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Insulation for ceiling of crawl space with foam sprayed walls?

Insulation for ceiling of crawl space with foam sprayed walls?

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  #1  
Old 05-13-19, 11:09 AM
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Insulation for ceiling of crawl space with foam sprayed walls?

Hi All,

Our house has a crawlspace, about 3-4 feet tall, with a concrete slab floor. A few years ago, we had the crawlspace walls professionally foam-sprayed with ~2" of closed cell foam ("Lapolla Foam Lock"), to an R-value of 13. Therefore, the crawlspace is (I think) now part of our conditioned space.

I was down in the crawlspace the other day and realized that portions of the crawlspace ceiling still have some of the fiberglass insulation between the joists. I have read two competing theories:

One is that there should be insulation between the ceiling joists (i.e., under the subfloor of our first floor above) even for such a conditioned space, in order to account for coldness coming up through the concrete floor. The second theory is that there should be no insulation between the joists because it is a conditioned space (it would be similar to putting insulation in the ceiling between my first and second floors, which I obviously just wouldn't do).

Anyone have any thoughts? I know cold air doesn't rise, but the "stack effect" is something I've never really understood and don't know how it would affect this.

Thanks in advance for any advice!
 
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  #2  
Old 05-13-19, 11:25 AM
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A typical basement floor is well insulated by the ground below. Heat that escapes that direction has a long way to travel before it reaches the air and gets blown away. Thus the soil acts like a heat sink and once warmed greatly slows any loss in that direction.

The advice you read in regards to treating that space like conditioned space is correct. In fact it is recommended you provide some airflow to mix that air with the house above.

From a heat loss point of view you are in good shape and keeping that crawlspace warm will provide warm floors throughout the house.

Note, not mentioned was the rim joist at the top of the foundation and i assume that was foamed as well.

Bud
 
  #3  
Old 05-13-19, 11:32 AM
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Hi Bud,

Thanks for the quick response.

Yes, "beam ends and band joists" were sprayed. My understanding is that "band joists" and "rim joists" are the same thing. Correct? (Either way, back when it was done, I had checked online in several places, and everyone believed that it was being done correctly.)

Still - it would be great if you could confirm. I know (I think I know!) the foam goes from the floor up past the concrete walls and onto the wood framing.)

Thanks again!
 
  #4  
Old 05-13-19, 11:40 AM
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I generally use rim joist to describe the top of the foundation and band joist to describe the perimeter between upper floors, first to second as an example.

As for performance there is usually a lot of air leakage along with heat loss at the rim and that spray foam seals as well as insulates. The one drawback is the need (often ignored) to cover the foam with a fire rated barrier. If it can't be enclosed in drywall then they do make a special paint that foams up with heat to prevent ignition, called intumescent paint. Local codes vary and sometimes attics and crawlspaces are viewed differently.

Bud
 
  #5  
Old 05-13-19, 12:29 PM
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Hi Bud,

Thanks again for the quick response.

So based on your definition, then our rim joists are foam sprayed.

Regarding the fire-rated barrier: the installing company had emailed me at the time that the foam spray has "an ignition barrier built into it. A thermal barrier by code is not required in an attic or crawl space that is not used for storage or is inaccessible." (And we definitely do NOT use the crawl space for storage.)

They also provided the relevant building code, and they seem to be correct that only an ignition barrier is required. (While my nighttime job is trying not to destroy my house, I am a lawyer by day.)

So, basically, I should NOT have the crawlspace ceiling insulated at all, and the stack effect won't be bad enough to make a difference. Right? In fact, we do have a small hole in the first floor's ground (maybe like a 3"x3" hole) that allows some air mixing.

Thanks again!
 
  #6  
Old 05-13-19, 01:31 PM
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I know I should keep my mouth shut, but what we talk about here becomes the guidance for hundreds who follow and read it.

One, never heard of a spray foam with an ignition barrier built into it. May be, but it needs all of the whatever certifications AND needs to be accepted by your local code department. They can accept or reject just about anything and if accepted you need it in writing to satisfy future inspectors and insurance companies.

Two, not sure what "a small hole in the first floor's ground " is? If that is a hole between the crawlspace and living space above effectively no air will flow. Stack effect is a pressure based upon a difference in temperature and height such as outside air temperature vs inside and the height of your house. Convection might be what you are thinking of but in that crawlspace the floor will be cooler than the ceiling (floor above) so no convection. It doesn't take a lot of air flow but often needs a fan involved.

