Structural Engineers

Category: Forensic/Foundation and Structural Repair Engineering

Why I Think Crawl Space Encapsulation is Unnecessary

Typical Crawl Space Encapsulation from Basement Systems

In my work with foundation repair for houses, I run into a lot of marketing hype about crawl space encapsulation.  Encapsulation of a crawl space is done generally by laying down a very thick water proof membrane across the bottom of the crawl space and up the walls.  The crawl space is sealed with this membrane, all the vents are closed.  A dehumidifier is put in the encapsulated space to make it dry.  It makes the area very nice to enter into, it’s clean, dry, and bright (the membrane used is always white).  It’s easy to move around in because you’re not crawling in dirt and trash like you find in many crawl spaces.  What I like about the system is you get a really dry crawl space that is free of mold and other issues.

The problem is it is really expensive.  The other problem, which is not an issue with the system itself, is it often sold to unsuspecting homeowners as a solution to problems totally unrelated to crawl space moisture, or they are not properly installed.  The worse case I’ve seen was when a salesman tried to sell a homeowner a crawl space encapsulation system as a solution to cracks over a large archway – which were caused by a header beam that was too small.  The homeowner would have spent $25,000 to for a “solution” that would not solve the problem.   

The other issues I’ve seen is encapsulated crawl spaces put in without attempts to solve the incoming moisture problems in the crawl space.  If a crawl space is flooding, you need to take care of that with drains/sump pumps and so on before encapsulating.

So, other than improper installation, is it worth it to encapsulate your crawl space?  I’m going to run through the logic of it in this article and let’s see where it takes us.  Also, for a contrary view, please watch this excellent video.

First off, we want encapsulation to cut down moisture, water infiltration must be solved separately.  Moisture presents problems in crawl spaces when it condenses on the underside of the floor and insulation.  Once the moisture condenses into water droplets the wood floor can rot, insulation loses its insulating value and begins to fall, mold grows, and a great environment is provided for termites.

What makes the moisture condense?  When the temperature of the air goes below the dew point moisture comes out of the air and will form on solid surfaces.  That’s why in the summer when the temperature goes down at night you will find dew on the grass, your car, and other surfaces.  The same happens in your crawl space.  In the summer, warm moist air will come into your crawl space, and it gets cooled by your floor system (which is cooler because of your air conditioner).  Moisture then condenses on the surface of the underside of your floor.  In the winter, you have cold air come in, and warm moisture migrates through your floor, comes in contact with the cold air, and condenses.

The traditional solution is to provide ventilation in the crawl space, and place a vapor barrier such as a sheet of polyethylene plastic over the floor of the crawl space (which is almost always dirt).  This is supposed to circulate air through the crawl space, which lowers the vapor pressure in the crawl space, which allows the condensation that forms a chance to evaporate.  The plastic on the ground is supposed to keep water in the soil from evaporating into the crawl space and increasing the humidity.

Vapor pressure is the pressure in the air formed by the evaporated water (it can be any evaporated liquid, like gasoline, but we’ll focus on water).  When the vapor pressure is at its maximum, the air is saturated with water, and water can no longer evaporate.  If we circulate air into the crawl space with a lower vapor pressure, we can evaporate the condensation.  What’s important to know is that warm air has a higher vapor pressure than cool air.  So, if we hit maximum vapor pressure on air at let’s say 50° Fahrenheit (10° Celsius), it is at 100% relative humidity.  If we heat that air up to 70° F (21° C), our relative humidity will be much lower.  The air is dryer now, which is why your house is so dry in the winter.

The argument given by proponents of crawl space encapsulation is that when we ventilate a crawl space, we are bringing in more humid air, which adds to the condensation.  In the winter that doesn’t make sense, because the cooler air will cause the condensation that forms to evaporate quickly, because that cooler air is heating up in your crawl space.

