I have put together this guide as a one stop shop for anybody that may be considering making such an alteration. As with any such modification there are always going to be alternative ways of getting to the same end result, but I feel that this may be a good basic insight to what is involved.

Our van was made in 1990 and the original skylight above the living space had clearly seen better days and was starting to let water in during heavy rain. We had noticed a few times that the bedding was damp when we had collected the van from storage as we tend to leave the upper bed down most of the time. However, I didn’t realise just how bad the situation was until I got the ladder out to have a closer look.

Suffice to say we could no longer put off replacing the unit. I had been watching a few people on social media replace their original skylights for similar reasons, and one of the options was the Dometic Heki 2. This was considerably larger than the original, so a definite upgrade in relation to the amount of light it would let in, and improved ventilation during warm weather. That said, at £640, the cost was the main reasons we had delayed it so long.

The first thing to do was to remove the original skylight. Inside the van the plastic trim was held into place by a number of self tapping screws which were hidden behind small plastic lugs. There was also a self tapping screw that held the winding handle on. I positioned a set of step ladders against the side of the van with some foam to provide padding where they rested on the van. This gave me reasonable access to unit from the top. If you do not have the Fiamma roof box fitted at the rear, or a solar panel as is the case in my situation (you can see this to the left of the picture below), you may prefer to climb the ladder at the rear and work your way forward from the back. Just be mindful of where the roof support bars are beneath the fiberglass structure, and use those.

The original unit was fixed into place by Mastic tape, and the only thing properly securing it to the roof were the parts we had already removed inside the van. So with a little prying and some gentle persuasion the original unit was removed,

Moving back inside, It may be a good time to consider protecting as much of the interior of the van with dust sheets or blankets as there is no real way of keeping the van free from dust and debris during the process going forward. Carefully remove the ceiling trim. This is made of thin ply so be careful as you work the ceiling out of the grey rails. You only need to take the piece surrounding the skylight itself!

This will expose the fibreglass wadding / insulation. This is nasty stuff and can irritate the skin and cause chest issues. I would recommend suitable clothing with full length trousers and long sleeved top (overalls ideally), along with a face mask, eyewear and gloves. Don’t wear shorts and T-Shirt like I did…”Do as I say and not as I do” 🙂 . The wadding is glued to the roof so a wide wallpaper scrapper would be the ideal tool to get behind and carefully manipulate away from the roof to remove. Place the trim and wadding on one side as these will need to be modified later to fit the new aperture.

The next thing to do is to mark the roof ready for cutting making sure this sits in between the roof metal roof supports. I used the template that’s printed on the outside of the box that the skylight is shipped in.

That said, I decided to cut slightly in of the line, which meant the hole was smaller with the option of opening out if too small. This was the case, but better that way than to have the aperture too large with no option to add material back.

I offered the template up on the inside of the van and estimated that there would be between 8 and 10mm of room if the hole was cut centrally, front to back, between the roof supports. With this information to hand I measured 8mm back from the front roof support at two locations either side of the van and made a mark.

This would be about 850mm apart, or 425mm off the vans centreline, but well within the template of the skylight, before the curve (See below).

P.S. If you are anything like me, you would double and triple check that you are clear in your head why you are doing what you are doing, and that you have your measurements right, because this is the point of no return!! With these reference marks made I took drill with a 2mm drill bit and drilled up and outwards through the fibreglass roof.

From the outside of the van this would provide a valuable visual reference in which to draw a straight line connecting the two drill holes. (I apologise for not documenting this with photos as I was up against the clock to some degree). I also marked the centre line of the van roof externally based on the original skylight position, and in turn marked the centre line of the cardboard template. From here I could use those two reference lines to centre the template on the roof, and align the long front edge against the drill bit line. Once the template was in position, I taped it to the van roof and drew around it.

There were a couple of different ways to cut the roof. Suggested for the rounded corners were a 130mm core drill with the straight edges cut with a 1mm cutting disk on an angle grinder, or a jigsaw. As seen in this gallery below, a very neat solution to making the roof hole by Peter Ferry.

Alternatively the whole roof could be cut with the jigsaw. I chose the jigsaw route due to the fact I couldn’t get the core drill short notice locally. With the starter hole done with a 10mm drill as a starting point to drop the saw blade in, I used a a narrow profile blade similar to the one pictured below, as this would offer better and more precise work at the rounded corners.

I found the best way to access this whilst doing the cut was to move the upper bed into position (after removing the mattress and furnishings) and stand up on that, through the old skylight aperture. I worked my way around the marked line during the cutting, stopping at intervals to stick gorilla tape between the two cuts to support the inner part, which would eventually be the discarded part of the roof. Once the final part had been cut I removed the gorilla tape and the waste material. You can see the part removed in the image below which still has the Gorilla tape stuck to it.

The next thing I did was thoroughly clean the roof around the aperture. I used Cif on a sponge and cleaned with a damp cloth. This is suggested in the fitting instructions, and the main reason (if not obvious), is to present a suitable surface to provide good adhesion between the roof and skylight at the point the components are assembled for the final fit.

Once this was done it was time to drop the new unit in. For me this was a process that took a couple of attempts as I had cut the hole slightly small. This was refined to the point where it eventually dropped in. The tolerance suggested is 1 > 2mm of clearance around the unit. I can only assume this was for any slight expansion / contraction of materials.

