Planning – The construction of the house

In order to get it right in the aspect of selecting the right VELUX roof window, you need to incorporate it from the early stages of construction of the house, while considering; the needs of the user, and the current building regulations. In general, a standard VELUX roof window can meet the primary needs of its user, however, going out the regular style, and selecting a different windnow type in addition with matching accessories can add more ‘color’ to your window, and enhance its functions.

Planning must include the following aspects:

The size of the windows is dependent on the length of the space between the rafters. If you don’t intend to take the route of cutting them, and leverage on trimmers. So, you need to be certain of the position and size of the roof windows, whether they align with the current roofing construction, or if there is a need to cut the rafters for them to fit.

A critical aspect to consider in the selection of windows and flashings is the roof pitch. VELUX products would perform optimally in roof pitches ranging from 15° to 90°. But, they are irregularities, so be sure that the products that you select can function in the roof pitch in which it is to be used in. Again, the variation of flashing depends on the type of roofing material that is used in the construction. This is done to ensure a waterweight installation.

In an event of an underfelt in the roof construction, the underfelt and the window frame must be firmly connected to guard against driving rain and snow. Underfelts can be efficiently managed with VELUX underfelt collar BFX.

After the installation of the windows, it is important to insulate the frame to allow fpr continuity of the insulation level in the roof. The simplest and most efficient way to do this is by using VELUX installation set BDX.

An important point to note is the connection of the vapour barrier in the roof to the window. VELUX vapour barrier collar BBX is the simplest and most efficient way to get this done. There must be a connection between the window frame and the interior ceiling finish, whether it’s done with identical materials, or with the use of a VELUX lining.

Considering the level of humidity, which is relatively high in certain areas like the room; this type of windows are specifically for this case. The best solution for this situation is th the VELUX polyurethane windows. At VELUX, we advise that users properly insulate glass units with laminated glass on the inside, this is especially advocated for roof windows that are positioned high above where people sleep, play or work. In an event of breakage, safety is assured, because the lamination binds the fragments together.

In a case where you stand in need of an additional protection from the heat that emanates from the sun, VELUX has you covered. From insulating glass units, internal and external blinds to awnings and shutters which are built to minimize heat are available.

Whether you sit or stand, you can get the best of views. Remember that the best windows size is fully dependent on the roof pitch. With the use of a centre-pivot, you can easily place furniture right below the window, without inhibiting window movement.

The top-hung window design makes it incredibly easier to catch a glimpse of the entire surroundings whilst looking through the window. This feature brings a feeling a of additional space with it, because of the easy access it provides with that extra headroom. Besides the luxury of looking left and right through thhese type of windows, they are also very useful in urgent situations that require emergency escape/access.

In case the window is situated beyond your reach, consider putting an electrical or solar outfit in place through which you can easily control the motor to open or close the window, and also control the interior and exterior sunscreening products with the aid of a remote control.

Velux Roof Windows

Means of escape

If this is specifically for emergency reasons, it must be possible for the roof window to open without any form of hinderance, and the opening of at least 0.03 m2 with a width and height of at least 450 mm


The frame at the base of an opening window has to be 0.8m above floor level.
For Centre-pivot windows with sills that are below the aforesaid level, restrictor locks can be employed. For windows that will serve as an emergency escape/access, the frame at the base of the window must meet the specifications stated in page 7.


If the room is to be occupied by people, then air needs to move freely for health and safety purposes. VELUX roof windows offers purge (rapid) as well as background ventilation to satisfy this need. In addition to this, there is a need for mechanical extraction in kitchens and bathrooms or any part of the house where huge amounts of aqueous vapour emanates from.
Carefully study the Building Regulation requirements to make sure you provide ventilation in compliance to the necessary standards, and allow for the right amount and type of ventilation pending on the size and use of the room.


For appropriate natural lighting, it is advised by VELUX that at the minimum, the daylight area should cover 15% of the floor area. As a standard in Scotland, it is required that all buildings should have a window, or windows of an aggregate glazing area which is equivalent to at least 1/15th of the floor area of the building . Also, these windows must be positioned in an external wall or roof.


Standard Building Regulations allows the use of glass which are positioned 800mm from the floor under the condition that safety glass must be installed alongside the glazing units. It is also reccomended by VELUX that the use of laminated glass should be employed in the inner pane if windows are positioned in places that are high, and out of reach. So, in an event of breakage, the lamination will keep the pieces of the glass together and prevent it from totally collapsing. This applies mostly to public places including schools, sporting facilities, conference centres and other high rise buildings.

Replacement of windows

Different areas have their specific Building Regulations, in some, replacement windows is the covered under the Building Regulations. For that reason, a proper request must be made to the local authorities prior to the commencement of work. However, companies that are duely registered with FENSA can undertake the replacement once the breakage happens, and then report it to the Local Authorities when the job is completely done. The most improtant point is to work in compliance to Local planning rerquirements in your area.


