Installing windows seems simple, but even a small installation mistake can lead to serious problems — draughts, moisture in the walls, mould and higher heating costs. Below are the three main weak spots that most often cause problems for years.
The most common problem areas
1 The rubber (seal) on the sash
Problem
A worn, damaged or poorly fitting seal creates a gap between the sash and the frame. Even a small 1–2 mm gap is enough for a draught to form in the room and for heat to escape.
Consequences
- draughts and cold air entering the room
- condensation forming on the glass and frame
- heat loss and higher heating costs
- increased noise from outside
- further damage and hardening of the seal
Technical recommendations
- check the condition of the seal around the entire sash perimeter
- clean and treat regularly with silicone products (twice a year)
- if damaged, replace the seal as soon as possible
💡 Check the seal easily: close the window on a sheet of paper. If the sheet pulls out easily, the seal is not tight enough and it is time to replace it.
2 The joint between the glass unit and the frame / windowsill
Problem
Incorrect sealing of the installation joint under the windowsill, or mistakes in fitting it, is one of the most common causes of moisture ingress. Water collects in hidden places and damages the structure from the inside.
Consequences
- moisture getting into the installation joint
- damage to the wall and the assembly foam
- peeling of the finish
- condensation building up under the windowsill
- mould forming in hard-to-reach places
Technical recommendations
- fit the windowsill with an inward slope (5–10°) — so water does not run onto the wall
- tuck it under the frame by at least 20–30 mm — to prevent bridges forming
- seal the joint under the windowsill with an elastic sealant
- close the side joints with end caps or decorative tapes
⚠️ Problems under the windowsill are often discovered only years later, when the wall is already seriously damaged. A regular inspection once a year helps notice the problem in time.
3 Unprotected assembly foam on the outside after installation
Problem
The assembly foam on the outside is not protected by plaster, tape or sealant. UV radiation breaks down the foam structure within a few months — it becomes crumbly, absorbs moisture and no longer performs its insulating function.
Consequences
- breakdown of the foam under UV radiation
- moisture absorption and damage from freeze/thaw cycles
- gaps and draughts forming
- cracks in the finishing layer around the window
- loss of insulation around the entire window perimeter
Technical recommendations
- once the foam has cured, trim the excess to a depth of 10–20 mm
- always protect it with plaster, sealant or special tape
- follow the principle: vapour-tight on the inside, vapour-permeable on the outside
💡 Special window installation tape (e.g. ILLMOD, ISO-BLOCO) simultaneously protects the foam, provides vapour permeability on the outside and vapour tightness on the inside — the optimal solution for fast, durable installation.
Causes of problems and prevention
The most common causes
- use of poor-quality materials
- breaches of the installation method
- incorrect windowsill installation
- lack of seal maintenance
- skipping protection of the assembly foam
- thermal deformation and UV exposure
- building settlement
How to prevent problems
- use certified windows and materials
- carry out installation according to the manufacturer’s instructions
- fit the windowsill correctly with a slope
- maintain the seals regularly
- protect the assembly foam on the outside
- ensure ventilation of the room
- carry out regular window inspections
Technical regulations and requirements
The following regulations and standards are mandatory for window installation in Latvia:
| Document | Content |
|---|---|
| LBN 002-19 | Thermal performance of building envelopes — requirements for insulation and the elimination of cold bridges |
| LBN 231-15 | Building ventilation — requirements for air exchange in residential and public premises |
| EN 14351-1 | Windows and external doors — product standard, performance characteristics including air permeability, watertightness and wind load |
| Manufacturer’s installation instructions | Every window system profile has its own approved installation instructions; failure to follow them may void the warranty |
Note. Regular window inspections (at least once a year) help identify and fix problems in time — before they become expensive. Pay particular attention to the seals and the condition of the installation joints before and after the heating season.