Proper velux skylight installation

hi all,

i’m wondering if someone can outline steps for installing skylights in general. we’re going to have a velux skylight installed (FS C04 2004, decked, rough opening of 21"x38")

our roof is asphalt shingles and steep, 9/12 pitch (ie. 37 degrees). no insulation underneath the roof deck (single story, unfinished attic)

i have seen youtube videos of the installation, including from velux/wasco, but want to be sure to know if there are any other best practices that may be just as good or accepted practice when installing skylights (if any deviation from manufacturer’s recommendations is warranted). such as:

  • type of caulking to use
  • places to have caulking that would give additional waterproofing protection
  • foam or glue/caulking to hold the skylight frame down to the deck (in addition to the screws)
    anything else that people have found to be added waterproof protection or ease of install

i want to try and avoid any situation like the recent post:

velux official:
wasco (now owned by velux) youtube[dot]/watch?v=DJ_Rawbul9U


They’re pretty simple, you watched the video. You could DIY it and not worry about it leaking!


That and read the supplied instuctions.

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i think it’ll be straight forward. not sure about simple! i’m hoping to also test with a hose just to be sure there aren’t any leaks immediately. i can’t really think of any other method to test the water-proofness

yes, i definitely will read the instructions. i haven’t purchased the window yet but have downloaded instructions from velux’s website and it does seem pretty straight forward for the install.

creating headers and cutting into the roof deck won’t be nearly as easy since i have very little experience working on a roof. i’m getting the 21-inch wide product line (unsure of the length right now) so i wont need to cut more than 1 rafter.

If you don’t trust the installer, don’t hire him. Velux rep should have a list of people to install them.

well, i’m trying to figure out if its reasonable for me to do it myself. is hiring yourself as a contractor mean i have a fool for client?

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Depending on your locale, cutting a rafter and framing around the hole might require a permit and framing inspection. Get a couple of roof brackets and a piece of 2by sized from them (some take 2x6, some 2x8 etc). That said 9/12 isn’t a pitch I’d recommend a first time skylight installer to jump on.

If you have no clue, yes!

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yes, it is a bit steep but i will have at least 2 other hands, both other people have done this before for their own homes (different product, different type of roof).

i did submit a permit and it was approved (though inspections is a different beast)

it seems straight forward just not sure if there are any other tricks or if anyone came across tips they found useful for installing skylights

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Been awhile since i set one. If there are still steel L brackets screwed to the deck and frame you can run ice & water shield on the roof and up the frame to the gasket after the brackets and before shingling and flashing the unit.

I agree…they’re pretty simple and straightforward to install.

When shingling, ice and water bottom-sides-top… don’t nail to close to the window or nail the flashing… Don’t go to tight to the wall with your shingles, leave a little space, I usually give it an 8th or so room so the water got somewhere to run easy. Pretty much it.

Hope this helped some :sunglasses::+1:

The flashing kit will come with a small roll of Ice+water shield. Don’t let it set in the sun and get hot or it will be even a bigger PITA to deal with. Good luck and post a pic of the finished install.

photo from above/outside
photo from inside


  • clean up edge/rough opening
  • headers for ceiling joist for skylight tunnel
  • frame skylight tunnel for drywall and insulation
  • use black roof sealant to fill in some nail holes in the re-used shingles (i missed a row of holes, about 4)
  • water test to see, at the very least, it isn’t leaking water

difficult decisions

  • roof had water and ice shield all the way up so decided to leave the shield in place and place skylight on top (hope this doesn’t cause leaking, not sure how it would contribute to leaking) my home is old and had planks so removing the water and ice shield would mean i would just have to re-apply water and shield again over the roof deck planks.

  • i used the velux flashing kit (EDL kit) so i used the velux supplied adhesive as instructed. the main issue here was the white colored backing looks like it could peel off. it does not. the slightly darker grey backing is the one that peels off.

velux’s instructions for how to make the diagonal cuts for the corners of the skylight was made me more confused. they should have 3 images to really make it fool proof:

(1) one with the adhesive flat and the cuts shown as lines
(2) one perspective (i.e. look dead onto the face) that the adhesive will be adhering to
(3) one perspective (i.e. skewed perspective of the corner) showing the cut ‘projected’ onto the actual corner of the skylight

  • nailing or not to nail the metal step flashing: i decided to nail the step flashing as far from the window as possible but ‘high’ up enough to be well covered by the roof shingle course

who knows if this will hold up. i did it carefully so aside from the issues above, i think it should hold up. let me know if there are issues, not too late to do it again.

You did it correctly, congratulations.

these shingles shouldve been under the flashing ears.
all type of flashings gotta go past middle part of shingle.

i think what your’e saying is that the entire course of the bottom row of shings should be moved down ~3 inches? (lets forget the rest of the shingles above it and just this one course to the left and right of the bottom edge of the skylight)

here’s another shot of the ‘left’ side of the window:

here is the instruction page:

if it doesnt leak with tap hose test then call it a day