Crawl Space Moisture Management_Encapsulated Crawl Space

[HMH]

Hey folks,

I've picked up enough knowledge from this site, outside of general woodworking, to know that several of you are pros in the construction field as well, and though I'd ask some collective advise on an upcoming home project.

For a little background - we moved into our current (forever?) home roughly 18 months ago after searching for some time for either land to build on, or the "perfect" existing home w/ access to acreage. We were lucky enough to find our place at a great price, needing a little work here and there to bring things up my standards, but I kind of enjoy that side of things anyway, (I'm a structural engineer by trade), so it has worked out well thus far.

I did a thorough inspection prior to purchase, and had a list of projects that I knew needed to be addressed at some point, one of which being the crawl space, (damp, dirty w/ an existing vapor barrier in need of replacement). Fast forward to last fall, my wife mentioned a musty smell in her reading nook off of our bedroom, that I initially didn't think much of, but one afternoon a few days later, while replacing the HVAC filters (in the afternoon vs. at night which is usually when I find time to do such things), I saw daylight when I opened a small return grill in that room - no bueno. I got into the crawl space, (of course at the opposite end of the house from the access door, and noticed that the duct had fallen away from the register. I fixed that, and went through the rest of the ductwork the following weekend, taping several other areas I found that were partially separated, (learning to wear gloves when working w/ foil tape in the process - that stuff is sharp!)

In addition to the seam issues mentioned above, the ductwork itself (flex-duct) was heavily condensated in some areas, and "heavy" like moisture was trapped between the inner duct and the insulation itself, which I assume to be from the "blow-by" of the leaking seams getting between the 2 layers and condensating internally. As is typical, the first floor ductwork is under the floor, and I found all sorts of construction debris i the duct when reaching in from above as well, so in light of all of the above, I've decided to replace the first floor ductwork completely in the Spring, (when the weather permits going w/o HVAC for a few days).

Before I replace, (or have replaced), the ductwork, I also want to trace the root source of the condensation. We have a relatively large home, w/ approx 2000 sq. ft of crawl-ranging in height from 5' to 2.5, w/ typical foundation vents. I've installed a couple remote humidity monitors at opposite corners of the crawl, closed the vents, and put in a few box fans for circulation over the winter, and have noticed that the humidity levels are still pretty high, even w/ the low ambient winter humidity, and spike after a rain, leading me to believe that there may be some benefit to routing the downspouts away from the foundation as well.

To resolve all of the above, and also to help w/ making the home more efficient, I am heavily researching encapsulating the crawl space, w/ new rigid insulation on the inside face of the CMU, and pulling the batt from the joists - does anyone have any experience in this arena?

A quick search for "order-of magnitude" pricing to encapsulate a crawl-space quickly led me to discover, that this will be a DIY project for the most part, (not that I blame the contractor's pricing - hanging out in someone else's nasty crawl-space for a few days doesn't sound like much fun to me either).

My proposed project sequencing is as follows:

1. Trench and run lines to re-direct the downspouts 10' or so away from the foundation.

2. Remove the existing flex duct in the crawl space, and replace w/ new.

3. Seal the existing foundation vents, and install 2" RI to the inside face of the CMU, (leaving the req'd/ 3" termite inspection gap at the sill plate). I'll either pack the rim joist w/ batt, to include the termite inspection barrier, (the batt can always be pulled back for inspection, or look into having the cavity above the sill insulated w/ spray-insulation, and adding in a removeable 3" strip of RI to cover the inspection requirements.

4. Pull the existing batt between the joists, and seal all penetrations through the floor.

5. Line everything w/ a new 10mm vapor barrier, to include walls and piers.

Please forgive the long post - just trying to get all of the pertinent info in. If anyone has gone down this road, either as a homeowner or as an installer, I'd love to talk to you! Also, I wouldn't mind a "sanity check" from the group to make sure I'm not way over-doing it here. I understand that vented foundations are, and have been, around in the South for decades, but I also know that construction methods and bast-practices evolve, and am of the "if you're going to do something - do it" camp. Coupled w/ the above, I do have 2 young boys, on of which is asthmatic due to pre-maturity, that is heavily weighing my decision making here as well.

Thanks guys - looking forward to the advise.

