I have read many of the threads here on insulatiing crawlsapces, and it seems confusing, with contradictory statements, lack of real sentences, and what not.
I have a crawlspace, that is not sealed, it has two entry points. There isnt any insulation down there, and I want to change that. So my questions are:

1. Do I insulate between the joists?
2. Along the foundation walls? If so, can I use styrofoam?
3. Do I only cut holes in the ducts if its sealed to let heat down there?
4. Should I seal it up? If so what is the best way to seal it up if the access points are obviously big enough for me to get in there?

Basically i want to know if its not sealed up, how should I go about insulating?
And if I do decide to seal it, then how should I go about insulating?
I've read the websites that have been listed on here too, I just want some straight answers.
Thanks A LOT in advance!!

 

I am confused as well. It appears that there are two approaches. While it would be nice to "heat", either directly or indirectly, the crawl space, I was always under the impression that the theory behind a "non-conditioned" crawl space was primarily to NOT trap moisture and cause rot in the sill. I have known several people with homes that needed to be jacked and have the sill fixed, and this was attributed to improper venting of the crawl space which resulted in condensation/moisture/rot. This can also lead to mold problems, which are also not insignificant.

How does plasic and insulation of the crawlspace envelope prevent this from happening, it will definelty trap moisture, won't it?

 

There are two schools of thought concerning crawl space insulating and ventilation. Both argue that their method is better at conserving energy and moisture control and the other is poor at accomplishing it.

It will be good at this point to distinguish some terms used with crawl spaces. VAPOR BARRIERS deal with heat transported moisture and are only applied with insulation. MOISTURE BARRIERS deal with pressure induced moisture and when applied with insulation with a VAPOR BARRIER can produce the double Vapor Barrier Effect. Far too often people interchange the terms Vapor and Moisture that usually contributes to the confusion.

Moisture and Vapor Barriers do not stop moisture flow, they slow it down. This is because the moisture vapor molecule is so small it will penetrate almost all known materials. Example, steel rust. The term used to describe the ability of materials to absorb and expel moisture is known as PERM RATING. All materials known have a Perm Rating. What this explicitly implies is that all materials absorb and expel moisture but they do it at different rates.

Moisture problems occur within confined spaces of a structure when the introduction of moisture is greater than the ability of the materials within the confined space to absorb and expel the moisture. Since Moisture and Vapor Barriers do not stop moisture flow, they slow it down to give the materials in the crawl space the time they need to absorb and expel the moisture. Since some materials absorb and expel moisture faster than other materials, ideally you what the introduction of moisture to be less than the material that has the slowest absorption rate in the affected area.

To apply this to a crawl space is to first understand the aforementioned. Insulation slows down heat flow but does not slows down moisture flow, vapor barriers slows down moisture flow. Since all heat has moisture in it, you must address the source of the heat in order to prevent a moisture problem. The operative term here is HEAT FLOW. Where is the heat coming from? The ceiling of the crawl space or inside the crawl space? If you believe the heat source is from the floor inside the house, then insulate the ceiling of the crawl space. If you believe the heat source is inside the crawl space, then insulate the walls of the crawl space.

Moisture Barriers are basement water proofing paints and the plastic you lay on a dirt floor in a crawl space. Both slows down moisture flow, they do not stop it. They address hydrostatic pressure and/or capilliary action. An example of this is putting a corner of tissue paper in water. After a period of time even though only the corner is in the water, the entire tissue paper gets wet. The operative term here is TIME not Moisture Flow. As the ground outside obtains water, it is absorbed by the ground in the crawl space. The difference between the two is the water in the ground outside is absorbed by its surroundings, especially by the air, whereas inside the crawl space it gets absorbed by the materials of the structure. In most cases the introduction of moisture from the ground inside the crawls space is greater than the ability of the materials of the structure to absorb and expel the moisture. A Moisture Barrier applied to the top of the ground in a crawl space slows down the moisture flow to provide enough TIME for the moisture in the ground to be absorbed by the surroundings outside the crawl space, especially the air.

It was this type of thinking that led to installing vents to a crawl space to allow air to enter it and absorb moisture (Equilibrium Relative Humidity/ErH%). Later it was applied to attic and was so useful that it is a standard with attics today.

Moisture Barriers have a side effect that concerned energy conservation. Which was that it prohibited evaporation. An example of this is after taking a shower in the summer we feel cooler. The reason for it is the moisture on our skin was evaporating. It would take our body heat to create the evaporation, thereby lowering our body temperature. In a crawl space it was found that the moisture in the ground was evaporating inside the crawl space by extracting the heat from the structure, thereby making the floor above the crawl space cold. A moisture barrier prohibited the evaporation, thereby making the floor above the crawl space warmer.

Generally speaking, the insulatiion in crawl spaces should go in the ceiling of crawl spaces with the vapor barrier facing upwards, a moisture barrier (plastic) applied to the dirt floor of the crawl space and vents should be installed and open during the winter and closed during the summer (reasons for closing of vents during the summer are; high pressure is attracted to low pressure and heat condenses on cooler surfaces).

I know that this is old school thinking. The new school thinking application clearly disputes the aforementioned. I suggest that you ask them for their position and then you decide which one is more applicable for you.

 

Thanks for the info. I appeciate the fact that I have two points of views and solutions. I have read both reercon's and imeduc's point of views. Now if we could just get you guys to meet in the middle and have one solution

One thing I was not aware of was that the vents should be open in the winter and closed in the summer, I always practiced the exact opposite.

While I am most familiar with the "old" school, or unconditioned crawl space, I am most intrigued by the "new" school. It would be nice to have some heat under the floors to keep them from being completet dead cold. I would install radiant floor heating except this is an old farmhouse with 18-22 inch wide pine floor boards!

