Green Building Forum - Skylights, roof windows and clerestory skylights Sat, 30 May 2026 00:53:50 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234718#Comment_234718 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234718#Comment_234718 Mon, 11 Jan 2016 16:22:22 +0000 tony
U values assume steady state and an indoor and out door temperature

But skylights can radiate heat to outer space which is at absolute zero.

This heat loss dominates on any clear night.

Should heat losses from these be reassessed?]]> Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234749#Comment_234749 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234749#Comment_234749 Mon, 11 Jan 2016 21:30:57 +0000 Silky Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234750#Comment_234750 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234750#Comment_234750 Mon, 11 Jan 2016 22:05:35 +0000 Ed Davies
To weigh against the increased heat loss per m², roof windows also let in more light so a smaller area is possible.

Posted By: tonyBut skylights can radiate heat to outer space which is at absolute zero.
Well, about 2.7 K, not that that makes much difference from a building perspective.

More substantially, the effective radiant temperature of even a clear sky is a bit warmer than that though still pretty chilly at something like -30 or -40 °C. Obscure thing often referred to as the greenhouse effect. Anybody hear of it? Not that the UK winter sky is clear that often, particularly in winter when it matters, so usually it's effectively a bit warmer.

Vertical windows usually see at least a bit of sky, too.]]> Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234772#Comment_234772 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234772#Comment_234772 Tue, 12 Jan 2016 08:16:16 +0000 PeterStarck Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234785#Comment_234785 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234785#Comment_234785 Tue, 12 Jan 2016 10:16:49 +0000 dickster Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234791#Comment_234791 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=234791#Comment_234791 Tue, 12 Jan 2016 11:52:52 +0000 Ed Davies Posted By: PeterStarckIf the skylight outer pane of glass is reflective or tinted how does that affect any loss by radiation if at all.Depends - the reflectivity or tint might have a lot of effect at short wavelengths (e.g, visible light and near IR) but no effect at longer thermal IR wavelengths.

I suspect it wouldn't make much difference - if there was a coat that could be put on the outside or in the outer pane that reduced the thermal IR emissivity significantly they wouldn't bother with expensive and (somewhat) delicate coatings on the internal faces.]]> Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=310716#Comment_310716 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=310716#Comment_310716 Fri, 29 May 2026 21:36:18 +0100 Victorianeco
We were thinking of no windows in the roof itself but maybe clerestory windows on the east and west gable and above he rear glazed doors.

Any thoughts on this or will it become a dark area with no Velux or roof lantern?]]> Skylights, roof windows and clerestory skylights https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=310717#Comment_310717 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13951&Focus=310717#Comment_310717 Fri, 29 May 2026 22:16:46 +0100 Mike1
It may also be possible to incorporate north-facing clerestory window in the new roof close to the old rooms, depending on the roof design.

Due to solar gain I'd be cautious about any significant west-facing glazing that doesn't have a brise-soleil, unless it's going to be shaded by trees / a pergola / other buildings.]]>