Insulation

Roof and ceiling insulation limits heat flow through the roof. It is bulk (glasswool, rockwool, polyester, cellulose, natural wool), reflective (foil laminates and foil-faced blankets), rigid board (PIR, PUR, XPS, EPS, mineral fibre) or sprayed foam. It works with vapour control layers, sarking, ventilation and the airtightness of the ceiling to manage condensation.

Some older insulation is hazardous: loose-fill asbestos (the Mr Fluffy homes in the ACT and New South Wales), vermiculite that may contain asbestos, and foil laminates stapled over live wiring under the 2009 and 2010 Australian Home Insulation Program.

What shortens life:

• Disturbance by trades running cables, ducts and downlights.
• Leaks and condensation.
• Poor vapour control on the warm side.
• Vermin nesting in batts.
• Dust on foil, which defeats its reflectivity.

Performance falls long before the material wears out. Batts compressed to half their depth lose much of their insulating value; foil covered in dust loses most of its reflective benefit; loose fill settles and blows into drifts. A roof can have insulation throughout and still deliver a fraction of the labelled value.

Gaps, compression and displacement

Small gaps cut performance out of proportion to their area. Batts pushed aside by trades, compressed under boards and storage, or cut back from downlights leave cold spots, mould on ceilings and higher energy use.

Condensation

Warm moist air from below reaches a cold surface: the underside of metal sheeting, the deck of a cold flat roof, or sarking with low vapour permeability. Water forms, wets the insulation, drips on ceilings, corrodes metal and decays timber. Tightly sealed modern roofs in cold and alpine climates are more prone than older draughty ones, which is why codes now include condensation provisions.

Wetting from leaks

Bulk insulation that gets wet loses most of its value and holds water against the ceiling and structure. In warm flat roofs, wet boards spread water across the roof and must be removed.

Thermal bridging

Rafters, purlins, steel framing and slab edges carry heat past the insulation; they show as lines on thermal images and as pattern staining on ceilings.

Fire and electrical hazard

Batts over downlights and transformers can overheat and ignite; foil laminates in contact with damaged wiring can become live. Combustible boards in roof build-ups on tall buildings are restricted.

Spray foam

Foam applied to the underside of roof coverings or rafters makes the structure impossible to inspect, can trap moisture against timber, and makes covering repairs harder. In Britain, many lenders and surveyors will not accept it without evidence it was correctly specified and installed.

Inverted roof faults

In inverted roofs, rainwater running under the insulation boards cools the membrane and reduces performance; boards float or blow away where ballast is light; boards absorb water over time if not closed-cell.

In the roof space

• Gaps, displaced and compressed batts; insulation missing over areas.
• Batts over or against downlights and transformers.
• Wet, stained or mouldy insulation; water marks on the underside of sheeting.
• Foil laminates sagging onto wiring.
• Loose fluffy grey-blue material or granular vermiculite.
• Spray foam on the underside of the covering or rafters.

Inside the building

• Mould spots on ceilings, often in a pattern following framing or near external walls.
• Water drips on ceilings in cold weather with no rain.
• Rooms under the roof much hotter or colder than others.

In the records

• Insulation type and R-values; installation certificates.
• Energy ratings: NABERS, EPC, ENERGY STAR.
• Mr Fluffy register (ACT and New South Wales) and asbestos register.
• Spray foam installation records and manufacturer documentation.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A building surveyor or energy consultant leads, with a hygrothermal assessment where condensation is suspected.

• Roof space inspection of coverage, depth, condition and clearances.
• Thermal imaging from inside in cold weather.
• Core samples through flat roof build-ups.
• Condensation risk analysis of the build-up (BS EN ISO 13788 or dynamic modelling).
• Sampling of suspect materials for asbestos.
• Electrical inspection where foil is near wiring.

The report should state insulation type, coverage and depth, any wet areas, condensation risk in the build-up, any hazardous materials, and what an upgrade would require.

• Depth and coverage measured on a grid across the roof space and compared with the labelled R-value.
• Sarking and membrane identification from labels or product data, to establish vapour permeability.
• Ventilation check: eaves, ridge and gable openings, and whether insulation blocks them.
• Hygrothermal modelling before retrofitting insulation into cold or tightly sealed roofs.

• Top up and refit batts; install downlight covers or replace downlights with insulation-contact rated fittings.
• Remove and replace wet insulation; fix the leak or condensation source first.
• Vapour control and ventilation: add a vapour control layer on the warm side, ventilate roof spaces, use vapour-permeable sarking.
• Convert cold flat roofs to warm roofs when the roof is renewed.
• Remove spray foam where it is hiding decay or causing condensation, and reinstate a ventilated build-up.
• Licensed removal of asbestos-containing insulation.

• Loose-fill top-ups with depth markers so coverage can be checked later.
• Eaves baffles to keep ventilation paths open over the insulation.
• Confirmed loose-fill asbestos: licensed assessment and, in the ACT and New South Wales, the government purchase and demolition programmes.

Inspection is a lump sum. Top-up and replacement are priced by area. Wet insulation removal adds strip-out and disposal. Asbestos removal is licensed, with clearance testing. Upgrades triggered by roof works are carried in the roof line.

Upgrades triggered by works are code compliance; replacement is lifecycle; top-ups are repairs and maintenance; hazardous insulation is code compliance.

Top-ups are inexpensive where access is easy; costs rise sharply in low or obstructed roof spaces and where downlights and cabling must be made safe first. Flat roof insulation upgrades are carried in the membrane replacement line, not separately.

• Australia. The National Construction Code sets energy requirements in Section J and the Housing Provisions, and condensation management for houses; insulation materials follow AS/NZS 4859.1 and installation AS 3999; downlight clearances follow AS/NZS 3000. The ACT and New South Wales maintain registers of loose-fill asbestos (Mr Fluffy) homes.
• United Kingdom. Approved Document L sets thermal requirements and triggers upgrades on renovation; Approved Document C and BS 5250 govern moisture and condensation; RICS has published guidance on spray foam insulation.
• United States. The International Energy Conservation Code and ASHRAE 90.1 set requirements; International Building Code Section 1202 covers attic ventilation and Chapter 26 foam plastics. The EPA publishes guidance on vermiculite that may contain asbestos.

Insurance and lending can turn on insulation type in all three markets: spray foam on rafters and asbestos-containing products affect mortgage, insurance and sale decisions.

• Insulation type, R-value and installation records.
• Energy ratings.
• Asbestos register; loose-fill asbestos register status in the ACT and New South Wales.
• Spray foam installation documentation.
• Records of condensation, mould and leaks under the roof.

• Photographs of the roof space.
• Any hygrothermal or condensation assessment.
• Electrical safety inspection of the roof space where foil insulation is present.