 

[rcarmac]

When I purchased my house a couple of years ago, it had a sealed crawl space. However it was constructed a little different. For mine, I have a vapor barrier, maybe 10 mil but I am not sure. As a side note, I spec out products for large public products such as schools. On those type projects I spec 15 mil vapor barrier under the slab. Might be something to think about is to price 10mil against 15mil. So anyway, I have a vapor barrier down on the ground and then on the foundation walls is sprayed a closed cell foam insulation. That helps in 2 ways as it insulates the walls and creates a vapor barrier on the wall. A mechanical duct was placed in the crawl space to basically move air around. No insulation in between the joist is needed since I basically have a seal / insulated / conditioned crawl space. So that's the crawl space. I also have drains on 3 sides of the house that helps move the water around the foundation. If you do plan to seal the crawl space, make sure you do some type of radon testing. If you have some high levels of radon, at least it can escape though foundation vents. If you seal the entire crawl space, hopefully all your seals etc. are good enough to seal out the radon. You might need to consider some type of radon mitigation systems so it is not trapped. Also most vapor barriers on just taped on to the foundation wall. Taping is need, but using some mechanical fasteners is also good so you are not 100% depending on the tape. Let the mechanical fasteners hold the barrier and the tape just seals the top.

If you do install rigid insulation, make sure you tape all the joints. When I use rigid in commercial walls, we spec for it to be installed in layers. So for you case I might consider installing (2) 1" layers so you can stagger the joints as well as tape all the joints. When you stagger and tape the joints, you are getting closer to a vapor barrier like the spray foam.

 

[Gofor]

Sounds like you have a good plan:

Our house was a new build, but they did not include gutters. 1st problen was water actually flowing under the house. Gutters solved some, but also had an area under the back deck where the ground actually sloped toward the foundation. Fixed that by correcting the slope and putting 6 mil plastic on top opf the slope. Then had water flowing down a sloped sidewalk and intruding under the bottom of the brick steps. Fixed that with a couple tubes of concrete caulk. Still had high moisture in a couple areas so extended the drain spouts out from the house. During this time also discovered termites a couple times starting to climb up the concrete block foundation which the termite company retreated for free. Still had some high moisture content in the joists in one area, so crawled under the house with a 5 gallon bucket, raked and collected all the construction debris (15 to 20 bucket fulls) to give me clean dirt/sand, and covered it with 6 mil plastic. Now have about a 12% mc on the joists, so have it pretty much contained. I still have a couple areas where I need to do the duct repair you are planning.

Based on my experience, your plan seems to be right on target with maybe the exception of the plan to encapsulate the walls of the foundation if I understand it correctly (not sure what the "CMU" stands for). IMHO, 3" right below the sill is not much area to catch the termite tunnels before they hit the base plate sill. We caught all of ours before they reached it, but some of the tubes were 12" up the wall in just the time between annual inspections. If it were me, I would do all of your plan but the encapsulation, which I would leave until last. After you have laid the moisture barrier on the soil, it will also be a lot easier and cleaner to move around if you do decide to encapsulate. You may want to give it some time to dry out and see where you stand before investing the effort and money into doing that.

If you decide to keep the vents, they do make some that automatically open and close for temp changes, but I still do mine the old fashioned way by hand. There is one school of thought that it is best just to leave them closed if your moisture readings are good.

Just my opinion. Hope it helps

Go

 

[Dutchman]

Hey Heath,
+1 to the start with gutters that drain the water away from the foundation. Install quality covers or keep them cleaned out. I use a back pack blower with a long pvc pipe with a 90 degree elbow configuration that I use to keep mine cleaned out. Landscaping can help you build up and hide any needed piping to route the water away from your house.

 

[Phil S]

I had the same problem. I regraded to direct the runoff away from the house, replaced the worn 80% vapor barrier with a 10 mil 100% barrier then added a dehumidifier and a small exhaust fan running 24/7. The fan size is based on 1 cfm/50 soft. I left the floor insulation in. Big improvement

 

[HMH]

Thanks for all of the feedback guys - exactly what I was looking for.

Robert - good points, but keep in mind that the vapor barrier thickness is a function of wear resistance more-so than added moisture protection. 15mm makes sense below a slab placement that will have WWF laid on it prior to the pour, (though I rarely see it that thick - I think the Building Code still calls for 6mm), but for a residential crawl space, that will see very little if any traffic once installed, the need just isn't there IMO. Great point about the radon testing.

Buddy, Mark - Thanks for the verification, it sounds like we all have, or had similar issues - I'm hoping that replacing the 80% barrier that is in-place now w/ a quality 100% barrier will do the trick for the moisture.

