Complete Guide to Roof Windows

With so many options available on the market, it’s hard to know which roof window might be right for you! With a range of frames, functions and glazing types available online, have a read of this handy guide to help narrow your options.

Glazing

Double Glazing, Triple Glazing and Quadruple Glazing – standard glazing with multi-layered options for additional protection
DW6 Glazing Unit – an energy efficient form of glazing that boasts external laminated, toughened and anti-slip panes. This glass is wider around the perimeter and internal safe laminated pane.
Energy Saving Double Glazing – energy efficient glazing includes toughened panes with an inert gas filling to improve heat insulation and reduce the amount of heat loss. This helps to improve the U-Value (see below).
Secure Double Glazing and Secure Triple Glazing – this glazing form offers higher resistance against breakage. The glass consists of two sheets of 4mm glass with a 1.52mm layer of PVB in the middle. It is installed on the inside of a window and includes and low-emission coating. There are double and triple glazed options available.
Sound Reducing – this glazing style significantly reduces noise penetration. It is comprised of toughened glass on the exterior, and the interior is made of laminated glass that includes a soft, soundproofing layer of epoxy resin.

U-Value

The U-Value refers to the insulating ability of the windows. Heat loss happens due to the difference between indoor and outdoor temperatures. The U-Value measures how much heat flow or loss can occur through the glass.

The U value is measured in watts per square metre Kelvin (W/m2 K), and the lower the number, the better the insulating ability. The values tend to range from 0.1 (very little heat loss) to 1.0 (higher heat loss).

Acoustic Insulation Rw

Rw stands for the ‘Weighted Sound Reduction Index’. This is used to measure the sound insulating abilities of roof windows, and is monitored in decibels (dB). The higher the Rw number, the better sound insulation a skylight window provides.

Air Inlet Type

An air inlet is a device that continuously delivers fresh air to a room. FAKRO roof windows feature one of two styles of air inlets:

Automatic V40P Air Inlet – this air inlet is positioned at the top of the frame. The capacity of the air inlet rises to 49m3/h with a 10Pa pressure difference. As the pressure difference grows, the airflow capacity stays at a consistent level, due to the elastic pneumatic flap. This flap limits the amount of inflowing air by reducing the air inlet duct area.
Air Inlet V35 – also located at the top of the window frame, this air inlet supplies up to 41m3/h of fresh air at a 10Pa pressure difference. This helps greatly in reducing a room’s humidity, and therefore its condensation. The V-35 air inlet can in part discharge air when normal gravitational ventilation isn’t working properly.

Air Inlet Air Flow

The attribute above refers to the style of air inlet, whereas the air flow refers to the speed at which fresh air is supplied into the room. This is measured in m3/h.

Number of Seals

The roof window seals create a watertight 'weatherseal' to prevent leakages into a property. The majority of our FAKRO roof windows boast 4 seals located on all four sides of the opening sash, dubbed the 'Quadruple Sealing System' for maximum protection. The rooflights also have two condensation channels to prevent any moisture from entering the timber frames of the window.

Window Fill

FAKRO roof window glazing is filled with gas in order to improve the performance of the window. This can include assisting with insulation and minimising the amount of heat transferred through the glass, hence why they are often referred to as insulating gas. There are two different gases used in these rooflights for flat roofs:

Argon - Argon is the most used gas, as the cost to impact ratio is good. The least expensive out of the two, Argon windows can increase the energy efficiency of the window by up to 30%, as well as improving the sound proofness of a property.
Krypton - Krypton gas is a step-up cost wise compared to Argon, but it is denser, making it more energy efficient and insulating as a result.