Velux Window Installation

I have 3 velux roof windows (GGL style) installed in a newly built room. The
roof is a standard wood rafter construction, felted and tiled. The felt and
batterns were put on the roof before the velux went in. The velux flashing
then went on, then the tiles. Around the edges of the velux installation,
the roofing felt was tucked into the window aperture, then the velux fitted.
Problem we have now is some water leakage around the edges of the velux. It
is running down on the felt that was tucked in. Now I know firstly that if
the tiling has been done properly there shouldn’t be any leakage through
onto the felt, that is one problem to sort out. However, if any water does
get passed a tile onto the felt, then this should run down and of the felt
to the bottom of the roof. The way the felt was tucked into the aperture
does not seem right, especially above the Velux, as the felt does not
overlap the top section of velux flashing, meaning if any water on the felt,
runs down to the velux it goes under the velux flashing, then into the room.
the builder assures me it is the correct installation and that once the
leaks passed the tiles are sorted out then there will be no problem. the
information on the velux site and the brochures I have are not very clear.So
am I right in saying the roof felt, especially at the top of the velux
should overlap outside/on top off the velux flashing?


No, the felt goes down first. The flashing goes down after. There is a hem at the top of the flashing that keeps the water from flowing off the flashing on to the felt.

The flashing directs water back onto the roof material.

Lefty, I think he is talking about the felt under the tile being cut even with the bottom of the skylight instead of being run up the back of the skylight.

IMO the felt should run up the skylight curb on all four sides.

Hi Dennis,

I agree with you on the felt. He wrote the felt should be on top of the back flashing pan. I may have misunderstood him.

Here is what he wrote that I am refering to.

as the felt does not
overlap the top section of velux flashing, meaning if any water on the felt,
runs down to the velux it goes under the velux flashing

I would use Grace IWS to wrap all sides of the frame prior to flashing and tiling.
I would also slide felt into a horizontal lap to cover the head flashing-even though the roof has been in place.
That helps direct water back onto the head flashing then down and off.

I would pull the tile from around the sky lights,remove the flashings,cut back the battens(18" to 24"), install ice & water shield on the deck and up the sides of skylights,seal corners where IWS wraps around with urethane caulk, tuck the top or back pan area under existing felt,reinstall battens several inches back from sidewall(may be able to install flashing on top of battens? does skylight sit on battens?), then I do not know what kind of tile you have?the velux kits I am familiar with would not work for a Tile roof-unless you are installing shingle tile? you need a continuous hem style flashing flat on the deck & up the sides,the bottom of hem flashing would be on top of batten and headlap of the tile needed to divert water past edge of skylight,the back pan should also be on the deck with the felt or IWS directing water over top of the top edge of flashing,you would need to tuck felt under your existing felt,you could also seal top edge of back pan before installing felt or turn up a hem on the top edge(the velux back pan does have a hem)–also all the edges of hem flashing should be sealed,but do not block inside channel with sealant–reinstall tile–,I would eliminate the single step type flashings if this is what they used? Or I would make a complete new base flashing and back pan soldered together out of TCS or Lead Coated Copper…

How was it done before IWS? Skylights didnt all leak before it, did they?

Aaron, depends on who installed the skylight. :smiley:

I agree you do not need the IWS - but for tile roofing you need to have a good water tight base under your tile it could be felt paper,IWS ect…properly installed to keep the water moving down the roof,no back seams or IWS installed that would lead water to wood deck…so around skylights,chimneys have to do it the right way,and the proper style of flashing is a must,really the way to go is with soft copper or lead especially if you are installing a S type tile…flat tile you can use cold rolled metal…Velux may make a special flashing kit for tile but I am not aware of it. I just repaired an old Spainish tile roof had to lift the tile ,remove the old dried out felts,roof had 4 leaks all at the ends of the valleys and down the roof about 5’,when removing the tile just after a rain the felt was wet from water working its way under the tile,8/12 pitch,tile had proper headlap,original roof and felts 65 years old, all the spots were almost identical,rotted wood,dried & cracked felt, we installed 2 new layers of 30#,made sure to roof cement any errant nail holes ect.and where the flow of water was the heaviest installed spots of tar where the tile was nailed -probably not needed but just an extra precaution…had several good rains since seems to be doing fine…

No they didn’t all leak before IWS, but why not use a great waterproofing product when it is developed and at your disposal? I agree with the others that suggest wrapping the skylight with IWS, but even this must be done propoerly.

Mant thanks for the replies…It does seem not be installed very well. I am coming to the conclusion that it really needs the roof tiles removing and the felt relaying in a much better fashion as well as the tiles reposition so they are closer to the velux window itself. As I am fairly handy I will either get the builder to do it properly or get a substantial discount…and do it myself (with some help from brother!)
Room is 18 metres sqaure, 3 sided, 3 way pitched tiled roof, single storey (so not to much climbing) in Surrey. What is is worth trying to get back from the builder if I redo the roof my self. (Most materials here already, may have to get one or 2 more tiles but thats easy)

The problem I see with these self adhesive ice barriers is that they have been perverted into this pseudo cure all in lieu of good roofing practice and proper technique.

I agree that they shouldn’t be used to cover up poor roofing practices, that would be like using abortion as a method of birth-control. However, I don’t have a problem using the peel and stick membranes in a belt and suspenders type application. If you put your roofing down properly AND seal around penetrations with IWS, then it can only be better than without the IWS.