DIY Developer
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16 November 2014

I’m going to show you how to replace your old acrylic dome skylight. It sure beats a hole in the roof… unless you want a hole in your roof.

Skylights are not always standard sized

My house came with a 30 year old dome skylight. Rain, hail, even sufficiently sized bird crap made me nervous. I was worried that one day my skylight would disintegrate. This would devalue my property and may even let rain in. It would probably upset my wife too.

My skylight is crap

Should be easy to swap out right? just order one the same size, right?

Nope.

The size I have is 1200x700(ish), and that size is not made any more. Damn. This next best option is to replace the dome with a much better tempered glass skylight. These skylights are made by Velux, and available from Bunnings. Unfortunately they do not come in the right size either.

What we can do - is to buy a bigger skylight. Then we make a collar, which will sit on top of the existing skylight frame.

Which Skylight do I need to buy?

Buy one that is both taller and wider than the model being replaced. When measuing your skylight, you will need to get on the room and measure from the edge of the dome (including the flashing securing it in place). At the same time, verify that there is actually a “lip” supporting the dome.

If your existing model does not have this lip, then this method will not work.

Buy the size closest to the old model as you can find. Don’t bother getting a fancy model, just a plane one that doesn’t open or have a curtain attached, or anything. Keep things easy.

Building the collar

Here is the plan for the collar, which will support the new skylight:

Collar plan

My initial plan was to use aluminium L-channel to fabricate the collar. I used my sliding mitre saw to cut the L-channel. Since aluminium is a soft metal, it cuts just fine with the wood blade. Make sure you wear safety glasses, and a face shield if you have one. As with all cutting, the material being cut can catch and be flung by the blade. A sharp aluminium off-cut in the face could kill you, or at least ruin your day.

I mitred all 4 sides, positioned inside the skylight, and screwed the L-channel in place.

Whacked out collar

Nice L-Channel corner eh? Perfectly mitred! Sadly, my existing skylight sits close to the roof tiles… which means that this collar caused the new skylight to sit on the roof tiles. That’s no good (for many reasons, including water run off).

To fix the height issue, I added a timber frame:

Timber frame

Removing the old Skylight

This is going to be a one attempt only affair. Your old dome skylight will probably be brittle, and quite likely to crack/break when you remove it.

Removing the skylight will vary between models. As a general rule, there is a lip holding the dome in place. The lip will be screwed or riveted down. In my case, I had to drill out about 10 rivets, which allowed me to remove the dome.

Timber frame

Installing the new skylight

Skylights are heavy

Skylights are heavy, and awkward. A larger model, could be 50kg or more. Get help lifting it in place.

If your measurements are right, the skylight collar should fit over the top of the old opening.

The new collar now needs to be secured. Screw the skylight frame into the collar. The skylight should have pre drilled holes you can use.

To secure the skylight to the old opening, you will need to put some screws up through the old lip, and into the collar. If you can’t fit a drill or screw driver under the collar, use hex head screws or bolts. That way you can use hex/allan keys, or a socket set to secure the skylight.

Skylight in place

Too easy, eh? Now I’m ready for storm season.



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