 

We have sealed them up for over 30 years. with registers in the duct down there. No vents to the outside at all. Have not had any trouble with any of the homes. When we first started with electric heat they called for insulation in the floor and vent the crawl space. We had to use insulated duct for down there. It didnt work and we went back and pulled the insulation out of the floors also had to cut registers in the insulated duct. to let some air out down there. If you go to a full open crawl under the home or room. There we use a cheap plywood or masonite on the underside of the joist. Put a R19 paper side up to the room in the joist there. A 6 mil poly over the joist . The subfloor on top of that and then start with the walls. Now in the attic for sure vent the H*** out of it and use power vent fans there on a tstat .
Did you look at http://aboutsavingheat.com/crrawlspace.html

My .02 cents ED

 

I am in the same boat and could use some help from Ed and resercon.
My whole house sits on blocks with bare earth underneath. There is a slab which my hot water heater and boiler (baseboard hot water heat) sit on which was dug out in this crawl space. This slab has block walls which basically is a retaining wall for the bare earth. The bare earth goes from the retaining wall to the block foundation the house sits on. In this block foundation I have two basement windows (windows for the crawl space?) that are so old the frames are falling apart and the windows can't be closed.
Whew, enough of that description but I wanted you to get the picture before my questions.
I have read about both theories (poly on bare earth and insulate the walls versus poly on the bare earth and insulate the floor (ceiling of crawl space). The problem I have is that since the boiler and water heater are in this crawl space I need combustable air and I am going to get it even if I don't need it because of the windows. The baseboard heat pipes are also in this crawl space and they are wrapped. I know the residual heat from the boiler and water heater keep it pretty warm down there but my floors still get cold. Keeping this in mind is it best for me to just poly the floor and insulate the floor/ceiling of crawl space or do either of you have any additional ideas. I have poly on the floor and wanting to get on with the next step. Also, if either of you suggest the insulation on the floor/ crwal ceiling would it be ok to use window screen stapled to the joists to hold the insulation in and to keep the environment out (sometimes get a mouse or two running around the crawl space floor. I noticed it is alot cheaper then the poultry mesh .Thank you

 

You have to make up your own mind how you want to go here. Did you check all the www on the web we gave you here The last ones said to insulate the wall is the best not the floor. You have a boiler and all its pipes down there with the water heater. Id seal it up insulation on the walls and on the sill plate. You can check with code there for combustion air. Run a small pipe to the outside and down just where the boiler is. This way any heat off the boiler pipes will help warm the floor.

ED

 

Ed,
Thanks for the response and I will have to make up my mind either way. The problem I have are the open windows that go to the crawl space/basement. I can not secure those w/o extensive repair/costs. Having the open window allows air to get in the crawl space but the window is right by my lr floor thus the out side air travels right up to the floor and it gats/stays cold. I think because of that I have to insulate the joists and just wrap all the pipes. Another thing, I had heard today that plastic on the bare earth is not a good idea because of the radon and the moisture. I am hoping that this is a fraek tgheory because I alredy put the plastic (6 mil) on the floor and am just determining how I want to insulate the rest of it.
Thank you very much for all of the help. Fred

 

Resercon

thank you for such a thorough explanation, I've been reading the forum and asked questions.

I just bought my home, and so far there is only one thing that makes me feel all warm and fuzzy every time I think about it, the way I insulated my crawl space!

First I put new 6 mil on the dirt floor and taped the seams with the same tape you use with Tyvek, then I taped ( with foil tape) and insulated all the duct work, then I put r-19 between the floor joists (vapor retarder toward the living space). The header had insulation previously so I left that, there the kraft paper faces inside the crawl space (I figured this was right since it did face the warmest side). I have also started taping the 6 mil to the cinder block.

Since we have cold winters I closed the vents and put a bit of insulation to stop the draft.

Additionally I have a nice dehumidifier down there, just checked it and the humidity is 35%, as the air gets drier as the weather gets colder I figure I won't need to run it much more.

Thanks for all the help I've gotten. I get excited everytime I get my utility bill now, I go to work and compare bills! $44.99 for gas and electric for use thru 10/19.

Prior to this the AC would run for 20 minutes shut down for 10 and start up again, after it ran for 10 and shut down for near an hour. The whole house just seems quieter and the HVAC system is at least 50% quieter.


Julie

 

I have a year old home that I bought new here in Virginia. It is on a crawlspace. I have inspected the space, and found that the contractors did a bad job. They did not seal where pipes and things go up throught the floor. The insulation is very shoddy too. I want to fortify this area so as to maximize my energy efficency. Do I leave the old insulation in place and put more up between the joists? Should I use the same stuff ( Fibreglass batts) or use foam sheets? And if I use the foam sheets, should I go between the joists or just attach them across the whole underside? Also if I decide to redo the plastic that is on the dirt, can i just put it on top, or should I first remove the old stuff? Would leaving in the old plastic help at all? Also is it recommended to insulate the cinder blocks that support the house? Does this help much?

Is there such a thing as to much R factor under the house in the crawlspace? I would go over board to make sure that I am getting the most out of it, ie, I would fill up the joists with fibreglass then seal over them with the foam sheets. Has anyone done this? Or would it be a waste?

Thanks in advance for any help,
Jesse

 

deefish look at the www. that are on here.

http//aboutsavingheat.com/crawlspace/html

Http://www.advancedenergy.org/buildi...y/craw;+spaces

Then make up your own mind what to do. We seal them alland no insulation in the joist. on the walls.

ED