Hello everyone,
We are currently planning our floor layout and have come across differing recommendations regarding the amount of window area needed, depending on whether you:
Of course, we understand that calculating illuminance (lux) is much more complex than just a simple rule of thumb, but for budgeting purposes, we want to estimate a reasonable number of windows upfront to avoid being caught off guard later when we might need to add windows costing an additional $10,000–15,000.
So, we are wondering how a roughly 20m² (215 sq ft) room in a 1.5-story house could possibly meet a 20% window-to-floor area ratio. Even with two skylights (Velux) providing an effective window area of 1.16m² (12.5 sq ft) and a 160 x 140 cm (63 x 55 inches) double window (estimated at about 100 x 110 cm (39 x 43 inches) effective window area after accounting for frames, etc.), we only reach 17.3%! The same applies to the closed kitchen downstairs, where two windows each measuring 120 x 100 cm (47 x 39 inches), estimated at about 90 x 70 cm (35 x 28 inches) effective window area after frame deductions, wouldn’t even reach 10% – somehow it feels like we might be missing something here.
So the question is: how much window area (as a rule of thumb) should you really aim for? Where is the sweet spot so that you don’t have to install two floor-to-ceiling windows and 10 skylights in every room? As mentioned, we just want to understand whether 20-25% is a realistic guideline to aim for, or if it’s mostly marketing hype — especially since Velux tends to promote these figures heavily on their websites. We want to avoid building a dark, poorly lit home, and retrofitting windows later sounds like a real hassle.
Thanks a lot!
We are currently planning our floor layout and have come across differing recommendations regarding the amount of window area needed, depending on whether you:
- follow the national building code – according to information online, this would suggest having about 10-12% of the floor area as window area
- follow newer guidelines such as DIN EN 17037, which recommend 20-25% as a rough rule of thumb
Of course, we understand that calculating illuminance (lux) is much more complex than just a simple rule of thumb, but for budgeting purposes, we want to estimate a reasonable number of windows upfront to avoid being caught off guard later when we might need to add windows costing an additional $10,000–15,000.
So, we are wondering how a roughly 20m² (215 sq ft) room in a 1.5-story house could possibly meet a 20% window-to-floor area ratio. Even with two skylights (Velux) providing an effective window area of 1.16m² (12.5 sq ft) and a 160 x 140 cm (63 x 55 inches) double window (estimated at about 100 x 110 cm (39 x 43 inches) effective window area after accounting for frames, etc.), we only reach 17.3%! The same applies to the closed kitchen downstairs, where two windows each measuring 120 x 100 cm (47 x 39 inches), estimated at about 90 x 70 cm (35 x 28 inches) effective window area after frame deductions, wouldn’t even reach 10% – somehow it feels like we might be missing something here.
So the question is: how much window area (as a rule of thumb) should you really aim for? Where is the sweet spot so that you don’t have to install two floor-to-ceiling windows and 10 skylights in every room? As mentioned, we just want to understand whether 20-25% is a realistic guideline to aim for, or if it’s mostly marketing hype — especially since Velux tends to promote these figures heavily on their websites. We want to avoid building a dark, poorly lit home, and retrofitting windows later sounds like a real hassle.
Thanks a lot!
W
WilderSueden20 Sep 2023 21:51roookeee schrieb:
Thanks, that helps. For now, we’ll plan to make some of the currently planned windows a bit larger and set aside money for any additional windows we see as a nice option, so we have enough flexibility during discussions with the architect.The cost of extra windows also depends a lot on your builder. With us, the general contractor calculated walls and windows separately. Others make a fortune just by enlarging windows.11ant schrieb:
No typical homebuyer reads a state building code at the start of their research – only when something in their specific development plan raises questions and they want to understand how much the municipality is imposing regulations beyond the scope of the state building code. I advise prospective builders in all federal states except Mallorca, and without a specific reason, I have never actually read through a state building code. It’s a reference book, not a novel! I don’t know why some people here think we have read the state building code. The floor plan included windows, we adjusted something to our preferences, searched online for “are there any rules about windows?” => “yeah, state building code says about 10–15%, but that’s a bit old-fashioned; the EU recommendation is more like 20–25%” and based on that result, we are asking questions. We have not opened the state building code, and we won’t open it.
11ant schrieb:
I’d rather call it looking through a distorted lens. Not a single provider advertises floor plans with only a minimum number of windows (and as I said, they have no incentive to be stingy here). Catalogues promote competitively attractive models, and this applies across all price ranges. The “most cited” floor plans are those that are rated as attractive and often used as templates for custom designs. A company that “skimped” on windows would be cutting off an important marketing channel in visual platforms. As mentioned before, it seems we have developed a distorted impression from our previous conversations with 4–5 construction companies; I clearly stated that this could be the case 🙂 Personally, I have seen several new buildings with very few windows that exactly match the floor plans I meant.
