Crawl space questions for you insulation gurus

[Comanche79p]

Here is my situation.
I have a log cabin in the mountains of CO that is built on pier and beam and 32" concrete stem walls, 2X10 floor joists on 16" centers. The only insulation in the crawl space is 3/4" extruded foam on the interior concrete of the stem walls. The area is dry in the winter and by late summer it gets a little damp with the wall vents open. The floors are very cold in the winter. I just installed a Homestead soapstone heater and it heats the 1100 sq ft area with cathedral ceilings pretty well, but know it would do better if I made some improvements in the crawl space. I have been reading a LOT about the proper way to encapsulate a crawlspace and seem to get a variety of opinions. I would like to be able to not have to drain the water lines every time I leave in the winter. I am in the process of installing extruded foam board in the floor joist rim area and foaming around that to get a seal hoping that will improve the heat loss.
I am also kicking around the idea on putting down a vapor barrier on the dirt floor and attaching that to the existing foam board on the concrete exterior walls.
Here are some questions that I need answered.

1) can you get the liner to stay attached to the existing foam board on the walls and get a good seal?

2) since I don't have forced air or any air movement in the crawl space (I plan to completely close off the vents) should I consider a de-humidifier? I don't think they work very well when it is above 45F but know absolutely nothing about dehumidifiers.

3) am I kidding myself to think once I get everything done that I have listed above that I can keep from draining the water pipes when I leave for a few weeks even if I have a couple of light bulbs on in the crawl space? I would not leave the well pump on either. I would like to leave a small heater on just to keep part of the house around 45-50F.

It does get pretty cold at the 9200' elevation. I plan to eventually retire there and want to get it right.

Any help would be very much appreciated.

 

[EatenByLimestone]

Is the foam board faced with foil or plastic or raw foam? Great stuff would probably work either way, But if the foam is faced you may be able to get by with tape and that will be cheaper. You may want to consider foam underneath the vapor barrier also. I don't know if you have good enough access to get pieces of any size down there.

I think I'd wait to see if you'd need a dehumidifier before I went out and purchased one.

I think I'd drain the pipes. Empty pipes don't freeze. Even if the light bulbs hold the temperature, I'd plan on power outages... one will eventually happen and the clean up could have been avoided.

Matt

 

[semipro]

Could you run the liner to the top of the stem walls over the existing foam?
Rather than light bulbs, could you use thermostatically controlled heat tape on the pipes with insulation around them.
Insulated pipes are a good idea anyway for quicker hot water delivery and minimization of heat loss (hot lines) and condensation prevention (cold lines).
I'd also wait on the dehumidifier.

Overall, I believe the best way to handle a crawlspace is to treat it like an insulated basement. That is, seal and insulate at the crawlspace floor and walls and don't worry about sealing or insulating between crawlspace and house.

 

[GaryGary]

Here is my situation.
I have a log cabin in the mountains of CO that is built on pier and beam and 32" concrete stem walls, 2X10 floor joists on 16" centers. The only insulation in the crawl space is 3/4" extruded foam on the interior concrete of the stem walls. The area is dry in the winter and by late summer it gets a little damp with the wall vents open. The floors are very cold in the winter. I just installed a Homestead soapstone heater and it heats the 1100 sq ft area with cathedral ceilings pretty well, but know it would do better if I made some improvements in the crawl space. I have been reading a LOT about the proper way to encapsulate a crawlspace and seem to get a variety of opinions. I would like to be able to not have to drain the water lines every time I leave in the winter. I am in the process of installing extruded foam board in the floor joist rim area and foaming around that to get a seal hoping that will improve the heat loss.
I am also kicking around the idea on putting down a vapor barrier on the dirt floor and attaching that to the existing foam board on the concrete exterior walls.
Here are some questions that I need answered.

1) can you get the liner to stay attached to the existing foam board on the walls and get a good seal?

2) since I don't have forced air or any air movement in the crawl space (I plan to completely close off the vents) should I consider a de-humidifier? I don't think they work very well when it is above 45F but know absolutely nothing about dehumidifiers.

3) am I kidding myself to think once I get everything done that I have listed above that I can keep from draining the water pipes when I leave for a few weeks even if I have a couple of light bulbs on in the crawl space? I would not leave the well pump on either. I would like to leave a small heater on just to keep part of the house around 45-50F.

