack to put insulation under them. We are insulating with IsoWool (left over from loft insulation) and wool fleece insulation.

Is there another solution? (I was considering making a tunnel for the cables from one half of a 100mm plastic pipe, but I guess that will not allow the dissipation of heat) Are cables OK to be buried in insulation if they are tacked to a joist?

Cheers - Adam...

[cynic]

Everything depends on the rating of the cable(s), the current being carried under full load and the material used for electrical insulation. Generally if a cable is enclosed in thermal insulation for more than

0.5 metres it should be considered to only have half the current carrying capacity of the same size if clipped direct to an exposed surface. You "may" be able to insulate without problems if the cables you mention are lighting circuits and only lightly loaded

[John]

If a cable is getting hot then it is too small. They don't in normal domestic situations.

[andyv]

Wow. I recently had an extra thickness of fibreglass insulation fitted in my loft, all done by a government approved contractor on a grant. They also filled my cavity walls and did new tank jackets. However, they just went over all the cables.

This makes me wonder if there are safety issues to consider?

[Adam-the-Kiwi]

-88-

OK, thanks cynic. That was what I thought (the 50% current capacity) - but I'm not sure I can identify what cable does what. Several iterations of renovations (before we or our neighbour moved in) have left a maze of cables and pipes and I'm not confident that I even say for certain what is ours and what is next doors (and identifying the load on next door's cables will be difficult if not impossible).

Is there an alternative? I was thinking along the lines of something that could be used as a heatsink, as I understand that the regs say that cable that has one side attached to a thermal conductor can be buried in insulation...

Thanks again - Adam...

[jrwalliker]

Why not insulate the inside of the roof? Then there will be nothing directly over the cables and the whole space will be warmer. This might reduce heat loss through the wall which adjoins the shared space.

John

[RobertL]

A shared space? Surely the boundary must really be divided into your bit and their bit, legally speakling. Usually the party wall continues up through the roof space so that fire cannot spread acros from one roof to the next.

Robert

[sm_jamieson]

Yeah, I was going to say this too. If there is a shared space, this is no t OK for fire regs AFAIK. You also get noise transmission and food smells between houses ? I would get this area properly bricked up ASAP. Simon.

[Andrew Gabriel]

In many terraces, it didn't. Extending up to the roofline, and then above the roofline in some locations were later requirements.

[sm_jamieson]

Anyone remember Frank Spencer going up in the loft to fix a leak, and after various disasters and bungles, falling through his neighbour's bedroom ceiling ? Simon.

[<me9]

There /are/ terraced houses in use, where the separating wall doesn't extend much above ceiling level. Built in the days before BRs. A loft conversion would require remedial work, but otherwise nothing. I hate to think what a fire would do.

It would make it easier for burglars etc, I would brick up in any case.

[Tony Bryer]

The one near-disaster in my plan drawing days was the Edwardian ex-Council house with a half brick party wall which stopped at ceiling level. Above it someone had built a stud and plasterboard fire partition, so I had no idea that this was so - had it been taken up to the tiles in brickwork, the bond would have given it away. Major crisis when the loft conversion co. strips this partition out and finds precious little to plant their steel beams on! Solved by putting a steel along the entire length of the wall to disperse the load, justified by some frantic calculations.

[Andy Wade]

Possibly. The NICEIC published an article in its magazine /Connections/ a couple of years ago giving practical advice on this topic. It doesn't appear to be on their website any more, but a copy can be downloaded from Voltimum, starting here:

background reading from IEE /Wiring Matters/ here: