Crawl Space .... To encapsulate or no?

[Johnboy2978]

If this is the wrong forum, feel free to move. Wasn't sure where to post.

I have a 2 story house built in about 1978 in southwest Va. The crawl space is approximately 800 sq feet and is vented and a very tight space. Previous owners failed to put vapor barrier down to cover the entire area, so only about half is covered. Much of the back half which didn't have a barrier has wet and saggy insulation and I just recently had to get a termite treatment where I noticed they've taken advantage of the damp space.

I know I need to basically yank everything and do it right but I'm very confused about leaving it vented or going for encapsulation and enclosing the space. I know encapsulation can get pretty expensive and I'm not entirely sure that's the way to go, but this is pretty far outside of my knowledge base. I've googled the topic a bit and I see pros from those sites who make their business from doing encapsulations and cons from others. I don't want to go down that path and spend a lot of money if it's not going to be effective and if it's going to cause other issues down the line.

Anyone care to give me some experience in the area and a push in the right direction? It will certainly be appreciated.
Thanks

[pushkins]

If I was building from scratch and money wasn't an issue for the client I'd always reccommend encapsulated. A correctly installed encapsulated crawl is to have it sealed 100% on the ground and walls and there must be heating and cooling ducts installed or at the VERY least a dehumidifier. If there is going to be zero airflow then there must be a way of reducing the moisture content. Some of the best crawls I've seen (and I seen a lot) are encapsulated and heated and cooled, this doesn't mean that you have to keep it at the house temp. though that would be ideal, it means that via a HVAC line you can somewhat keep the moisture levels constant. A true encapsulated crawl also means removing the floor insulation to allow the conditioned air to circulate the entire space.
IMO it's seldom worth the money to try after the fact in most crawls to retrofit an encapsulated system, good installation of the vapor barrier and correct circulation of air via the foundation vents will give you more than adequate results.

[Johnboy2978]

Interesting. So in your experience, it's not worth the investment to try and get it encapsulated then. What has been your experience as far as the problems with a retrofit? So I guess my option based on your recommendation is to put a proper vapor barrier down, and redo the insulation? What mil vapor barrier should I be looking at to do it properly? What are your thoughts about TerraBlock (insulation and crawl space liner in one) such as that which is found at socosupply dot com ? What about a dehumidifier? I've always been a bit confused about the vents as well, that is when to open and when to close. Is around 40° and below the time to shut and above that, leave them open?

Thanks for taking the time to respond.

[pushkins]

One of the biggest problems with retrofitting them is the sealing of the crawl, when building new the sill plates are installed over foam strips. this seals the crawl wall to the sill plate a major place of air migration. A correct vapor barrier should be 6 mil. thick, it should cover the entire ground and be sealed to the piers (although adequate protection is given by cutting it in close to the piers and pinning it to the ground. The pins are a MAJOR part of a good vapor barrier install, too many times I see the plastic all pulled up in bunches due to cable guys, pest guys etc...
Vents open or closed ? 5 out of 10 people will agree on either side of the argument, my thoughts are (long as your not living in a heavy freeze zone are automatic vents they close at around 40F My belief is it's more important to get correct airflow, you should be able to feel a considerable temp. difference of the air leaving the crawl when you put your hand near the vent (cooler).
Dehumidifiers generally are a waste of money IF you have a good airflow there should be little need of one (I know many termite companies will try to talk clients into them at an overinflated cost) again if you have good airflow why would you need one ?
Unless you have water standing in your crawl (which is a whole different problem) a correct vapor barrier usually solves moisture issues in crawls at a minimal cost.

[Johnboy2978]

Thanks so much for taking the time to reply. I've got two different companies scheduled to come and take a look at the space and give me estimates. Based on their websites though, it looks like they're probably going to recommend encapsulation but both say they'll present the full range of options. Based on what I'm hearing from you, this sounds like a DIY job. I've bought 6 mil vapor barrier that I was planning on doubling to make it 12m but I haven't put it down yet until I hear what their recommendation is after seeing it. If the price is right I may just have them do it and install new insulation.

Most of the water that I see down there is directly under insulated duct work which I'm guess is from condensation. Again, I appreciate you taking the time to give some input.

[pushkins]

Do not double the vapor barrier (huge no no ) if you do that moisture will build between the two layers and eventually run out and be sitting on top of the barrier which is what your trying to stop.
The vapor barrier should overlap approx. 6".
6 mil is used ONLY because it has a strength value with people crawling around on it for example. technically speaking you could use saran wrap as it won't let moisture through either BUT it's so thin it would deteriorate very quickly.
Some thinking is that there should be a bare strip under the trunk line to allow condensation to be absorbed into the ground. (I have that in my personal home). The older trunk lines were insulated on the interior side and these condense considerably, newer trunks are insulated on the exterior side and have far fewer issues.

[Johnboy2978]

Thanks for the heads up. I didn't even think about that.

There's going to be about 4 joists that need to be sistered down there. The joists are about 12' in length but the entire length isn't bad. Is it acceptable to use a 10' length and attach it to the other as long as you have 2-3 feet of the original that is healthy?