It does get pretty cold at the 9200' elevation. I plan to eventually retire there and want to get it right.

Any help would be very much appreciated.

Hi,
I have a similar crawl space in a similar climate (SW MT).

It was originally a vented crawl space with no floor insulation.
I went to a conditioned crawl space by,
- closing up the vents
- putting down 6 mil poly on the floor and sealing all the seams and sealing the poly to the concrete wall footing.
- insulating the concrete walls with 2 inch polyiso for R13
- insulating the rim joist with 1 inch rigid foamboard that is glued in place and sealed around the edges with Great Stuff.

Its been about 10 years since I did this.
It has worked out well.

The humidity of the crawl space seems fine, and I don't see any need for a dehumidfier (may not be true for all climates, but everything recent I have read indicates that conditioned crawl spaces control humidity better than the traditional vented crawl spaces in all climates).

Temperature in the crawl space is always well above freezing when the house is heated -- typically about 50F in the winter.

We typically set the house thermostat to 50F when we leave on vacations, and while I've never logged the crawl space temps under these conditions we have never had a frozen pipe even with outside temps down toward -20F.

The sealing of the poly to itself and to the concrete footings has held up fine. Wish I could remember exactly what I used, but can't -- might have been construction adhesive or might have been polyseamseal -- it is not silicone.

I don't think that you will be able to leave the house with no heat for extended times in the winter without having freeze issues. Keeping the crawl space above freezing depends on some heat loss from the room above into the crawl space.

You might look into some solar air heating collectors that add heat to the crawl space when there is sun. These are very simple and cheap to build and would be quite efficient in that the crawl space air they are heating starts out cool, which makes for less collector heat loss.
You would still need some backup heat for cases of cloudy days, but it would cut down a lot on run time of the backup heater.
Some examples here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

http://www.builditsolar.com/Projects/SpaceHeating/VacationHome/PipeFreeze.htm

I've actually thought hard about working out a way to just let the house go cold when away -- this would involve draining the plumbing and maybe a few other things, but I think its really the best way to go if you can work out a smooth way to do it. I used to go to a ski area that was user run and only open on weekends -- we had a way to drain the plumbing, protect toilets, ... that only took about 5 minutes to do. This method was used for decades with very little problem. No energy use, no carbon emissions, much lower danger of fires when away. Just as a side note, this three story ski lodge was wood heated with a wood furnace in the basement that dated back to the 30's.

Gary

 

[Comanche79p]

Is the foam board faced with foil or plastic or raw foam? Great stuff would probably work either way, But if the foam is faced you may be able to get by with tape and that will be cheaper. You may want to consider foam underneath the vapor barrier also. I don't know if you have good enough access to get pieces of any size down there.

I think I'd wait to see if you'd need a dehumidifier before I went out and purchased one.

I think I'd drain the pipes. Empty pipes don't freeze. Even if the light bulbs hold the temperature, I'd plan on power outages... one will eventually happen and the clean up could have been avoided.

Matt

No, it is not a faced insulation.
Thanks for the reply

 

[Comanche79p]

Could you run the liner to the top of the stem walls over the existing foam?
Rather than light bulbs, could you use thermostatically controlled heat tape on the pipes with insulation around them.
Insulated pipes are a good idea anyway for quicker hot water delivery and minimization of heat loss (hot lines) and condensation prevention (cold lines).
I'd also wait on the dehumidifier.

Overall, I believe the best way to handle a crawlspace is to treat it like an insulated basement. That is, seal and insulate at the crawlspace floor and walls and don't worry about sealing or insulating between crawlspace and house.

My only concern is the heat tape. I have heard a few stories about the tape causing a fire.
Might be best just to simplify the pipe drain and keep a compressor there.
Thanks for the reply.

 

[Comanche79p]

Hi,
I have a similar crawl space in a similar climate (SW MT).

It was originally a vented crawl space with no floor insulation.
I went to a conditioned crawl space by,
- closing up the vents
- putting down 6 mil poly on the floor and sealing all the seams and sealing the poly to the concrete wall footing.
- insulating the concrete walls with 2 inch polyiso for R13
- insulating the rim joist with 1 inch rigid foamboard that is glued in place and sealed around the edges with Great Stuff.

