MB-Slimline aluminum window

Aluminum · No. 03 · Slim

Less frame. More Northwest.

U-factor from 0.15 · Hidden sash option · Narrow sightlines

MB-Slimline is about one thing: how little frame you see. The visible aluminum outside is very narrow, and with the hidden-sash version (often called SG), the opening sash disappears behind the frame altogether. Fixed and opening windows look the same from the street. Inside, there's still a full thermal break and room for glass up to 81 mm thick, which is enough for triple or even quadruple glazing.

Why sightlines matter

Sightline is the width of frame you see. On a 3-foot window, saving an inch on each side is a few percent more glass. On a wall of eight windows, it changes how the room feels. In grey months, every bit of daylight counts.

A modern replacement for old steel windows

Old steel windows have very thin frames, which is why they're hard to replace without the house looking different. MB-Slimline gets close to that look with a thermally broken frame, so you keep the character and lose the condensation. For a more literal steel look, see MB-Ferroline Pro and SlimLine Elite.

Hidden sash is the detail architects notice first. You can't tell which window opens.

What you give up

Narrow frames mean smaller maximum sash sizes than MB-86N (product data lists heights up to about 7.9 ft), and the frame's sound rating is a little lower (up to 42 dB). For very tall operable sashes or noisy sites, MB-86N may be the better choice.

MB-Slimline specifications

Why choose it: narrowest frames we offer · hidden sash · very thick glass possible.

Trade-offs: smaller max sizes · lower sound rating than MB-86N · NFRC rating: ask us for current status for your project.

MB-86N · SlimLine Elite · Steel-look windows guide

Want the thinnest frame possible?

We'll check your sizes against the system limits before you fall in love with a drawing.

Get a free consultation

Book a showroom visit