Green Building Forum - Velux - air tightness/thermal bridge (BBX, BFX, BDX) Sun, 24 May 2026 16:25:05 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154069#Comment_154069 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154069#Comment_154069 Thu, 16 Aug 2012 11:09:43 +0100 nikhoward
Has anyone ever used these, are they worth it? About to order the Velux's and is it better to use these rather than the traditional GB techniques of foam/silicone/Pro Clima tape to minimise air leakage and thermal bridge (without the debate of tapes failures, etc)?

Any help/experience would be appreciated, some info on products below, thanks



Insulation Collar – BDX

• Insulates around the Roof Window frame, reducing heat loss and eliminating cold bridges.
• Makes insulating and installing the window a simple process.
• Comes with Underfelt Collar (BFX)
• Made to all standard window sizes.
• Click fittings ensure fast and accurate assembly.

Underfelt Collar – BFX

• Ensures a weather tight seal between Roof Window and the roof.
• Can also be purchased separately from the Insulation Collar (BDX).
• Pleated material ensures a flexible and tight seal to the underfelt of the roof, whatever its construction.
• Made from diffusion open material to minimise risk of condensation.
• Comes with transverse drainage gutter to lead water away from head of the window if a tile or slate is broken above the window.
• Welded corners ensure watertight and simple installation.

Vapour Barrier – BBX

• Helps prevent condensation from forming in the roof construction.
• Complete Vapour Barrier collar, fully welded in all corners.
• A fully welded rubber gasket with double pressure seal guarantees speedy installation and a vapour and air tight solution.
• Reinforced corners for extra security against perforation.
• VELUX installation tool helps fit the collar in a matter of minutes.]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154167#Comment_154167 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154167#Comment_154167 Fri, 17 Aug 2012 18:31:32 +0100 MikeRumney (Also, see elsewhere on here for discussion of low level flashings that are "coming on stream" and attempts to bring the DG nearer to the inner face of the roof to reduce heat loss thru the frame ... )]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154178#Comment_154178 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=154178#Comment_154178 Fri, 17 Aug 2012 21:33:39 +0100 borpin Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155466#Comment_155466 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155466#Comment_155466 Sun, 02 Sep 2012 17:55:07 +0100 nikhoward Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155758#Comment_155758 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155758#Comment_155758 Thu, 06 Sep 2012 23:56:21 +0100 nikhoward Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155867#Comment_155867 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155867#Comment_155867 Sat, 08 Sep 2012 21:10:39 +0100 borpin Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155950#Comment_155950 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=155950#Comment_155950 Sun, 09 Sep 2012 23:25:39 +0100 nikhoward Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=157455#Comment_157455 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=157455#Comment_157455 Tue, 25 Sep 2012 22:00:51 +0100 aa44
I bought and used the underfelt collars for the windows that I installed last year. They were pretty easy to fit although, as we had an M08 window above an M34 fixed element, we had to cut the bottom off the underfelt collar for the main window and cut the top off the collar for the fixed element and then staple / tape them together at the sides.

I haven't fitted the insulation in the roof yet so i don't know how I'm going to do the air tightness bit!]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=157515#Comment_157515 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=157515#Comment_157515 Wed, 26 Sep 2012 12:35:34 +0100 fostertom Posted By: aa44i don't know how I'm going to do the air tightness bit!http://www.natural-building.co.uk/news/2010/files/SIGA-Airtightness-manual.pdf pp28-31]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159002#Comment_159002 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159002#Comment_159002 Mon, 15 Oct 2012 22:57:35 +0100 nikhoward Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159015#Comment_159015 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159015#Comment_159015 Tue, 16 Oct 2012 04:16:19 +0100 wookey Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159030#Comment_159030 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159030#Comment_159030 Tue, 16 Oct 2012 09:15:03 +0100 nikhoward Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159136#Comment_159136 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=159136#Comment_159136 Wed, 17 Oct 2012 00:00:43 +0100 nikhoward Posted By: nikhowardNot perfect, but as you say a hard to treat area, the builders merchant says they hardly ever sell them

Have got the vcl/airtightness bits as well, which if you diyed it or got pro clima stuff would cost much more and/or be fidly]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161359#Comment_161359 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161359#Comment_161359 Wed, 14 Nov 2012 23:13:56 +0000 borpin http://www.borpin.co.uk/2012/10/13/slow-progress/ and http://www.borpin.co.uk/2012/11/10/nu-lok-roofing-system/

Key thing I have learnt is that when fitting these on externally fitted insulation, just fitting them to the oversized counter battens works just fine. I had all sorts of ideas of building a wooden frame fitted through to the rafters but in the end we didn't bother. So there is virtually no thermal bridge except through the window frame itself. Sealing inside will be an interesting task. I think I should have used a breathable tape on the outside but I was not on sie when they were done and to be honest I have only just thought of it!

Oh and the triple glazed Velux are heavy!

(edit) In case you are wondering and have been following the saga, I ended up having Slate from Nu-Lok instead of the ceramic tile. These flashings are actually Tile flashings rather than the slate ones. Because of the fixing system it won't matter though.]]> Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161362#Comment_161362 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161362#Comment_161362 Wed, 14 Nov 2012 23:58:53 +0000 seascape Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161372#Comment_161372 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161372#Comment_161372 Thu, 15 Nov 2012 08:05:52 +0000 Cav8andrew Velux - air tightness/thermal bridge (BBX, BFX, BDX) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161411#Comment_161411 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9451&Focus=161411#Comment_161411 Thu, 15 Nov 2012 17:33:32 +0000 borpin
Posted By: Cav8andrewyou really need a sustained spell of dry weather for tackling the roof
I wasn't too bad on that front. The PIR insulation once on is pretty weather tight and once the membrane was on even more so. Actually sunny dry weather (UV) would have been bad for the membrane as it sat for a while!]]>