Sun tunnel vs skylight vs window

[Malc]

Does anyone have any data on how these compare?

I've stairs and landing in the corner of an L shaped house. Downstairs is a glass front door, but with a porch, and upstairs a 1m x 2m (wxh) window, both in the corner. The upstairs landing is ~4.7m x 3.8m, plus a bit of corridor going off. This is an extension, not built yet, here's a screen shot of the plans:



I'm concerned that the stairs/landing will be dark. The window faces North (well NE as stairs are due N-S) which doesn't help. Roof is very tall so a skylight would be at the end of long tunnel, not to mention impossible to reach to clean or paint. I was wondering about a sun tunnel around the top of the stairs to give fill in light away from the window and maybe another at the end of the corridor. Just going straight up would be ~2m or just under. But I'm not sure how those would compare with the light already coming in from the window. Has anyone used sun tubes light like?

I reckon they might work, or it might be turn on the ceiling during the day in a normal room, makes no visible difference. And given the price of them it would be an expensive mistake. The velux calculated seems to be saying I could expect 1-2 100W bulbs which doesn't sound a lot to me.

Also, has anyone ever done a DIY version? I was thinking along the lines of a velux window in the loft, boxed in with some acrylic mirrors and 5 wall polycarbonate set into the ceiling. You could then get access from the loft for clean, painting etc.

 

[noseall]

Sun tunnels do work and are a more practical option to a roof window. The problem with a roof window is the trimming out of the rafters/joists etc as well as dealing with any wires or pipes that may be criss-crossing the ceiling joists.
the obvious advantage of a roof window is it can be opened.

I was thinking along the lines of a velux window in the loft, boxed in with some acrylic mirrors and 5 wall polycarbonate set into the ceiling

Completely baffled by this statement.

You would normally 'tunnel' the window down from its position in the roof to the ceiling, using studwork and celotex etc.

 

[Malc]

I should have made clear that this is an extension with a new roof so the tunnel or window would be fitting with the roof. Assuming 600 centre trusses and 550mm wide velux there is little difference in the work in fitting in the tiles.

The issue I think is the capture area. A 14in 350mm light tunnel is an area of 962cm2. However, arguable we should take that as a hemisphere, or a bit less say 25mm up so it would be a spherical cap, radius 17.5cm, height 15cm, which is an area of 1649cm2. A 55x78cm roof window is an area of 4290cm2. The glass area will be less, ~2100cm2 but again we need to allow for light entering from the edge so the light collection area will be more than 2100cm. Hence the smallest velux is more area than one roof tunnel and I could go 55x98 or 55x118 maybe.

You're right that the normal way would be to build a plasterboard and celotex tunnel to the roof window. There are some problems with that in my case. The roof is ~2m (maybe a bit less say 1.8m) which is a very narrow tunnel. Unless I ask the roof truss designers to make a bit hole maybe by removing part of the bottom chord of one truss, I'll check up on that. But what I was thinking is that I would need to line the sides of this tunnel with a mirror, at least at the bottom. This would then bounce the light out (like a light tube does) and overcome the narrow tunnel effect, just one bounce makes the tunnel effectively 3 times wider. Think of it like a window butted up to a mirror, the window looks twice as big, you get twice the light (roughly, say 190%). So in this case the window is effectively 3 times wider and so is the tunnel (ignoring double bounces which make is wider again). Seems to me that this will gather far more light than a 14in sun tube.

The problem with this is that it's not very pretty and how do I clean the mirrors, paint, etc. as this is above the stairs. I'd estimate say, -1m down the stairs, 2.4m ceiling, 1.8m to roof, 5.2m total. Also, I have a roof window in my current house. Gives lots of light but since hot air rises there is a tendency to get condensation on this window which then drips off. The window is ~1.5m from the bathroom door which doesn't help but I reckon the bathroom isn't the sole cause as that bathroom is often making steam (there is a separate shower room). Hence my idea is to put a second window in at ceiling level with 5 wall polycarbonate like used in conservatories (U=1.6). Boxing in is done in the loft just to hold the mirrors and keep everything clean and insect free. Plus it helps decrease the U value. If I box in with a removable panel then I can get access from the loft to clean the glass, etc. if I need to. And flush ceiling should remove the tendency for hot wet air to rise in a tunnel and condense.