Three, Have you tested for radon?

Last, you are correct that insulation is not needed in that crawlspace ceiling.

And my sympathies for your handicap (being a lawyer), I have a few friends in that position and they struggle at times.

Bud
 
  #7  
Old 05-13-19, 01:54 PM
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Hi Bud,

The installer was from the town next to us, and they checked their product with my town's building inspector and it was apparently good-to-go. I'll get in touch with the installer to see which exact product it was.

The "small hole" is where my utility room on the first floor sort of connects to the crawlspace. Small hole on the floor of the utility room/ceiling of the crawlspace. I'm guessing that's probably not enough air, so I need to somehow get air in there? If so, what do you suggest?

Yep, we tested for radon when we first moved in ~8 years ago - there was none.

Thank you for the sympathy - it is a day-to-day struggle at times!
 
  #8  
Old 05-13-19, 06:24 PM
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What you have is sealed from the outside so it needs to be opened to the house air. Some means of either pushing air into the space like by adding a vent from the furnace/AC down there or a means of causing the air there to push into the house, like a return for the HVAC system - along with another passive means of air moving to account for the change in pressure caused by the forced means. So, the easiest thing would be if you have any ductwork in there.
 
  #9  
Old 05-16-19, 12:00 PM
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Unfortunately, we don't have any ductwork in the crawlspace, so that's out. I'm thinking I'll install like a 40 CFM fan to blow house air in there, and then a little vent from the crawlspace to the house to allow the pressure to equalize. I found Section 308.3 (or maybe 408.3, I forget the exact number) which seems to pertain to my situation. I need cfm of air moved per 50 square feet, and I can use conditioned house air.

Coupled with a dehumidifier set to 40% humidity, I think that would make the crawlspace good. Thoughts on whether I am correct?

Also, I'm thinking of putting a vapor barrier down (6 mil plastic sheeting, I believe?), but I read somewhere that some people recommend using an epoxy on the ground instead. Anyone have thoughts on which is better, plastic sheeting or epoxy?

Thanks again.
 
  #10  
Old 05-16-19, 01:55 PM
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You have a concrete floor, I would quit worrying about the floor. Vapor barrier is important when you have a dirt floor. I think the rest of the plan sounds like at least a good place to start.
 
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  #11  
Old 05-17-19, 06:48 AM
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Thanks, Stick and Bud.

Last question (I think): my crawlspace is something like 1700 sq. feet (and about 4 feet tall). Is one dehumidifier enough? Meaning, if I put one large dehumidifier down there, will that just dry the area around it? Should I instead put two smaller dehumidifiers in different areas that that they each can do their own areas?

I have read a few different things, and I'm not sure which (if any or all) are true:
  1. humidity in the air always "levels" itself, almost like a vacuum (where air would rush to fill the vacuum); here, taking moisture out of one area would mean moisture from another area would rush in to fill in where there is less moisture so that the humidity always stays the same in the overall area;
  2. dehumidifiers move the air enough by themselves so as to circulate the air sufficiently so that all the air gets dried;
  3. I should put an oscillating fan down in the crawlspace (along with the dehumidifier) to help with air movement so that the dehumidifier will work on all the air;
  4. the 40 cfm fan-and-vent-to-living-space we will install will be sufficient to move air throughout the crawlspace for my purposes; and/or
  5. I should just use two smaller dehumidifiers.

(If I need to use two smaller dehumidifiers, it would be a pain to do (I'm hoping to put the single dehumidifier near the access hatch in the closet so that I can easily get to it to change the filter, etc.)

Anyone know which (if any) of the above are true? I just got a 70-pint dehumidifer but I started wondering if 1 large is a good idea or if 2 medium/small is a better idea.

Thanks again!
 
  #12  
Old 05-17-19, 07:47 AM
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I would start with just the one.
 
  #13  
Old 05-17-19, 08:50 AM
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Hi Oopey, as great as the internet is it is becoming so filled with opinions we need sites like this to sort them out.

In your case you want some RH numbers to support your need for a dehumidifier and since the closed cell foam has been on the walls for a couple of years you should smell or see any problems. Adding the vent fan from house to crawlspace will also help assuming you heat and air condition the living space above. I suspect you will find the RH numbers acceptable and thus not have to deal with the electricity or the inconvenience of maintaining that dehumidifier.

