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Which vapor barrier should I use?

This is an email from a gentleman from Virginia. His questions are based on obstructions and product selection.


John Sent: Sunday, April 20, 2008 10:08 PM

Subject: Attention Customer Service

I live in Virginia and have a crawl space that is above ground level and ventilated with foundation vents. The plastic vapor barrier is a mess. The crawl space is 1300 sq ft and contains approximately 20 footings creating quite a challenging environment in which to install a vapor barrier.

Do you recommend SilverBack® in this case and if so does it make sense to cover the foundation vents, or just cover the ground as best possible?


John Kane

Chesapeake, VA



Thanks for the email. That is a lot of supports (footings) and your right it will make it more challenging but not all is lost. There is a process to wrapping these supports so they are sealed. We can help you with how to do it. The best is to eliminate the vents and condition the crawl space like it was your home, because it is. What I mean is heat and cool it with your existing furnace and A/C, this will give you the best results. If that is not possible then you should look at a dehumidifier, but look at the good ones like an OscarAir. The only way you can control the moisture is to seal out the dirt floor, wrap the supports and close the vents. Even though you have some challenges it may not be as bad as you think. If you like, in the near future we can make a video of how to wrap the supports and let you know when it will be ready to view (approx 2 weeks). My recommendation is to use the SilverBack® on the floor and walls and close the vents. To keep the cost down (depending on what you will use the crawl space for) you can use our 8 Mil. It is very durable and will hold up to regular maintenance type traffic.

I hope this answered your question. Please feel free to keep in touch and let us know if you have any other question.

Matt Leech

CrawlSpace Concepts

More questions from John


From: John Sent: Monday, April 21, 2008 11:11 PM

Subject: Attention Customer Service


Thanks very much for the information. A few more questions.

If I understand your recommendation, I should cover the crawlspace floor and walls up to the floor joists, to include the supports with SilverBack®. In doing so the foundation vents will be covered over and should be closed. I should then add an A/C-Furnace vent into the crawlspace to help regulate the humidity.

My crawlspace is 32’x32’ with a connecting 20’x13’4” room off to one side. That is approximately 1300 sq ft. The walls are mostly 3’ with some areas (sunken floor) at 2’. This means a 1300 sq ft roll will not suffice. Can I purchase a smaller roll to cover the remaining space?

The crawlspace is only used for termite inspections and occasional maintenance on cable TV, phone wiring, plumbing, etc. So it you think the 8 Mil will do, then that is what I’ll go with. The working space is extremely tight due to all the A/C ducting, gas pipes, plumbing, etc. Thus the 8 Mil should be easier to handling.

John Kane

Chesapeake, VA



When you add the ducts (supply and return) to the crawl space do both of us a favor and consult with a heating and cooling contractor to make sure you get enough air flow in the crawl space. In other words if you only put one heat vent in or no return it may not be enough to regulate the humidity properly. On the other side if you put in to many heat vents you may rob your home of the proper volume to heat it comfortably.

We actually have several options to help you. The 8 Mil comes in several different widths we only offer the selection we have on the site to simplify the purchase of the material. We keep an eye on what is ordered and if we can make suggestions to save our customers money we do just that. The 8 Mil comes in widths of 6.67’ up to 32.5’ X 100’ long so you can pretty much get what you need without buying way too much. On top of all of that the 8 Mil is the easiest to work with.

I hope this helps.


From: Papania, Dom Sent: Thursday, April 17, 2008 9:12 AM

Subject: Install Information

Looking at your photos online it would appear as the side walls of the Crawl space are typically covered 1st is that correct? My side walls are about 5 ft high with gravel on the floor. No water issues in the Crawl space but I will pre-laying ventilation pipe under the liner for future Radon Mitigation.

Is this how I would go about installing in a small crawl space 15×18 ft with 5ft walls on 3 sides

1. Remove the Fiberglass insulation from the side walls.

2. Rack out and level gravel

3. Clean along top of cinder blocks

4. Cut liner to fit side walls with enough to allow a 8-12 inch overlap at the bottom.

5. Apply the double stick foundation tape along the top edge of the block.

6. Put up the liner.

7. cut and install the liner to the floor

8. seal the sides to the floor with the Seam Tape


1. would I overlap the side piece on top of the floor piece or would I overlap the floor on top of the extra that will be left at the bottom of the side piece or does it really matter?

2. when sealing the sides to the bottom, would I only use the Seam Tape or would I also use the Foundation Seal Tape™ along with the Seam Tape.

I will be placing an order later today and will determine the amount of Tape required based on your install recommendations

Thanks for your help.

Dominic Papania

Senior Database Engineer, Enterprise Tech & Business Solutions



To answer your questions, yes you are right the walls go up first and you listed the steps correctly.

The proper install method is to lap the floor on top of the wall. The reason is this, if you were to have water ever leak through the foundation it would be directed to the floor unobstructed. If you installed the wall on top of the floor water could run down the wall and get trapped at the floor flap (overlap) and hold water potentially causing water to leak onto the SilverBack™. This actually happened to us on a job that was very muddy. We laid the floor first to get out of the mud then the walls. At the time we did not see what the difference would be if we just taped the wall to the floor. Well the sump failed on a power out and there were gallons and gallons of water trapped at the floor flap. Since that job we always recommend that you tape the floor on top of the wall.

When sealing the floor to the walls the typical procedure is to use just the Waterproof Pro Seam Tape™. But if the crawl space has a history of going under water then using the Foundation Seal Tape™ on the seams as well is another line of defense against the pressure caused from water build up. You will gain no advantage against sealing out moisture using the Foundation Seal Tape™ along with the Waterproof Pro Seam Tape™ the only advantage is where water may build up under the vapor barrier. The Waterproof Pro Seam Tape™ alone is a bit of an overkill for just moisture problems, its greatest value is the longevity of the performance.


From: Bettilou Sent: Tuesday, April 22, 2008 1:58 PM

To: Subject: Old house with a small cellar and crawl space

My husband and I live in New York State and bought an old house (1826, I think) three years ago that has a 13 x 13 dirt floor stacked stone cellar. From that cellar in many directions are crawl space areas anywhere from two feet to 3 feet high or so. All dirt in the crawl spaces with nothing flat and even. Some of the stacked stone wall has openings to the outdoors. There are places where concrete blocks have been stacked as well as a few jack posts to support the house. This house has been added onto in every direction imaginable. Some of the rooms even extend over the foundation walls and just kind of hang over without any support.

We are currently getting estimates on drainage away from the house as we live in low area where water collects and runs into our crawl space and fills the cellar area with water. We have installed a sump pump in the cellar area to carry away the water.

We have been trying to figure out what is the best way to insulate and clean up our cellar and crawl space. We’ve talked to some contractors, but have not gotten any real solutions.

We also have a 275 gallon fuel tank in the 13 x 13 cellar which we intend to remove next year and place a tank outside our home.

The floor joists above the cellar area have become spongy and weak. We plan on placing sister boards or it may be daughter boards in that area once we get rid of some of the moisture. I can tell there has either been termites or some boring beetle that was in that area years ago.

I would appreciate any advice or suggestions you might have that could solve our need for insulating and cleaning up our crawl space and cellar.

Thank you.

Bettilou Galbraith

New York



Your situation is not uncommon, and certainly not unsolvable. Please understand that the advice I am giving is based on the information received in your email.

Homes built in the 1800’s were built without having building codes or regulation to guide the construction. That usually meant that the home was built with insufficient framing and support. Chances are very good that the home was built with hardwood studs and floor joist and the spacing varies. The mortar used to hold the field stones together are probably deteriorating and some of the stones have fallen out. The bad news is your home is almost 200 years old and the good news is your home is almost 200 years old. What I mean is the home has made it this far and that alone says something for the craftsmen that built it but it needs some TLC to keep going. The wood destroying insects that had their way with your home have hopefully gone but to keep them from coming back you need to control the moisture.

To control the moisture you have to control the water, seal out the dirt, close the vents and either use a crawl space dehumidifier (a good one not a Wal-Mart dehumidifier) or run heat/AC ducts and a return to the crawl space or both (depending on the moisture levels). When I say both I mean for a while until the moisture is under control. To control the water, the perimeter of the home is your frontline. It sounds as though the perimeter of the home is the crawl spaces. Because they were additions built at different times they are going to be individual craw spaces, which makes your job a bit more difficult. A drain system is needed to keep the water out of your crawl spaces and out of your cellar. The drain system is a 4” drain tile (tube) buried in the dirt (greater detail can be explained by phone) along the inside of the perimeter foundation wall. This tile is then taken to a sump that pumps the water out and away from the home. Now if you have many different crawl spaces your choice is this, connect the entire drain tile to one sump (which means cutting through the foundation from one crawl space to the other- only a large enough hole for the tile) as long as the length of the tile does not exceed 180 ft then you will need two located in opposite ends of the home. Or you install separate sumps in each crawl space. Once the water is under control then it is time to seal the dirt.

If you do not plan to use these crawl spaces for storage you can use our 8 Mil DiamondBack™ to cover the walls and the floor. With the fieldstone foundation it is near impossible to completely seal the vapor barrier to the walls but it still makes a profound difference and it will give you the ability to control the moisture and humidity. Some of our customers that have a fieldstone foundation install the SilverBack® about half way up the wall and then use a spray foam insulation to seal the gaps caused by the uneven stones. If you have vents you will want to seal them up as well. Now you decide on a dehumidifier and plumb it into the sump. We recommend the OcarAir. We also carry a 45 Mil that you can put down on the cellar floor to keep the moisture out there as well. The benefits are clean dry crawl spaces, clean dry air, NO more bugs eating your home, no more rot and no more water.

This may sound like a lot and it is but any attempts at a shortcut will result in this problem becoming your hobby. I hope I answered your question. If for some reason I did not or you have others please send me another email or call our office (toll free 877 379 7658) and schedule a time we can have a phone conference so that I can better understand your problem. I want to get you the right advice.