Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Insulation, Radiant and Vapor Barriers
Reload this Page >

For a quasi-crawl space: should I insulate walls and/or ceiling?

For a quasi-crawl space: should I insulate walls and/or ceiling?

Reply

  #1  
Old 04-17-13, 11:31 AM
Member
Thread Starter
Join Date: May 2012
Posts: 262
For a quasi-crawl space: should I insulate walls and/or ceiling?

I've read through many posts on this forum but wanted to post with my specific information.

I'm in CT and recently moved into my home.

The house is 40 years old with a 20 year old addition that created a 'crawl space' that's about 40' long x 6' wide x 7' high (so not really a 'crawl' space as one can easily walk throughout it).

The outside wall of crawl space is made of cinder blocks (poured concrete on the wall adjacent to the house) and (knock-on-wood) has so far been very dry.

It has 3 vents to the outside which let in a lot of air (was very cold in crawl space and kitchen above it this winter).

Between the crawl space and original basement are the 2 original casement windows (which we keep closed) and a full size, decently-sealed, door.

The main basement area has a powerful Sante Fe dehumidifier.

I've been told various things by various people (insulation companies, basement companies, contractors...) and wanted to get some opinions here on the following:

1. Should I permanently close off the 3 vents in the crawl space? I know that the purpose of them is for air circulation, but someone told me that the new theory is not to do this, and instead treat the crawl space like part of the house and not let air in. Plus, perhaps the Sante Fe will help with any humidity problems?
2. Should I insulate the walls of the crawl space? The basement and insulation people say to do this.
3. Should I insulate the ceiling of the crawl space? I've had 4 different contractors tell me to do this, all saying that the other guys are telling me to do the walls because that's how they make more money...

In summary, I've been told basically the opposite on all of these questions: yes close the vents they are not necessary, no don't close them as you need the airflow. Insulate the walls of the crawl space since if you insulate just the ceiling it will drop the temperature of the crawl space and could freeze my pipes. Insulate just the ceiling as that will warm up the kitchen and won't make the crawl space colder or cause moisture issues, etc...

Thanks for your help!
 
Sponsored Links
  #2  
Old 04-17-13, 01:04 PM
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 18,651
Two ways to go:
1. Seal it from the outside and open it to the house and HVAC system. In this case, you insulate the walls.
2. Seal it from the house and open it to the outside (you're here now). In this case, you insulate the ceiling.
 
  #3  
Old 04-17-13, 01:23 PM
Member
Thread Starter
Join Date: May 2012
Posts: 262
Thanks so much for the quick response. I'm definitely inclined to keep the current situation (sealed from the house). I certainly like the answer of insulating the ceiling (with the typical pink stuff, correct?) as opposed to doing the walls with more expensive foam board.

What would your thoughts be about the vents? Most contractors have said to leave it open for ventilation, the basement and insulation people all say to seal them off.

Thanks again!
 
  #4  
Old 04-17-13, 01:26 PM
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 18,651
That space needs air circulation - either it's part of the air circulating within your house (option 1 in my original response) or the air outside. If you go with option 2, you leave those vents open.

Also, if you search the forums, this topic has been discussed quite a bit in the past and Bud has posted a link from buildingscience.com which contains good information. He'll probably be along later to re-post it as well.
 
  #5  
Old 04-17-13, 03:15 PM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,994
BSI-009: New Light In Crawlspaces — Building Science Information

What else is down there. You mention pipes, hot water heat or forced hot air?

During winter the air from that crawl space is moving up through your house carrying the cold, moisture, and anything that may be growing down there. So, if you choose to insulate the floor, you need to first do some extensive air sealing. We have links for that as well.

In hot humid climates, it is a must to seal the crawl space from outside. In your case, if you seal and insulate the floor, you will still need to deal with the moisture, especially in the summer when the air carries more moisture.

Does this crawl have a dirt floor or concrete, and if concrete did they install a plastic layer below the concrete?

I'll let you read, but I do like a clean sealed and insulated crawl space and yours is very large.

Bud
 
  #6  
Old 04-18-13, 06:44 AM
Member
Thread Starter
Join Date: May 2012
Posts: 262
Thanks so much for the link. That seems to be what the basement/insulation people were telling me, when they said not to insulate the ceiling of the crawl space. This would also contradict (I think) the post from mitch17 when he said it's ok to do the ceiling since the crawl space is blocked off from the rest of the basement.

To answer your questions, the floor is concrete but I have no idea if there is any sort of plastic layer below it. There are pipes bringing water to the kitchen, a bathroom and a laundry room. Our house has hot water heat.

I did actually have an insulation company seal the rim joists with spray foam.

Again, historically (at least looking at the current condition) there were no issues with anything in the crawl space (in fact anyone who's ever seen it has commented on how great it looks), and I of course don't want that to change. I do however want to attempt to warm up the kitchen above it. That being said, if there's a chance of creating an 'icky' situation in the crawl space I'd rather just leave it alone.

So, given all that I've mentioned to this point, what would you do if you were me?

Thanks again!
 
  #7  
Old 04-18-13, 07:15 AM
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 18,651
Look at figures 6 and 7 in Bud's link - you should insulate the ceiling but how you do it is important.

If I were you? I like the crawl space sealed to the outside and made part of the house air circulation system.
 
  #8  
Old 04-18-13, 08:43 AM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,994
Insulating the ceiling of that crawl space must also include a rigid air barrier and a vapor barrier (directly under the floor) with all leaks sealed. Any air leaks will transport moisture vapor up into the floor above.

Then there is the question of the desired warm floor. The floor above will always be colder than the coldest air in the kitchen. Cold air goes to the floor and some of that heat will be lost to the crawl space, insulation cannot be perfect.

If you use the rigid foam around the crawl space walls, rim is already sealed, and add some heat down there then the kitchen floor will be warmed by the heat in the crawl space.

If a warm floor is a primary concern, a radiant heat loop can be installed under that area, not inexpensive, but very warm. The #1 lady will be very happy.

In the summer you will need to run a dehumidifier in the crawl space. Venting of that space is always perceived backwards. People want to open the vents in the summer and close them in winter, when their actual intent is the other way around. Cold winter air is dry and warm summer air is humid and moisture is the concern.

Sheetrock on the crawl space ceiling would not be good, so not sure what to recommend to cover the insulation if you go that direction. There are volumes of articles on this topic and still confusion remains. The reason is that every home and location is different. What works perfectly in one area may result in a disaster in another.

Bud
 
  #9  
Old 04-18-13, 09:49 AM
Member
Thread Starter
Join Date: May 2012
Posts: 262
Thanks again for all your help. I'll continue to think it over and report back if/when we make a final decision.

Thanks!
 
  #10  
Old 04-19-13, 06:33 AM
Member
Join Date: Apr 2011
Location: USA
Posts: 5
Is the adjacent basement conditioned with HVAC air or just the dehumidifier?
 
  #11  
Old 04-19-13, 06:40 AM
Member
Thread Starter
Join Date: May 2012
Posts: 262
Just the dehumidifier. And electric baseboard heat.
 
  #12  
Old 04-21-13, 06:07 PM
Member
Join Date: Mar 2013
Location: USA
Posts: 457
Foamboard is expensive, as you said. To insulate the walls, you need the house to heat the space for the air exchange, you cannot just close the vents. http://www.buildingscience.com/docum...ance-and-codes

With the floor insulated, you can partially close the vents, keeping an eye on the humidity or leave the door/windows open to exchange air to Santa Fe. But, you can insulate the floor - full contact-cavities with f.g. (not the best choice) and install housewrap with joints taped for an air barrier. So the money saved on f.b. (and a possible ignition barrier if required- plywood, etc.) can be spent for H.W. Have you done a moisture test of the slab with taped plastic?

Heating the space and insulating the walls will cost more; http://www.advancedenergy.org/buildi...l%20Spaces.pdf

Gary
PS. Frost King E/O 1/2 in. x 6 ft. Tubular Pipe Insulation-P10XB/6 at The Home Depot
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes