Aluminum windows are significantly more expensive than uPVC windows. But freezing, drafts, condensation on the frames, structural deformation — all of these issues occur here as well. In my practice, in 70% of cases the cause of these problems is not the profile or the insulated glass unit, but the installation. An expensive product installed improperly becomes an expensive problem.
The installation of aluminum windows is fundamentally different from PVC installation. Different requirements for fixings, different nuances with the thermal break, a different approach to sealing the joint. An installer who is skilled at putting in uPVC windows does not automatically become an aluminum specialist — this must be understood when choosing a contractor.
I will break down three main installation substrates — concrete, brick, autoclaved aerated concrete (AAC) — and separately discuss the key features that determine installation quality regardless of the opening type. All of this is based on practice: what I have seen on sites, what works, what does not work, and why.
Why Aluminum Requires a Special Approach
The first and most frequently violated rule: steel must not come into direct contact with aluminum. Direct contact between these two metals creates a galvanic couple — an electrochemical reaction that gradually destroys the fixing. After one, two, or three years, the screw corrodes completely. And a window weighing 80–100 kg hangs on those fixing points.
The correct solution is stainless steel fixings. Stainless steel does not enter into a galvanic reaction with aluminum. Where stainless steel screws are difficult to find in the required length (e.g., long screws for concrete anchoring), use galvanized fixings — but with a thick, high-quality coating. A low-quality zinc-plated concrete screw is not suitable: the zinc layer strips off during driving, and contact with steel still occurs.
If stainless steel fixings cannot be used for any reason, a separating layer must be placed between the metal fixing and the aluminum frame. Options: PVC shim, bitumen tape, expanded polyethylene foam. In some cases, the vapor barrier tape already adhered to the frame may serve this purpose if it lies between the profile and the plate. But do not rely solely on that — it is safer to install a separate isolator.
Thermal Break: How Not to Create a Thermal Bridge Through the Mounting Plate
A thermally broken aluminum profile consists of three parts: the outer aluminum profile, a polyamide thermal break in the middle, and the inner aluminum profile.
In sub-zero temperatures, the outer part cools down and freezes. The thermal break is a barrier that prevents cold from transferring to the inner profile. That is why the interior side of a thermally broken aluminum profile remains dry and warm even in freezing weather.
Now imagine an installer taking a mounting plate and screwing it through both the outer and inner chambers simultaneously. The metal plate is an excellent conductor of heat. Cold from the outer profile will instantly travel through the plate to the inner profile, and from there to the reveal. The thermal break ceases to function exactly where the plate is attached. The result: freezing, condensation, mold at the fixing point.
Correct practice: the mounting plate is attached only to the inner chamber of the aluminum profile. The outer chamber remains untouched. The thermal break is not compromised.
An additional measure: insulate the plate with expanded polyethylene foam on both sides — or at least apply a thermal isolating pad before installation. This creates an extra barrier between the cold substrate of the opening and the plate itself. The plate heats up more slowly, and condensation does not form.
Another nuance regarding plates: no thin-gauge sheet metal of 0.8–1.0 mm thickness. Such a plate cannot handle static loads — wind loads, forces from opening sashes, or the weight of the structure. The minimum thickness per standards is 1.5 mm. In practice, it is advisable to use 2 mm Z-shaped plates: this shape provides the necessary stiffness under all load types. The plate must be fixed to the frame at two points — otherwise it will wobble, and the fixing will be unreliable.
Fixings: How Many Points and at What Spacing
The number of fixing points is another area where installers like to «optimize.» The simple logic: fewer points mean lower costs for plates and fixings. On a project with twenty openings, the savings seem tangible.
In practice, the fixing spacing for aluminum structures should typically be 400–600 mm depending on system and wind load requirements. From the frame corner — typically 150 mm. This is not a recommendation but a requirement driven by the weight of aluminum structures and wind loads. For a standard opening of 1200×1500 mm, the calculated number of points is around 12. An installer who puts in four points and thinks «PU foam will hold it» either does not know the technology or is deliberately cutting corners at the expense of safety.
