Dormer lifespan: 2026 guide

PVC dormers last 30 to 40 years if installed with UV-stable coating and quality MS polymer sealant. Lifespan is rarely set by the PVC itself (it lasts 50+ years) but by sealant joints, lead and trim. Cheap dormers with acrylic sealant and lead 20 often last only 20-25 years before first major maintenance is needed.

Timber dormers reach 50 to 70 years with consistent paint schedule (every 4-8 years per species) and preventive sealant replacement. Pine and spruce sit low (40-50 years realistic), meranti and larch mid (50-60), Western Red Cedar and oak top (60-80). Without maintenance all species last only 12-20 years.

Polyester and zinc-aluminium dormers are a niche segment. Polyester (mostly 1970s-90s use) is materially very durable but prone to UV yellowing after 25-30 years. Zinc and aluminium are practically indestructible (50+ years) but expensive at purchase and not for every architecture.

Sealant joints are the weakest: 8-12 years on acrylic (budget), 25-30 on MS polymer (premium). Replace preventively to avoid water ingress. Cost: DIY €15-€25, contractor €150-€350 for all joints on a 3-metre dormer.

Lead flashings sag after 10-20 years from temperature changes. Timely repair (re-dressing: €150-€300) extends lifespan 5-10 years. Full lead replacement €450-€1,500 every 25-35 years. On replacement always choose lead 25 or heavier, not lead 20.

Window gaskets harden after 8-12 years and let in draughts. Replace €25-€50 per window, easy DIY. Locks and hardware last 10-15 years at standard quality; premium hardware (Maco, Roto) reaches 20-25. Hardware replacement €120-€280 per window by pro.

HR++ glass loses its argon fill after 20-30 years, U-value worsens from 1.1 to 1.8 W/m²K. Visually invisible; only measurable. Replacement €150-€350 per pane depending on size. On replacement consider upgrade to triple glazing for extra insulation and sound.

The threshold for replacement over repair is stacked repair cost of €3,500-€5,000 within 3 years — especially when affecting major structural parts (frames, roof panel, lead). Above that a new prefab (€5,000-€8,500 for 3 metres) is economically defensible.

Additional reasons to replace: old R-value (1.3 or 2.0) vs modern R 6.3 with direct saving of 350-600 kWh/year; dated look hurting saleability; need for larger or wider dormer; material switch (timber to PVC) to eliminate future maintenance.

Counter-arguments: monumental or character status (replacement needs new permit and aesthetics approval); rented housing (owner responsible, not tenant); plan to move within 5 years (then a €600-€1,200 refresh often pays better than replacement).

Three principles practically double the lifespan of any dormer: preventive maintenance (don't wait until problems are visible), quality over budget on replacement parts (MS polymer sealant, lead 25, premium gasket), and yearly visual inspection (10 minutes, free) plus 5-7 year thorough check by roofer (€100-€200).

For PVC: clean 2x per year, check sealant joints, extra attention on dark side. For timber: keep paint schedule strict, fix early rot with epoxy immediately, check sill connection yearly. For all materials: keep gutter free of leaves, check ventilation, and don't add anything heavy (awning, antenna) without engineer's advice.

Document all interventions: note when sealant was replaced, when painted, when lead repaired. Keep invoices and paint product names. On sale a well-kept maintenance log raises selling price by several thousand euros because buyers gain confidence in the property's state.