What about summer?  Here we are bringing in warm air that is high humidity, and we cool it down in the crawl space.  Yes, that’s a problem.  You could argue that air movement from the ventilation would keep the vapor pressure down, which will evaporate any condensation.  This is the argument I’ve seen for crawl space fans.  I’ve recommended crawl space fans be put in, and they seemed to work well.  However, to really know you must observe them operating over time.  Also, if we have a wet day where the outside temperature is close to that of the crawl space, you are not getting any advantage from air circulation, since you are circulating saturated air throughout.

So, I think we’ve got some good logic for encapsulation.  The other question I have is, can we go short of crawl space encapsulation?  What if we place a vapor barrier on the ground, and put in a dehumidifier?  In such case, we need the crawl space vents open to comply with Code.    I’ve seen this work well on one job where we had serious warping issues in the floor due to humidity in the crawl space.  However, to make a judgement, we really need to do a controlled experiment of a number of houses.  I think this makes sense because in crawl spaces I’ve entered where water infiltration is controlled, there really isn’t a moisture issue.  So, encapsulation could be overkill.

Now, if we do encapsulate a crawl space, the cost of the membrane installation is very high.  Also, to comply with the latest Code, the following requirements must be met in Georgia:

  1. Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall or insulation; and
  2. One of the following is provided for the under-floor space:

     2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1103.2.1 of this code;

    2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2 of this code;

    2.3. Plenum in existing structures complying with Section M1601.5, if under-floor space is used as a plenum.

I haven’t seen any of this done in the encapsulations I’ve examined.  All of the encapsulated crawl space I’ve looked at were totally sealed, which is a violation of Code in this state and most other states that use the International Residential Code or its variations.  That doesn’t mean the system is bad though, it means you need to assure your contractor is following the Code.

Based on the above, I don’t think crawl space encapsulation is bad.  You must solve the water infiltration first, you don’t encapsulate a wet crawl space.  Also, the encapsulated crawl space must be ventilated.  My issue is, is it cost effective compared to a simpler method of controlling water infiltration, a vapor barrier, and possibly a dehumidifier?  In my opinion it isn’t.

I’ll go one step further.  If you have problems with moisture in your crawl space, you have the water infiltration problem anyway.  Laying plastic on the ground in your crawl space isn’t expensive at all.  A dehumidifier is not prohibitively expensive either.  If that solution doesn’t work, you won’t be spending much more to come back and encapsulate the space.  You are going to be out the minor expense of laying plastic on the ground, and possibly a few hundred for the dehumidifier if the contractor won’t leave it in the encapsulated space (which it can be, there is no “special” encapsulated crawl space dehumidifier).

Therefore, I will almost never recommend encapsulating a crawl space when I make a structural assessment.  It’s an expensive solution that may not be necessary.  Now, if you are a contractor that puts in these systems and you disagree with me, please send a rebuttal to me at georger  My opinion is not written in stone, and I am interested in counter arguments.  


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This (Really Surprising) Old House

Our company does a lot of structural condition assessments of residences, oftentimes for Architects when there is a planned major renovation of an old house.  The City of Atlanta requires an engineer to evaluate the foundations of old homes if a second story is proposed, because there are often problems with the existing foundations.  This house was at first unremarkable, it was an old home in the west side of Atlanta, and was a fairly standard small home built in the 1920’s for working class people that had employment in the cotton mills and factories that once dotted the City.  However, this one had a surprise.  Let’s look at it:

House view from side.

House view from side.

View of house from front

View of house from front

It was just what we call a “shotgun shack”, it was an old duplex that had been subdivided into apartments as the neighborhood got poorer.  I was surprised though when I looked around the side20170512_115649

Notice the subwall is stone – that was not typical of these type of houses.  Usually they didn’t have subwalls, they had brick piers and were open underneath. You usually see concrete block that was placed around the brick piers at a later date to close in under the house and add some space for storage and usually a washing machine.  Also, what was the deal with the blocked up window? Around back  the subwall changed to block, which was odd:

Block placed at the back of the house.

