Picking windows for your house seems an easy task at first, but when you dig a little deeper, things get complicated.
Things like size and color are obvious... but what about stuff like energy performance, sun protection, safety features?

The truth is that windows are quite complex objects and, when choosing the right ones for your home, there is a lot to consider.
On top of that, you have a limited budget to work with.

So how do you make sure you don't overlook anything and you get the best bang for your bucks?

Here is how we approach this problem every time we have to pick windows for our projects...

Windows are an essential part of any building, helping to create a good indoor climate for your wellbeing.
Energywise, they are the building component that spills out the most energy... so their quality is very important.
They also are important in helping you to feel part of the surrounding nature and landscape.

Moneywise, they can be one of the largest cost items in your budget.

When evaluating the right type of windows, you need to consider how you plan to use the space where the windows will be installed.

If it is a space where you'll spend a lot of time, then you need to make no compromise on quality.

If it is a space where you'll spend time sporadically, then you can probably choose using more relaxed criteria and spend less money on the windows.

The 9 criteria for choosing windows

Overall there are 9 criteria you should follow to make your evaluation.
Here they are, listed in order of importance:

  1. Energy Performance and indoor comfort
  2. Opening (& fresh air)
  3. Window frame material
  4. Shape & Size
  5. Window frame division
  6. Safety & Security
  7. Surface & color
  8. Price
  9. Availability

If you consider all these 9 aspects, I can almost guarantee you'll pick the best windows you can possibly afford.
Let's see them one by one... 

1. Energy Performance and indoor comfort

This comes first because it set the tone for the entire discussion.

Good performing windows are (of course) more expensive.
So picking low-energy windows will set you on the expensive side from the very start.

As a rule of thumb, the bigger the windows, the more weight you should give to energy performance.

Sidenote: this in turn make the whole thing even more expensive!
My suggestion is to think twice about the size of your windows (more on that at point 4).

katus.eu how to choose windows energy

As mentioned above, the planned use for the building is of vital importance in this choice.
If your cabin or house is well insulated and you plan to use it through the year, then you should make everything you can to get low-energy windows.

As shown in the image, windows can be responsible for over 30% of the energy you need to keep your house warm!

The weak link

Now, when looking into the energy efficiency of a window, the frame is the weak link.

Today, triple-glazed windows are the most common option... and I'd recommend you stick with it.
Not only they perform about 40% better than double-glazed ones, but they might cost less!

In fact, as double-glazed panes become less common, some window manufacturers are treating 2-glasses as "special orders".

But why is the frame the weak link?

Because the U-value of a good triple-glazed pane is around 0.6 W/m2K.
For comparison, the U-value of a good frame is about 1.3 W/m2K.

The U-value

Woooo... what's this thing now?

The U-value is a measure of the capacity of a material to exchange energy with the environment

The lower the U-value, the more energy-efficient the material is.

So, for the same surface, the frame of a window loses more then twice the energy spilled out by the glass.
It follows that to limit energy losses, you want to keep the frame to a minimum and maximize the glazed area.

Some went overboard with this and built tiny houses entirely made of glass (like the Ööd house)... is this a good idea?
Well, a glazed wall is about twice as expensive as a traditional one and its energy performance is at least 3 times worse.
You do the math...

In our opinion, glazed surfaces should be used strategically throughout the building.

Large glazed areas, not only spill out energy but considerably affect the indoor climate.
In fact, in winter the interior temperature of a large glazed surface can drop significantly and become a source of "breeze" inside the house.

For this reason, the glass on those windows must have outstanding energy performances.

2. Opening & fresh air

Some windows need to be openable.
If you are building a small cabin or a tiny house, there is a chance that you do not have any ventilation system.
In this case, the windows must double as air inlets/outlets for your house.

There are mainly four different types of openings:

  • inward opening windows (also known as German type windows)  
  • top-swing
  • sash window
  • sliding windows

Each one comes at a different price point and the energy performance of the frame is different from type to type.
Also, the material in which they are available might be different.

Inward-opening windows often allow for what's called "micro-ventilation", which is essentially the window being closed but not fully sealed. That's a good feature to have.
Generally, all the types allow for opening just a bit and lock it in position.

Be aware that the direction of the opening of the window will affect the price quite a bit:

  • inward-opening is usually the cheapest of the types that can be opened;
  • sliding is usually the most expensive.

...and there are also fixed windows, which are the cheapest of all.

In the end, choosing the type of opening is not only a fictional and aesthetical problem, but it also affects energy performance and price.
You'll have to balance what you like with what makes sense for your wallet.

3. Window frames

We've seen already that the frame is the weak link of the window when it comes to energy efficiency.
We've also seen how the opening of the window affects the price, and or course its usability.

Logically, it seems that choosing the right frame is the most critical choice in picking the right windows.

Sidenote: interestingly enough, windows manufacturers are actually frame manufacturers. I mean, they don't make the glass panels!
Glass panels are ordered to measure from glass factories and then assembled into the frame at the window factory.

Also, note that frame is what gives the window rigidity and durability.
For example, the maximum size (generally height) of a single window, is limited by the material and thickness of its frame.

There are mainly three materials you can choose from:

  • PVC;
  • wood;
  • aluminum.
katus.eu how to choose windows pvc profilekatus.eu how to choose windows energy wood triple glazedkatus.eu how to choose windows aluminium profile

From an energy point of view, they are all equivalent.
When evaluating the price, PVC can be as much as three times cheaper than wood or aluminum.
When evaluating the need for maintenance or replacement, aluminum wins... followed by PVC.

As you can see, different materials perform different on different metrics.
So there is not a definitive answer on "which is the best material for a window frame?". 

Sidenote: actually, if you are brave enough you could even venture into using no frame at all.
For larger and fixed windows (not openable) you can have the glass pane directly installed into the wall frame.
When done correctly, the result is often a minimalistic look that is simply astonishing.
Unfortunately, this method is usually a home-made solution and it does not give any guarantee when it comes to energy performance and air-tightness, therefore it is something that, although beautiful, we cannot really recommend.

4. Shape & Size

Windows do not have to be randomly placed on the walls of your room... they can be designed and placed in a way to improve the functionality of the room and the aesthetic of the house.
Of course this requires know-how and taste, but it is an important aspect of a new building and it deserves the right amount of attention.

Here are a few questions that can help you think about the windows from a different perspective:

What's the view out of the window?
...is it in the corner of a small yard or in beautiful surroundings in the countryside?
You can see how the answer to this question might affect how big you want your window to be.

What's your preferred lifestyle?
...do you prefer privacy and value a place to hide?
...or you like an unobstructed connection with the outside?
Again, this calls for different sizes of windows.

Oh, are you building a small cabin?
What you use it for?

...is it a quiet retreat for yoga classes, meditation? 
...is it a place to sleep and look at the stars?
...is it a guesthouse or just a man cave?

You get the idea.
Windows are produced one-by-one to specification, therefore they can be designed one-by-one.

Keep in mind...

  • Rectangular shapes are of course easier to manufacture, therefore they are cheaper.
  • The larger the window, the more you should focus on its energy efficiency (see section 1 above).
  • The larger the window, the more natural light you'll get in the house... but this could lead to overheating if the window is located on a south or south-west facade.

5. Window frame division

The main issue here is weight.

As a rule of thumb, one square meter of a triple glazed window (about 3ft x 3 ft) weighs around 40 kg (88 lbs).
A large window - for example, 9.3 sqm (100 sq.ft) - will weigh more than 370 kg ( 815 lbs).

...good luck moving that thing around.

If you like large windows and unobstructed views, you might have to pay a considerable extra for handling your windows (you'll need a crane).

What's the alternative?

Simple, dividing the window into smaller sections.
Now, while this is effective for handling and installing the windows with less trouble, it introduces some extra issues.

In fact, dividing the window into sections adds extra frame... and by now you should know that this introduces energy losses... which calls for better frames.
So again, complex decision.

One thing in favor of sections is that, if a glass ever breaks, you then have to replace a smaller glass section.
Think about that.

6. Glass properties

The glass makes for the most part of your windows.
Despite the simplicity of this component, there are several characteristics that can be ordered to come with it.

Here is a list:

  • energy efficiency
    As mentioned already, the typical U-value of a triple-glazed glass pane is 0.6 W/m2K.
    More performing glasses are available for an extra price.

  • light absorption/reflection
    There are special types of glass that reflect most of the radiation to the outside, effectively avoiding overheating.
    This is particularly important in areas with lots of solar irradiation (south locations).

  • safety features
    Most building codes require that glasses of relevant size must be tempered.
    Tempered glass breaks into a million tiny pieces, hold together by a plastic membrane so they don't go all over the place with the risk or causing injuries.

  • security features
    If you are concerned about break-ins, you can order glasses that cannot be broken.
    This generally applies to windows on the ground floor.

  • self-cleaning
    If you live in a place where dust or salt accumulates on the exterior surfaces, it can be a good idea to invest in self-cleaning glasses.
    This costs extra money but can make your life easier, especially for those high windows that are not easy to reach.

