How to Install Aluminium Windows: Step-by-Step Guide for South Africa

Installing an aluminium window correctly is about more than placing the frame into a wall opening and fixing it in position. The window needs to be correctly measured, level, square, securely fixed and properly sealed so that it opens and closes smoothly and helps keep wind and rain outside.

This aluminium window installation guide explains how to install aluminium windows in a typical South African home, from checking the brick opening and positioning the frame to fixing, sealing and carrying out the final checks.

The basic process is:

Check the opening → Prepare → Position → Pack → Level & square → Fix → Seal → Test → Finish

The exact aluminium window fixing method may vary according to the window system, size, wall construction and manufacturer’s requirements. Large, heavy or difficult windows are generally better installed by an experienced aluminium window installer.

1. Can You Install Aluminium Windows Yourself?

Small aluminium windows can sometimes be installed by a competent DIY customer or builder with the correct tools and basic installation knowledge.

However, installation accuracy is important. A window that looks straight can still be slightly twisted or out of square. This may cause the opening sash to catch, handles and locks to become difficult to operate, sliding sashes to run poorly or gaps to develop around weather seals.

Professional installation should be considered for:

• Large or heavy aluminium windows
• Large glazed combination windows
• Upper-floor windows
• Replacement windows
• Uneven or damaged openings
• Difficult access
• Installations requiring specialised waterproofing or structural work

If you are uncertain about the structural opening, glazing requirements or fixing method, use a competent installer.

2. Tools and Materials Needed to Install Aluminium Windows

Having the correct tools ready makes aluminium window installation easier and helps improve accuracy.

Basic Tools

You may need:

• 5 m steel tape measure
• Long spirit level
• Drill
• Suitable drill bits
• Screwdrivers
• Hammer or rubber mallet
• Pencil or permanent marker
• Straight edge
• Caulking gun
• Step ladder where required

Installation Materials

Depending on the window and wall construction, you may also need:

• Suitable masonry screws or anchors
• Aluminium window fixing lugs or brackets
• Packers or shims
• Exterior-grade sealant
• Backer rod where required
• Cleaning materials

Safety Equipment

Use appropriate gloves, safety footwear and eye protection.

Take extra care when handling glazed aluminium windows. Larger windows can be surprisingly heavy, and glass edges must be protected from impact.

3. Check the Window Opening Before Installation

Before installing the window, carefully check the structural opening.

Do not assume that a brick or plastered opening is perfectly level, vertical or square.

Measure the Width

Measure the opening in three positions:

Top → Middle → Bottom

Record the measurements in millimetres.

Measure the Height

Measure:

Left → Centre → Right

Compare all three measurements.

Check the Sill Is Level

Place a long spirit level across the bottom of the opening.

An uneven sill may require correction or appropriate packing before the window can be installed correctly.

Check the Sides Are Plumb

Use the spirit level vertically against both sides of the opening.

Check the Opening Is Square

Measure diagonally:

Top left → Bottom right

Then:

Top right → Bottom left

If the diagonal measurements are significantly different, the opening is out of square.

Correct serious problems before trying to force the aluminium window into position.

4. How Much Installation Gap Should You Leave Around an Aluminium Window?

An aluminium window should not be manufactured so tightly that it has to be forced into the opening.

A small aluminium window installation gap provides room for positioning, packing, levelling and perimeter sealing.

For applicable Sigmadoors made-to-measure windows, our measuring guidance uses a 10 mm overall deduction from the measured width and 10 mm overall deduction from the measured height.

For example:

Measured opening: 1,810 × 1,210 mm

Using the 10 mm deduction rule:

Window size: 1,800 × 1,200 mm

This creates a nominal difference of approximately 10 mm overall—not 10 mm on every side.

The correct installation allowance can vary according to the window system and opening, so confirm the required manufacturing size before ordering.

Measure Twice — Order Once.

5. Check the Aluminium Window Before Fitting

Before placing the window into the opening, inspect it carefully.

Check:

• Width and height
• Window configuration
• Opening direction
• Aluminium colour and finish
• Glass specification
• Handles
• Friction stays or hinges
• Weather seals
• Opening sashes
• Frame condition

Also identify the inside and outside of the window.