As I eluded to at the start of this post, I never really felt comfortable about the fitting of the skylight because there were a lot of unknowns, and the major concern around taking a hacksaw to the roof did not fill me with confidence. The advice I had was good, but insufficient quality photos at every stage to make it clear in my head exactly how the whole thing went together, left a lot of questions remaining. I had the new skylight and some instructions with it, but until fitting, it was never really that clear. So as the install moves forward there was a few head scratching moments to come.

I had brought a couple of different sized batons of wood to act as bridging pieces / packers, as I had been advised that this is what I would need to assist with the install. It wasn’t until I had dropped the skylight in that I could really start thinking about how this was all going to fit together. The fixing kit that comes with the skylight is for the shallowest roof depth, which is 25mm – 35mm and colour coded ‘Grey’. The actual roof depth of the Florida is between 45mm – 50mm dependant on where you are measuring from. Other fixing kits are available and come in different colour coded options dependant on their depth to cater for the appropriate roof depth.

The information I had from other people installations was that the grey kit would work OK if the fixing screws that came with the kit were changed for longer ones. I decided to go down this route after a little testing as I couldn’t see it would be a problem. That said, I did see that another person chose to use the ‘Yellow’ fixing kit so this may be an option others may want to consider. Especially if you can buy the kit in advance of the installation under the agreement by the supplier this can be returned if not required if you don’t use it, as it is an extra expense at approximately £45.

The replacement screws I used can be seen above, and were 15mm longer for the longest screws (40mm), and 10mm longer for the shorter screws that are used to fix the lower trim (25mm).

I decided, that two lengths of 20mm x 25mm wooden batons would work for the 5 fixing points along the long edge of the skylight which would brace up against the metal roof supports. These were laid with the widest face top to bottom , narrowest front to back.

I didn’t feel the length was critical, but just long enough to provide a decent level of pull into the roof beyond the outer two fixings. The batons left and right for the 3 outer fixings were 25mm x 35mm and were cut to fit in between the two metal roof supports with the deepest profile top to bottom, narrowest against the roof / fixings.

The initial fitting was just a dry run to make sure that the roof pulled in sufficiently when all of the fixings were torqued down. This was more of a test for the sides as the roof of the van does start to slope off further out. Not massively, but this is where there will be a gap.

Photo showing baton positioning around skylight

Once I was happy that everything was within tolerance, I proceeded to remove the skylight ready for the final installation.

I chose to follow the advice I had from others to use W4 Mastic Sealing Tape to secure the skylight to the roof. It comes in varying widths, primarily available in three standard widths, 19mm, 32mm, and 45mm. The other option was Sikaflex, but there would be no way back from the install with that, should something go wrong, as this a ridiculously powerful bonding adhesive, where as the tape would be more forgiving. I used 19mm for my install.

With the skylight out and lying face down, run the tape into the channel (depicted in purple on the image below). I found at the corners it was better to remove the backing paper and slowly work the tape in uniformly, or else the paper makes the tape pucker up. Then continue along the next edge. Rinse and repat till you meet the start point. I did have one messy corner (the first in the run) where the tape had puckered up due to not removing the backing paper. I’m hoping it’s OK. Just try and follow the above considering my explanation.

Before I dropped the skylight back in, I ran a bead of quality white bathroom sealant along the inner edge of the mastic in the corner, all the way around as a belt and braces approach. This is depicted as the blue line on the image above (Again, sorry for lack of images at time of install, I have just had to improvise).

Now repeat the fitting procedure as done previously with the dry install, and torque in to the roof, checking its seated sufficiently close on the outside.

Next you will need to mark and cut the inner roof liner. I used a ruled and made sure that it was pushed as far as it would go into the outer grey locating bead (where the plywood roof trim sits), and measured to the mid point on the grey roof fixing.

Transpose this measurement onto ceiling trim and work your way around for each edge. I marked the trim on the upper face (not the visible face), but just make sure you understand the orientation as it may not be equal distance / mirrored. I found that this should roughly align with the original roof template if place on top.

As far as the corners are concerned, I chose not to round off the edges as per the original template, but cut diagonally to leave a little more material there. The main thing is that the roof liner doesn’t get in the way of the lower (HEKI) trim fixings screws.

Once the roof trim is in place, you can offer up and assess the lower (Heki) trim fixing points. I could see that the outer three on each side were almost perfect, where as the 5 on the front and rear edge looked like they needed some spacers (or the alternative yellow fitting kit if purchased prior to install) . I found a sacrificial rubber mat in my garage that looked like it would be a suitable depth to form a spacer. I cut it into ten small packers, drilling a hole in one side to align with the screw hole for the lower HEKI trim, and stuck them on each of the grey fixings with double sided tape.

I then offered up the lower trim and carefully screwed it into position being careful not to over tighten. I tested the operation of the blind from time to time, and all seemed to work fine. However, I have been advised to take care as you do this as any twisting of the lower frame could case issues with the blind movement.

So all that is required now is to fit the trim to hide the screw fitting points, and that is the end of the install.

I hope you found this guide useful. I have tried to do my best with this, and it seems to make sense to me, but there may be some points that are not clear and need some refining. If you could post a comment with any suggestions or questions it would be much appreciated.