Secondary glazing for skylight.

[Richard Caley]

[ I could just pay someoen to do this, but it looks like it might be an
interesting small project ]

I have a skylight in a small room. This is basicly a pyramid shaped
0.8m square window at the top of a 0.5m vertical tunnel.

I know from last winter when I was decorating and had the radiator off
that the room loses heat and gets cold quickly in winter. So, it is
probably worth working out how to insulate that skylight.

What occurs to me is to build a frame and put a couple of sheets of
clear plastic `glass' at bottom of the `tunnel', ie at ceiling
height.

This is not beyond even my limited abilities, probably, on a good day,
but I suspect condensation in the chimney between bottom and top windows
might be a problem. Is there an obvious solution to this which hasn't
occured to me?

I'd rather not do _anything_ to the external glass part as that would
involve going up on the roof which in turn would involve going up a
ladder next to a 4 floor drop, and, being one of those who has to
build up courage before changing a lightbulb, frankly I'd rather
freeze to death.

Quick diagram:
_^_
/ \
/ \ <- Glass
/ \
-------------| |--------------- ROOF
#############| |###############
#############| |###############
-------------o=========o--------------- CEILING
^
New Plasic Window

 

[BigWallop]

[ I could just pay someoen to do this, but it looks like it might be an
interesting small project ]

I have a skylight in a small room. This is basicly a pyramid shaped
0.8m square window at the top of a 0.5m vertical tunnel.

I know from last winter when I was decorating and had the radiator off
that the room loses heat and gets cold quickly in winter. So, it is
probably worth working out how to insulate that skylight.

What occurs to me is to build a frame and put a couple of sheets of
clear plastic `glass' at bottom of the `tunnel', ie at ceiling
height.

This is not beyond even my limited abilities, probably, on a good day,
but I suspect condensation in the chimney between bottom and top windows
might be a problem. Is there an obvious solution to this which hasn't
occured to me?

I'd rather not do _anything_ to the external glass part as that would
involve going up on the roof which in turn would involve going up a
ladder next to a 4 floor drop, and, being one of those who has to
build up courage before changing a lightbulb, frankly I'd rather
freeze to death.

Quick diagram:
_^_
/ \
/ \ <- Glass
/ \
-------------| |--------------- ROOF
#############| |###############
#############| |###############
-------------o=========o--------------- CEILING
^
New Plasic Window

Firstly Richard. Does the existing window have an open vent at the ridge ?
I mean, does it have any open vent at the very top part of its frame work ?

If it isn't open to the elements, then I think it would be quite feasible to
frame the tunnel at ceiling level, then, as long as it is sealed air tight,
which is really what you want it to be, it shouldn't have any problem with
condensation.

If the ridge does have an open vent, then I think I'd first try to find a
way of being able to close it up during the winter months.

 

[David H.]

I have a skylight in a small room. This is basicly a pyramid shaped

0.8m square window at the top of a 0.5m vertical tunnel.
...the room loses heat and gets cold quickly in winter. So, it is
probably worth working out how to insulate that skylight.
......to build a frame and put a couple of sheets of
clear plastic `glass' at bottom of the `tunnel', ie at ceiling
height....... but I suspect condensation in the chimney between bottom and
top windows

might be a problem.

I am wondering about doing this when I install a skylight in a future
project. I'm inclined to use glass instead of perspex since it won't become
opaque/scratched as easily - although the safety kind that has two sheets
laminated together & won't shatter when broken.
Perhaps some grilled vents could be put in the 'chimney' sides allowing a
(slow) exchange of air with the loft space? The next question is whether or
not to insulate the sides of the chimney? And how to make the sheets
removable for cleaning?

And I've got the same reservations as to the validity of the whole thing!

 

[Richard Caley]

Thanks for the reply.

s> Firstly Richard. Does the existing window have an open vent at the ridge ?
s> I mean, does it have any open vent at the very top part of its
s> frame work ?