This is particularly important because aluminium window systems may contain drainage paths designed to direct water towards the exterior.

Check that any drainage or weep holes are facing the correct direction and are unobstructed.

6. Prepare the Brick Opening

A good aluminium window installation into brickwork starts with a sound, clean opening.

Remove:

• Loose mortar
• Dust and dirt
• Building debris
• Protruding pieces of brick or concrete
• Old silicone or sealant
• Unnecessary old fixings
• Loose plaster

High spots can prevent the frame from sitting correctly.

Repair badly damaged brickwork, large cracks or unstable areas before installing the window.

The opening does not necessarily have to be perfectly finished, but it should provide a solid base for positioning, packing, fixing and sealing the aluminium frame.

7. Position the Aluminium Window in the Opening

Carefully lift the aluminium window into the opening.

Use two or more people where the size and weight require it.

Avoid dragging powder-coated or anodised aluminium across rough brickwork because this can scratch the finish.

Position the frame approximately where it needs to sit, but do not permanently fix it yet.

Check:

• Position within the wall
• Bottom level
• Vertical alignment
• Installation gap
• Relationship to the finished plaster
• External sill position

Take time to get the position correct before drilling or fixing.

8. Use Packers to Position and Level the Window

Aluminium window packers, also called shims, are used to support and accurately position the frame.

Suitable packers can help establish the correct:

• Height
• Horizontal level
• Vertical alignment
• Installation gap
• Frame position

Packers should provide firm support without twisting or bowing the aluminium profile.

Do not force oversized packers into the gap.

The objective is to achieve a straight, level, square and properly supported aluminium window frame before permanent fixing begins.

9. Check the Window Is Level, Plumb and Square

This is one of the most important stages when learning how to fit aluminium windows.

Check Level

Use a long spirit level to check the appropriate horizontal frame surfaces.

Check Plumb

Check both vertical jambs.

Check Square

Measure the frame diagonally from opposite corners where practical.

The two diagonal measurements should correspond within the appropriate installation tolerances.

Check for Frame Distortion

Look along the aluminium sections.

The frame should not appear:

• Bowed
• Twisted
• Pulled inward
• Pushed outward

Adjust the packers until the frame is correctly positioned.

Do not rely on the brick opening to make the window square. The opening may be imperfect while the window itself still needs to be installed correctly.

10. How to Fix Aluminium Windows to Brickwork

Once the window is correctly positioned, it can be secured to the surrounding structure.

Depending on the window system, aluminium window fixing methods may include:

• Fixing lugs
• Installation brackets
• Suitable masonry anchors
• Approved through-frame fixings

The fixing must be appropriate for the aluminium system, window size and building material.

Do not simply drill through any convenient part of the aluminium profile.

Incorrect drilling can interfere with:

• Glass
• Drainage channels
• Hardware
• Seals
• Internal profile chambers
• Window operation

Follow the fixing details specified for the particular window system.

11. How to Use Aluminium Window Fixing Lugs

Some aluminium windows are supplied with fixing lugs to assist with installation.

Where applicable, the basic fixing principle is:

Aluminium frame → Fixing lug → Suitable wall fixing → Masonry

Fixing lugs can allow the window to be secured to the surrounding structure without unnecessarily drilling through visible or sensitive parts of the aluminium frame.

The number and position of fixing lugs will depend on the window size, configuration and system requirements.

A small bathroom window and a large combination window should not automatically use the same fixing arrangement.

12. Do Not Over-Tighten the Fixings

A common aluminium window installation mistake is using the fixing screws to pull the frame towards an uneven wall.

For example, if there is a gap behind one section of the frame and the screw is aggressively tightened without suitable support, the aluminium profile may bow towards the masonry.

This can result in:

• Uneven sash gaps
• Difficult opening and closing
• Locks not engaging correctly
• Poor weather sealing
• Frame distortion

The frame should first be correctly supported with suitable packers.

A useful installation sequence is:

Pack → Check → Fix → Recheck

13. Recheck the Window Before Final Tightening

After installing the initial fixings, check the window again.

Do not assume it has remained perfectly aligned.

