Blown-In Insulation and Attic Mold: Does the Insulation Have to Go?

Attic mold insulation removal is not automatic. In most attics the mold is on the roof sheathing overhead, and blown-in insulation that is dry and clean can be covered during the work and left in place. It has to go when it is wet, matted, contaminated or sitting in the way of repairs to the ceiling below it.

Why the insulation is usually not the problem

Attic mold grows where warm, damp air meets cold wood, and that is the underside of the roof deck. The insulation sits on the attic floor, a few feet below, on the warm side. It is not where the condensation forms. Fibreglass is made of glass and does not feed mold. Cellulose is treated with borates, which resist it. So in a typical condensation case the sheathing can be black and the insulation underneath perfectly fine.

What insulation does do is collect things. Dust settles on it, and so does anything that falls from the roof deck. That is why protecting it during the work matters.

When attic mold insulation removal is necessary

• It is wet. A roof leak, heavy frost melt or a fan duct dripping for years leaves insulation soaked or crusted. Wet insulation holds water against the ceiling drywall and framing and has lost its insulating value.
• It is matted or compressed. Cellulose that has been wetted and dried packs down into a dense, grey layer and does not recover.
• There is visible growth in or on it. This happens mostly on the paper facing of batts, on soaked cellulose and on heavy dust layers on old fibreglass.
• It is fouled by animals. Rodent, bat or raccoon droppings and nesting are a separate contamination issue and a common reason to clear an attic completely.
• The ceiling needs air sealing. If the cause of the mold is air leaking up from the house, the gaps are underneath the insulation. Sometimes it can be raked aside in sections. Sometimes removing it is the only practical way to reach everything.

How insulation is protected or removed during the job

The insulation is covered with plastic sheeting before any cleaning starts, so material coming off the sheathing lands on the plastic and not in the fibres. A negative air machine runs the whole time, pulling attic air through HEPA filtration. When the removal is finished, the plastic is HEPA vacuumed, folded in on itself and bagged.

Often a strip of insulation along the eaves has to be pulled back to reach the lowest part of the roof deck, which is usually the most affected area. It is pushed back afterward, clear of the soffit vents.

Blown-in insulation comes out the way it went in, through a hose. A large insulation vacuum sits outside, and a long hose runs up through the house or a roof opening to the attic. The material is collected in big filter bags outdoors, so it never passes through the living space in the open. Batts are rolled, bagged in the attic and carried out sealed. The attic floor is then HEPA vacuumed.

Removal adds labour and disposal to the job, which pushes the price toward the upper end of $2,300 to $6,500. It can also add most of a day. The quote should state clearly whether insulation is staying, being partly removed or coming out entirely.

Fibreglass, cellulose and vermiculite

• Loose fibreglass is white, pink or yellow and fluffy. It does not absorb water but holds it between the fibres. It dries fairly well if the wetting was brief.
• Cellulose is grey and looks like shredded paper. It absorbs water readily, stays wet longer and tends to mat. Wet cellulose is usually removed.
• Vermiculite is loose, pebbly and grey-gold, and is found in some older homes. It may contain asbestos. It must not be disturbed or vacuumed by anyone who is not a qualified asbestos abatement contractor, and it has to be dealt with before mold work can proceed in that attic.

After the insulation is out

An empty attic floor is an opportunity that does not come often. Every wire hole, plumbing stack, pot light, duct boot and wall top plate is exposed and can be sealed with foam or caulk in a few hours. This is the repair that stops humid house air from reaching the roof deck, and it is far harder to do with a foot of insulation in the way. Baffles can go in at the eaves at the same time, and bathroom fan ducts can be replaced with insulated ones.

New insulation goes in last. Current practice for new homes in Ontario is far deeper than what most older houses have, so a refill usually leaves the house better insulated than before. We do mitigation only, so the new insulation is installed by an insulation contractor, and we can point you to local ones.

What to check in your own attic

From the hatch, look at the insulation directly under the stained sheathing. Fluffy, even and the same colour as the rest means it is likely fine. Crusted, flattened, darker or water-marked patches mean it got wet. Note the type and the depth, take a photo and include it when you ask for a quote, so the insulation question is answered in writing before the work starts.

Common questions