Crawl space encapsulation, start to finish
Encapsulation turns a vented crawl space into a closed one. Ground moisture is held under a liner, outside air is kept out, and the air that remains is dried by a machine. Done in the right order it ends the summer condensation that rots joists and feeds the musty smell upstairs.
This page walks through the job so you can follow what a company proposes and spot what is missing.
What a finished crawl space looks like
- AThe liner lies over all of the soil, with seams overlapped and taped.
- BIt runs up the foundation wall and is fastened and sealed near the top.
- CEach pier is wrapped and taped so no bare ground shows around it.
- DFoundation vents are closed and sealed from the inside.
- EA dehumidifier dries the air. Its drain line leaves through the wall or runs to a pump.
- FThe access door is replaced or weather-stripped so it shuts tight.
The order matters
Companies differ in products. The sequence below should not change much.
Stop liquid water
Gutters, downspouts and yard slope are corrected. If water still collects under the house, a drain and a sump pump go in before anything else.
Clear the space
Old plastic, fallen insulation, scrap wood and debris come out. Anything left under the liner will rot or puncture it.
Check the wood
Joists, beams and sills are looked over and measured with a moisture meter. Damaged wood is repaired now, while it can still be reached.
Lay and seal the liner
Sheets are run across the floor, up the walls and around every pier, with taped seams and mechanical fasteners at the top edge.
Close the openings
Vents get airtight covers. Gaps around pipes and wires are sealed. The access door is made to close snugly.
Dry the air
A crawl space dehumidifier is set on blocks or hung from the joists, plugged into a proper outlet, and piped to a drain.
Four things to settle before the vents are closed
- Flood zone. In a mapped flood zone, the City of Tuscaloosa's floodplain code has its own rules for foundation openings. Enclosed areas below flood level in newer and substantially improved houses must have openings that let floodwater flow in and out, and closing or altering them breaks those rules. Ask the Office of the City Engineer about your address first. The local guide explains how.
- Gas appliances. A furnace or water heater in the crawl space that burns gas needs air to burn safely. Tell the company it is there and ask how it will be supplied once the space is sealed.
- Termite cover. If you hold a termite bond, ask your pest control company what it needs to stay valid. Many want a strip of bare wall left visible at the top so they can inspect.
- Standing water. A liner is a vapour barrier. It will not hold back a puddle. Water that collects has to be drained first.
What it is like while the work is going on
Nearly all of it happens under the house. People and materials go in through the crawl space hatch, so the path to it needs to be clear and anything stored underneath has to come out. Expect some noise under the floor and a pile of removed insulation and plastic in the yard until it is hauled off.
Indoors, the main change is an electrician's visit if the dehumidifier needs a new outlet. Ask whether that is in the price or yours to arrange.
Questions for the company
- How thick is the liner, and is it reinforced? Thin plastic tears the first time someone crawls over it to reach a pipe.
- How far up the wall does it go, and how is the top edge fixed? Tape alone lets go in time. Ask about fasteners and sealant.
- What controls the humidity, and where does its water drain? A drain line that ends inside the crawl space puts the water back where it came from.
- Who measures the wood before it is closed in? Ask for the moisture readings in writing, with the date.
- What does the written warranty cover, and who stands behind it? The liner maker and the installer often cover different things.
- Will you come back to check it? A sealed space with a failed dehumidifier can end up wetter than a vented one, so someone needs to look now and then.
What usually goes with it
Encapsulation is often quoted with other work. Yard drainage keeps rain off the foundation. A sump pump handles groundwater. Crawl space repair covers wood, insulation and old plastic. A dehumidifier is the part that needs looking after for years.
Ask for each of these as its own line in the proposal. The price guide explains why the totals vary so much between houses.
Encapsulation questions
Can the crawl space still be reached after it is sealed?
Yes. The hatch stays, and plumbers and electricians can still get in. Ask them to lay a board or mat where they crawl so the liner is not torn, and look the liner over after any trade has been under the house.
Does the insulation between the joists stay?
It depends on the design. Some companies take the batts out and insulate the foundation walls instead. Others leave dry batts in place. Wet or mouldy batts come out either way. Ask which approach is proposed and why.
Will encapsulation fix floors that already sag?
No. It stops the dampness that weakens wood, but wood that has already rotted or a pier that has settled needs its own repair. Have that looked at before the liner goes in.
Is a permit needed in Tuscaloosa?
Ask the company which permits apply to the scope and who will apply for them. New electrical work for a dehumidifier and any work on a house in the regulated floodplain are the usual triggers.
Tell someone what you are seeing
Call and describe what is going on under the house or in the basement. You will be put through to an independent local waterproofing company that works in your part of Tuscaloosa County.
Calls may be recorded. The company pays this site for the introduction. See the referral disclosure.