Male worker dressed in a white coverall suite in a crawl space under a house with a white PVC vapor barrier on the ground.

In the small community of crawl space contractors encapsulations are all the rage. They do offer quite a lot of benefits, but I believe that those benefits need to be weighed accordingly before committing to such a large project. What is encapsulation? Simply put, encapsulating a crawl space means you seal the crawl space from the outdoors creating a conditioned space. Most crawl spaces in the North West are vented. That means exactly what it sounds like, it is vented and not sealed.

In a vented crawl you have a vapor barrier no less than 6mil in thickness covering the entire floor of the crawl. In an encapsulation the vapor barrier is still fastened no less than 12” up the wall of the foundation, but instead of overlapping 12” at the seams, you only overlap 6” and you seal the seams. This practice is the first step in stopping moisture from getting inside your living spaces.

Of course it is never that simple. When encapsulating you also need to install an interior drain system. To do this you dig a trench around the entire perimeter of the interior of your crawl space. Then you install drain pipe and to route all the water that does manage it’s way into the crawl to a sump pump and sump pump basin. The sump pump will then pump the water out of the home.

Now that you have the water being pumped out of the crawl space and you have successfully blocked moisture and soil gasses you need to condition the space. What that means practically is that you move the thermal envelope of the home from the insulation in the floors, to the walls of the foundation. This gives an entire conditioned space below your living space. That is what it means practically, but to execute that it is much easier said than done.

First you remove all the insulation between your floor joist as it is no longer needed and likely was nothing more than a place for rats to nest any how. Then you insulate the walls of the foundation with foam board. The foam board is installed before you install the vapor barrier, and is secured with epoxy and with concrete fasteners.

Your foundation walls are insulated and you have installed a interior drain system and vapor barrier in your crawl space, but it is still cold and damp. Of course it is, you have not sealed your space yet. We now need to seal all the vents in your foundation, leaving one open for a crawl space fan that will run non stop creating negative pressure. Seal the sill plate to the foundation wall with spray foam or caulk. Insulate the rim joist. And finally, seal any and all penetrations with spray foam.

Finally, you have encapsulated your crawl space! True, it is encapsulated at this point. But is that everything? Maybe to some. But is this a conditioned space? No not really. Now you need to install a dehumidifier and ensure that your condensate line goes to your sump pump or all that moisture you suck out of the air will just go right back into it. Some contractors will say to just put your HVAC vent into it but I do not recommend that. Your HVAC system was not designed for the added square footage and your system also does not run at all times or manage humidity like a dehumidifier does.

Who is encapsulation for? Well that is a loaded question as it really is the best thing for your home. It significantly cripples the growth of mold. It controls the humidity in the rest of your home and increases air quality, and if dimple board is installed below the vapor barrier you can now use your entire crawl space for storage. So why is it not for everyone? It is expensive. Quite expensive when compared to traditional crawl space methods. It is not maintenance free. Now you have a sump pump and a dehumidifier to add to your list of home service needs. The benefits may also not outweigh the cost for everyone.

So why would anyone do it? You just told me it is a lot of work to do, it is expensive and it requires maintenance. If you are sensitive to mold, have an auto immune problem, allergies, or really need the storage, encapsulation is probably a good thing to have if the pocket book allows it. It is also probably something you should consider doing if you live in your forever home and getting the return on your investment is not always your top priority. People who will notice the most drastic differences are of course those that started with really damp crawls and homes with moisture problems. The maintenance is not really THAT bad, just make sure you get eyes on your system every 6 months or so and address any problems right away.

What does a proper crawl space encapsulation have?

  • Insulated foundation walls
  • Interior drain system and sump pump
  • Vapor barrier
  • Dimple board under vapor barrier if using space for storage
  • Sealed rim joist and sill plate
  • Sealed foundation vents
  • Dehumidifier