Vermiculite Attic Insulation (Asbestos)

Loose grey-brown pebble insulation in a pre-1990 attic.

24High burden · out of 100

Cleaner swapLeaving it sealed and undisturbed; an accredited asbestos contractor if it must move

If it is in your attic

Recognise it: a pebble-like, pour-in insulation, usually grey-brown or silver-gold, often sold as Zonolite.
Assume it contains asbestos. EPA says further testing is not needed to take the right precautions.
Leave it undisturbed. Do not store boxes in that attic, and do not let children play there.
Do not remove it yourself. Before any remodelling or renovation that would disturb it, or if it must come out, hire a trained, accredited asbestos contractor — EPA advises one independent of the firm that assessed it.
Its insulating value: about R-2.7 per inch of depth, per a 2012 US Department of Energy guide for contractors.

How this score is built

100Start
54Chemical hazard 10 × 4.6−46
47.2Everyday exposure 2 × 3.4−6.8
24Persistence 9 × 2.6−23.4, then rounded to 24
HighThe band24 sits in 20–39.

What each input rests on

The three ratings behind the score, and the studies each rests on
Input	Rating	Evidence
Chemical hazard	10/10	Workers who mined and processed the asbestos-contaminated Libby vermiculite died significantly more often of asbestosis (SMR 165.8), lung cancer (SMR 1.7) and mesothelioma, rising with cumulative exposure. Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update of a cohort mortality study · Environ Health Perspect 2007 DOI 10.1289/ehp.9481 · PMID 17450227 · Abstract, Results · read 2026-10-02
Everyday exposure	2/10	In tests in three homes, airborne amphibole asbestos was not elevated when Zonolite attic insulation was undisturbed; cleaning, remodeling and other activities that disturbed it produced significant airborne concentrations. Zonolite attic insulation exposure studies · Int J Occup Environ Health 2010 DOI 10.1179/107735210799160219 · PMID 20662420 · Abstract · read 2026-10-02 In homes with vermiculite attic insulation or other asbestos materials, amphibole asbestos was detected in the living space of 12 (26%) of the homes tested, chrysotile in 45 (98%). The presence of asbestos-contaminated vermiculite attic insulation or other asbestos-containing materials in homes and the potential for living space contamination · J Environ Health 2012 PMID 23091967 · Abstract · read 2026-10-02
Persistence	9/10	Among 198 adults exposed to Libby amphibole only in childhood and adolescence, 96 (48%) had pleural thickening as adults, with likelihood rising with years lived in the area. Pulmonary abnormalities as a result of exposure to Libby amphibole during childhood and adolescence-The Pre-Adult Latency Study (PALS) · Am J Ind Med 2017 DOI 10.1002/ajim.22674 · PMID 27859510 · Abstract, Results · read 2026-10-02 In rats inhaling Libby amphibole for 13 weeks, lung fibre burdens declined only gradually over 18 months, and inflammation and interstitial fibrosis persisted up to 18 months after exposure. Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats · Part Fibre Toxicol 2016 DOI 10.1186/s12989-016-0130-z · PMID 27083413 · Abstract, Results · read 2026-10-02

Ratings are editorial. A study listed here supports the rating; it did not compute it. How the index is built

What this means for you

The persistence rating is the standout concern here — these compounds linger in the body and environment for years. A single Montana mine supplied over 70% of US vermiculite between 1919 and 1990 and its ore was contaminated with asbestos, so vermiculite loft insulation from that era — often sold as Zonolite — should be assumed to contain it. Undisturbed it releases little; disturbing it during DIY is the risk.

Evidence strength: strong

Sources: US EPA — Protect your family from asbestos-contaminated vermiculite insulation (updated 2026-04-17); US EPA — My attic has vermiculite insulation in it. Am I at risk? (updated 2026-07-20); US DOE — Energy Renovations: Insulation, a guide for contractors to share with homeowners (May 2012), Table 2.2

See where your whole exposure load is highest — free Exposure Score →

This entry and the whole Index, on your phone.