 

[Burnerman]

How about a Velux Integra electric window?
Superb for ventilation (and letting the flies out!)
John

 

[Malc]

House is having MHRV so ventilation is already sorted. Anyway the issue is a roof window at the end of narrow tunnel. Either you need mirrors or a wider tunnel.

 

[DIYWell]

I had a similar problem a few years back so thought I'd chip in how I solved it, and how I might think about it now.

Dull landing, wanted more light, and solar tunnels were being pushed by some big manufacturers. I saw a few different designs, and went for a 250mm Solarpipe in 2011 since they had the highest transmittance for the cross section, and I wanted illumination, not a reading light. Avoid anything that doesn't have a smooth wall to it. Mine had a dome on the end that collects light from all angles, but since the dome projects upwards, needed planning permission. Not a problem since we were doing a lot to the house anyway. Works a treat.

I did seriously think about a about a sealed rooflight boxed in with mirrors to a larger (600 x 600) difuser. However it does make a seriously large cold spot in the ceiling and potentially a condensation problem. Also, the amount of light is dependant on the angle of the sun. If you decide on doing this, bear in mind which ever trades you use to fit it will most probably have poor understanding of what you're trying to achieve which could lead to a sub optimal result.

Two things to think about if you do go down the hole-in-the-roof route is where will you position ceiling lights? I built mine into the light pipe. And do you need to add a blind to stop the light going out in the dark. Again, I built a baffle into our pipe but it still leaks a fair amount much to the puzzlement of the neighbours though I did tell one kid I could call Batman with it.

One option that's practical now but wasn't 5+ years ago is simply to fit a large daylight LED panel to the ceiling and dress it up to look like a rooflight. I've seen one that even mimics the external light levels. They're cheaper than a lightpipe to buy and fit and cost pennies to run.

 

[Malc]

Interesting ideas. I'd do the boxing in and ceiling myself so not issue trying to get a tradesman to get it right. Ceiling cold spot is addresses by polycarbonate 5 wall, OK U is still 1.6 for that but I've then got air in the box, then double-glazed 1.6 window. Won't be as good as the rest of ceiling but would be better than a roof window.

I was think of having separate ceiling lights, more decorative. I love the idea it's for calling batman, LOL.

The idea of LED lights, is very interesting. A quick google has found a panel 600x600, 40W, 3800 lumens for under £50. Clear sky, outside, is ~10k lux or 1k lux if overcast. That would be 3600 lumens to 360 lumens for 600x600 tube (lux = lumen/m2). Velux suntunel calculator for a north facing roof and a corridor 4x4m, 2.4m, reckons 3 sun tunnels are needed, cost £1044. Each tunnel gives out 608/528/384 lumens (sun/sun-cloud/overcast). So on those figures the LED panels is equivalent to 6 sun tunnels. Even if I face the sun tunnel south (which I couldn't) the figures are only 1760/1232/384 so the LED panel is still better.

Cost wise, 40W for 12hrs/day, at 12p/kWh is £21 pa, but that's full on and ideally the unit varies the level so it looks realistic. Call £7.50 pa, which is 1/2 power for 1/2 yr and 1/2 power start and end of the day. Unit lasts say 10yrs so £125 for 10yrs. Although, really the reduced heating loss should be considered too. I've come up with a figure of extra heating of £2.5 pa, so £100 for 10yrs, although half of that is the unit replacement cost so if it lasted 20yrs the cost would come down to £75 for 10yrs.

That compares well with the cost of sun tunnel (~£300 upwards to 600-700, for one). Or my DIY unit, ~£300 for materials (£230 for window) with an estimated 15k-1.5k lumens (which is from a tube of 0.6x0.98 with mirrors making this be ~3x wider). And the advantage of LED is that you can put it where you want to and if you find you need it (I have a window, but not sure if it is enough). Definitely needs looking at, maybe getting and trying in a similar situation to see how it performs.