DIY Velux Install - Learnings and Mistakes

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Just popped in three windows, this post aims to summarise my experience. Massive thank you to everyone here that gave me advice. Maybe someone will find this post useful too.

I’m a DIYer, made my fair share of mistakes. If you spot any in this post let me know and I’ll revise.

My place is a 1890s Victorian end of terrace with a 30degree pitch roof. Non breathable roofing felt with Marley Eternit Ludlow tiles.

Here are a couple of time-laps videos of the installs. They start with the area marked out and the rafters reinforced:

Window #1, PK06 -

Windows #2 & 3, CK06 -

Selection:
I chose Velux for no good reason other than they are well known. There are several others out there like Keylite & Fakro.

Apart from the smaller windows, Velux’s windows tend to go up in steps of 20cm in width and 20 cm in height so there is a whole lot of choice.

The Kit:
The window is only part of the story, you need to get other stuff!
Flashing Kit: This goes around the window on the outside and provides an aluminium waterproof ‘shell’. Sized for the window you choose. Flashing kit type depends on your tiles and if you want a recessed or normal window position. I got an EDW 2000 kit that included the flashing, insulation collar and underfelt collar.

I suggest getting the felt collar if you’re doing DIY, it seems like it would be a very fiddly hit and miss job making your own.

Size of opening:
It’s not as simple as cutting a hole the same size of the window.
You need an additional 40mm on the width and quite a lot from the bottom (80mm in my case, but more for others esp the recessed install). See the flashing kit install instructions (downloads available from the Velux website) they have nice diagrams which take a little deciphering!

Width: Chances are you’re going to cut some rafters to fit your window. My bigger window needed two cut rafters. The smaller just one cut rafter.

Height: The bottom of the measurements must start from the top of a tile row. Unless you fancy fiddling around relocating rows of tiles.

I didn’t want to disturb my ridge tiles so I picked a window that would finish a couple of rows from the ridge, even then I did have to wiggle tiles which moved the ridge. Probably need to rebed these soon.

Useful to draw up all the gaps and measurements before you start, so you’re not fiddling with a calculator with gloves on.

Framing:
The PK06 needed two rafters cut. I reinforced the rafters each side of the cuts with 2x4s running from the ridge board to ~80cm below the ashlar wall. I used several coach screws to fix the reinforcements in place.

At the top of the window a doubled up 2x4 trimmer provided strength. At the bottom just a single 2x4 trimmer, as it was so close to the ashlar wall and a purlin. I re-used the cut bits of rafter to save timber. Building control was happy with this setup.

Note the flashing kit’s instructions regarding location of the trimmers. They place them away from the window to allow for an angled plaster board reveal, letting in more light apparently.

Cutting the Felt:
You’ll be folding the felt over the new batten and over the cut out battens, best to start with a modest central cutout, until you know where everything is going.

Removing the tiles:
Very apprehensive at this stage! Probably for the best. As soon as one tile was out and daylight was in, the rest came off fairly easily. Needed to take tiles off one row above and below the opening, and one to the left and right, so a lot more than I first thought.

Battens:
Existing battens need to be cut tight back in the opening. First I had some overhanging by 10mm-ish and the frame just wouldn’t fit. Ended up popping a bit of sheet metal between the batten and the felt so I didn’t slash the felt while sawing though

The new battens were simple to screw in, instructions there were straight forward. Be sure to get the same batten size as the rest of your roof uses!

Insulation Collar, Frame & sash:
Window Screws: The screws Velux supply are Torx 20 heads.

Insulation collar was a doddle to assemble and slip in. It was really light and an excellent indicator that the opening was correct.

The frame is a bit of a beast to manhandle through the opening solo. But once through the hole and propped at the base, quite stable. The insulation collar needed a bit of assistance to fit round the frame to start, but then quite easy to slide home.

At this point I really recommend getting some cardboard and taping it to the bottom of the frame to protect it from scratches, if you’re keen temporarily on the sides too. Scratches happen all too easily!

The instructions say to fit the sash, check gaps. I did this one the large window and it was okay. Didn’t bother on the smaller MK06s and it was still fine. Probably more of an issue with the big windows? Just a few screws and the frame is fixed in place.

Underfelt Collar & hidden gutter:
I took to installing the sealant strips at the underfelt cut just before screwing the hidden gutter. They tend to stick to the collar when installing it.

Collar was a bit fiddly, but got there instructions were fine. It’s important to have it tight to window and 90degree where it meets the insulation collar, if it’s off the flashing kit won’t fit correctly. The glue sticks like the proverbial to a blanket and just as messy.

