HF 520 Flush Timber-Aluminum Designer Window
From outside, the HF 520 looks like fixed glazing: its glass sash hides the sash frame entirely, leaving a flush, studio-style face. Inside you still get real timber and a window that opens, with triple glazing, concealed hardware and a Uw as low as 0.71 W/m²K.
A window that reads as glass, not frame
In a conventional window, the glass unit sits inside a sash frame, and that frame is what you see from the street: a second border inside the outer frame. The HF 520 removes it. Internorm’s glass sash carries the glazing so that, from outside, no sash frame is visible and an opening window looks the same as a fixed pane. The facade stays flush and uniform, even where an elevation mixes opening and fixed units.
Inside, timber takes centre stage. The HF 520 pairs a natural timber interior with hard-wearing aluminum cladding, concealed hardware and I-tec Glazing for stability and burglary resistance. Internorm aligns it with its studio design style, the minimalist profile it reserves for architecture in which large glazing is the main design feature.
It is the timber counterpart of the KF 520 uPVC/Aluminum. The aluminum cladding is the same, so both windows can share one facade while the interior material changes from room to room.
For facades designed around glass
The HF 520 is at its best on modern houses where the architect has drawn the windows as clean rectangles of glass: long horizontal bands, stacked clerestories, corner compositions, or a grid of opening and fixed panes meant to look identical. On those elevations a visible sash frame on every opening unit would break the pattern. The HF 520 keeps it intact.
Its particularly slim frame also lets more daylight reach the room, which Internorm notes reduces how often you need the lights on. With timber inside, the window becomes part of the interior architecture rather than a hole in the wall: warm to the touch, matched to floors and millwork, quiet in profile.
Where a pane never needs to open, the HX300 frameless glazing embeds the glass into the wall itself, with a 58 mm visible frame on the outside only.
HF 520 technical data
Current figures from InterHaus product data and the Internorm 2026/27 catalogue.
| System | Timber-aluminum window with glass sash, no visible sash frame outside |
|---|---|
| Thermal insulation | Uw as low as 0.71 W/m²K |
| Sound reduction | 35–47 dB |
| Security | Up to RC 2, with I-tec Glazing |
| Locking and hardware | Fully concealed |
| Construction depth | 90 mm |
| Profile width | 101 mm |
| Design style | Studio (flush) |
| Interior timber | Spruce, larch or oak, varnished or oiled; opaque timber H9016 |
| Timber core | Solid timber core; PEFC-certified timber on request |
| Exterior | Powder-coated aluminum, all RAL colours available |
| Expected service life | 40+ years |
Best-case published values. The final Uw and sound figures for your windows depend on size and glass, and are confirmed on your quote.
Why choose the HF 520
Appearance of fixed glazing
No sash frame shows outside, so opening and fixed panes read as one flush surface across the whole elevation.
Particularly slim frame
Less frame means more daylight in the room and less need for artificial lighting through dark Canadian winters.
Concealed hardware
Hinges and locking stay out of sight, keeping both the timber interior and the glass exterior clean, with RC 2 resistance available.
I-tec Glazing stability
Glass bonded to the sash all round gives the glass sash its strength and helps resist break-in attempts.
PEFC timber on request
The solid timber core can be made from PEFC-certified timber from sustainably managed forests.
Up to 47 dB
Sound reduction of 35–47 dB, matching the HF 510 as the best acoustic rating among the HF windows.
Interior timber options for the HF 520
The HF 520 brochure lists these interior timbers and finish codes. Timber is natural, so grain and shade vary from print; we recommend choosing from physical samples.
Spruce, varnished
The lightest, most even grain, in six finishes: FI500, FI501, FI503, FI505, FI510 and oiled FI512. A calm choice for pale, Scandinavian-leaning interiors.
Larch, varnished or oiled
A warmer, more figured timber in LA600 or oiled LA604, suited to rooms with natural stone, plaster and linen.
Oak
Five tones: EI700 and EI701, plus oiled EI706, EI707 and EI708. On a flush profile with no ornament, oak’s grain becomes the main decoration.
Opaque timber
H9016, a solid opaque finish that keeps the feel and stability of timber while blending with painted walls and minimalist millwork.
HF 520 opening types
The flush look is available in tilt & turn, tilt-only and turn-only sashes, fixed glazing and combined units. Because the glass sash hides the sash frame outside, an opening sash and the fixed light beside it look alike, so ventilation can go where the room needs it rather than where the facade can tolerate it.