Block placed at the back of the house.

I thought the whole thing was rather unusual, but the answer came when I went into the basement.  I found this:

Doorway to old house.

Doorway to old house.

The house had been built on top of an older stone house!  The stone house underneath has to date back to the mid 1800’s.  It’s rare to find such things around here, most of the older homes were built of timber, which is long gone.  Apparently when they built the shotgun house, there was an old house already on site, and the builder just built on top.  Here’s some more photos:

Interior of older house - note the old window that was blocked in.

Interior of older house – note the old window that was blocked in.  Very impressive stone masonry around the windows.

The front corner - note the newer stone work - it is under a fireplace.  Also, we see a window blocked in.

The front corner – note the newer stone work – it is under a fireplace. Also, we see a window blocked in.

Old timber used to support first floor - this was also salvaged from even older buildings, it is rough sawn.

Old timber used to support first floor – this was also salvaged from even older buildings, it is rough -sawn.

Another view of the recycled timber.  The workmanship here is very poor, unlike the workmanship on the original stone house.

Another view of the recycled timber. The workmanship here is very poor, unlike the workmanship on the original stone house.  The builder simply stacked stone and set the timbers that he salvaged on top.

I have seen the older homes containing salvaged timber, that is rather common.  Reusing timber from old houses or barns that were torn down would have made sense to the builder.  The cost of materials vs. labor probably was more in favor of using the labor and trying to save on materials.  Hopefully the investor that bought the house and the Architect will make use of the old house in the basement and make this a more distinctive house.  This is one of the most interesting homes I’ve ever visited.


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Worst Basement Failure Ever

I was going through my photos this morning, and I found this one:

Basement Subwall Failure

This was the subwall in an apartment building.  The building was built back in the 70’s, and was built as part of a development of low income apartments.  If there is ever a case for proper building permitting procedures, these types of apartments in the Atlanta area make it.  In every one of these buildings it appears to me that there was almost no structural engineering, the foundations are often minimal or non-existent, the structure is all wood and all of the members are overspanned, there is no consideration for wind bracing, and as you see here, the subwalls are never strong enough.  I suspect all that was done for the design was a floor layout, some elevations, and that was it.

It also appears that there was no inspection in most of these because the errors in construction are often so extreme that even the most inexperienced building inspector should have caught them.  I always wonder how this worked.  I assume the that at the time the builder submitted the floor plans and elevations, fees were paid, and the permit was issued and that was that.  I suspect there was no inspection at all, or maybe just plumbing and electric.

In this one the subwall was not reinforced properly, the site wasn’t drained properly, and there was not a working underdrain system.  As it rained, water pressure built up against the outside wall and we had a catastrophic collapse.  Fortunately, no one was hurt.  Sad thing is, I have been in one building where a tenant was seriously injured in a failure  – while he was in bed the ceiling collapsed on him.  The ceiling was not nailed to the joists above, it was glued.  In time the glue deteriorated and the ceiling fell loose and seriously injured the person below.

View of Outside – Note the bracing.

The brick wall in in danger of collapse.  By this time the building was condemned and apartments cleared out.  It could have been much worse.  The repairs were done (by replacing the subwall with an engineered one) and the building put back in service.

Every time I go to the old low income apartment buildings I come back away irritated.  The shoddy construction is downright criminal, and shows a total lack of concern for the people that live in the buildings.  The structural problems are many, and in addition the bathrooms are never adequately designed to contain the moisture.  In every building of this type you will find rotted wood all around the bathrooms.  This is not only a danger for the structure, but presents a great place for mold to grow. Also, the windows are usually improperly flashed, so you will see moisture in the structure around the windows – again, causing structural issues and mold.

How was this allowed to happen?  Were the building officials corrupt?  Were they incompetent?  Were they racist (figuring it was primarily minorities that would live in these buildings and thus they didn’t care)?  Was the system itself too lax?  Most likely it was a combination of all.  The sad thing is it hurts people that have no other options in life.