Hidden gutter clips were a faff until I realised you can pre-squeeze them by hand to make them clip in easier.

Flashing kit:
Not going to say much about this. It was nice and straight forward, bit of head scratching over the instructions but not bad. Some bits were slightly bent and took a bit of persuasion back but not dramas.

Re-tiling:
I was lucky, the outside rows and bottom row will got straight back in, no problems. The rest was a matter of measuring and angle grinding tiles to fit. My poor neighbours. This was the longest process of the install.

Cutting the foam was much easier with scissors than a knife and worth spending a little extra time on – it really is an important water seal if you’re tiles finish at the max. spec’d distance from the window.

Many of the tile’s profile bits (the overhangs that protrude below the tile) fowled the flashing kit and needed to be lopped off with the trusty grinder. But that left nothing to positively attach the tile to roof. The answer? Well not 100% sure on this one, but forums recommended sticking them with gripfill, I’ll report back if any fall off!

Sash:
Sash is a pain to navigate through the opening, but like the frame stable once through and balanced on the bottom (you did use the card protection right?) . Glad no one was watching me get the hinges located, it was probably like some sort of exotic dance using all limbs, face and the force. Good luck. If there was anything Velux need to improve on, it’s this!

Screwfix does some cheap plastic suckers. Two double suction lifters allowed me to solo fit a PK06. £7 each sucker – bargain and surprisingly sturdy! Also got a 3x sucker which took a ratchet strap, just in case it tried to drop on the neighbours.

Congratulations!!! You now have an installed loft window…

POWER Tools:
You can probably get away with very little but these really made things easier:
Impact Driver - Cheapo Makita from screwfix, love not drilling pilot holes!
Mitre saw – from them big cuts to shaving a mm off.
A cheap staple gun is a false economy, grrrr.

Reading up:
These are your friends and all available on the Velux website:
Velux Flashing Kit install Instructions,
Velux Installers Handbook,
Velux install video on you tube (varies for different flashing kits)

Times:
Window #1 (the big one) took a good day,
Windows #2 and #3 took a day in total.

Hope that helps someone. Happy to answer any questions as best I can.
 
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...some random pics taken through the install:And finally just
 
Looks ace - I cheated on mine and got a builder to install the actual velux - mainly in case I messed up. I bottled it, worried about breaking something and leaving a hole in my dorma roof for days waiting for spare parts.

I did the rest tough - and once in they look amazing.
 
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Just found this old post. Really useful for me as I am planning to do the same thing. I am curious though: my local building control require that I install full length rafters from ridge to hip if I cut any. Was it different for you?
 
Just found this old post. Really useful for me as I am planning to do the same thing. I am curious though: my local building control require that I install full length rafters from ridge to hip if I cut any. Was it different for you?

My Velux recommended fitter didn't go that far. May depend on your window sizes though?
 
Thanks Shagster. Was BC involved at all? The technical advice I have received: "Without knowing the roof design. I would suggest the full length of the rafters are doubled up, and fixed at 600mm. Assuming the smaller windows fit between the existing rafter this should be acceptable, however should you need to cut out a rafter and trim then once again you will need to double up the supporting rafters."

I'm at a loss as to how I can get full length rafters in to the roof (it's a chalet bungalow). Seems like it's not going to be a straightforward job.
 
Thanks Shagster. Was BC involved at all? The technical advice I have received: "Without knowing the roof design. I would suggest the full length of the rafters are doubled up, and fixed at 600mm. Assuming the smaller windows fit between the existing rafter this should be acceptable, however should you need to cut out a rafter and trim then once again you will need to double up the supporting rafters."

I'm at a loss as to how I can get full length rafters in to the roof (it's a chalet bungalow). Seems like it's not going to be a straightforward job.

I don't know what you mean about chalet bungalow, but I assume you've got a flat bit of ceiling that you don't want to go into? My doubled rafters went about a foot above the window and no problems so far. I only had a single rafter removed for each window, I put in two small windows instead of single large one because I felt it would have a lower impact on the roof structure, and give more uniform light distribution, and the cost wasn't much greater. BC wasn't involved because the fitter would have notified.
 
I'll let you know what I find out once I have talked to some fitters and builders. I'm really hoping I don't have to insert full length rafters.
By chalet bungalow, I mean a house which has a low roof. It's still two floors but the rooms upstairs have sloped ceilings. I want to put roof windows in the bedrooms and ensuite.
 

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