Installing Velux Windows

Installation of Roof Windows


This guide is to be used as an aid when installing roof windows (aka skylights, rooflights and Velux windows). Most roof windows come with clear and easy to read installation instructions, but this step by step guide should provide an extra helping hand.

At no time should anyone try to install a roof window without the aid of scaffolding.

This guide will account for the installation of Velux windows onto a plain tiled roof.


Step by Step

Before you start, plan the site for your proposed Velux. Think carefully about the impact on any timbers, wiring and plumbing, as well as how you want it to look from the inside. This guide will use the standard installation onto a plain tiled roof. Other roofs may require slightly different installation methods.

You should have a clear idea where the window will be located, both externally and internally. It may help to mark out the location with a pencil etc.

Inside the roof, the window will sit between two roof trusses. Usually to allow installation of the window, a centre truss will need to be cut out below the brace.

On the roof, remove the tiles with a flat pry bar. To get yourself started, use a lifting and twisting motion.

Once you have cleared the site of tiles, you will see the shape of the wooden trusses underneath the felt, laths and timber. To give yourself a guide to work with on the inside, poke a hole in the felt.

Using the lines from the hole you poked in earlier, cut out the felt to expose the install site.

Inside the main Velux box you will see the window itself, the instructions and some window trims.

Open the window to familiarize yourself with the mechanism and take careful note of how the window separates from the frame itself.

Now press the release clips and remove the window from the frame. This allows much easier access to the frame and helps keep the double glazed unit safe.

Now you need to mark out the install site onto the timber laths so you can cut them. Mark it out either by using a tape measure or by placing the frame in position onto the timber itself.  It's important to double check your measurements if you go down the tape measure route.

Allow 20mm all around the window as per the instructions, including the top and the bottom of the window. Using a saw, cut the laths where you have marked.

Now that the laths have been cut back, remove the fouling section of the truss.

Now that the fouling section of the truss has been removed, you can move on to putting the supporting timbers back in.

Fit a section of 3 x 2 or 75mm x 50mm piece of timber between the sides of the two trusses, and fix it into the end grain of the cut middle truss with 4inch or 100mm screws. Then do the same to the bottom of the window with another piece of  3 x 2.

The two side pieces can be cut and fixed into the timber pieces you have just fitted. The end of the lath should finish nicely with the edge of your new side timbers.

Now you can re-nail your laths to the freshly inserted timbers.

Fit the metal corner brackets to the Velux frame. These screw into pre-cut grooves. Use the fixing pack that came in the main Velux box.

The frame can now be fitted in position. If you need to add additional timber to support it, you can use some of the lath you cut out earlier. Again, fix with the screws from the main Velux box. You should now have a nice sturdy frame with an even gap all around the outside.

Next, tile up to the underneath of the frame, ready for the bottom flashing to be fitted.

Now, get out the flashing pack. This consists of two side flashings, a bottom flashing, a top flashing and clips for fixing the side flashings.

Fit the bottom flashing, along with the window trim that came in the main Velux box.

Now put both side flashings on and fix with the clips supplied. The clips allow you to keep the flashings tight down to the laths. You can now bend over the tabs where the flashings meet.

Now the two side window trims and the two upper window trims from the main Velux pack can be fitted.

Next fit the top window trim, again, from the main Velux pack. Now slip the top flashing into place and bend down the upper window tabs.

Now it's time to start fitting the tiles. If you are fitting small plain tiles, it's recommended you use tile and a halfs. These stop any small tiles having to be cut and the nails puncturing through the flashings underneath. Tile and a halves can be bought in any good tile and roofing merchant. Fix the tiles up to the tile stop. Any excess foam can be cut off to allow the tiles to sit without distorting the foam underneath.

Eaves tiles should now be rested on the adjustable triangular bar. Slide the bar up and down to get the correct angle. Then simply lock into place with the straps supplied.

You can now apply your chosen inner studding and plastering.

Once decorated your newly installed Velux roof windows will look great.

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