I thought I understood service voids but we built one room with one (a timber-framed sun room outside the thermal envelope) and now I think I don't! Can anyone explain?

The major purpose as far as I know is to create a cavity inside the vapour barrier for running services, especially electrics. What I've actually found though is that it's very difficult to route electric cables:

* every batten has to be cut, chiselled, routed etc to allow the cable past

* the battens don't allow much surface to secure the cables as required by regs

* dealing with the previous problems causes frequent penetrations of the vapour barrier. My wall looked like a poor shaver's face with toilet paper stuck all over it!

What am I missing?

pre plan the cable run and cut the battens before fixing them, leaving a gap so you dont need to cut them after wards.

Using metal studs is less green but easier to pass services through and come with pre made holes to pass cables etc.

Leaving gaps a top an bottom should do it. Shouldn't have too many cables traveling across battens as I don't think it's best practice to have horizontal cable runs but should instead travel vertically up from service point.
Clipping could be cable tied groups of cables that are then fixed through the tab end of tie?

There exist special clips for metal studs to hold the cables inside the metal studs. They are not ties and stay inside the stud.

Yes; cables running in metal C-studs a bad plan!

(across them in safe zone ok)

I'm struggling to see the advantage of service voids. In most of the scenarios I've worked with, most of the services, cables and pipe runs are easily accommodated within floor voids; this having the advantage of being more easily accessible should there ever be a problem.

Where there are socket outlets, they are generally at low level with only short cable runs (600mm max?) running through the insulated zone. such cables easily clipped to studs in timber frame; or chased in where masonry.

Copper pipe runs also in the floor void and often hidden on the surface in bathrooms and kitchens anyway. For those who really want them hidden they can still be accommodated on the internal edge of the insulated zone (though I dislike heating pipes in any insulated zone).

So why lose internal space and build in the potential for air losses from a service void? Am I missing something?

Posted By: bot de pailleHere in france they run the cables inside a flexible plastic tube. You install the tubing first and then pull the individual earth, neutral and phase wires through them afterwards as needed. Cables reserved for exterior or low voltage.

We can use conduits in the UK as well, but it's not so usual. More emphasis on keeping initial cost down at the expense of more difficult maintenance, I suppose.

Posted By: Mike GeorgeI'm struggling to see the advantage of service voids. In most of the scenarios I've worked with, most of the services, cables and pipe runs are easily accommodated within floor voids; this having the advantage of being more easily accessible should there ever be a problem.

Most of our cabling and plumbing is in the first floor void too, and we haven't found the lack of service voids to be a problem. But then I have forbidden any services in the external walls at all! So I don't care as much about air leaks through backboxes and suchlike.

cables easily clipped to studs in timber frame; or chased in where masonry.

It does seem like the wiring regs were written by people more familiar with masonry than timber frame, though. It's all very well saying the safe zone goes up, down or sideways from the socket or switch. But if you interpret that too literally, it means you have to notch out a stud or noggin for every backbox!

Posted By: TimberService voids are a great idea for air tightness

How so?