To answer your questions:
1. If the crawlspace is all open and connected, not two spaces joined by a small opening, then yes one dehumidifier would be fine, IF one is needed.
2. Although the moisture in the air will equalize by itself, areas next to cooler walls will have a higher RH reading, temperature changes that number. But first you need those numbers.
3. I doubt an extra fan will be needed.
4. the 40 cfm fan pushing air into that space should be more than enough.
5. If all open one is all that would be needed if even that.

Pick up a couple of inexpensive remote reading moisture meters and start taking readings, and don't unpack that dehumidifier .

Bud
 
  #14  
Old 05-17-19, 09:52 AM
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Hi Bud and Stick,

Thanks again.

I'm in NJ where we have had, literally, rain (and lots of it) for something like 30 of the past 35 days. So, the crawlspace is a bit damp. Everyone's yards are like mini-swamps, and there is definitely water in the sump pump pit (the pump itself seems to kick on every few hours).

In the past, I had run 2 dehumidifiers down there and everything was dry, to the point where I did a moisture test (or whatever its called - tape a 2'x2' piece of heavy plastic to the ground so its sealed, wait 48 hours, and then see if there is moisture on it - it came up dry).

However, there was a recall on the dehumidifiers I was using, so I stopped using them - and never replaced them (whoops).

Now that there is evidence that some water can come up through the cement (concrete?) floor during very heavy rains (note: it was dry during Superstorm Sandy), I'm thinking I'll definitely need a dehumidifier.

Yes, we do heat/cool the living space above the crawlspace (its our living room, kitchen, dining room, etc.) Also, its only one crawlspace, not two separate but adjoined crawlspaces. I'm also thinking of eventually dropping a loop from the boiler into the crawlspace to keep it warm-ish so that the floors of our first floor get a bit warm (I know they won't be warm like with radiant floor heating, though).

I'll get some moisture meters and see what they say, but I know it is humid down there right now.

Also, since the perimeter is foam-sprayed and its all one room, why would some walls be cooler than others?

Thanks again for all the help and advice!
 
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Old 05-17-19, 10:24 AM
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The 2' x 2' piece of plastic test is misleading. The results only tell you that today it is dry but provide zero long term information for decisions to be made. Sounds like you understand that you do have a moisture issue and your current dehumidifier is probably good.

Dropping a loop down would be good just add it to an existing loop that cycles often as opposed to a new loop with its own thermostat.

You are correct that temperature differences between your walls and center of that space should be minimal. I was just pointing out the relative nature of a RH reading. If you pick up a meter that gives you both temp and RH that answers the question.

Bud
 
  #16  
Old 05-17-19, 11:00 AM
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No more questions from me, just another "Thank you" to both of you (Bud and Stick):

Thank you!
 
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  #17  
Old Today, 09:20 AM
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Ok, it turns out I do have another question (or two). I've been (dangerously) reading building codes and summaries and interpretations online. I understand that code requires that, in my situation, I should have ~40 cfm mechanical ventilation going from living area above down into the crawl space, and that separately there should be some sort of register between the house and crawlspace to equalize the pressure caused by the ~40 cfm fan.

First question is - if I dehumidify the air in the crawlspace down to maybe 40-45%, why do I need to blow conditioned air from the above living area into the crawlspace? What will that actually do? I know its code, but what would happen if I don't blow air into the crawlspace? (I've read a few blogs that indicate that, while its required by code, its not necessary to blow conditioned air into the crawl space.) Thoughts on what would happen if I have dry, warmish air in the crawlspace and don't mechanically ventilate it with living area air?

Second question - if I do blow conditioned air from above down into the crawlspace, why do I need a separate register to let air back into the house? 40 CFM is not a lot - its weaker than most bathroom exhaust fans. Even if the crawlspace is under very slight positive pressure, so what? Also, won't some air find its way back into the living area above just through normal cracks/holes/etc. between the crawlspace ceiling/living area floor? (Especially if its under some very slight positive pressure?)

I understand that code may differ from what I'm asking, but I'm asking from purely a building engineering perspective.

Thanks again!
 
  #18  
Old Today, 11:50 AM
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The reason for the second vent to equalize pressure is because the fan pushing air into the space will have a hard time if it has to overpressure the area. Same concept applies to HVAC systems and rooms with vents but no returns.

The idea behind this instead of just dehumidifying the air is to create circulation so that there is no buildup of anything in the air in the crawlspace.
 
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