PU foam is not considered a structural fixing and must not be relied upon for load transfer. The window must be rigidly secured with proper fixings at the correct number of points. The foam seals the joint and provides thermal and acoustic insulation. But holding the window in the opening is not its job.
Case 1: Concrete Opening — Through Fixing
The most common installation detail is concrete with direct through fixing. The screw passes through the frame and goes into the substrate of the opening.
For this type of fixing, specialized high-performance concrete screws are used — not standard concrete screws. The difference is fundamental: a quality high-performance screw works in any substrate (concrete, brick, AAC, wood), has the correct thread geometry, and holds the load without damaging the base material.
A concrete screw made of low-grade metal with a thin coating will eventually loosen in the hole, especially under cyclic loads from opening sashes.
Drilling technique in concrete also affects the outcome. The quality of the drill bit matters: different bits create different hole shapes, and a fixing in a poorly drilled hole holds less well.
The hole in the profile is made in two steps: first with a large bit in the near wall of the groove to countersink the screw head, then with a thin bit through the far wall and into the concrete. The head is countersunk, and the hole is covered with a decorative cap matching the profile color. From the outside — neat, no protruding head.
Case 2: Brick Opening — Bracket and Chemical Anchor
Brick is the most variable material in terms of installation conditions. Solid brick, hollow brick, ceramic block — each has its own characteristics. A new opening and an opening after demolition of an old structure are also different situations.
If the opening is after demolition, it must be professionally prepared: dusted, primed, treated with a primer. Tape will not adhere to a dusty or loose substrate — neither immediately, nor a year later. Skipping this step means condemning the installation joint to premature failure.
Fixing into hollow brick or ceramic block requires a chemical anchor.
The principle: a sleeve is placed into a pre-drilled hole, a two-component adhesive is injected, then a threaded rod is inserted. After polymerization, the nut is tightened with a torque wrench to the correct force. Overtightening can damage the substrate; undertightening results in insecure fixing. A chemical anchor in hollow materials performs significantly better than standard wall plugs, which rely only on the brick wall surface.
An alternative for hollow brick and ceramic blocks is specialized brackets with an integrated fixing element. Procedure: drill a hole, insert the element, and a screw from the outside locks the entire assembly without chemicals. This is faster and cheaper than a chemical anchor, but requires
Case 3: AAC — The Most Demanding Substrate
AAC (autoclaved aerated concrete) is today the main material for suburban construction. In my practice, about 70% of suburban homes we glaze are built from it. And it is here that the installation of aluminum windows requires special attention.
The issue with AAC is that it is significantly less strong than concrete or brick. If you drive a standard concrete screw into AAC and then apply cyclic loading — opening a heavy sash, wind loads — the substrate around the screw gradually crumbles. The screw starts to wobble. It is easy to verify: a standard screw made of soft steel with fine threads can literally be pulled out of AAC by hand after a few months of loading.
The correct solution is a specialized AAC screw with a coarse, widely spaced thread, designed specifically for cellular concrete. The thread geometry of such a screw creates a significantly larger bearing surface in the porous material, making it impossible to pull out.
Additionally, increased-thickness plates — 2.5 mm — are used with a load-distributing function: the plate expands the bearing area, and under lateral loads, the AAC substrate degrades much more slowly. Every plate must be backed with expanded polyethylene foam before installation — creating a thermal break between the plate and the cold AAC.
Base Profile: The Bottom Zone as the Most Vulnerable Area
The bottom of the structure is the highest-risk zone for freezing and complaints. The standard base profile that comes with most window systems is non-thermally broken. Inside it is hollow, with significant heat loss.
Solution: a thermally broken base profile — reinforced and with insulation inside. Such a profile is installed on the bottom edge of the opening using silicone sealant and a layer of expanded polyethylene foam. This isolates the profile from the cold substrate and eliminates freezing at the bottom.