Honest numbers for a flush window in a Canadian winter
The HF 520’s Uw of 0.71 W/m²K is higher than the 0.64 of the HF 410 and the 0.65 of the HF 510, and we would rather explain that than hide it. The flush glass sash is a deliberate trade: the cleanest possible exterior in exchange for a slightly higher heat-loss figure than its siblings.
It is still a triple-glazed timber-aluminum window with concealed hardware and gaskets that shut out drafts. It helps keep the room-side glass warm, which reduces the chance of interior condensation in a well-ventilated home through an Ontario January. On the coldest clear mornings you may see dew on the outside of the glass; Internorm points out that this is a sign of good insulation, not a fault.
Sound reduction reaches 35–47 dB, equal to the HF 510. If your house will be modelled for Passive House or Net Zero, our team can show where the HF 520 makes sense and where a lower-Uw sibling should take the largest north-facing openings.
HF 520 against its siblings
The three HF windows share a timber interior and an aluminum exterior. The HF 520 is the one to choose when the exterior appearance comes first.
| HF 520 | HF 510 | HF 410 | |
|---|---|---|---|
| Exterior appearance | Flush, looks like fixed glazing | Slim square sash, visible | Classic visible sash |
| Design style | Studio | Home pure | Studio, home pure, home soft, ambiente |
| Uw as low as (W/m²K) | 0.71 | 0.65 | 0.64 |
| Sound reduction | 35–47 dB | 35–47 dB | 33–46 dB |
| Security, up to | RC 2 | RC 2 | RC 2 |
| Construction depth | 90 mm | 85 mm | 85 mm |
| Profile width | 101 mm | 70 mm frame + 29 mm sash | 70 mm frame + 38 mm sash |
| Matching uPVC/aluminum window | KF 520 | KF 510 | KF 410 |
The KF 520 uPVC/aluminum twin has a uPVC interior and offers I-tec Secure locking up to RC 3 on request.
“This was a VIP experience from start to finish. Fast, friendly and effective service. It really helped that Vik is an architect, she was able to guide us through the entire process and coordinated directly with our designer. The windows are top-notch, but the service was better than the product.”
HF 520 questions
Yes. It looks like fixed glazing from outside, but it is a fully operable window, available as tilt & turn, tilt-only or turn-only, and in combination with fixed sections. The sash frame is hidden from the exterior; inside, you have timber and a handle as on any other window.
Both are flush and minimalist, but the HF 410 keeps a classic sash frame that is visible from outside, framing the glass within the frame. The HF 520 uses a glass sash with no visible sash frame externally, so the elevation reads as pure glass. The HF 410 has the better Uw (0.64 against 0.71); the HF 520 has the cleaner exterior and up to 47 dB of sound reduction.
For most homes, yes. It is a triple-glazed window with a Uw well within high-performance territory, and it keeps interior glass surfaces comfortable. On energy-critical projects, one approach is to use the HF 520 on the street-facing or feature elevations and a lower-Uw sibling such as the HF 410 or HF 510 on the largest north-facing openings.
The HF 520 brochure lists spruce in six finishes, larch in two, oak in five, and opaque timber H9016. Walnut is part of Internorm’s wider timber programme but is not shown in the HF 520 brochure, so please confirm it with us before your interior design depends on it.
Yes, with the KF 520 uPVC/aluminum, which Internorm designed as its perfect match. The aluminum cladding is identical, so the exterior is uniform while you choose timber or uPVC inside, room by room. The KF 520 also carries I-tec Secure locking, available up to RC 3 on request, which can suit ground-floor openings.
On request, the solid timber core can be made from PEFC-certified timber from sustainably managed forests. The glass helps too: Internorm uses low-carbon iplus insulating glazing as standard, built on a 4 mm float glass of 5.8 kg CO2 eq/m² against 10.6 kg for standard float glass.
Continue exploring
Systems that share the HF 520’s exterior or complete the same facade.
Wood/Aluminum windows
All Internorm timber-aluminum windows and how they suit the Canadian climate.
Explore
KF 520 uPVC/Aluminum
The flush uPVC/aluminum twin with I-tec Secure locking.
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HX300 frameless glazing
Fixed glass embedded in the wall for panes that never need to open.
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HS 330 lift-slide door
Timber-aluminum lift-slide door for wide terrace openings.
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HV 450 integrated blinds
Timber-aluminum window with blinds protected between the panes.
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HF 510
The slimmest square timber-aluminum sightline, built on an I-tec Core.
ExploreData sheets & brochures
Dimensions, profile sections, glazing build-ups and performance values — ready for your architect or builder.
See the HF 520 before you specify it
The difference between a glass sash and a classic sash is easiest to judge in person. Visit our Oakville showroom or send your elevations, and our architect-led team will show where the HF 520 works best on your facade.