Perished or missing window and door seals
When a window or door is closed but cold air is still getting through, or when you notice condensation building up on the inner face of the glass, the seals are usually to blame. This is a straightforward problem to fix, but it's often misunderstood - largely because there are two quite different types of seal involved, and they fail in different ways.
The difference between external sealant and compression gaskets
Many homeowners use the word "seal" to mean everything around a window. In practice, there are two separate components, and they have different functions.
External perimeter sealant
This is the flexible bead of sealant that runs around the outside of the frame where it meets the brickwork, render or stone. Its job is to bridge the gap between the rigid frame and the rigid masonry, accommodating movement between the two while keeping water out. It is applied externally and is visible from outside the property.
When this fails, the main symptom is water ingress during rain - particularly wind-driven rain. You may see damp appearing internally at the frame edge, or a visible crack or gap in the joint from outside.
See our external sealant replacement service for detail on how we address this.
Compression gaskets
These sit inside the frame itself - running around the glass unit (glazing gasket) and around the opening edge of sashes and door leaves (perimeter gasket). They're made of rubber or EPDM foam and work by compressing when the window or door is closed, creating an airtight seal.
When gaskets fail, the main symptom is draughts even in dry weather. The cold air comes through the frame when shut, not through the wall around it. You may also get condensation forming on the inner glass surface because the frame is no longer thermally sealed.
These are different problems with different solutions. Applying external sealant when the problem is a failed gasket won't resolve the draught - and replacing a gasket won't fix a failed external joint.
Signs that seals are failing
External sealant:
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Visible cracks, splits or lifting along the bead
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A gap between the sealant and either the frame or the masonry
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Discolouration or shrinkage of the joint
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Damp at the internal frame edge after rain
Compression gaskets:
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Cold air detectable around the closed frame (hold your hand to the frame edge in cold weather)
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A draught that persists in dry conditions
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Condensation on the inner glass surface (different from condensation between panes - see below)
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Visible compression loss - the gasket looks flat, hard, or has pulled away from the corner joints
Condensation between panes (the glass going foggy inside the sealed unit) is a different problem again - it means the double-glazed unit seal has failed and the unit needs replacing, not the frame gasket.
How seals degrade
UV exposure causes rubber and silicone to harden and lose flexibility over time. South-facing windows tend to degrade faster for this reason.
Temperature cycling puts continuous stress on seals as they expand and contract with warm and cold weather. The Yorkshire climate, with warm summers and cold winters, accelerates this process.
Age is simply a factor - most seals have a useful life of 15 to 25 years depending on material and exposure. An older property that has never had its seals replaced is very likely to have failed seals on at least some frames.
Cleaning products can degrade sealant and rubber gaskets over time, particularly solvent-based products used on UPVC frames.
UPVC, timber, aluminium and steel - does the frame type matter?
The material used does affect seal type and replacement approach.
UPVC frames use rubber compression gaskets that are typically pressed into a channel in the profile. These can usually be replaced without replacing the frame, though the correct profile gasket needs to be matched to the existing frame.
Timber frames may use various gasket types, and older frames may use brush-pile seals rather than rubber. Timber also carries the risk of warping, which can affect how well the seal compresses. Where the frame itself has distorted, seal replacement alone won't fully resolve the problem.
Aluminium frames typically use rubber gaskets with a compression profile suited to the frame system. Replacement follows a similar approach to UPVC but requires matching to the manufacturer's profile where possible.
Heritage steel frames, common in properties built between the 1920s and 1960s, present a different challenge. Original steel windows were glazed with linseed oil putty rather than a rubber gasket, and many have since been reglazed with various compounds over the years. Where putty has failed, cracked or pulled away from the frame, the correct approach depends on the building's status. On non-listed properties, resealing with an appropriate flexible sealant is a practical and durable solution. On listed buildings or in conservation areas, like-for-like repair using linseed oil putty or a heritage glazing compound is typically required by conservation officers - flexible sealant may not be approved, and using it without consent could constitute an unauthorised alteration.
