Insulation · Service

Blown-in insulation, and whether to blow it yourself

The bags and the blower are at the big-box store, and for some attics that genuinely is the right answer. Here is how to tell whether yours is one of them — and what a professional crew does that a rented hopper does not.

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In short

What is blown-in insulation?

Blown-in insulation is loose material — usually cellulose or fibreglass — fed through a hose from a hopper and distributed to an even depth over an attic floor, or densely packed into an enclosed wall cavity. Its advantage over batts is coverage: it flows around wiring, pipes and irregular framing instead of being cut around them, so it leaves fewer gaps. It is sold by the bag with a rented blower, which is why the decision here is genuinely DIY or not rather than which contractor.

Triggers

Signs you need blown-in insulation

The existing attic insulation is uneven, compressed, or shallow enough that joist tops are visible
Your attic floor is crowded with wiring, junction boxes and pipes that batts would have to be cut around
You have closed walls you want insulated without opening them up, which is a dense-pack job
Previous batts were installed with visible gaps, folds or compression around obstructions
You want to add depth over existing insulation without removing what is already there
The house is older and the framing bays are irregular widths that standard batts do not fit

Seeing something not on this list? Browse insulation problems by symptom →

The job

How blown-in insulation actually works

Air seal first — while you can still reach the ceiling

ENERGY STAR names the attic penetrations that matter: kneewalls, the attic hatch, wiring holes, plumbing and pipe holes, dropped soffits open to the attic, recessed lights, and the furnace flue chaseway. Loose-fill is air-permeable and buries all of them.

Watch for: The single most consequential mistake on this page, DIY or professional. Once the material is down, every seal you skipped is under a foot of fibre. Sealing is cheap now and expensive forever after.
Baffles at every eave, before any material moves

Rigid baffles hold the loose-fill back from the soffit vents so the soffit-to-ridge airflow path stays open. They cost very little and go in before the hose does.

Watch for: Blowing deep at the perimeter with no baffles. Loose material slumps straight into the soffits, cuts the ventilation, and blocked soffit vents are a well-known route to ice damming and a damp roof deck.
Protecting fixtures and the flue

Recessed lights not rated for insulation contact get dams or covers. The furnace flue gets metal flashing and high-temperature sealant with the clearance the appliance requires — never ordinary expanding foam.

Watch for: Loose-fill piled onto recessed cans. Fixtures not rated for contact can overheat when buried, and you cannot tell which type you have from the room below.
Setting depth markers

Markers are placed across the attic before blowing so depth can be checked as the work proceeds and audited afterwards. This is what turns "we blew it in" into a verifiable result.

Watch for: No markers. Loose-fill settles to some degree, and without a record you cannot tell normal settling from a job that never reached target depth in the first place.
Blowing to even depth, perimeter included

One person works the hose in the attic, another feeds the hopper below. The material is walked out across the whole plane, working back toward the hatch so nobody crawls over finished work.

Watch for: Depth that fades at the edges. The perimeter is the hardest place to reach and the coldest part of the ceiling, so it is where a rushed job gets thin — and it is the last place you will ever notice.
Dense-packing closed walls

For existing walls, holes are drilled per bay, material is packed to a density that resists settling, and the holes are plugged and finished. Density is the whole job — under-packed cavities settle and leave a cold void at the top.

Watch for: A wall job priced like an attic job. Dense-pack needs higher pressure, a fill tube, and one hole per bay including above and below fire blocking. Missed bays are invisible until an infrared camera finds them.

Money

What does blown-in insulation cost?

Blown-in is among the cheapest ways to buy insulation performance, priced by coverage area and target depth. Big-box bags plus a rented blower are cheaper still on materials, but exclude the air sealing and baffles that decide the result. Dense-packing walls costs considerably more. See the Cost Guide.

See the full blown-in insulation cost guide — by material, size and region →

Insulation depth & savings tools → Check target depth for your climate zone before you buy bags or accept a quote.

Straight answer

When blown-in insulation is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

The attic has not been air sealed and you are not going to seal it. Blowing loose-fill over an unsealed ceiling buries every penetration you needed to reach. You will get some benefit and permanently lose access to most of it. If sealing is out of budget this season, wait — do not spend the insulation money first.
There is vermiculite, knob and tube wiring, or moisture up there. ENERGY STAR says vermiculite "may contain asbestos" and must not be disturbed unless lab-tested, classes pre-1930 knob and tube as a fire hazard in contact with insulation, and flags wet or mouldy insulation as a professional finding. Any one of the three stops a blowing job dead.
The soffit vents are blocked and baffles are not on the plan. This is the specific failure mode of a rushed blown-in job. You will not see it, and you may find out about it as ice dams the following winter, by which time the material is in place and moving it is a removal job.
You want it in an open, accessible wall you are already renovating. If the studs are exposed, batts or board go in faster and are directly inspectable before the drywall goes up. Dense-packing exists to solve the problem of a wall you cannot open. If yours is open, that problem does not apply.
Your ducts and air handler are in the attic and leaking. Loose-fill on the attic floor leaves them outside the thermal envelope. You are insulating against a space that your own system is actively conditioning through its leaks, which is a different problem and needs a different answer.
You want a vapour or air barrier out of it. Loose-fill is neither. It slows conduction and does very little to stop air movement, which is exactly why the sealing step is not optional. Anyone presenting blown-in as an air sealing measure is selling you the wrong thing.