Check:

1. Horizontal level
2. Vertical plumb
3. Frame square
4. Sash alignment
5. Opening and closing
6. Handle operation
7. Lock operation
8. Gaps around opening sections

If the frame has moved or distorted, correct it before completing the installation.

14. How to Seal Around Aluminium Windows

Correct aluminium window sealing is essential for weather protection.

Even a well-manufactured window can allow water or air through the perimeter if the joint between the aluminium frame and building is poorly sealed.

Clean the joint and apply a suitable exterior-grade sealing system appropriate to the installation.

The finished perimeter seal should be:

• Continuous
• Neat
• Properly bonded
• Weather resistant
• Suitable for the joint size

For deeper or wider joints, an appropriate backing material such as backer rod may be required before sealant is applied.

Avoid simply spreading silicone over dirt, loose mortar or wet surfaces. Good sealing starts with proper surface preparation.

15. Keep Aluminium Window Drainage and Weep Holes Clear

Many aluminium windows are designed with drainage paths that allow small amounts of water entering the frame system to drain back outside.

These outlets are commonly known as weep holes or drainage holes.

Do not block them with:

• Silicone
• Mortar
• Plaster
• Putty
• Paint

A small opening in the bottom section of an aluminium window may look like something that needs to be sealed, but it could be an intentional drainage point.

Never seal an opening in an aluminium frame unless you know what it is for.

16. How to Waterproof Around Aluminium Windows

Good aluminium window waterproofing involves more than applying silicone around the frame.

Pay attention to:

• External perimeter joints
• Bottom sill
• Corners
• Frame-to-masonry junctions
• Cracks around the opening
• Surrounding plaster
• Drainage holes
• External water flow

Water should be encouraged to move away from the building rather than towards the interior.

If an aluminium window continues leaking after the perimeter has been resealed, investigate the surrounding wall and construction.

Water can enter higher up the wall and only become visible around the window.

17. Installing Aluminium Windows With Glass Already Fitted

Many aluminium windows are supplied fully glazed.

Sigmadoors aluminium windows, for example, can be supplied complete with the specified glass, handles, friction stays and weather seals.

This makes installation more convenient, but it also increases the weight of the unit.

When handling a glazed aluminium window:

• Consider the total weight
• Use enough people
• Protect glass edges
• Protect the aluminium finish
• Plan access to the opening
• Use suitable lifting methods for larger units

Never lift a heavy window by its handle, opening sash or another component that was not designed as a lifting point.

18. Should You Remove the Glass or Sashes Before Installation?

Not always.

Removing an opening sash may sometimes make a window lighter or provide better access to fixing points, depending on the system.

Removing the glass unnecessarily can create additional risks.

These include:

• Glass breakage
• Damaged glazing beads
• Damaged gaskets
• Incorrect re-glazing
• Poor weather sealing

If the complete glazed window can be safely handled and installed as supplied, there may be no reason for a DIY installer to dismantle it.

Large and heavy glazed windows should be assessed by an experienced installer.

19. Installing Different Types of Aluminium Windows

The basic installation principles are similar, but each window configuration requires additional checks.

Top-Hung Aluminium Windows

After installation, check that:

• The sash opens smoothly
• Friction stays operate correctly
• The sash closes evenly
• The handle engages properly
• Weather seals make even contact

Side-Hung Aluminium Windows

Check:

• Sash alignment
• Hinge or friction-stay operation
• Handle operation
• Lock engagement
• Weather seals

Fixed Aluminium Windows

There are no opening mechanisms to test, but frame alignment, fixing, glass support and perimeter sealing remain important.

Horizontal Sliding Aluminium Windows

Pay particular attention to:

• Track level
• Sash movement
• Rollers
• Interlocking sections
• Locks
• Drainage

An aluminium sliding window installed out of level may not slide or lock correctly.

Large Combination Windows

Large aluminium windows require additional attention to:

• Frame support
• Mullion alignment
• Glass weight
• Fixing positions
• Handling
• Structural requirements

Do not treat a large glazed assembly like a small standard window.

20. New-Build vs Replacement Aluminium Window Installation

The installation process can differ depending on whether the window is going into a new building or replacing an existing window.

