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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    I have a roof on my extension with a slope of 13 degrees. This is at the limit of the specifications for the contoured tiles and Velux windows. Consequently, I have over the last 10 years often had to clear out tiny bits of moss that have lead to leaks. The seals between the glass and the Velux frame gave up a few years ago, and I removed them and used Sikaflex instead. That has lasted till now, but it's all leaking again, and the timber at the lower corners of the Veluxes is black and rotten.

    I've decided to replace the Veluxes with fixed diy rooflights, reusing the Velux glazing (it's double glazed and coated and I think argon filled - seems pretty good) and making some fixed timber upstand boxes to support the glass. We don't need opening rooflights - there are plenty of alternative ventilation options in the room, so we can skip that complexity.

    Two questions:

    I am thinking of using Sikaflex to attach the glazing onto the top of the timber (which will be covered in EPDM). Is Sikaflex resistant enough to UV to make this viable? If not, can anyone recommend another sealant?

    I've been looking online for pleated lead to make the apron flashing around the bottom of the window. My tiles are heavily contoured. The Velux flashing is contoured lead but there isn't enough to reuse for my diy windows. I can only see the stuff available in rolls in Germany. I don't fancy trying to ship a roll of lead from Germany. If it isn't available in the UK, is there an alternative material to use?


    • CommentAuthorGreenPaddy
    • CommentTimeDec 28th 2020
    Is this type of thing any use for you flashing?? Often comes with solar panel kits. I usually just use lead instead, as invariably slates around here, but don't see any particular issues with it.


    Sikaflex - if the sealant is covered by the black "warm edge" of the DG unit, and the roofing membrane, is it likely to get any UV? Are you mech fixing down the glazing in any way?
    John, are you insulating the sides of the upstand boxes?

    Ours consisted of a 4-sided open hardwood box frame. On 3 sides there was a rebate cut in the wood to hold the glazing unit at a sloping angle. On the 4th (lowest) side, the glazing projected an inch over the frame, to shed water away from the frame. The whole thing was wrapped in lead which ran over the edge of the glazing, down the side of the frame, and out under the slates. Sadly no insulation. Sorry I didn't ask what sealant was used but it was protected by the lead.

    Manufacturing all this cost us more than buying a ready-made roof light, but we had very odd rafter spacing. Have you looked at the velux flat-roof products?
    Thanks for the link Paddy - that looks like what I need. The stuff looks flexible enough that I might be able to mould it to the shape of the tiles. Expensive though!

    I'm not planning to use any mechanical fixings to hold the glass. I've previously used something similar on a boat, and it held up really well - no leaks after years of hard use, including a couple of years of tropical sun. No mechanical fixings there. However, I did have to replace one of those windows (someone sailed into it), and I used Sikaflex for that one and it didn't last more than a year or so. I might not have had the right variety though.

    Will: the shape of my frame is dictated by replacing the Velux wood parts, with a box made of OSB. There's lots of room for insulation. I'm thinking I'll just install the outside box and flashing first and leave it a few weeks to check for leaks, before adding an internal box that slides up into the external box, with the insulation attached to the outside of the internal box. That way, if there's any trouble, I can just lower the internal box and fix it.

    I'm not too keen on buying more Velux. I have the glass I can reuse, and the box I made from scraps from other projects. I'll paint the box with some left over epoxy paint from my boating days, then cover it with EPDM, which I'm also planning to use for the top and side flashings. So far, it's the lower flashing that is going to cost the most of the whole project.

    Thanks for your feedback and suggestions.

    • CommentTimeDec 29th 2020
    I believe the 'right variety' is Sikaflex 295 UV Marine Adhesive & Sealant :bigsmile:

    I found it was a lot easier to get a smooth finish with yacht varnish rather than epoxy, but then my painting skills aren't up to much. And I expect epoxy will last longer.
    Hi djh,

    I think that's the stuff I need. The epoxy I mentioned is paint, not the clear stuff. I'm just coating the timber in it before covering in EPDM, to help keep out any moisture that might get there. The paint is meant for ships hulls, steel pilings in harbours. It's extremely durable to UV and abrasion. And I've found it works with wood as well.

    It's not exactly green, but it's leftover stuff anyway. It's got to go somewhere.
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