What is the lifespan of the different types of insulation?

A chilly loft, a forgotten crawl space, a garage that smells slightly of dust: insulation sits quietly in the background while your bills do the talking. You rarely think about it until a draught sneaks under the door or condensation blooms on a cold morning. The real question is simple and awkward: how long does each type of insulation actually last before it starts slipping, slumping or soaking up trouble?

The homeowner swore the place had “done just fine for decades,” but the edges told a different story: greyed glass fibre, a flattened path to the water tank, a dark streak under a long-fixed roof leak. Heat rises. Money follows it. The house didn’t feel broken, only slightly tired, like a jumper that’s been washed once too often. Sometimes the rot isn’t dramatic. It’s incremental.

How long does each insulation really last?

Longevity isn’t a one-number promise; it’s a range shaped by water, air movement, sunlight, and people stepping where they shouldn’t. **Fibreglass and mineral wool: 50–70+ years if kept dry.** Cellulose: often 20–30 years before settling asks for a top-up. Closed-cell spray foam can run 50+ years; open-cell, typically 30–50 if UV and moisture are managed. Rigid foams like PIR, EPS, and XPS usually sit in the 30–60-year band, with XPS holding up well in damp spots. Natural materials—sheep’s wool, cork, wood fibre—span 25–100 years, with cork at the upper end when conditions are benign.

Take two houses on the same street in Leeds. One has loft fibreglass from the late 80s, still springy and near full depth because the roof stayed tight and the storage boards sit on raisers. Next door, a Victorian terrace with retrofitted cellulose shows 25 years of living: a neat 20% settle, a little dust, and a patch under a previously leaky flashing where the R-value sagged. The owners notice it on windy nights, when the landing feels sharper. Same postcode. Different fate. A drip here, a footfall there, and the timeline diverges.

Why the spread? Insulation fails quietly in four ways: gets wet, gets squashed, gets eaten, or gets leaky around the edges. Moisture collapses the microscopic air pockets that do the insulating. Compression reduces loft depth and performance. Rodents love cosy corners in lofts and crawl spaces. Air leaks bypass even perfect insulation like gaps in a winter coat. Warranties tell a quieter story too: many products come with 10–25-year guarantees, not because they die at 26, but because manufacturers can’t underwrite decades of roofers, tenants, and storms. The science lasts; the setting changes.

What extends — or shortens — that lifespan

Start with a simple ritual: a five-minute seasonal sweep. Peek at the roof from outside after big weather. Open the loft hatch and sniff for mustiness. Check two things with your hand—felt or membrane under tiles should be dry, and insulation near the eaves should feel fluffy, not claggy. If you’ve got rigid boards on a garage ceiling, run your palm along joints: cold seams hint at gaps. *Heat always finds the weakest point.* A tiny bead of mastic in autumn can save a decade of performance.

We’ve all had that moment when a DIY shortcut felt clever on Saturday and expensive by February. Common missteps? Pushing insulation hard into the eaves and choking ventilation. Mixing materials in layers that trap moisture—vapour-open wool below a vapour-tight board can backfire without a proper vapour control layer. Skipping raised loft legs so storage boards crush the blanket. Forgetting that reflective foils lose bite once they’re dusty, so they’re brilliant in clean cavities and mediocre in messy ones. Let’s be honest: nobody does that every day.

Think of longevity as a triangle: the product, the installation, and the environment. Neglect one, and the timeline shrinks.

“Insulation doesn’t really ‘wear out’—homes do,” a veteran surveyor told me. “Keep the water out and the air where it belongs.”

For quick wins and fewer surprises, keep this mini-checklist handy:

• Cellulose: 20–30 years before a sensible top-up; monitor settling lines.
• Spray foam (closed-cell): 50+ years, but watch roof coverings and disclosures for resale.
• Fibreglass/mineral wool: 50–70+ years dry; replace sections touched by leaks.
• Rigid foams (PIR/EPS/XPS): 30–60 years; protect from UV and solvents.
• Natural options: wool/cork/wood fibre 25–100; match to moisture conditions.

What to expect over the decades

Insulation lifespans aren’t a countdown. They’re a relationship with your building’s habits. A loft that stays bone-dry will treat fibreglass like an old friend—maybe a little flattened near the hatch, still competent everywhere else. Cellulose in walls can hum along for decades if the cladding is watertight, then lose its edge if a gutter overflows in one bad winter. Spray foam stiffens structures and shrugs at draughts, yet a future buyer might pull a face if paperwork is patchy.

Cork quietly shrugs off time. Wood fibre loves to buffer moisture swings and then needs design care around splash zones. Reflective foils are sprinters, not marathoners, unless they remain clean and correctly spaced. The pattern is simple: dry, ventilated, uncompressed insulation keeps its promise. So ask yourself less “How long?” and more “Under what conditions?” That small shift in thinking brings your house into focus—and your energy bills into calmer water.

FAQ :

• How long should my loft insulation last before I think about replacing it?Dry fibreglass or mineral wool can run 50–70+ years, with occasional patch repairs after leaks. Plan for a top-up if depth has settled below current guidance or traffic has flattened key areas.
• Can I add new insulation on top of old material?Yes, if the existing layer is dry, clean, and not mouldy. Top up to the desired depth and use loft legs for storage boards to avoid compression. Wet or contaminated sections should be removed and replaced.
• Does spray foam really last longer than other options?Closed-cell spray foam often retains performance for 50+ years because it resists moisture and air leakage. The caveat is documentation: surveys and mortgage lenders in the UK may scrutinise poorly recorded installations.
• Why did my cellulose settle, and is that a problem?Gravity and micro-vibration cause loose-fill cellulose to settle 10–20% over time. It’s normal. Maintain coverage by topping up and keeping the cavity or loft dry and well-detailed.
• What’s the quickest way to extend insulation life without major work?Fix small leaks, clear eaves vents, lift storage off the blanket, tape obvious gaps in rigid boards, and protect exposed foam from sunlight. A quiet hour on a Sunday can buy you years.