New-Build Aluminium Windows

A typical new-build installation follows:

Check opening → Position → Pack → Level → Square → Fix → Seal → Test → Finish

The structural opening should already have been formed to suit the intended window.

Replacement Aluminium Windows

Replacement installations may first require:

• Removing the existing window
• Cutting old fixings
• Removing old sealant
• Cleaning the opening
• Repairing damaged masonry
• Correcting uneven reveals
• Making good surrounding plaster

Always inspect the opening after the old frame has been removed.

Do not assume that the new aluminium window can simply be installed into the space left behind.

21. Replacing Steel or Wooden Windows With Aluminium

Replacing old steel or wooden windows with aluminium is common when renovating South African homes.

Removing the old window can expose hidden problems such as:

• Damaged brickwork
• Cracks
• Rusted embedded steel
• Rotten timber
• Water damage
• Uneven plaster
• Out-of-square openings

Correct these problems before permanently installing the new aluminium frame.

Where the work involves changing an opening, structural alterations or changes that may affect approved building plans, check the applicable project and municipal requirements before proceeding.

22. Common Aluminium Window Installation Mistakes

Avoiding installation mistakes is just as important as knowing the correct installation procedure.

Ordering the Window Too Large

A window that has to be forced into the opening leaves insufficient room for proper alignment, packing and sealing.

Not Checking the Opening for Square

Correct width and height measurements do not automatically mean the opening is square.

Installing the Window Out of Level

This can cause opening and sliding sections to operate incorrectly.

Incorrect Use of Packers

Do not rely on fixing screws to compensate for an unsupported or uneven frame.

Over-Tightening Fixings

This can bow or distort the aluminium profile.

Drilling Through the Wrong Part of the Frame

Incorrect drilling may interfere with drainage, glass, seals or hardware.

Installing the Window the Wrong Way Around

Incorrect orientation can compromise drainage and weather performance.

Poor Perimeter Sealing

Gaps between the frame and building can allow wind-driven rain and air into the building.

Blocking Drainage Holes

Do not cover intentional drainage openings with silicone, plaster or mortar.

Using Incorrect Glass

Glass should be suitable for its size, position and intended application.

Not Testing Before Finishing

Always open, close and lock the window before plastering or completing surrounding finishes.

23. Aluminium Window Installation and South African Building Requirements

Aluminium window installation in South Africa should take applicable building and glazing requirements into account.

Part N of SANS 10400 deals with glazing and includes requirements relevant to the safe use of glass in buildings. Safety glazing can be particularly important in critical locations such as doors, low-level glazing and areas where people may accidentally fall against the glass.

Part XA of SANS 10400 may also be relevant to energy performance on applicable new buildings and projects.

The correct glass type should therefore not be selected on price alone.

Consider:

• Window size
• Glass size
• Position above floor level
• Location
• Risk of human impact
• Building use
• Energy requirements where applicable

For regulated, unusual or technically demanding installations, obtain advice from an appropriately qualified professional.

24. Final Aluminium Window Installation Checklist

Before considering the installation complete, carry out a final inspection.

Frame

• Window is level
• Jambs are plumb
• Frame is square
• Frame is not bowed or twisted
• Installation gap is properly finished

Fixings

• Correct fixing method has been used
• Fixings are secure
• Packers provide appropriate support
• Fixings have not distorted the frame

Window Operation

• Opening sashes move freely
• Sliding sashes run smoothly
• Handles operate correctly
• Locks engage properly
• Sash gaps appear even

Weatherproofing

• Perimeter is properly sealed
• Corners have been checked
• Sill area is properly finished
• Drainage holes remain clear
• No obvious gaps remain

Glass

• Glass is undamaged
• Glazing beads are correctly fitted
• Gaskets and seals are correctly positioned
• Appropriate glass has been used

Final Finish

• Aluminium is clean
• Frame finish is undamaged
• Building debris has been removed
• Surrounding plaster or brickwork is properly finished

25. How to Install an Aluminium Window Step by Step

For a quick overview, the aluminium window installation process can be summarised in 13 steps.

Step 1 — Measure

Confirm the structural opening and aluminium window dimensions.

