What does crawl space encapsulation actually involve?

Three things rather than one, which is where most of what gets sold under the name falls short. Michigan's code for a closed crawl space asks for a continuous Class I vapor retarder over all exposed earth with joints lapped six inches and sealed or taped and the edges carried at least six inches up the stem wall and sealed to it; then air exchange, either continuously operated mechanical exhaust at one cubic foot per minute for every fifty square feet of floor with an air path to the house, or a conditioned supply at the same rate with a return path; and the perimeter walls insulated to the energy code. A sheet of plastic laid on the dirt with no air exchange is the half of the job that traps moisture instead of removing it.

Should I insulate the crawl space walls or the floor above?

Whichever matches the design, and the mistake is having no design. If the crawl space is being closed and encapsulated, insulation goes on the perimeter stem walls and the rim joist and the floor above is left alone — the space becomes part of the house. If it stays vented, insulate the floor above and leave the walls. What you do not want is the hybrid that happens by itself: somebody stuffs the vents with insulation one cold fall and nothing else changes, so now there is a closed crawl space with no membrane, no air exchange and no wall insulation. That is the combination that grows mold on the joists.

Will encapsulating my crawl space fix cold floors and a musty smell?

Usually both, and the smell is the better reason. Warm air leaves the top of a house and the replacement is drawn in at the bottom, so the air in a damp crawl space ends up in the rooms above it — a crawl space you can smell in the living room is telling you exactly that. What it will not fix on its own is water. If the space takes standing water after heavy rain, the drainage comes first, because a membrane over that is sealing water in with the house.

Is crawl space insulation covered by a rebate in Michigan?

Crawl space insulation, rim joist insulation and floor insulation are all on the Consumers Energy measure list, and that program has no income test — the eligibility check is whether Consumers sends you a gas or electric bill. Rim joist air sealing is on the list because it has one of the best ratios of cost to energy saved of anything in a house. One rule decides whether the money is actually available: the rebate has to be reserved after a full diagnostic assessment rather than after the work, so the order of operations matters more than the paperwork does.

What is a rim joist and why does everybody mention it?

It is the band of framing where the floor structure meets the foundation wall, running all the way round the house. It matters because it is a long run of thin wood with a gap at every joist end, it sits exactly where cold air gets in, and in most houses it is completely bare. Air sealing and insulating it is the single best value item in a crawl space or basement, which is why it appears on rebate measure lists and why it is worth doing even if you do nothing else down there.

Do you dig out a crawl space to make it taller?

No. Lowering a crawl space floor means excavation and usually underpinning, which is heavy equipment and a licensed residential builder's work, and this company holds no such license. What gets done here is everything inside the space as it stands — clearing it out, dealing with the water, the membrane, the stem walls, the rim joist, pest exclusion and an access hatch that actually seals.

What does crawl space encapsulation cost?

There is no rate card, and headroom changes it more than area does — a space you can kneel in and one you can only lie in are different jobs at the same square footage. It is set by what has to come out first and how far it has to be dragged to the hatch, whether there is water and what fixing that involves, how much insulation is going in, whether the vents are being closed and the air exchange that brings with it, whether a licensed mechanical contractor is needed for the appliances, and how bad the access is. Somebody goes down there, photographs all of it, and puts a fixed price in writing. Coming out is free.

Crawl Space Encapsulation: It Is Three Things, Not One — and the Question That Comes First

Q: Is it safe to close up a crawl space with a furnace or water heater in it?

Not without dealing with the appliance first, and this is a safety matter rather than a question of scope. Michigan's code requires a combustion water heater in a conditioned crawl space to be power vented or direct vented, and does not permit an unvented combustion space heater at all. The reason is carbon monoxide: closing up the space an appliance draws its combustion air from, and changing the pressure around its flue, can bring exhaust gases back into the house. Being careful does not fix it — the appliance being addressed by a licensed mechanical contractor does. Any company willing to encapsulate around a natural-draft appliance without raising it is telling you something about how they work.

The air in your crawl space ends up in your living room. Warm air rises and leaves through the top of a house, and the replacement gets drawn in at the bottom. So a damp crawl space with mold on the joists is not a sealed-off problem under the floor — it is the supply end of the air in the rooms above it.

That, rather than the cold floor, is the real reason to do this work. The cold floor is just what prompts the call.

Want somebody to look at it? Send photographs and we will tell you what you are dealing with. Somebody comes out, looks properly, and you get a fixed price in writing before anything starts. Book a free quote or call 517-505-7135.

First: what is down there, and how does it vent?

This question comes before everything else on this page, and the answer can stop the job.

Michigan's code is blunt about it. A combustion water heater in a conditioned crawl space must be power vented or direct vented. An unvented combustion space-heating appliance is not permitted at all.

The reason behind the code is carbon monoxide. Closing up the space an appliance draws its combustion air from, and changing the pressure around its flue, can bring exhaust gases back into the house instead of sending them out. Being careful does not fix that. The appliance being addressed first does, by a licensed mechanical contractor.