Not so far as I can see from where I can get to with a step ladder
(high ceiling plus height of roof plus height of pyramid means there
could be somthing in a side I can't see) I strongly suspect it is
just a wooden frame with triangluar pieces of glass. Way back when
when this building was put up I think keeping out the cold was a
priority and ventilation wasn't.

(they also aparently had not invented the right angle, which may make
the frame building more fun).

s> If it isn't open to the elements, then I think it would be quite feasible to
s> frame the tunnel at ceiling level, then, as long as it is sealed air tight,
s> which is really what you want it to be, it shouldn't have any problem with
s> condensation.

That sounds good.

I suppose there is a limited amount of air up there, so a limited
amount of water to precipitate out. Maybe throwing a small bag of
silica gell up there might be a worthwhile belt and braces move.

 

[Richard Caley]

dh> I'm inclined to use glass instead of perspex since it won't become
dh> opaque/scratched as easily

Mine is so high that nothing inside is going to touch it, and of
couse, there is no access to the other side, so simplicity of cutting
made me think of plastic.

dh> (slow) exchange of air with the loft space? The next question is whether or
dh> not to insulate the sides of the chimney?

I'm assuming that even if the space gets down to exsternal
termperatures, a double layer of plastic at the base will provide
reasonable insulation for the room.

dh> And how to make the sheets removable for cleaning?

Removable frame on some kind of removable fastening?

I was seriously considering velcro. I have a trestle table I hold
together with high-strength velcro and quite small amounts happily
hold a heavy trestle when the table top is lifted. Certainly heavier
than a frame and perspex I was thinking of. Glass would be another
matter.

/|
/|---------
/| |
W /| wooden |
A /| batten |
L /| |
L /|---------
/| ######## <- velcro
/| ---------
/|| |==============================================
/|| wooden | Glass/Perspex
/|| frame |
/|| |==============================================
/| ---------
----


Perhaps a more conventional attachment on the same lines would be to
put the kind of rubber draft excluder used around doors where the
velcro is above and use (reasonably presentable) bolts through the
frame into threaded fixtures in the batten.

 

[David H.]

Removable frame on some kind of removable fastening?

That looks like a workable solution. I'll go with using bolts and hide them behind
some architrave - attached using your velcro idea. Thanks!

 

[Richard Caley]

I have seen small pseudo nuts (ok they probably have a real name)
which are basicly a narrow tube with an inside thread with a flat
collar at one end, the collar having a couple of prongs sticking
down. In crosss section, something like

___ ___
\/ |//| \/
|//|

The tube goes into the hole the bolt will come up through, the prongs
get hammered into the top of the batten and so stop the whole thing
from rotating.

Alternatively, there are fixings Ikea seem to be in love with which
are basicly short pieces of steel rod with a threaded hole through
them cross ways, the bar goes into a horizontal hole, the bolt comes
up from below and through the threaded hole in the bar. These also
presumably have a real name. Have to find my Screwfix catalogue. I
suspect these would be fiddly to get right when you can't get to
rotate the bar to get the bolt in to it, because the glass is in the
way.

 

[BigWallop]

Thanks for the reply.

s> Firstly Richard. Does the existing window have an open vent at the ridge ?
s> I mean, does it have any open vent at the very top part of its
s> frame work ?

Not so far as I can see from where I can get to with a step ladder
(high ceiling plus height of roof plus height of pyramid means there
could be somthing in a side I can't see) I strongly suspect it is
just a wooden frame with triangluar pieces of glass. Way back when
when this building was put up I think keeping out the cold was a
priority and ventilation wasn't.

(they also aparently had not invented the right angle, which may make
the frame building more fun).

s> If it isn't open to the elements, then I think it would be quite feasible to
s> frame the tunnel at ceiling level, then, as long as it is sealed air tight,
s> which is really what you want it to be, it shouldn't have any problem with
s> condensation.

That sounds good.

I suppose there is a limited amount of air up there, so a limited
amount of water to precipitate out. Maybe throwing a small bag of
silica gell up there might be a worthwhile belt and braces move.

That idea sounds good to me.