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Replacing roof windows - which ones to choose?

06 of February '23

Roof and attic renovations associated with thermal upgrading should include the replacement of roof windows to preserve the building's energy efficiency.

Roof windows installed decades ago were not covered by standards in line with those of today, and over the years the technology for their production has developed in care of energy efficiency. Therefore, when doing a roof or attic renovation, it is imperative to consider the replacement of roof windows. It is assumed that their replacement should take place once every 20 years.

Energy efficiency

When buying a good quality roof window, you need to take into account its energy-saving parameters. The most important role in determining the quality of windows is the Uw thermal coefficient - the lower, the better. There are roof windows on the market not only meeting the standards, but also having a thermal transmittance lower than required by the regulations (no more than 1.1 W/m²K). Roof windows are a building material that must be tested - so the window parameters specified in the documents are sure to be reliably tested by independent testing centers. Restrictive building standards are aimed, among other things, at energy optimization - reducing heat loss in buildings and using natural resources wisely. When building a house, renovating an attic and repairing a roof, it is important to consider the thermal performance of all solutions used including wall, floor or roof structures, as well as windows and doors. It is estimated that heat loss through window joinery can be as high as 15-30% - its choice is therefore crucial in achieving maximum energy efficiency of the entire building.

© Okpol

Which energy-efficient windows should you choose?

The Polish manufacturing company OKPOL offers 3-pane roof window models. The offer includes windows with a wooden profile - ISOV I22 and IGOV N22 with a profile made of multi-chambered PVC. OKPOL 3-pane roof windows have two inter-pane frames, a handle with a key, and a ventilator that allows fresh air to flow in constantly, without drafts. Low-e coatings in the glazing packages reduce heat loss in winter and protect against overheating in summer. The heat transfer coefficient for the ISOV I22 window is 1.06 W/m²K, and for IGOV N22 it will be Uw=0.83 w/m²K.

Are roof windows environmentally friendly?

OKPOL roof windows are made of the best quality materials - wooden windows with SuperTermo technology are made of glued pine wood sourced from sustainable sources. OKPOL has an FSC certificate in this regard. During wood processing, knots are cut out of the profiles to make them safer and more durable for use.

The company has also taken care to utilize post-production waste. To this end, it has purchased a machine that converts unused wood parts into pellets and heats the plant in this way. PVC profiles are a reusable material so they will be recyclable in another few decades.

© Okpol

Window selection

When installing windows for the first time, it is advisable to measure how much light will be needed for the comfort of the user, then a hint for the selection of the size of the windows is provided by the standards for the correct illumination of the room with natural light - it is expressed by measuring the ratio of the size of the glazing to the floor area. In a place where people stay, it should amount to 1 window per 8 sq m of floor. When replacing windows, most often investors opt for a 1:1 replacement, i.e. inserting a new window in place of the old one. Building standards have changed over the years, and in order to meet them - for the sake of your own comfort - you can add the appropriate number of windows in the roof, but inserting them involves more renovation. A much larger glazing area can be obtained by combining windows into sets(check how to choose a window combination).

© Okpol

When choosing a window, you should be guided by your own preferences and the comfort that this change is expected to bring. An additional criterion is the selection of the window with regard to the type of room in which it is to be located - windows with a PVC profile are dedicated to rooms with increased humidity, i.e. kitchens, laundry rooms and bathrooms(see how to arrange a kitchen in the attic). In contrast, wooden roof windows look better in living rooms, bedrooms and children's rooms. The most important thing is to choose an energy-efficient window that will protect users for years to come.

An additional aspect is the choice of opening method (location of hinges).

Roof windows usually rotate 180 degrees. OKPOL's offer includes innovative tilt and slide windows, which, thanks to two ways of opening - one tilting and the other sliding - do not take up space in the room in either position. The sash in the tilted position opens up to 62°, while the sliding function allows the outer pane to be turned toward the room, which makes it much easier to keep it clean.

© Okpol

If the windows are installed so high that access to them is difficult, it is worth thinking about buying remote-controlled ISC and IGCV windows (see electric windows). Their parameters are the same as those of other roof windows, plus you can open them from the level of a sofa or comfortable armchair.

It is worth paying attention to accessories, thanks to which we can not only spruce up the space, but also darken it, soundproof it and even cool it down. In lowering the temperature, awnings and external blinds are reliable. Awnings reflect the sun's rays even before they reach the glass, while not completely obstructing the view. Roller blinds, on the other hand, darken completely and reduce the level of noise reaching the room from outside. Internal blinds and pleats not only provide a barrier to the sun, but are also an interesting aesthetic aspect.

An extensive selection of colors, materials and guides can be found in the Roof Window Accessories catalog on OKPOL's website.

Awning blind for OKPOL roof window, elbow window with installed internal blinds of pleated type

© Okpol

Installing new windows

Replacing old windows does not have to involve troublesome demolition of walls, damage to the stile or violation of the roof structure. Properly executed window replacement will not cause the installer such problems. The installation of a new window follows the removal of the old one and involves inserting it in the same place, provided that the same size of woodwork is used again. To improve aesthetics, investors often use the replacement of the entire window recess, and we recommend this type of wall refreshment, although it is not necessary.

Care should be taken to ensure that the installation is commissioned to a specialist. Roof windows should be installed by roofers, in accordance with the art of construction and according to the instructions supplied with the window. A poorly installed roof window will not perform its function, will negatively affect the energy balance of the building, and may even lead to damage to the walls or roof trusses.

Technical assistance for roof window installation

OKPOL recommends following the window installation instructions and adhering to the well-known and prevailing construction art. While facade windows can be installed in a less restrictive and complicated way, roof windows require expert knowledge. The best solution is to hire an expert roofer for this purpose.

OKPOL has launched a Technical Assistance Department, which you can contact for advice, and provides on its website the contact details of Technical and Sales Advisors who support customers from the moment of purchase and even before it up to the installation (

All windows can be found in a clear catalog. If you have any questions, the company encourages you to contact a Technical and Sales Advisor.

© Okpol

OKPOL Company

OKPOL is a Polish company with 30 years of experience in manufacturing windows and roof hatches.The company's headquarters and production plant are located in Opolskie Voivodeship in the Skarbimierz municipality, on the site of a former airport, which is now the area of the very well-located Walbrzych Economic Zone. Our company is located in its immediate vicinity.

For more than 30 years we have been taking care of the high quality of the products we offer. We believe that it translates into the quality and comfort of your life. We are a family business that does not lose its enthusiasm for creating novelties over the years. We know perfectly well how important the safety of your loved ones is to you, so we still want to guard it. We supply windows to many countries in Europe and even abroad, and we are constantly investing in equipment and upgrading machinery to be able to deliver safe, comfortable and durable products to your home.

Confirmation of the high quality of the manufactured products are the attestations, certificates and diplomas we have obtained, awarded to the best manufacturers in the industry. OKPOL products are durable, reliable and easy to use. In the rich and varied offer everyone will find a product for themselves. The windows we produce have a 10-year warranty. Get to know our products and see for yourself that it is worth investing in domestic products, enjoying recognition throughout Europe.

For more information, visit the company's OKPOL Sp. z o.o. page on the PdA portal.

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