How to Install a Velux Top Hung Roof Window on a Profile Tile Roof - Part 3

Finishing the BDX Collar installation and fitting the transverse drainage gutter

Top Hung Part 3:

In this 4 part guide, Mark - A Velux Technician takes you through the full installation of a Velux GGU Centre Pivot Roof Window with a White Polyurethane finish. This window is being installed onto a plain tile roof so we’re installing an EDP Flashing Kit and BDX Insulation Collar.

In Part 3, Mark completes the installation of the BDX Collar, Securing the underfelt collar to the frame and fitting the transverse drainage gutter.

View the other parts here:

Part 1: Unboxing and preparing the window for installation
Part 2: Installing the BDX Insulation Collar and fitting the Window Frame
Part 4: Installing the EDW Flashing Kit and Finishing Installation

Video Transcription

Preparing the roofing felt for the Transverse Drainage Gutter

Once the brackets are secure, we're already at the head of the window so now would be a good time to do the preparation work for the drainage channel which we're going to fit along with our under felt collar. So we're going to cut some of this felt away here to form a small flap that's going to enable this membrane to run inside the drainage channel. So to do so, bring the drainage channel up onto the roof. If there were counter batons, we would need to remove a section of the counter baton to enable this to sit on the membrane, but for most standard roofs, you want to just rest it on the membrane, treat it as any gutter would be and give yourself a small fall on that gutter. Then, use the straight edge of the gutter itself to cut along the felt. We’re going to cut from rafter to rafter and once you've come to the end of the truss, just extend the cut just in towards the middle and then return the cut about 50mm or so. And the same on the other side. And this gives you a nice little flap in that membrane which will eventually slot inside, like so.

Having cut this membrane, we have now unfortunately created a potential area for water ingress to come in beneath the drainage channel. To prevent that from happening, part of the kit that's provided with the under felt collar includes two strips of butyl putty. Now, we're going to apply these strips of butyl to the roof and once the drainage channel is secured, it will seal between the channel and the roof and create a waterproof barrier. So we're going to peel off a section of the butyl and we're going to stick it just along the outside edge of each cut. Now, use the whole strip because you can’t really go wrong with putting too much butyl because the more we apply, the more we are protecting that cut. So just push this down so it adheres to the membrane. So peel off the upper layer and we're ready for the next strip to go on. Do exactly the same on the far side of the window, just sticking it along the outside edge of the cut.

So as before, just place it well above. Push down into the membrane so it adheres to the membrane itself, and then we'll just peel off this top layer again. So now we're ready to actually fit the under felt collar itself. So for that, we'll need to come back down to the bottom of the window.

Fitting the felt collar around the frame

Now, the under felt collar is just simply a section of breathable membrane that's flat at the top and bottom and as you can see, for the sides, we have pleated sections to allow you a little bit of flexibility to dress them up and over the batons as you'll see during the next stage of the installation. So what we'll do first is we're going to completely open this up to its full extent. And that’s going to enable us then to fold the whole section up and over the window using these welded corners which will actually help initially bond the felt collar tightly to the window itself. So the next stage with it all sat around here, is we will tuck this underneath the baton and then we can start fixing this to the window. So we'll now take this section and just lift up the baton to allow the membrane to tuck underneath. And then once that's in place, we'll fix the baton back down.

Now, to secure the felt collar to the window itself, we've incorporated more of the butyl putty that you saw earlier. That way, it doesn't matter if it's pine, white painted pine or polyurethane, or whether it's centre pivot, top hung or what have you; you can still attach the collar to the window in the same way. So we'll just be lining this up so it remains level to the top edge of that frame. So peeling off the cover here, we'll start to expose the butyl and this first little tab, we're just going to tuck around the corner of the window and secure that. And as we peel, we'll just stick this to the window as we go. By doing this, we're also helping enhance the air tightness of the window itself as well. As we get to the end, just remove the last part of the protective cover and fold this section around the side and stick that to the side of the window as well. So with this in place, we'll now do the same on either side of the window. Pushing that down and attaching that to the sides of the frame itself. So we'll peel off the side. Now, as we stick the side section on, it’s important that we just push our hand tight into the bottom of the window so that we keep a nice, tight 90 degree angle at the side here.

So don't try to push the membrane flush to the top edge of this frame. It is designed to sit about three quarters of the way up. So once we get to the top, we'll just fold this section around the head of the window and once we've done the same on the other side, we're able to just peel off this section along the top, fold that corner around as we've done previously and then just follow this along, applying it to the window as we go. Fold the last corner around and the collar is secured to the frame. We're now ready to start stapling the side sections around the batons and that’s the next part we're going to look at.

Securing the felt collar to the battens

So what we need to do next is to try to get this membrane to sit in as close a contact as possible to the existing roofing membrane. So we're just going to break these pleats apart where they bridge over the batons, and that then just gives you that little bit of flexibility to be able to then staple them to the baton like so. We're going to then carry that process on as we work our way up the roof. So when we come to the next baton, do the same again. Bridge around and then just staple these in. And just carry that on, on both sides of the window until you've covered the full length of the window itself. So the drainage channel itself is extendable, as you can see. So depending on which way you extend, you'll have a single hole at one side and multiple holes to select from on the opposite.

Installing the Transverse Drainage Gutter

I've extended it this way because I tend to find it easier to fix the single hole at the higher end of the fall as your first fixed reference point. This groove hole should be lined up above the structure because we're going to be screwing this into the roof once we have it in position. To get the position right, we just fold the felt collar over. We open up this membrane flap in the roof and just slide the gutter up until it hits this junction point here. Then we just check to make sure the screw hole is still over the rafter and then we take the bag of screws that are supplied with this and we'll fix this into the roof. So with the gutter in position, line up your initial screw. And fix that one into the roof structure. So with this one fixed, we'll come across to the other side. Follow the same principle of just sliding up until we meet this junction point. Fold the felt collar away, pin those in with the extra clips to keep it out of the way, if you like, and then just extend this so that the gutter is protruding beyond the membrane but we also have one of these holes lined up over the fixing point. Then just fix in with one of the other screws provided to secure that to the roof structure. With the gutter fixed, we fold the membrane over. We bring that membrane flap over and just with your fingers, push into the channel and you're just going to create a little sort of gulley with the membrane.

So just run your hand all the way along, so any water that runs down here is being brought into the channel. This membrane is now going to be held in place with the gutter clips. Each of these clips are wedge shaped, as you can see so the thin end is going to slot into the gutter, therefore allowing any water to travel through this channel. The easiest way I find to pop these into place is simply to pop your fingers inside, line the thin end of the wedge into the gutter like so, put your thumb underneath and then pull it down. And you'll feel it bite and that’s it clipped in. We then carry that process along the rest of the gutter, just popping them in and clipping them in place as you need. The number of clips required will vary on the length of the gutter and also, how likely it is that you're going to get this covered over with the flashings in one day. If this is going to be left exposed for a short period of time, you may want to put extra clips all the way along to ensure that if the wind gets up, it doesn't pull the membrane out of the gutter, meaning you have to re-clip before you can flash. With that in place, we're now ready to fit the external flashings.