I have had my crawl space encapsulated. It has made a big difference in the air quality inside the home (80 years old). However, I am now seeing cracks throughout my home in the walls closer to the top half of the walls and also on my fireplace brick. It has been approximately two - three months since having the encapsulation done. My concern is the cracks seen in my fireplace - the walls I can fix but the fireplace is pretty much a 'fixture'. Is the age of my home so old that the encapsulation is doing more damage then good? Do I need to be concerned, especially with the fireplace now having a 'Z' crack going on? Also, when will the 'cracking' stop...lol. I appreciate all those who can help me with these questions. Asking someone in the 'foundation' business around where I live brings all kinds of 'issues' that may or may not be true issues. Thanks!

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    Encapsulation of a crawl space, bringing it within the building's heating envelope, would have no immediate impact on the stability of the structure. Feb 20, 2017 at 3:05
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    The explanation I have seen of 'encapsulation' is that it provides moisture control but not temperature control. The most important element is a polyethylene sheeting vapor barrier on the soil surface in the crawl space of a pier and beam foundation, but an enhancement might include mechanical dehumidification. If the encapsulation lowered the moisture content of the sills, beams and joists, could that significantly change dimensions? It doesn't seem likely. Could this raise the soil moisture content enough to shift the foundation? Feb 20, 2017 at 18:02
  • Were any drains placed under the poly sheeting? Where is the property located? What is the soil type? Feb 20, 2017 at 18:07
  • Thanks much to each of you - There is a dehumidifier installed set at 55-60%. Tehre were no drains placed under the sheeting. The property is in Southeastern Virginia - Hampton. There is sand under the poly sheeting.
    – Robin
    Feb 21, 2017 at 23:44
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    @JimStewart encapsulation brings the crawl space within the building envelope, presuming it is completely sealed, and appropriately vented so that air from the living space is drawn into the crawl space. This does control humidity, by making the humidity in the crawl space identical to the humidity in the living space. It isn’t just a matter of laying polyethylene on the ground, it is also run up the walls, and all of the seams are completely sealed, completely separating the crawl space from the soil. Oct 14, 2020 at 15:38

2 Answers 2


Encapsulated? I assume you had rigid insulation boards added to the interior side of the foundation walls. If there were foundation vents, did you have them sealed? If not, water could blow in and get trapped between the inside of the foundation wall and the new rigid insulation. It could then freeze and expand. I doubt if it could "move" the foundation wall, unless it could run down and get under the footing. (Some footings are "L" shaped not "T" shaped.) Water may have blown in the crawl space in the past, but it was dried out with the crawl space vents.

By the way, we always design walls so that the bricks are stronger than the mortar. That way, when the wall settles, the mortar cracks, not the bricks. The mortar can be repointed (scraped back a bit and refilled with mortar.)

  • Thanks Lee - so the fireplace mortar is what is cracking (along with the interior walls...). I have crawled under the house and the company did a good job based on what I have learned - I am just concerned with all the cracking going on especially the fireplace. Do I need beam sistering to add support?? If I am worrying for no reason, please let me know - When will the cracking stop :-) Thank you again!
    – Robin
    Feb 21, 2017 at 23:48
  • Lee - Yes the boards are on the interior walls, vents have been sealed and crawl entry areas are sealed with doors.
    – Robin
    Feb 21, 2017 at 23:51
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    Encapsulating a crawl space to me means insulating the perimeter foundation walls and placing a vapor barrier on the ground...but not insulating the floor over the crawl space. Is this what happened? If so, what has happened is that you've significantly reduced the moisture in the crawl space. By blocking the crawl space vents, you've change (raised) the temperature in the crawl space (in the winter) and probably raised the temperature in the house, thus the increased quality of air you described, but I doubt any of this could crack walls and fireplace.
    – Lee Sam
    Feb 22, 2017 at 1:53
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    Rather, I suspect an outside force. Has there been other construction in the area? Underground sewer construction, road construction, equipment parked on or near your property (house), tree removal, can all contribute to changing the soil conditions enough to cause the house to settle. If you live on a slope, construction above or below you can make the soil shift. Houses of that era did not have a lot of reinforcing in the footings and they didn't worry much about earthquakes or tornados. Have any of these conditions occurred?
    – Lee Sam
    Feb 22, 2017 at 2:02
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    You can't add wood beams (sistering) to support masonry...not code allowed and it would take a HUGE beam. Cracking masonry is always movement...up or down. If not settlement (no construction in the immediate area,) then the ground could be heaving. Do you live in a clay soil area? Has water been diverted around this area? Any pending water around there? (Water can seep into the ground in one area and migrate to this area and affect the soil.)
    – Lee Sam
    Feb 23, 2017 at 18:12

I realize this is an older question, but the "community" bumped it back to active. Sorry Robin, but encapsulation is only a good idea for crawlspaces in the arctic and only a bad idea anywhere else.

The encapsulation problem is that it suffocates the ground and forces all moisture to the perimeter...where the building's structure is. I believe it should've never been done and has greatly increased the humidity within the walls (including foundation) as long as the encapsulation remains.

What should've been done is to simply insulate and vapor barrier the bottom of the floor joists. This, seals out the moisture and temperature changes while still letting the crawlspace breath and dry. The only thing that should've been done to the crawlspace itself is the addition of more venting for improved breathing and drying.

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