Your options

Types of blown-in insulation

Cellulose

Recycled paper fibre, treated for fire resistance. Denser, packs well, and is the usual dense-pack choice for walls.

Blown fibreglass

Lighter, does not absorb water the same way, and is the common big-box attic product.

Sealing, then blowing

The sequence matters more than the material. Air sealing is what makes the depth pay.

Start from the symptom instead

Cold rooms, ice dams and inadequate depth each have their own diagnosis page in the Problems archive.

Compare insulation options side by side →

Straight answer

Can I do this myself?

Three hard stops, all of which apply whether you hire out or not. Do not blow insulation over knob and tube wiring — pre-1930 wiring is a fire hazard in contact with insulation. Do not disturb vermiculite until it has been lab-tested for asbestos. Do not bury recessed lights that are not rated for insulation contact; they can overheat, and you cannot identify them from below. And never blow to the eaves without baffles — blocking your soffit vents is the classic DIY own-goal here.

Reasonable to DIY

Topping up an accessible, dry, hazard-free attic that has already been air sealed and baffled
Installing the baffles yourself before the material goes in
Adding depth over existing loose-fill that is clean and dry — no removal needed
Setting depth markers so you can check your own work against the bag's coverage chart

Call a licensed pro

Any attic with vermiculite, knob and tube, moisture staining, or no safe footing
Dense-packing closed walls, which needs correct density, one hole per bay and a fill tube — under-packing is invisible and permanent
The air sealing step, if you are not confident detailing the flue chaseway with metal flashing and high-temperature sealant
Anywhere with bath, kitchen or dryer vents discharging into the attic, which must be corrected first
Low-clearance attics where working the hose means crawling over joists with limited visibility

Before you sign

What to check when hiring for blown-in insulation

What material, and what installed depth are you targeting?

The answer should name the product and a depth tied to your climate zone. "The usual" is not an answer you can check afterwards.
Is air sealing included, and which penetrations specifically?

Loose-fill buries them all. This is the last opportunity to reach them and it should appear as a priced line, not an assumption.
How many baffles, and at which eaves?

A number, not a gesture. Blocked soffit vents from a blown-in job are common and the fix afterwards means removing the material you just paid for.
How are you handling recessed lights and the flue chaseway?

Dams or covers for fixtures not rated for contact; metal flashing and high-temperature sealant at the flue. Both are fire-safety details.
Will you set depth markers and leave me a coverage record?

It is your only way to distinguish settling from underdelivery a year later, and efficiency programmes typically want to see it.
For a wall job — what density, and how many holes per bay?

Dense-pack succeeds or fails on density. One hole per bay is often not enough where fire blocking splits the cavity, and a missed section is invisible behind finished drywall.
What did you find in the attic before quoting?

A contractor who can describe the existing depth, the ventilation state and where the vents terminate has actually been up there. One who cannot has not.

All insulation hiring checklists →

Local pros

Blown-In Insulation near you

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Related work

Often done at the same time

Air Sealing

The step that has to come first

Attic Insulation

Where most blown-in ends up

Wall Insulation

Dense-packing closed cavities

Insulation Removal

When the old material cannot stay

All insulation services →

FAQ

Blown-In Insulation — questions people ask

Still have a question? Talk to our team →

Cellulose or blown fibreglass — which is better?

Neither is universally better; they fail differently. Cellulose is denser, fills irregular spaces tightly and is the usual pick for dense-packing walls, but it is a paper product and reacts badly to sustained water. Blown fibreglass is lighter and does not absorb water in the same way, but it is easier to underdeliver on depth because it looks fluffier than it is. The full argument is in the Comparisons archive.

Can I rent a blower and do it myself?

For a straightforward attic top-up, genuinely yes — that is why the machines are available with a bag purchase. What decides it is not the blowing, which is easy, but everything around it: whether the ceiling has been air sealed, whether baffles are in, whether your recessed lights are rated for contact, and whether there is vermiculite or knob and tube up there. If any of those is unresolved, the rental saves you money on the wrong step.

Does blown-in insulation settle?

Loose-fill settles to some degree after installation, which is why installers work to a target installed depth and why the bag's coverage chart distinguishes what you put down from what you end up with. This is also the practical argument for depth markers: without them you have no way of telling ordinary settling from a job that was thin to begin with.

Can blown-in insulation go over my old insulation?

Usually yes, and it is normally the right call. If the existing material is dry, clean and evenly spread, blowing over it keeps the value of what is already there. It becomes a removal job instead when the existing material is wet or mould-affected, rodent-contaminated, smoke damaged, or vermiculite that has tested positive for asbestos.

Can walls be insulated without opening them up?

Yes — that is dense-packing. Holes are drilled in each stud bay from inside or outside, material is packed in at a density high enough to resist settling, and the holes are plugged and finished. The two things that go wrong are under-packing, which leaves a cold void at the top of the bay as the fill settles, and missed bays where fire blocking splits a cavity and only one hole was drilled.

Will blown-in insulation stop draughts?

No, and expecting it to is the most common disappointment with this product. Loose-fill slows heat conduction but air moves through it fairly freely. If your complaint is draughts rather than general coldness, the money should go to air sealing first — and since air sealing has to happen before blowing anyway, that is not a detour.