Glass block windows are common in basements — privacy with light transmission, durable, secure (much harder to break than regular glass). The install involves laying the blocks in mortar, similar to brick laying. Pre-built glass block panels (with a metal frame) drop into an opening like a regular window — much easier for DIY.

This guide covers installing a pre-built glass block panel — the most common option for a typical basement.

Before you start

Three things to settle:

1. Pre-built panel vs custom-laid blocks. Pre-built panels: factory-assembled glass blocks in a frame. Drop into rough opening, secure with screws and caulk. DIY-friendly. Custom-laid: blocks laid one at a time in mortar. Slow, requires masonry skills. For DIY, pre-built is the right choice.

2. Match opening dimensions. Glass block panels come in standard sizes. Existing opening must match — sometimes opening must be widened or narrowed to fit standard panel size.

3. Egress consideration. Bedroom windows must meet egress requirements (Ontario Code 9.9.10.1). Glass block windows are often not openable — not suitable for bedroom egress. Verify Code application.

What you'll need

Tools

Tape measure
Level
Caulk gun
Drill with bits
Trowel (if mortar)
Putty knife

Materials

Pre-built glass block panel (sized to opening)
Mortar (if mortared install)
Acoustic sealant
100% silicone caulk
Concrete adhesive (for direct-bond install)
Screws (for frame anchoring)

Caulk continuously around perimeter

Glass block panel weighs 75-150 lbs.

Sealing perimeter prevents water entry — important for basement windows.

Inside and outside continuously sealed.

Step-by-step instructions

Verify rough opening dimensions

Glass block panel size + 1/4 inch clearance = rough opening.

Standard panel sizes: 16×16, 24×24, 24×32, 32×32 inches.

Existing opening may need adjustment — concrete cutting if too small, infill if too large.

Prepare opening

Remove old window.

Inspect frame; address rot or damage.

Apply concrete adhesive at perimeter (for bonded install).

Position glass block panel

Lift panel into opening.

Center; verify equal gap on all four sides.

Verify panel is plumb and level.

Shim if needed.

Anchor panel to frame

Pre-built panels have a metal frame around them.

Drive screws through frame's mounting flanges into existing rough opening framing.

Multiple anchors per side.

Mortar around perimeter (if mortared)

Apply mortar in the gap between panel and rough opening.

Tool smooth.

Mortar matches surrounding masonry colour.

OR seal perimeter with caulk (if non-mortared)

Backerod foam in the gap first (sized for the gap).

100% silicone caulk over backerod.

Continuous bead inside and outside.

Smooth bead with finger or tool.

Verify weather-tight seal

Pour water on outside of window; check inside for leaks.

Address any leaks with additional caulk.

Critical for basement windows below grade.

Add airbrick (if old vent was integrated)

If old window had a small vent (for basement air): glass block is often non-vented.

Add separate airbrick or vent if needed.

Or: don't replace the air function (rely on bath/laundry venting).

Common mistakes that cost you

Wrong opening size. Panel doesn't fit. Match standard sizes.
Skipping caulk. Water enters wall behind panel. Always seal.
Not anchored to framing. Heavy panel can shift over years. Anchor mandatory.
Using glass block in egress location. Doesn't meet egress requirements. Verify Code.
Incompatible adhesive. Adhesive must be rated for masonry. Verify product.

Frequently asked questions

Why glass block in basements?

Privacy: opaque or patterned glass.

Security: harder to break than regular glass.

Durability: long-lasting, low maintenance.

Minimal heat transfer compared to regular glass.

Can I add a vent to a glass block window?

Yes — pre-built panels often available with integrated vent slot or fan.

Or: add separate airbrick adjacent to window.

Verify need before install.

What drives glass block panel pricing?

Panel size and block pattern (standard basement panels cost less than large or decorative layouts).

A vent slot adds a modest amount for the operable insert.

Whether you install yourself or hire out the mortar/silicone work.

We provide a clear written breakdown so you know exactly what is included.

When to call us instead

Glass block windows are common in basement renovations. Our team handles them as part of basement renovation scope.

Book a free 60-minute site visit →

Related Ottawa services

If you're renovating a basement, our basement renovation team handles glass block installation. Book a free 60-minute consultation.