They are great for a short span, maybe a metre, but mine stretches over 2 metres and is a bit poor....

Rachel, what type of tube is yours - rigid or the concertina type?
as you infer performance definitely goes down with increase in length, and also with any bends.
j40 - these tubes are fairly well advertised in the building press and at shows etc. There have been a number of threads on here discussing them.
Will be fitting our solatubes soon.

Rachel- you might want to check out Solatubes- they have the most highly reflective tubes out of all of them- and apparently the bigger ones (350mm) can span 9mtrs- although I doubt that! Mine span 2 mtrs each and are excellent. Terry, who is fitting your Solatubes or are you doing it yourself?

I've fitted a couple of the velux rigid tube solar tubes,was quite impressed with efficiency in a middle of house bathroom,Travis Perkins sell them but not cheap outside of trade.

No they are square on the outside of the roof -- round flat pearl on the ceiling.

How do they affect the insulation of the roof they penetrate? I seem to remember getting the impression from somewhere that the cost of light would be increased heat loss...

They cannot even be described as thermally efficient -- they are not and they are problematic to both try to insulate and to stop drafts.

But then the tube itself is totally uninsulated and must cause big heat losses.

Havn't insulated or draft proofed solar tubes,with a 4" extractor 3 feet away going directly to a tile vent didn't seem much point worrying about a minimal heat loss.

Seem to recall one of the manufacturers advertising bumff giving a U-value of 2.0

this seems to be 1 of 2 threads from 2008 on sun tubes, just been doing some googling, there's a website for a British manufacturer called Addlite that are claiming u-values 'up to' 0.43 and a patent double glazed thermal break ( double glazed insert in the tube ). Anyone else have the inside track on this, ie. does this Patent explain why the other systems from Velux et al. don't seem to do the obvious thing and have such poor u-values? Has anyone tried the Addlite product?

But you are not in the UK are you.

Yes I am in Italy but that makes no difference whatsoever to this thread. At least I have them and, indeed, fitted them myself as part of a refurb.

Just had a look - nice bit-o-kit! I am only dubious as to the light collection claims - the best orientation is to mount the domed collector horizontally and pass through the sloped roof vertically - which isn't an option for obvious reasons given their thermal break needs to be in the same plan as the roof. In addition, the glass thermal break will reflect light (twice!) so absolutely cannot get close to non-thermal break transmittance tubes of well over 95%. Still all-in-all looks good and not as expensive as I imagined.

If anything (dust water) falls on the DG section it'll be a bugger! Looks easy to ensure air tightness. You are certainly going to need to trust their engineering and R&D. Would I have paid more than a third more for it? - probably not but then I only have 100mm of white EPS in my roof. Reckon I could DIY the DG break without too much effort though, now I have seen the idea

We had 2 in the Energy Centre in Sheffield (UK).

I agree that they are not great thermally, but in terms of getting light to inaccessible places - excellent. I have not had a close look for a few years, but the one upstairs lit an otherwise unlit WC.Roughly 2.4m and a good bend to get to the roof slope, and it looks as if you have left the light on! No major condensation issues except when the local 'darlings' broke the dome.

In this case a high-performance roof-light and a 'tunnel' simply would not have worked.

There are also options with fibre optics which may be more appropriate for passiv hus. Don't know how the cost compares....