For entrance doors where the threshold sits directly on a concrete base, the cold zone around the threshold is additionally insulated with a cellular PVC accessory: on the outside it goes under the screed, on the inside under the finished floor. The appearance is clean, and there is no freezing.
Support Blocks: What the Structure Rests On
The window structure must not transfer the load of its weight directly through the installation joint or fixing plates. The load must be transferred to the opening via support blocks — rigid shims placed under the bottom of the frame.
Support blocks must be made of hard, moisture-resistant materials. The optimal choice is PVC shims: they do not absorb moisture, do not rot, and do not freeze. Hardwood shims are technically permitted by standards, but wood changes size with humidity over time. Scraps of old frames or pieces of plywood are not even worth discussing.
An important point when placing shims: they must be oriented along the length of the structure, not across. Placing them across creates an obstacle for foam application — the foam cannot properly fill the joint in those areas, leaving voids.
Sealing the Installation Joint: Foam and Tapes
The installation joint — the space between the frame and the opening — must be correctly filled and properly sealed on both sides. It is not a single material but a three-layer system.
Outside — breathable membrane or sealant. Its task is twofold: prevent water from entering the joint from the outside, while allowing water vapor that forms inside the joint to escape. If the joint is sealed on the outside with a non-permeable material, moisture will remain inside, causing the foam and reveals to degrade, and possibly leading to mold.
Inside — vapor barrier tape. It protects the joint from humid indoor air. Vapor from cooking, showers, and breathing must not enter the installation joint — otherwise it will condense there and trigger deterioration.
Between the tapes — PU foam (polyurethane foam). The quality of the foam matters. Cheap foam loses elasticity over time, becoming hard and brittle. Under temperature-induced movements — aluminum expands and contracts, the building «breathes» — rigid foam cracks, creating gaps. The correct foam is one that returns to its original shape after compression. For wooden houses with settlement and seasonal deformations, an elastic foam specifically designed for moving joints is critical.
Foam Application Technique: Two Passes
The installation joint should be foamed in two stages. First pass — without trying to fill the entire volume at once. Wait for partial polymerization. Then second pass — fill the remainder. This is necessary because the foam expands upon contact with moisture in the air. In a confined space without air access, it expands less, leaving voids and cavities.
Best practice: before foaming, moisten the opening surface with a spray bottle. Moisture accelerates the reaction and improves fill quality. This is especially important in dry weather.
After foaming, do not apply the tapes immediately. Let the foam reach its working shape: minimum 2–3 hours, preferably 24 hours. Where foam has extruded beyond the joint, trim it neatly. Only then apply the tapes.
Primer for Tapes: Mandatory, Not Optional
Tapes are applied to a prepared surface. Before application, the opening must be treated with a primer — a special compound that degreases and activates the surface. Without primer, the tape may stick initially and look fine. But after a few months, it will start to peel off where adhesion was insufficient. This is especially relevant in areas with temperature fluctuations: condensation, freezing, thawing — and poorly adhered tape begins to bubble.
Primer costs very little — one can is enough for ten openings. It works on all substrates: concrete, brick, AAC.
Tapes should be pre-applied to the frame before the window is placed in the opening. After installation, they are adhered to the opening substrate. This is the correct sequence: first fix to the profile, then unfold and stick to the wall.
Summary: What Determines Installation Quality
A quality aluminum window installation is not «put it in and tighten it.» It is a system of solutions, each affecting the long-term performance of the structure.
Stainless steel or properly isolated fixings — so the window does not fall out after three years. Plates attached only to the inner chamber — so the thermal break functions correctly. Proper spacing and number of fixing points — so the structure withstands wind loads. Specialized fixings for AAC — so the substrate does not degrade. Thermally broken base profile — to prevent freezing at the bottom. High-quality elastic PU foam applied in two passes — so the joint does not crack after a year. Primer and correct tapes — so the seal lasts for decades.
Each of these points may seem like a detail. Together, they determine whether an expensive aluminum glazing will perform as intended — or become a source of complaints, rework, and an unhappy client.