11ant schrieb:
You have – at least if you mean the draftsmen/technical specification assistants of the providers – romantic notions about “architect meetings.” Better show what you have planned so far – then you’ll get more concrete advice than you might want ;-) Thanks for the tip, we will keep that in mind. We still have an “architect meeting” to come; I don’t yet know who exactly will be talking to us, but I might ask. Maybe we’ll also post the floor plans here, depending on how much we feel like dealing with the forum’s tone (this isn’t a criticism, just reality – and that’s fine).
WilderSueden schrieb:
What additional windows cost also depends heavily on your builder. Our general contractor charged the same rate for walls and windows. Others make a fortune just by enlarging windows. Yeah, in that regard, we’re just doomed. We don’t want floor-to-ceiling windows upstairs and have to build a one-and-a-half-story house with a roof pitch between 40 and 60 degrees according to the development plan, so we would have to rely heavily on roof windows. The two suppliers in this sector know they basically have a monopoly, so you can literally inject money into their pockets for every square centimeter of window, not to mention the roller shutters that cost just as much as the windows. But whining doesn’t help here.
WilderSueden schrieb:
The cost of additional windows also depends a lot on your construction company. For us, the general contractor priced the walls and windows the same. Others make a fortune just by enlarging windows. For us, the KfW40 wooden window from local production was also cost-neutral compared to the wall price. We shifted things back and forth quite a bit—even the wider patio door (1.20m (4 feet)) made no difference.
We started here with a design that was called the "dark dwarf cave." I didn’t really understand that at first, but the more we got into it, the clearer it became what was meant.
After that, I began measuring windows in different rooms to get a feel for how it would look. In the office, at my parents’ house, with friends, all the windows in our rental building… Try that! You’ll be surprised, but it will also give you a better frame of reference for “no, too dark, phew, too big—that inherited sideboard doesn’t fit anymore, too much sunlight on the TV,…” You can read standards, but the feeling for what suits you best is not given by a 1.20×1.50m (4×5 feet) dimension from some building regulation or DIN standard.
roookeee schrieb:
We don’t want floor-to-ceiling windows upstairs and according to the development plan, we have to build 1.5 storeys with a roof pitch between 40-60°, so we’ll have to rely heavily on roof windows. If dormers fit the budget, that would be an option for the south side to provide the south-facing rooms with windows on two sides. Velux offers double window solutions like that, which we have just ordered. For around 10,000 (currency), we’re getting two double windows, each measuring 140x66cm (55x26 inches) with shutters – but we’re also really looking forward to the view of the stars from bed...
-LotteS- schrieb:
If dormers are within the budget, that could be an option for the south side to equip the south-facing rooms with windows on two sides. Velux offers these duo double-window solutions, which we have just ordered. We are looking at around 10k for two double windows, each 140x66cm (about 1.40-1.30m each) with roller shutters – but we’re really looking forward to the view of the starry sky from the bed... Currently, we pay about 3.2k for a Velux window measuring 94x118cm (width x height), fully equipped (including roller shutters, etc.). Depending on how practical it feels, we might go one size up here. Then our somewhat doubted “common sense” will need to decide whether to install two of these in the 19 and 17 m² (204 and 183 sq ft) rooms or not. Overall, the price per m² of roof window area doesn’t seem too bad for us—two of our windows would have more area compared to your examples and cost significantly less (of course, two combined side-by-side windows like yours probably look nicer).
A dormer would cost about 15k, excluding windows.
P.S.: Roof windows that are wider than the rafter spacing do not cost extra with our builder, since the spacing is 60cm (about 24 inches) anyway, so some trimming would be required regardless (according to the company).
The price I mentioned is the rough list price for everything combined, including roller shutters and controls. Depending on the ranking of your window manufacturer/roofer, you can usually get up to a 20% discount, which they then typically add back on to you variably.
What I ordered is called the "DUO Lichtband FK08," which has only 10cm (4 inches) spacing between the panes. Personally, I find a 10m (33 ft) wide and 5m (16 ft) high roof with just two individual 66×118 cm (26×46 inch) Velux windows quite challenging in terms of appearance... But aesthetics are only a secondary concern — the primary focus is on functionality and practicality.
What I ordered is called the "DUO Lichtband FK08," which has only 10cm (4 inches) spacing between the panes. Personally, I find a 10m (33 ft) wide and 5m (16 ft) high roof with just two individual 66×118 cm (26×46 inch) Velux windows quite challenging in terms of appearance... But aesthetics are only a secondary concern — the primary focus is on functionality and practicality.
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