Steel frames are also prone to rust at the rebate where the glass meets the frame, and any active corrosion needs treating before resealing - otherwise moisture will continue to track behind the new sealant and the repair will fail prematurely. If you have heritage steel windows and are unsure what's required, we can advise during an inspection before any work is carried out.
Energy efficiency and heating costs
Failed seals have a direct and measurable impact on energy use. Cold air entering around frames means heating works harder to maintain room temperature, and warm air escapes. On older properties with several windows showing seal failure, the combined heat loss can be substantial.
Replacing failed gaskets and resealing external joints will noticeably reduce draughts and is one of the simpler improvements a homeowner can make to reduce heating bills.
What a replacement involves
For external sealant: Old material is fully removed - no exceptions. New sealant is applied in the correct profile and tooled for a continuous, bonded joint. This takes between one and three hours per window depending on the size of the frame and condition of the substrate.
For gaskets: We remove the old perished gasket and fit a compatible replacement. In many cases this is a same-day job.
See our window and door seal replacement service for full detail on both types.
Frequently asked questions
Q1. What is the difference between a window gasket and a sealant bead? A gasket is a moulded rubber or EPDM compression seal built into the window frame itself - it sits between the glass or opening sash and the frame, creating a tight seal when the window closes. Sealant (typically silicone) is applied externally around the perimeter joint between the frame and the surrounding masonry. Both can fail independently. A draught coming through a closed window usually points to gasket failure; water tracking in at the wall junction usually points to failed perimeter sealant. Q2. How do I know if my seals need replacing? Common signs include cold draughts felt around a closed window or door, condensation forming on or inside the frame rather than just the glass, water trickling in at the frame edge during heavy rain, visible cracking, brittleness or gaps in the rubber seal, and a hissing sound in wind. You can also run your hand slowly around the closed frame on a cold windy day - any cold spots indicate a loss of compression. Northern Seal & Joint can confirm whether it is a gasket or sealant issue on inspection. Q3. Can a perished seal cause damp, mould or structural damage? Yes. A failed seal allows moist air and rainwater into the wall junction or frame cavity. Over time this causes timber frames to rot, creates conditions for mould growth on reveals and sills, and allows persistent damp to spread into plasterwork. In UPVC and aluminium frames it can cause water to pool within the frame profile. Catching seal failure early prevents what is often a straightforward replacement from becoming a more costly repair involving timber treatment or internal replastering. Q4. How much does seal replacement cost, and how long does the job take? Sealant replacement around a single window is typically a short job - often under an hour for external perimeter resealing once preparation is included. Gasket replacement takes longer depending on the frame type but is generally completed within a few hours per window. Costs depend on the number of windows, access, and frame material. Northern Seal & Joint provides clear written quotes so you know the full cost upfront. Most residential jobs across Yorkshire are completed in a single visit. Q5. Does it matter whether my frames are UPVC, timber or aluminium? Yes - the appropriate seal type and method differs between frame materials. UPVC frames use specific gasket profiles that must match the original section; incorrect replacements compress poorly and fail quickly. Timber frames often combine external sealant with internal draught sealing, and the substrate condition affects adhesion. Aluminium frames may use different gasket systems again. Northern Seal & Joint selects the correct material for the frame type rather than applying a generic solution, which is why the repairs last. Q6. Can draughts from failed seals contribute to damp problems? Yes, indirectly. Cold draughts lower surface temperatures on walls and reveals, increasing the likelihood of condensation forming on those surfaces. Condensation creates persistent moisture that encourages mould growth, particularly in corners and on north-facing walls. While draughts alone do not cause penetrating damp, the combination of a draught and a failed external seal often means both problems are present simultaneously. Fixing the seal addresses both the cold air entry and the moisture risk in one visit.
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