By the way, every time I go to these buildings I talk to a lot of the people that live there.  They don’t seem like the stereo type “welfare recipient/drug dealer/thug” to me.  All of the ones I’ve talked to just seemed like regular people, the kind you’d be happy to have as a neighbor.  They have jobs, families, hopes and dreams.  They just are poor.  That makes it even more irritating to me.

Above all else, it shows how when people don’t do their jobs, it can seriously hurt other people.



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At What Point Do You Do Structural Repairs?

A lot of houses I look at have issues with settlement in the foundations and floor slabs.  A lot of times I only recommend cosmetic repairs.  Why is this?  If the house has settled, should you put in piers under your foundations to stabilize it?  Not always, and here’s my rationale:

In many cases I am looking at houses that have been in existence for 20 years or more.  The settlement is often rather minor, and can easily be hidden with simple cosmetic repairs like spackling cracks in the drywall, and filling cracks in exterior mortar.  Let’s say the repairs cost $200.  Usually settlement occurs at its maximum in the first five years or so of the life of the house, from there the settlement never really stops, but proceeds at a much slower rate.  So you would have to do cosmetic repairs on a fairly regular basis – maybe every two years or so.

Generally, it takes at least two foundation piers to repair settlement.  With a budget of about $1,100 a pier, the cost of the repair will be at least $2,200.  How many years will it take for your regular cosmetic repairs to be greater than this cost?  It will take 22 years!  Now with more severe cracking, recent settlement, or if windows and doors are affected, the piers are the best option.  However, in many cases it doesn’t really make economic sense to put out that kind of money.

The other issue is floor slabs.  Often garage slabs are built on soft soil, and they settle over time.  It costs about $6,000 to $8,000 in Atlanta to replace a two car garage floor slab.  If your garage slab has settled about 1/2″ towards the center, and only has minor cracking, do you really want to spend $6,000 to $8,000 for a room that you park your car in and store all your junk?  I wouldn’t.

So, oftentimes I give people the option in my reports – you can do a permanent repair for X amount of dollars and this will happen, or you can cosmetically repair the issue for Y amount of dollars and this other thing will happen.  It often times boils down to economics and personal preferences.


In this case, the cracking is probably due to minor settlement. It would require at least three piers to repair ($3,300), or you could reparge the block every couple of years for the cost of a bag of pre-mixed mortar..

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Here’s a Good One!

I just got back from checking out a foreclosed house, and I am always surprised at what stuff people do to houses.  Look at this:

Do you know what it is?  It’s a WINDOW through the basement subwall.  The only thing holding the dirt back is the geo fabric that you see.  Obviously, it’s not working so well, the floor of the basement is covered in mud.  When I was in college, a couple of friends of mine and I were discussing the idea of underground houses, and one of my friends said they weren’t a good idea.  If you opened the windows, dirt would come in.  Well, here they opened the window to the dirt.

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Floor Slab Settlement – Look Out!

Floor Slab Settlement

This house looked like it was OK, but a closer examination and some experience shows a severe problem – very severe floor slab settlement.  The floor slab was poured on uncompacted fill – soil that was not tamped down properly when it was placed.  Over time the soil under the house settled, and there is now some very severe floor slab settlement.  It is so bad that the house probably will have to be demolished.  Look at the video and see whether you think you would have seen this.  This a good reason a inspection by a qualified home inspector before purchase is critical.

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Fire Damaged Trusses

This is a fairly simple fire damage job we were called to do the fire was concentrated above the ceiling and damaged the top chords of the trusses.

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The House of Pain

Every now and then you come across construction that is so bad it takes your breath away.  This house is the most extreme example that I’ve seen.  It’s not uncommon to see shacks out in the woods put up in a haphazard manor, usually that’s because the people that are putting them up have very little money, so they get stuff to build with as they can.  They also have little in construction skills and can’t afford to pay contractors to do the work.  This house was in a very nice suburban neighborhood, and actually looked somewhat OK from the street with the exception that it was on temporary power.  It hadn’t gone to permanent power because it hadn’t passed any inspections and there was no certificate of occupancy.