So if there is a natural-draft furnace or water heater down there, that gets sorted before anything gets sealed. Any company willing to encapsulate around one without raising it is telling you something about how they work.

Encapsulation is three things, and most of the trade sells one

"We laid plastic down" is not encapsulation. Michigan's requirements for a closed crawl space are:

A continuous Class I vapor retarder over all exposed earth. Joints lapped six inches and sealed or taped. Edges carried at least six inches up the stem wall and attached and sealed to the wall or the insulation.
Air exchange. Either continuously operated mechanical exhaust at one cubic foot per minute for every fifty square feet of crawl space floor, with an air path to the rest of the house — or a conditioned air supply at the same rate, with a return path.
Insulated perimeter walls, to the energy code.

Plastic on the dirt with no air exchange is the half of the job that traps moisture rather than removing it. It is also the version that gets quoted cheapest, which is not a coincidence.

Walls or floor? Pick one on purpose

There are two legitimate designs and most of the crawl spaces we look at have ended up somewhere between them by accident.

Closed and encapsulated: the insulation goes on the perimeter stem walls and the rim joist, and the floor above is left alone. The crawl space becomes part of the house.

Vented: the vents stay open and the floor above is insulated. The crawl space stays part of the outdoors.

What you do not want is the hybrid that happens by itself: somebody stuffs the vents with insulation one cold fall, nothing else changes, and now you have a closed crawl space with no membrane, no air exchange and no wall insulation. That is the combination that grows mold on the joists. Batts stapled up into the floor joists that have since sagged and are holding moisture against the subfloor are worse than nothing at all.

The water comes first

Same order as everywhere else. A membrane over a crawl space that takes standing water after heavy rain is sealing water in with the house.

Gutters, downspouts, grade, and a sump where one is genuinely needed all come before plastic goes down. There is a whole piece on how to work out which of those it is: why is my basement wet.

The rim joist is the best value in the building

If you only do one thing down there, air seal and insulate the rim joist — the band of framing where the floor meets the foundation wall, all the way round.

It is a long run of thin wood with gaps at every joist end, it sits exactly where cold air enters, and it is almost always bare. Air sealing it has one of the best ratios of cost to energy saved of anything in a house.

Which is also why it is on the rebate list. Crawl space insulation, rim joist insulation and floor insulation are all covered by the Consumers Energy program, and that program has no income test at all — the eligibility check is whether Consumers sends you a gas or electric bill. One rule decides whether the money is available: the rebate has to be reserved after a full diagnostic assessment, not after the work. Order of operations again. The energy rebates page sets out all four programs.

What else gets done while it is open

Clear it out — fallen insulation, torn barrier, forty years of debris.
Pest exclusion: the sill gaps, pipe and wire penetrations, the places a mouse has been using as a front door. This is the cheapest it will ever be to do.
An access hatch that actually seals. The best membrane in the county does nothing underneath an open hatch.
A sub-membrane pipe stub if a certified radon mitigator is coming, so their fan has something to connect to. See radon sealing.
Photographs of all of it. Most people have never seen their own crawl space, and the before-and-after is the only way this work is ever visible.

Where this stops

No mechanical work — installing the exhaust fan, or tying a conditioned supply and return into the existing duct system, is a licensed mechanical contractor's line, named on the quote and coordinated rather than absorbed. No structural work — sagging joists, a rotted sill plate or a failing pier is assessed, reported and referred, and anything load-bearing goes to a structural engineer first. No excavation and no lowering a crawl space floor; that means underpinning, which is a licensed residential builder's work and we hold no such license.

Mold: inspection and surface treatment only, with remediation past small areas referred to a certified specialist — the same line as everywhere else on this site. Framing is a hard surface and it cleans; fallen insulation and anything porous comes out and gets bagged. Growth across the whole underside of a floor is a remediator's job.

And in a house built before about the mid-eighties, old pipe lagging and duct wrap get sampled before they are disturbed, not pulled out and bagged on the day.

What to look at this week

Open the hatch and shine a flashlight in. Standing water, a torn barrier, insulation hanging out of the joists and black staining on the subfloor are all visible from there.
Find out what appliances are down there and how they vent. That one answer decides whether this job can be done in its usual form.
Does it smell? A crawl space you can smell upstairs is telling you where your indoor air comes from.
Check the vents. Open is a design. Stuffed with insulation is the worst of both.
Follow the downspouts, look at the grade.
Leave loose fallen insulation alone. It is holding whatever grew on it, and dragging it out unbagged is how that gets into the house.
Do not close the vents up for winter without the membrane, the insulation and the air exchange. That is the mold recipe.

Book it

Book a free quote · call 517-505-7135 · or read more about crawl space encapsulation and insulation.
Water getting in first? Wet basements. Mold on the joists? Mold removal. Rebates? Energy rebates and grants.
Serving Lansing, East Lansing, Okemos, Haslett, Holt and the rest of Greater Lansing.