Step 2 — Check the Opening

Check width, height, level, plumb and diagonals.

Step 3 — Prepare

Clean and repair the brick opening where necessary.

Step 4 — Position

Carefully place the aluminium window into the opening.

Step 5 — Pack

Use suitable packers to support and position the frame.

Step 6 — Level

Check the horizontal and vertical alignment.

Step 7 — Square

Check diagonals and opening-sash alignment.

Step 8 — Fix

Secure the window using the appropriate fixing method.

Step 9 — Recheck

Make sure the fixings have not bowed or distorted the frame.

Step 10 — Seal

Properly seal the perimeter between the aluminium and building.

Step 11 — Check Drainage

Make sure drainage and weep holes remain open.

Step 12 — Test

Open, close, slide and lock all applicable sashes.

Step 13 — Finish

Clean the window and complete the surrounding building finishes.

Aluminium Window Installation FAQs

How do you install aluminium windows?

The basic process is to check and prepare the structural opening, position the aluminium window, pack it until it is level and square, secure it using an appropriate fixing method, seal the perimeter and test the complete window before finishing.

Can I install aluminium windows myself?

A competent DIY customer or builder may be able to install a small, straightforward aluminium window. Large, heavy, upper-floor or complicated installations are better handled by experienced installers.

How do you install aluminium windows into brickwork?

Position the window in the prepared brick opening, use packers to make the frame level, plumb and square, and then secure it to sound masonry using the appropriate fixing method. Finally, properly seal the perimeter.

How much gap should be left around an aluminium window?

The required installation clearance depends on the window system and opening. For applicable Sigmadoors made-to-measure windows, the measuring guidance uses a 10 mm overall deduction from both the measured width and height. Confirm the required manufacturing allowance before ordering.

What screws are used to install aluminium windows?

There is no single screw suitable for every aluminium window installation. The fixing needs to suit the aluminium system, window size, wall material and manufacturer’s installation requirements.

Do aluminium windows need fixing lugs?

Some aluminium window systems use fixing lugs or brackets, while others may use alternative approved fixing methods. Follow the requirements of the particular system.

Where should aluminium window packers be positioned?

Packers should support and position the frame at appropriate points without causing the aluminium profile to bow or twist. Their exact position depends on the window design and fixing method.

How do you know if an aluminium window is square?

Measure diagonally between opposite corners where practical and compare the measurements. Also check that opening sashes have even gaps and operate smoothly.

How do you waterproof around aluminium windows?

Proper waterproofing involves correctly sealing the perimeter joint, paying attention to the external sill and surrounding finishes and keeping the aluminium window’s designed drainage paths clear.

Should you silicone over aluminium window drainage holes?

No. Do not cover intentional drainage or weep holes. They are designed to allow water to drain towards the exterior.

Should aluminium windows be installed before or after plastering?

The correct sequence depends on the construction method and installation detail. The important requirements are that the window can be securely fixed and weather-sealed and that the aluminium is protected from damage during plastering and other wet building work.

Can aluminium windows be installed with the glass already fitted?

Yes. Many aluminium windows are supplied fully glazed and can be installed as complete units where their size, weight and fixing method allow it. Large glazed units require additional care and suitable handling.

How long does aluminium window installation take?

Installation time depends on the size and number of windows, access, condition of the opening and whether an existing window needs to be removed. A straightforward new-build installation will generally be quicker than replacing old steel or wooden windows and repairing the surrounding opening.

Get Aluminium Windows Made to Fit Your Opening

Correct aluminium window installation starts with a window that has been properly measured and manufactured for the opening. Whether you are learning how to install aluminium windows into brickwork, planning a DIY project or arranging professional aluminium window installation in South Africa, the fundamentals remain the same: measure accurately, allow installation clearance, support the frame correctly, keep it level and square, use appropriate fixings and seal the perimeter properly.

Sigmadoors manufactures standard and custom aluminium windows for new homes, renovations and building projects. Our aluminium windows can be supplied complete with glass, handles, friction stays and weather seals, ready for installation.

Need aluminium windows manufactured to your measurements? Send us your opening sizes or building plans for a quotation.

Designed Right. Installed Right.