The homeowner called me because the county had shown up with an order for them to vacate the property.  Apparently they had bought the property “as is”, and they wanted to sue the seller.  I was asked to do a report on the property, and I knew immediately after I entered the house that I’d never get paid for my work.  However, curiosity took over and I did the evaluation, wrote a lengthy report, and of course got stiffed for the fee.  I never did find out what the final disposition of the house was.  I talked to one of the senior county inspectors about it, and he said the house had changed hands numerous times and the ownership wasn’t too clear.  That should be expected, because it’s hard to believe any financial institution would lend for something like this.

While this is an extreme example, there are a fair number of houses out there that have similar defects.  Towards the end of the housing boom a lot of people jumped in to build houses that shouldn’t have, and many of the foreclosures on the market have very significant construction defects.  What looks like a bargain price may be in the end an expensive transfer of misery.

Let’s start from the outside:
Rear of House

This is in the rear of the house – where do you start?  The stucco is totally jacked up, look at how it’s peeling from the house.  There are no joints in the stucco.  The deck is made from untreated lumber and is not supported correctly from the post.  There should be a concrete landing outside the door, and there is no drip edge under the stucco.  The paint is peeling off the windows, there is excess erosion, and it’s not a good idea to leave trash around your foundation, it attracts insects and vermin.

Garage entrance
No gutters, the roofing is sloppy, look at the garage door opening, it’s a mess too.  The difference in color of the stucco is due to lighting, it doesn’t actually have multiple tones.  Here’s a close up of the electric meter:
Electric meter
The holes are supposed to be sealed to keep the weather, insects, and rodents out.  I don’t think that meter was hooked up by the way.  Let’s go inside, it gets much worse:
Living room
Ok, the wallpaper is peeling off.  It also is two clashing styles.  The house was moderately messy, I’ve seen worse.  It was the rotting garbage in the sink that made it uncomfortable, but we’ve only just begun.

Let’s go up into the upstairs:
Yes the wires are hot
Yes, those wires are hot.  In the upstairs they didn’t finish the wiring, and it was hanging out of the junction boxes and fixtures.  By the way, the wires aren’t supposed to be all the same color.  Typically black is hot, white is neutral, red is hot, green is ground.  That’s so the electrician can wire things right and you don’t get electrocuted in your shower because the wrong wire was grounded.  Now we better go up and see what awaits us in the attic:
Attic 1
No junction boxes, the condensate piping is all wrong (note the tees are in for some unknown reason).  The framing is chopped up, and water damage is apparent in the right side.  How do you like the way the wiring is wrapped around stuff?

Attic 2
I couldn’t for the life of me figure why the vent pipe had the tee in it and branched out through two different outlets on the roof.  Note the wire that was used as a support.  The framing is completely wrong, and space doesn’t permit me to outline everything.  Note how the rafters aren’t properly supported at the bottoms, and the purlins are wrong too.
Attic Framing
Look in the rear of the photo wher the braces for the roof come down onto the beams.  There is nothing to keep those beams from twisting, which they will ultimately.  The framing is more or less randomly done.  Note the orbs in the center lower right – some believe those are spirits caught on film.  I think they’re dust particles, but maybe being confined to this attic is some poor soul’s punishment for misdeeds in a previous life…

More Random Framing
More random framing in the attic.  Note the ceiling joists seem to be placed with no rhyme or reason.  Also, look at the lower right and see the water damage.

Really Bad Wiring
We can’t stay in the attic forever, so we’re going downstairs.  But first, look at this wiring – it is sandwiched between the floor sheathing and ceiling joists.  That will wear the insulation off the wire and start a fire ultimately.  Although it will be a race between that and all the other wiring misdeeds to see which one will ultimately burn the house down, if it doesn’t fall down first.