[pushkins]

That's a tricky question as it would always depend on where the damaged section is, for example if the joist is damaged on both ends then the entire length must be replaced/sistered or if it is damaged from one end all the way up to 10' on the other end then again it should be replaced/sistered in entirety. Typically when sistering you need 2 - 3 feet past the damaged section on BOTH sides of the damage, the nails (screws are preferred) should be in sets of three spaced no further than 12" on center. Always use construction adhesive as well.

[Johnboy2978]

I had the first company to come and assess the situation and give an estimate today and they ball parked the fix at 12.5k for a 4 day job (pretty nice profit if you ask me). The recommendation was to put it drainage around the perimeter of the crawlspace (thought we were getting some water run off that was coming in from the vents being too low to the ground as well as humid air), sealing up all vents, complete encapsulation, and install of a humidifier. There was also a big "IF" they would even do it b/c the space is so limited (around 18" in a few areas) and the HVAC vents would have to be removed by an HVAC contractor before they'd do it.

There's no way I can see that I can justify that kind of money for this. I've got another company next week for an evaluation.

[pushkins]

A perimeter drain AKA as French Drain is effective IF you have water entering the crawl from the exterior, this is usually from poor grading around the house, grading should be a min. of 6" in 10' from the crawl wall. If it's rising ground water then a french drain will do little to dry your crawl, then the best option would be a sump pump in the crawl (often two depending on crawl size), this in my opinion is seldom really effective UNLESS is it truly either a high water table or rising water due to frequent rains.
Check the grading around your home. does the yard slope towards the crawl ? is the house downhill from the backyard ?

[Johnboy2978]

I had a second company come in this past week to give an assessment. This company also seems to make encapsulation their bread and butter. The estimate came to between 8-10K depending on the vapor barrier applied. Essentially, it boiled down to sealing the vents and insulating the walls with silverglo (graphite infused expanded polystyrene insulation) and then applying a "cleanspace" vapor barrier. They have two grades of barrier, a 6 or 20mil which accounts for the cost differential. The price also included a $1400 dollar dehumidifier and mold remediation. These guys were not concerned about the HVAC vents and weren't asking for them to be removed like the first company.

His assessment was that we don't have water coming in from the foundation, but rather our moisture issues are due to humidity and the water coming up from the ground.

[pushkins]

If the issues are rising moisture and humidity then there is an avenue I'd be traveling WELL before I dropped 10K. A simple 6 mil vapor barrier overlapped 6" at joins, wire hooks holing it down and if you really wanted to travel the road, install two powered foundation vents (one either side of the home) these vents often have humidity gauges on them to turn on and off.
Buy yourself a cheap moisture meter (around $10) you can test the floor joists for moisture content, they shouldn't be more than 19% anything less is perfectly okay. Poke the prongs into a floor joist and see what the moisture reading is, do this at several spots around the crawl space, this will give you your best idea of just what needs to be done.

I'm not dissing on any company, there are times encapsulation is the best option but you always have to remember, companies that specialize in encapsulation make their living by selling "encapsulation" there's a high profit margin in it as it's mainly labor.
Kinda of like calling a tree removal company and asking them does "that" tree need to come down......."oh yes sir it most certainly does".......they make a living removing trees.

[Johnboy2978]

Believe me, I'd much rather spend $500 on a quality 20mil vapor barrier and spend a weekend putting it down myself than going down this road if that's all it takes. I tend to believe that what I'm seeing is the cumulative effects of the 40 years of the house not having any vapor barrier and the previous owner putting down half a sheet in the space you can see just before we bought the house.

If it's merely a combination of ground moisture and humid air that comes through the foundation vents that turns into condensation, then a quality vapor barrier would fix the ground issue. What would you recommend doing with the vents? You mention 2 powered vents on either side of the home. Is there a brand you recommend? My home has 8 vents now, would 2 suffice (~1200 sq feet of crawl space)? If so, would manually close/open the others depending on the outside temp?

[pushkins]

You need 1 square foot of ventilation / 150 square feet of floor if the area is NOT covered by a vapor retarder and only 1/1500 if it's covered with a vapor barrier. that is code, however that said, the better the air flow regardless of barrier or not the better condition of the crawl. I treat all my additions and builds on the 1:150 rule and they are ALL covered by a vapor barrier now by code. Remember also a 8x16 foundation vent is not .88 square feet of free opening, safely estimated it is 1/2 square foot of free air space, also a vent be it foundation of attic will only work if it has the ability to pull an equal amount of incoming air as it is sending out, for example a 1500 square foot crawl that has one square foot vent and covered by a vapor barrier is a total waste of time the vent needs to source an air supply to work, like a straw in a strawberry thickshake, if the straw gets a berry stuck in the end your not sucking anything up

Again, get yourself a moisture meter and test several areas in the crawl for the wood moisture, this will give you the best view of just what condition it is, anything under 19% is ideal, don't test directly in front of a vent opening

Oh almost forgot, a foundation vent must be installed with in three feet of any corner of the foundation, regardless of how many others are installed, all to do with circulation of air, you don't want to create a dead air space.

[Johnboy2978]

Puskins I greatly appreciate your time and advice on this topic. I've posted this question in another forum and one member suggested Installing fit sheets of polystyrene below the joists, boxing them in, fit plastic sheet below the polystyrene, making sure to block all holes and cracks, with tape and canned foam.
Have you seen this and would you recommend it? I thought this was a definite no-no that traps moisture in the cavities and ends up rotting the joists. Thoughts?