Unique crawlspace issues

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  #1  
Old 02-10-17, 04:04 PM
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Unique crawlspace issues

Hello,

First, let me describe my crawlspace. I have access through a trap door in the hallway closet. There is a layer of uneven concrete covering the entire crawlspace floor. The floors of my home are not insulated, rather, the stem wall of the foundation is insulated. I have central air and there is a vent that is open and blowing hot/cold air into the crawl space. It is a conditioned space. There are vents in the foundation wall around the perimeter. The previous owners have ripped holes through the stem wall insulation to utilize these vents....

This seems to be a very odd set up. The concrete floor is constantly damp looking in many areas. There is a strong musty smell from the crawlspace. I bought a hygrometer and it currently measures around 90% humidity. This is way too high. I have crawled around underneath the house a few times and never noticed moisture on the wood or seen any mold.

I have some drainage concerns as well, but currently i have 4 foot pipes connected to my downspouts taking water away from my house. I also currently have a dehumidifier running in the crawlspace. I can't run it continuous due to lack of drain options. I empty the unit twice a day. It's probably about 1 gallon of water per day. These things are kind of experimentation to see if i can get that humidity number down and reduce the musty smell.

I guess my question is, what do I do with the crawl space assuming i solve my drainage problems (I fear this will involve digging up my drainage system...)? I feel like the space isn't committed to one style over the other. Do i lay down plastic sheeting over the concrete floor? Do I close the vent from my central air down there? Do I remove the stem wall insulation and insulate the floor instead?

I am at a complete loss here and looking for any ideas or input.

Thanks for reading!
Justin
 
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  #2  
Old 02-10-17, 06:03 PM
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Is the foam that is on the walls a spray applied or a sheet material? If a sheet, do you know what type of foam?

Are the walls concrete or block and if block are the hollow cores sealed at the top with either a solid block or in some other fashion?

Is there evidence of seepage into the crawl space? If you have an issue that shows water on the surface of the concrete you have to find the origin of that and deal with it.

If you have an issue with vapor diffusion through the slab then applying a 6 mil polyethylene material over the concrete and sealing it at the edges will help to control the ground moisture. There are better vapor retarders but the poly will suffice.

Is there a sump pit in the floor and does it typically show water in the base? If it is open on top it is constantly a source of water vapor as well.

Any ductwork in the crawl should be sealed at all joints.

I would seal the vents that open to outdoors, install the vapor retarder and not insulate the floor. I would also seal any mechanical openings that are in the floor assembly with foam or caulk.
 
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Old 02-10-17, 08:38 PM
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Conditioned crawlspaces are never vented to the great outdoors and vented crawlspaces are never conditioned. One or the other.

Conditioned crawlspaces require BOTH supply and return ducts. They should be placed to ensure the airflow covers the majority of the crawlspace area.

Sill plates must be sealed to the foundation to reduce/eliminate air leakage when you have a conditioned crawlspace.
 
  #4  
Old 02-11-17, 03:11 PM
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calvert,
the insulation on the walls is not sprayed or rigid foam. It's fiberglass insulation that is somehow attached. I haven't investigated beyond that.

The walls are concrete. There has been a couple spots i've noticed cracks. I've tried to correct them the best I could with foundation filler. There was also a drainage pipe outside that had cracked and was allowing water into the crawl space via the water main inlet hole. I have corrected the drainage pipe crack and filled the inlet hole with spray foam while i had things dug up. There has not been any water coming in there since.

I have heard mixed thoughts on putting plastic over the concrete floor. Good to know you think it's a good idea.

There is no sump pit in the floor.

Duct work could use some maintenance, but is overall in good condition.

What do you mean by seal any "mechanical openings"? Is the crawlspace access trapdoor considered a mechanical opening?



Furd,
I agree, the space has not committed either way. How would you suggest I correct the ripped holes in the insulation on the stem wall? Completely replace or just buy some fiberglass insulation and pack it in the holes in plastic bags or something?

The one vent that supplies conditioned air to the crawlspace is at one end of the space. There is one vent that is just passive to the outdoors and is meant as the "outlet". There is no fan pulling air out of the vent. I am not sure if the vent feeding the space is sized correctly for the size of the space. Should I add a fan to the outlet vent?

Justin
 
  #5  
Old 02-11-17, 05:17 PM
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As much as you may not like to hear it, I would probably replace the fiberglass insulation with closed cell foam. Look behind the fiberglass and see if the wall has a damp appearance or if there are any signs of water droplets forming in the insulation or on the back of the facing. If so, I would definitely be doing the foam.

Generally, the material you have is attached by nailing a strip of wood through it at the location of the wood sill that is at the top of the foundation.

Do you have any idea what may have been done to the exterior of the foundation to damp proof it?

If cracks seem to still be a possible source of water leakage, I would use an epoxy injection sealant.

Within the new building codes is a provision to seal any wall plates where a hole has been drilled for a wire, pipe, duct or any other utility. That sealant should be of a fire resistive nature. There are foams or caulks sold at big box stores or your hardware store that are designed for that purpose.

The concept behind sealing the holes is to eliminate air flows between various levels of a structure within the wall cavities. Moist air from the crawl space gets drawn up to the first floor by convective currents through the holes. The hatch for access should also be sealed as well as possible with foam gaskets or foam tape and an otherwise snug fit.
 
  #6  
Old 02-12-17, 10:35 AM
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calvert,

do you mean those rigid foam boards? Kind of like this:

Thermasheath Rmax Thermasheath-3 2 in. x 4 ft. x 8 ft. R-13.1 Polyisocyanurate Rigid Foam Insulation Board-613010 - The Home Depot

That may be a bit spendy...

I have no clue what they've done to the outside of the foundation to waterproof it. I have seem signs of wet insulation on one of the walls down there. I suspect there are small cracks I have not yet fixed.

If I fix all of the cracks, what is the advantage of the rigid foam over fiberglass?

I will work on sealing all other air flows within the wall cavities.

Thanks for taking the time to help me!
 
  #7  
Old 02-12-17, 08:32 PM
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That would be a suitable foam. The fiberglass may be showing some signs of moisture due to vapor migration across the foundation, not necessarily liquid water leakage. The water vapor can then condense on the wall at the interface of the insulation and foundation.

The foam is not affected by any water while fiberglass loses effectiveness when it gets wet. The ideal foam application would be spray applied closed cell foam which, due to the fact it binds directly to the wall surface, would not allow any condensation to form on the wall since there is no air gap between the wall and foam.
 
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