Its been about 10 years since I did this.
It has worked out well.

The humidity of the crawl space seems fine, and I don't see any need for a dehumidfier (may not be true for all climates, but everything recent I have read indicates that conditioned crawl spaces control humidity better than the traditional vented crawl spaces in all climates).

Temperature in the crawl space is always well above freezing when the house is heated -- typically about 50F in the winter.

We typically set the house thermostat to 50F when we leave on vacations, and while I've never logged the crawl space temps under these conditions we have never had a frozen pipe even with outside temps down toward -20F.

The sealing of the poly to itself and to the concrete footings has held up fine. Wish I could remember exactly what I used, but can't -- might have been construction adhesive or might have been polyseamseal -- it is not silicone.

I don't think that you will be able to leave the house with no heat for extended times in the winter without having freeze issues. Keeping the crawl space above freezing depends on some heat loss from the room above into the crawl space.

You might look into some solar air heating collectors that add heat to the crawl space when there is sun. These are very simple and cheap to build and would be quite efficient in that the crawl space air they are heating starts out cool, which makes for less collector heat loss.
You would still need some backup heat for cases of cloudy days, but it would cut down a lot on run time of the backup heater.
Some examples here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

http://www.builditsolar.com/Projects/SpaceHeating/VacationHome/PipeFreeze.htm

I've actually thought hard about working out a way to just let the house go cold when away -- this would involve draining the plumbing and maybe a few other things, but I think its really the best way to go if you can work out a smooth way to do it. I used to go to a ski area that was user run and only open on weekends -- we had a way to drain the plumbing, protect toilets, ... that only took about 5 minutes to do. This method was used for decades with very little problem. No energy use, no carbon emissions, much lower danger of fires when away. Just as a side note, this three story ski lodge was wood heated with a wood furnace in the basement that dated back to the 30's.

Gary

Gary
Good information-thanks.
I think I will tackle the vapor barrier this summer and find a way to attach it to the walls even if I have to use a 1X4 and a hammer drill along with some type sealant. It doesn't look like a big job as long as I can cut it to fit on the outside. I was thinking I might need to go thicker than 6 mil due to the sharp rocks that are sticking up here and there.

I assume that you do not have ducts under the house-correct? Did you introduce air from any part of the house or just depend on the heat from the living space to penetrate into the crawl space?

Thank you for the information.

 

[Floydian]

Hello Comanche,

Here is some good info on the subject in this blog:http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space as well as links to "Related Articles" and the discussion that fellows at the bottom of Martin's blogs can be interesting too.

GBA is a great resource for all things building related and in particular I really like Martin Holliday's Musings of an Energy Nerd. http://www.greenbuildingadvisor.com/blogs/dept/musings

Top notch stuff,

Noah

 

[peakbagger]

There is a heat tape used in industry called self regulating heat tape, it sis a lot more robust than hardware store heat tape. It varies its internal resistance to maintain a set temperature with no need for controls. It is expensive but lasts a long time. Raychem was one brand.

 

[GaryGary]

Gary
Good information-thanks.
I think I will tackle the vapor barrier this summer and find a way to attach it to the walls even if I have to use a 1X4 and a hammer drill along with some type sealant. It doesn't look like a big job as long as I can cut it to fit on the outside. I was thinking I might need to go thicker than 6 mil due to the sharp rocks that are sticking up here and there.

I assume that you do not have ducts under the house-correct? Did you introduce air from any part of the house or just depend on the heat from the living space to penetrate into the crawl space?

Thank you for the information.

Hi,
There are actually ducts and a small gas furnace in the crawl space, but none of the ducts dump into the crawl space, they go to the room above and other rooms. I've sealed the ducts with duct mastic, so if they leak any heated air into the crawl, its a small amount. The furnace draws its combustion air from outside via a PVC pipe.
The gas furnace does not get much use, as it only heats a small area of the house that we don't heat much.

So, basically, the crawl space is just heated by the heat loss through the floor above it. The more insulation you add on the crawl space walls, the closer it will run to the room temperature of the room above.

Gary