Round Top Wood Windows: Custom Fabrication Explained

A guide to how arched round top wood windows are built to measure and what to look for.

Round Top Wood Windows: Custom Fabrication Explained

Round top windows, also called arched or radius windows, bring a classic architectural line to a facade. Because the curve is rarely a stock size, these windows are almost always custom fabricated. Understanding how they are built helps you specify a window that looks right and performs for decades.

Why round tops are custom work

A true round top frame requires the head and sash to follow a precise radius. That curve is unique to each opening, set by the architecture and the rough opening. Mass production cannot economically match every radius, so the work moves to a custom shop that fabricates each unit from drawings.

How the curve is built

There are two main approaches to forming the arched components. Solid bent lamination glues thin strips of wood over a curved form, producing a strong, stable arch that resists the cracking of a single sawn piece. The alternative, cutting the curve from solid stock, is simpler but wastes material and can be weaker where the grain runs short across the curve. Quality shops favor lamination for the head and any curved muntins.

Species and stability

Exterior windows live in sun, rain and seasonal movement, so species matters. Mahogany and white oak are common choices for their rot resistance and dimensional stability. Properly dried and sealed, they hold the radius and resist warping. Softer interior species are not suited to exposed arched sash.

Glazing and muntins

The curve sets the design of the glass. Options range from a single curved insulated unit to a divided light pattern with radius muntins that follow the arch. Curved glazing is a specialized item and should be planned early, since lead times and tolerances are tighter than for flat glass.

What to specify

When commissioning a round top window, define:

- **The exact radius and rough opening,** measured on site. - **Species and grade** suited to the climate and exposure. - **Glazing type,** including any divided light pattern. - **Finish,** interior and exterior, and whether it is clad or all-wood. - **Hardware and operation,** since arched sash may be fixed or paired with operable lower units.

The case for a custom shop

A round top window is as much joinery as carpentry. The arch must be true, the sash must seal, and the finish must withstand weather. A shop that drafts each unit, laminates the curves and tests the fit delivers a window that performs and ages gracefully. Vertical Custom Supply fabricates arched and radius windows from measured drawings, treating each as a piece of architecture built to its exact opening.