It is a commonplace for VELUX roof and windows to be installed from inside. This is done to prevent working on the roof.
Also, some cases require special methods of installation, and the need to perform this installation from outside becomes imperative. In these cases, it is recommended that you work in complaince with the best safety practices.

A lot of attention should be given to safety measures in building sites where the risk of drops is above two metres. Hence, it is imperative to put an effective protection against falling in place at ll times.
Employing the use of a scaffold, or railing at the bottom of the roof is a viable option. Also, in cases where the work to be done is brief, leverage on safety belts with line/wire as your fall protection. The type of safety procedures that are taken are fully dependent on the nature of the building site, and the worker is fully responsible for it.

Installation of a roof window


Position the window in the room considering:

• what the room is to be used for

• a clear view when standing and/or when seated

• comfortable operation (centre-pivot or top-hung window)

• requirements regarding sill height, see chapter 1

• vertical wall, if any, see page 59

• optimum design of linings

• building regulation requirements


If the roof is not externally accessible, make a small hole of about 400 x 400 mm on the face of the roof, from inside and through the roof construction. After removing the battens, the final position of the window in the roof construction is revealed. When taking measurements, a major point to note is space allowance around the window frame for the purpose of insualtion.


If possible, in order to reduce the amount of adjustments on the roofing materials, tilt the window in sideways direction, to create the recommended distance to the rafter (support) (a) and roofing material (b).

The change in position, whether upwards/downwards is dependent on the type of flashing. For roofs with pofiled roofing materials, make provision for a full set of tiles at the base of the window. For slates, make sure that the needed overlap between the slates and flashing is put in place, see page 77 and installation instructions. Whn making the final decision with regards to the position and size of the hole on the surface of the roof, include a 20-30 mm allowance for the purpose of insulation. Employ the use of installation battens to fix the boundaries of the holes at top and bottom, and rafters on the sides. This can be seen in the installation instructions.


To easily and effectively cut and fold the roofing felt, and make sure it is waterproof, follow the directions in the installation guide.In a roof with an existing ceiling finish, project frame dimensions perpendicular to the ceiling finish and mark. Cut hole. Cutting an impermanent hole in the course of installing your window is very important. Also, a point to note is that the re-establishment of the vapor barrier around the current roof construction (if any) with the newly installed vapor barrier around the window must be practicable. Do not make any conclusive changes to the hole in the ceiling finish till you have finished installing the lining.

Removing sash

In cases where there is a need to install the window from inside, then the sahs must be taken out. After taking out the sash, lay it on a clean and uniform surface. If the installation would be done from outside, then there is no need to take out the sash.


Installation brackets come along with the window or flashings for certain installations. Windows with heights from -08 (1400 mm) and above, come with extra installation brackets which would be affixed at the middle of the side frames during installation. These brackets needs to be fitted before the windows are positioned in the roof. Certain products and combinations require special kinds of brackets. For example:

• If the window installation was done with recessed flashings EDN and EDJ, special brackets comes together with the flashing.
•With some combinations of windows and flashings, special brackets come together with extra window elements, such as GIL, VFE, or with the flashing, eg EBW.


The frame insulation collar from installation set BDX 2000 is made up of four lengthy pieces of polyethylene foam fitted on steel rails. Arrange the rails in the form of a frame, then place them on the battens within the roof opening prior to the installation of the window. It is then installed together with the window’s installation brackets. In cases of insufficient allowance between the rafters, it is important to make the necessary adjustments to make sure the insulation collar is positioned correctly. Adjustments can be made by tearing along the slit on the sides.


Making necessary adjustments to the square, and leveling the window is critical to achieving a weathertight seal between the sahs and frame, and also for efficiency. Begin by fitting the frame at the base to the lower installation batten, which must be uniform. Make adjudstments to the distance between the frame and sash to make sure the gap is equal on both sides. Bottom frame and bottom sash must be parallel. If the frame twists as a result of the difference in the lenght of the rafters, make adjustments to the from with the use of the wedge that came together with it as shown in the installation instructions. In a case where the roof is lopsided or slanting, refer to page 50-51. After making adjustments to the window, install it as shown in the installation instructions.


Leverage on the effectiveness of the underfelt collar BFX, for the simplest connection to underfelt. The underfelt can meet the requirements of roof constructions, regardless of if they are ventilated or not. This is owed to the fiffusion open material which it is manufactured from. Affix the underfelt collar to all sides of the frame, shape it around the battens and fix it to the counter battens. Put the drainage gutter in a position such that it is just above the first continuous batten over the window, so that water can flow off from the underfelt which is above the window.

Fit self-adhesive butyl strips supplied as shown
(a) To cover up the felt, where it was cut over the rafter, bend the underfelt collar and then the current underfelt down into the drainage gutter and attach the brackets that came with it.
(b). In order to put the underfelt and collar in the right position, which is just under the window, cut undeefelt as described.


Put flashing and covers successively as described in the installation instructions for the window and flashing. Each part has a number inscribed on their back that most times also represents the installation sequence. Another point to note is the position of the parts; left and right.