Interior & Exterior Insulation: Complete Guide

Interior & Exterior Insulation: Complete Guide for 2026

Why insulation matters

Proper insulation cuts energy loss, improves acoustic comfort, and protects the structure from condensation and mold. The right choice depends on building zone, climate, finish type, fire/moisture resistance, and budget.

Insulation types — where they excel, pros, risks, cost deltas (Δ%)

1) Mineral wool (rock/glass; various densities)

• Best for: façades (ETICS or ventilated), attics/lofts, partitions, suspended ceilings, floor/ceiling between stories (acoustic).
• Performance: very good thermally; excellent acoustically; stable at temperature; non-combustible.
• Materials cost: typically ~10–25% higher vs. EPS.
• Labor cost: similar or ~5–10% higher (precise cuts, fixing, protection).
• Pros: superior fire rating, strong acoustic performance, vapor-open (condensation risk reduced with correct layering).
• Risks: moisture sensitivity; needs proper vapor control/membranes and protection from leaks.

2) EPS (expanded polystyrene)

• Best for: ETICS façades, protected plinths, exterior walls (dry), under screed indoors (special grades).
• Performance: good thermal; modest acoustic.
• Materials cost: ~10–25% lower vs. mineral wool; ~25–40% lower vs. XPS/PIR.
• Labor cost: lower vs. mineral wool (lightweight, fast install).
• Pros: economical, low weight, quick installation.
• Risks: lower fire performance, solvent/UV sensitivity, weak acoustics, lower vapor diffusion (layering must be designed).

3) XPS (extruded polystyrene)

• Best for: moisture/compression zones—plinths, under slabs on grade, inverted roofs, trafficable terraces.
• Performance: very good thermal in wet conditions; high compressive strength.
• Materials cost: ~20–35% higher vs. EPS.
• Labor cost: similar to EPS; on inverted roofs can be lower vs. classic builds due to simpler layering.
• Pros: minimal water uptake; strong mechanically.
• Risks: poor acoustics; fire class below mineral wool; requires UV/mechanical protection.

4) PIR/PUR (boards or spray foam)

• Best for: roofs (especially flat), ventilated façades, lightweight enclosures; spray foam for hard-to-reach cavities.
• Performance: very good thermal at reduced thickness; medium acoustic.
• Materials cost: ~35–60% higher vs. EPS; ~15–30% higher vs. XPS.
• Labor cost: boards → similar to XPS; spray foam → ~20–35% higher (equipment/crew).
• Pros: low λ (thin layer for same performance), good continuity with spray.
• Risks: fire behavior depends on facings/linings; spray requires strict moisture and vapor control.

5) Natural fibers (blown cellulose, wood fiber, hemp, cork)

• Best for: lofts, interior/exterior in ventilated systems, acoustic tuning, eco projects.
• Performance: good thermal; good acoustic; high thermal inertia (summer comfort).
• Materials cost: generally ~20–45% higher vs. EPS; vs. mineral wool varies ±0–20%.
• Labor cost: blown cellulose often ~10–20% lower vs. panel installs (fast filling).
• Pros: vapor-open assemblies, sustainability, improved summer comfort.
• Risks: moisture/pest protection; check density during blowing to avoid settling.

6) Aerogel / slim thermo-reflective blankets

• Best for: limited thickness retrofits (interiors, reveals).
• Performance: very strong per mm; modest acoustic.
• Materials cost: ~200–400% higher vs. EPS (premium).
• Labor cost: similar to thin boards/mineral wool; meticulous detailing needed.
• Pros: top performance where space is tight.
• Risks: high cost; thermal bridges persist unless continuity is perfect.

7) Dedicated acoustic systems (dense mineral wool, acoustic boards, resilient channels)

• Best for: apartment party walls, home studios, conference rooms, inter-story floors (impact noise).
• Performance: excellent acoustic isolation/absorption; thermal varies.
• Materials cost: ~15–40% higher vs. standard drywall builds.
• Labor cost: ~10–25% higher (multi-layer builds, resilient tapes, special profiles).
• Pros: major reductions in airborne and impact noise transmission.
• Risks: reduced usable space; airtight joint sealing is critical.

Zone-by-zone recommendations

Façades (exterior)

• ETICS—budget: EPS (observe fire details—mineral wool firebreak bands).
• ETICS—premium & acoustic/fire: Mineral wool.
• Ventilated façades: Mineral wool or wood fiber with wind barrier.
• Plinths / wet zones: XPS with mechanical protection.

Roofs

• Pitched/attic: Mineral wool between/under rafters + warm-side vapor control; excellent acoustic benefit.
• Flat roof (conventional): PIR/XPS/rigid mineral wool depending on fire/moisture specs.
• Inverted roof: XPS above waterproofing (simpler build-up, inspections often ~10–20% less frequent vs. moisture-sensitive systems).

Interior walls / partitions

• Acoustic priority: double drywall + dense mineral wool + resilient channels/tapes (substantial transmission drop).
• Interior thermal correction (when exterior not possible): Mineral wool or low-λ boards (PIR/aerogel) with proper vapor barrier; manage dew-point to avoid condensation.

Inter-story slabs (impact noise)

• Recommended: floating screed on resilient layer (high-density mineral wool or acoustic membranes) + perimeter isolation strip.
• Effect: notable reduction of impact noise; more stable finishes.
• Labor cost: ~10–20% higher vs. classic screed, but much better acoustic outcome.

Floors on grade / unheated spaces

• Thermal & compression: XPS or appropriate-grade EPS under screed; choose XPS where humidity is high.

Design & installation essentials

• Vapor & diffusion: vapor barrier/retarder on the warm side; for vapor-open façades, allow outward drying.
• Thermal bridges: treat junctions (balconies, lintels, cantilevers) with dedicated thermal elements or correct detailing.
• Fire: in tall buildings/strict fire zones, mineral wool is preferred; include façade fire breaks.
• Moisture: protect hygroscopic materials; in wet zones use XPS/PIR or mineral wool with correct membranes.
• Acoustics: airtightness of all joints, mechanical decoupling (resilient tapes), and avoid “acoustic bridges.”
• Quality control: verify real thicknesses, layer continuity, sealing at penetrations, and rigorous workmanship.

Quick selector (by priority)

• Lowest materials budget: EPS (note: so-called “thermal paints” do not replace insulation).
• Top fire & acoustic: Mineral wool.
• Moisture/compression: XPS.
• Minimal thickness: PIR or aerogel (premium tier).
• Walls/ceilings for noise: Dense mineral wool + resilient channels.
• Summer comfort (thermal mass): Natural fibers (cellulose/wood fiber).

FAQs (short)

1) Can I insulate from inside if I can’t touch the façade?
Yes—but only with a dew-point calculation and a correct vapor barrier; otherwise risk of condensation/mold.

2) What matters more: thickness or material?
Both. Low-λ materials reach targets at smaller thicknesses, but detailing (bridges, vapor control) often decides performance.

3) How do I stop impact noise between floors?
Use a floating screed on a resilient underlay plus perimeter isolation; ceiling linings alone won’t fix impact noise.

4) Are “slim” premium solutions worth it?
When space is critical, yes. Otherwise, classic systems usually offer a better performance-to-cost ratio.

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We provide free site assessments & proposals and compare short-listed options with percentage-only differences in material and labor costs, plus a clear zone-by-zone plan (façade, roof, walls, floors).