Hoover and nearby towns
Crawl space encapsulation, layer by layer
An encapsulated crawl space is closed off from the ground and from outdoor air. The soil is covered, the walls are lined, the vents are shut and the air inside is kept dry by a machine. This page walks through each part so you can follow what a company proposes for your house and notice if a part is missing.
Call (205) 555-0115When it is the right job, and when it is not
Encapsulation deals with moisture that arrives as vapor: damp rising off bare dirt and humid air drifting in through the vents. The usual signs are a musty smell indoors in summer, ducts and pipes that drip, insulation that hangs or has fallen, and floor joists that feel damp or show dark staining.
It is not a cure for water that runs in. If rain leaves puddles or mud under the house, that water needs somewhere to go first. A liner laid over a wet floor only hides the pool. A company that looks under your house should say plainly which of the two you have, or whether you have both.
Drawing
The parts of a sealed crawl space
- Floor liner. Thick plastic sheet over all of the soil, with the seams overlapped and taped.
- Walls and piers. The same sheet carried up the foundation walls and wrapped around each pier, then fastened and sealed along its upper edge.
- Vents and door. Every outside vent is blocked and the access door is replaced or gasketed so it shuts tight.
- Dehumidifier. A unit sized for the space keeps the air dry and empties through a small hose.
- Drain and pump. Where water gets in after rain, a basin and pump below the liner send it outdoors.
- Wall insulation. Rigid foam on the inside of the walls takes over from fiberglass between the joists.
What has to happen before the liner goes down
Everything that the liner would cover gets dealt with first. Expect the company to talk about these, in this order:
- Clearing out. Old plastic, fallen insulation, scrap wood and anything else lying on the dirt is removed.
- Water. If the ground shows water marks or channels, a drain along the inside of the wall and a sump pump are fitted while the soil is still open.
- Wood. Joists, girders and subfloor are checked with a moisture meter. Soft or split lumber is repaired now, because nobody wants to cut a new liner to reach it later. That work is described under crawl space repair.
- Growth on the wood. If the framing has mold on it, ask how it will be cleaned and whether the price includes it.
The liner itself
Liner thickness is given in mils. A thin sheet is cheaper and tears when someone crawls across it to reach a duct or a pipe. A thick, reinforced sheet copes with foot traffic and storage. Ask which thickness is quoted and whether it is the same on the floor and the walls.
How the sheet is fixed matters as much as the sheet. Seams should overlap and be taped along their whole length. On the walls it should be mechanically fastened as well as stuck, because tape alone lets go on dusty block. Around piers and pipes it should be cut neatly and sealed, not bunched.
Vents, the door and the air inside
Closing the vents is what keeps August air out. Once they are shut, the space has no way to dry by itself, so something has to dry it. The common answer is a dehumidifier built for crawl spaces. Some houses instead get a small supply of conditioned air from the heating and cooling system. Either can work. A sealed crawl space with neither is unfinished.
The dehumidifier needs power and somewhere to drain. Ask where its hose will run and what happens to the water if the pump that lifts it fails.
Two things to raise that often get skipped
Termite inspection. If you have a termite contract, call the pest control company before the work is booked. Many ask for a bare strip left along the upper edge of the wall liner so they can still see the masonry. It is easier to leave the strip than to cut it afterward.
Gas appliances under the house. A gas furnace or water heater in the crawl space draws its air from that space. Sealing the vents changes its air supply. Tell the company if you have one and ask how that will be handled, and by whom.
What the work disturbs
Nearly all of it happens under the floor. Workers go in and out through the access door, so the path to it needs to be clear, and shrubs in front of it may be trimmed. There will be noise from below and bags of old insulation carried out across the yard.
Indoors you should notice little, apart from an electrician if a new outlet is needed. If drainage is part of the job, a pipe will be run through the wall to the outside, and a shallow trench may cross part of the yard to carry the water away from the house.
Questions for the company
Ask these during the visit and get the answers written into the proposal.
- Is water getting in as liquid, as vapor, or both, and what did you see that tells you?
- What liner thickness is quoted for the floor, and for the walls?
- How is the liner attached at the walls and around the piers?
- Which dehumidifier is included, where does it drain, and who services it?
- Is damaged wood or insulation removal priced in, or separate?
- Will a strip be left for termite inspection?
- If a permit is needed in Hoover for any part of this, who applies for it?
Looking after it afterward
A sealed crawl space is not something to forget about. Look in a couple of times a year, and after any very heavy storm. The liner should be dry on top. The dehumidifier should be running or resting, not showing a fault light. A cheap humidity gauge hung near the door tells you at a glance whether the air is staying dry. The Environmental Protection Agency's guide to moisture at home advises keeping indoor humidity under 60 percent, and that is a sensible ceiling under the floor too.
Encapsulation questions
Is a vapor barrier the same thing as encapsulation?
No. A vapor barrier is a sheet laid over the soil, often loose and with the vents left open. Encapsulation seals that sheet to the walls and piers, closes the vents and adds a way to dry the air. A barrier alone slows moisture from the ground and does nothing about humid outdoor air.
Do the vents really have to be closed?
In a humid climate, yes, if the aim is a dry space. Open vents let in summer air that is wetter than the air already under the house. Leaving them open while running a dehumidifier means the machine is trying to dry the whole outdoors.
Can I store things down there afterward?
Light storage is possible on a thick liner if the company says the sheet is meant for it. Keep boxes off the walls and away from the dehumidifier and the pump lid.
How long does the work take?
It depends on the size of the house, the height of the space and how much has to be cleared or repaired first. The company that looks at it can tell you, and the proposal should state it.
Will it lower my energy bills?
Some owners report a difference and some do not. Treat any saving as a bonus. The reason to seal a crawl space is to keep the wood and the air dry.