For the sake of completeness, we need to mention also:

  • shading
    Glasses can be equipped with a membrane that makes them opaque at the click of a button.
    Crazy expensive technology. Don't even look at it.

  • energy production
    Glasses even make energy with built-in solar panels.
    This technology is still super expensive and you better go with roof-mounted solar panels.

All the options mentioned above are independent and can be ordered separately when you design your windows.

7. Frame color

Back to the frame... we are now talking about aesthetics.

Things you should know:

  • whichever frame type and material you choose, there will be one or more colors preferred by the manufacturer that cost less. Ask for it.
  • in general, you can basically choose any color you want (from the RAL color chart), but it will cost extra money and it will require more time to get it.
  • you can have the interior of the frame in one color and the exterior of another color. This will cost you extra-extra money and it will probably take even more time.

8. Availability 

Every manufacturer has some sort of "standard window" that set the following characteristics:

  • the material of the frame
  • the type of opening of the window
  • the energy performance of the frame
  • the color of the frame
  • the type of glass panel and its energy performance

As windows are made one-by-one, size is never an issue.
However, any change from the standard adopted by the manufacturer will most likely result in expanding the time for producing and delivering the windows.

The typical time for delivery fo a standard order is 3-4 weeks from the order.
For customized orders, this time can extend to 6-8 weeks from the order.

If time is an issue on your project, this is something you have to consider.

 9. Price

Finally, we have now all the elements to talk about the price.

We have seen there are many aspects to pay attention to when choosing a window.
We have seen how each aspect is important in its own way.
We have seen how each aspect affects the price.

To summarize, if you want to get the cheapest possible solution while getting high-quality and high-performing windows, you have to:

  • choose PVC frames
  • choose inward-opening windows
  • choose the color suggested by the manufacturer (generally white)
  • use triple-glazed glass panes
  • limit the customization of the glass to tempered, where strictly necessary
  • keep the size of the windows to a reasonable size, so you can also limit the number of divisions in the window (less frame)
  • use fixed windows wherever possible

One suggestion...

I would suggest to always get an offer for this type of window and use it as a base for comparison with your "preferred" version.

You might like to get a 100% eco-friendly wooden window... I get it, I like that as well.
But when you compare the price of the window set, you'll most likely find our that's gonna cost you 3 times as much as the white PVC window set.
...for the same energy performance!

Which one will you pick?
...that's your call to make.

10. Measurement control & Installation

Finally, there are THREE more things you cannot overlook:

  • the exact measure of each window (to fit the opening in the wall);
  • the installation process;
  • the interior and exterior finish of the window.

Needless to say, you should always double or triple check the measurements of the openings in the wall and calculate the window size accordingly.
Ideally, you want to leave 1.5cm space (about half-inch) on the left, top, right... so the window has to be shorter than the hole and a little narrower.

You should get 100% clear on how the window should get installed and who'll do the job.
If you are concerned about airtightness and energy performance (you should) then you might want to stress that proper tapes, seals and membranes must be used.
If you do not take this into account, your installers will use simple foam... which is NOT a durable and acceptable solution when it comes to airtightness.

When buying windows, you should definitely think through how you would like them to look when finished.

Here are a few questions that can make you think...

Where will you position the window in the wall?
With walls now getting thicker and ticker, the window can either be installed towards the inside or the outside wall itself.
I warmly suggest to install it as far as possible towards the outside, mostly for 2 reasons:

  1. it offers better energy performance;
  2. you can use the space on the interior sills.

How will you close the gap between the window and the wall?
...composite or wooden boards?

What material will the interior sill be?

What material will the exterior sill be?

As you can see, these are tiny detail but they'll require your attention at some point... so, the sooner you focus on them, the better.


As you can see, choosing and ordering windows is not as easy as it seems.

We spent over 2000 words on this and we even didn't mention handles.
Yes, handles is another thing you'll have to spend time on... and they come in all sorts of material, shapes, and price!

Neither we covered different shading options or mosquito nets... which can be ordered as optional.

I'm sure you get the idea: you should not overlook the role that windows play in your building and you should carefully plan every detail about each window.
This is the only way to get a good indoor climate and a proper energy performance at a price that will not hurt your wallet.

PRO-TIP: in order to educate yourself properly, we recommend to not just sit and think, but also call different companies and ask more or less naive questions in order to learn more before finalizing this expensive decision.  


If you want more information or you have any other kind of question, feel free to reach out to us.