Phil - that's exactly what I'm hoping for w/ a quality 100% barrier vs. my well abused 80%. QUESTION: w/ the fan in-place do you still open the vents in the summer, or do you keep them closed as well? My thoughts on insulating the walls were to add a little extra insulation, (more efficent to spend the money there, than to re-invest in batt between the joists), but that is definitely a BIG extra step.

thanks again guys!

 

[srhardwoods]

I've been down this road, had moisture problems so we encapsulated the crawl space, ran a trench all around the inside edges with gravel. They lead to a hole with a sump pump. Heavy barrier installed, ran up the cinder block walls with mechanical and tape fastening just below the sill plate so it can still be inspected for termites. Spray insulation on the inside block, vents covered and sealed and put a dehumidifier in the crawl space. Dry now and the RH is the same +/- 5% as the inside of the house. This will help when we start to do our hardwood flooring from 10" wide quartersawn planks

 

[scsmith42]

Heath, lots of good advice from others. Just posting to remind you that I have a trencher that you can borrow.


Scott

 

[junquecol]

As for foundation vents, in summer they should be closed, and open in winter. I know this sounds crazy, but let me explain. In winter outside air has low dew point, meaning it's dryer than the air in your crawl space. But in summer it's dew point is often above the temp under your house, which means condensation occurs on everything, especially duct work which is even cooler. What I really love is when companies sell home owners thermostatic vents, which open in summer,and close in winter. Also love when companies do a crawl space treatment, including dehumidfier, then leave foundation vents OPEN. DUH! Remember if you have a furnace in crawl space, it has to have combustion air.

 

[Tarhead]

Heath,
Perfect timing on this as we have similar problems with our crawlspace and need to do something to fix it. We're also looking at pulling out all of the fiberglass insulation, HVAC ducts and doing mold removal/treatment. (I thought a crawlspace was a good thing:wconfused

There is another thread here from last week about Roxul insulation. http://www.roxul.com/products/residential It looks good for this application as it's a made in panels and batts, is non-combustible up to 3200F and doesn't support mold/mildew.

 

[Jeff]

Is the moisture issue seasonal?

1. Back grading and slope sufficient to drain water away from the foundation? Drainage pipes on downspouts to get that water away from the foundation?

2. Plastic moisture barrier is a necessity.

3. Close the foundation vents in winter for warmth (low humidity, low moisture content), open them in warmer months for air circulation despite the humidity.

4. Ducts should be rigid galvanized metal, supported by straps, and insulated. Joints and ingress air points sealed: Not duct tape or foil wrap tape; mastic is messy but remains flexible throughout the temperature/humidity fluctuations.


While we want an airtight home it's still gotta breathe somehow and get fresh air so don't overdo it!

 

[Phil S]

Sorry I missed your question. I keep the vents closed all year and the fan running 24/7. I also purposely did not seal every hole and crack in the floor - the idea is to pull a small amount of air from your living area into the crawl space - seems to work

 

[afn59999]

You might want to look at this site and do a search on crawl spaces.
http://www.greenbuildingadvisor.com/

 

[JimD]

My builder doesn't do gutters either. Houses need them, however. My last and current house have gutters which drain well away from the house via underground tubing. It's more work to bury the tubing but it looks a lot better. Adding gutters to the previous house solved a water intrusion problem in the basement. The current crawl space is dry. It has plastic over most of the dirt but not under the dining room. I will add that but the framing is dry under that room.

I went under a crawl space where I used to live to help a neighbor. His builder placed several inches of sand on the earth in the crawl space. It made it much cleaner and nicer to crawl around in. It would be a large effort to retrofit but it would also be nice every time you have to go down there.

You wouldn't have to change the filter under the house if your cold air returns had filters in them. Right now I have both on one heat pump and only filters on the returns on the other. I may pull the filter under the house and cover the opening next time I am under there. When we bought the house one of the returns was unfiltered but I got a housing and fixed that (you can order them on-line and some home centers have them).

I'm a bit leery on only insulating the walls of the crawl space. It sounds like that is what you plan. The large floor of the crawl space is going to be cold in the winter. I am thinking of closed cell foam on the underside of the floor and the walls of the crawl space where there is a slab on the other side of the wall. I don't plan to insulate the exterior walls or eliminate the vents. Maybe I should think about it. If the contractor was doing the floor it probably wouldn't add that much to do the walls. That would reduce heat gain/loss through the ducting.