Now, before we go in the basement, I want you to look at this shower:
This is the shower.  I’ve seen worse, but usually in places where the people are really poor, or in third world countries.  I wouldn’t step in here barefoot though.  However, look at the underside:
Under Shower
The shower doesn’t connect to the house sewer.  It just drains into the basement.  That sewer line slopes upward by the way.  They kept a plunger by the toilet to help things on their way.  Now, even though the shower didn’t drain into the sewer, the people here in this house were very clean.  Look:
They showered and bathed anyway!  Look at the water in the basement, AND the black mold.  The sheet rock was put up to cover worse mold behind it.  I am highly allergic to black mold, and I should have left.  However, like watching a train wreck, I couldn’t turn away.  I ignored my sinus pain and kept on…

While bathing may be healthful, it probably is risky in this house.  The rotten floor joists are under the tub and you might make a very quick trip to the basement.

Rough in Plumbing
Ok, they were roughing in a bathroom in the basement.  Look how close the sink drain is to the toilet.  That way you can sit on the throne and do your business while you brush your teeth.   The pipes were above the floor slab, so they never finished.

Water heaterWater heater 2
Part of the basement was bare ground, and that’s where the water heater was set.  The installation wasn’t quite completed.  Note the there is no pipe attached to the temperature and pressure valve, and the panels were left off.

Well, we’ve been here long enough, and just looking at this makes me have an allergic reaction, so let’s go, but…
The Stairs
Be careful going up the stairs.  These look like something you tried to climb in college after a night of heavy drinking, don’t they?

I hope you’ve enjoyed your visit in the House of Pain.  Please don’t buy anything like this.  If I find out what happened to the house, I will update this page.


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The Horror of Termites

I have done structural evaluations on a lot of homes where there was extensive termite damage, but this one I had a some time to do some extra exploration.  I was working on a separate problem in the house, and while there some blistering of paint on a window sill was discovered.  The contractor was asked to pull it up, and SURPRISE!   There was extensive termite damage.

On this one, we had time to do some poking around, and we did a bit of experimentation to see just how well termites can hide from site.  Watch this video:

Notice how well they have concealed themselves?  If you had banged on that piece of timber with a hammer, it would have felt solid.  Also, if you probed it with a sharp object, you probably would have felt anything.  Note, we had to pry in there with a wrecking bar to find the damage, which was extreme.

The termites left a nice shell of preserved wood to protect themselves and hide their presence.  They had no visible mud tunnels, they got in to the wood through the wall, which was backfilled with soil (which is against Code btw, but this was done a long time ago).   In the end, I checked the crawl space by taking a drill and drill holes all around the perimeter.  We found other damaged areas, but fortunately for the homeowner, nothing that needed serious repairs like are being done here.

The worst house I’ve seen is this one (it’s a foreclosure):

Sagging Floor

The joists holding up the floor above are completely destroyed by termites, the floor is sagging under its own weight.  The timber is so thoroughly destroyed that it is the vinyl floor covering holding up the floor.  I discovered this when I walked on it.  Fortunately I was able to run off of the floor before making it collapse.

This house was built in the seventies, and it appears that the roof may have leaked for a long time, which fed the termites moisture.  Here’s a picture underneath:

Floor Joists Damaged By Termites

The photo above is rather confusing to look at because of all the hanging insulation, white mold and rotted wood, but it gives a good indication of the damage to the structure underneath.  Note how grey the subfloor is – it was heavily rotted.

For a house to get to this kind of condition, extreme neglect is required.  I’m not sure how the occupants lived in it.  It was pretty nasty, and I was told it looked worse before the cleanup.  Foreclosures don’t always look this bad, but if you buy one at an auction you don’t get a chance to do a thorough investigation.  I would consider the risk, you wouldn’t have wanted to buy this house at any price.


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