Question regarding insulating crawl space

[frosty2013]

Hey guys..

I live in Northern Canada where winters are below zero for at least 6 months and range from -25 to -40 in the coldest months.

I live in a mobile home that is on a cribbing foundation system. Last year I decided to do something about my freezing pipes during the winter. The home already had plywood skirting around it that was in bad condition, and not insulated. I removed it and replaced it with 2x4 frame and 1/2" plywood.Then from the inside I insulated each cavity between the 2x4 with 2" ridgid foam board and sealed the seams with spray foam. I also covered the entire dirt floor with 10 mil vapor barrier. I even went as far as putting the plastic under each of the cribbing supports.
I completed the work around mid september last year and because we were already getting pretty cold out at night I didn't bother to cut Vents in the skirting, for the heating season.

The winter came and went and was one of the coldest in a long while. -30 Celsius steady from November until pretty much March. I never had one issue with frozen pipes and even saved a bit on my oil bill...

Then Spring came and I decided it was time to cut vents in the skirting for the summer. I cut a hole for 6 vents . I also purchased a humidistat to monitor the relative humidity in the space. We can also get very warm summers with temps about 30 - 35 Celsius. In July we had a little mini heat wave for about a week were the temps were close to 40 degrees. One day I went into the crawl space to check on things and was shocked to see that the humidistat was reading 94% RH!!!
Also there was water droplets on the underbelly material and on top of the plastic on the ground.. I started to panic a little and installed 2 exhaust fans, one at each end of the house and placed other fans to help dry the area. It took about 4 days and everything was mostly dry. Was the hot outside air condensing when entering the crawl space?
Should I have closed off all my vents in summer as well?

After I installed the exhaust fans, I hooked a humidistat to each and which controls when they kick in if the humidity is over 70%... Seems I can only get RH down to 70 in the summer

Is there anything I can do to lower the humidity further? or is 70 fine in this situation? Thanks for any help or advise. I feel like I kicked the winter issue, but created a summer headache!

[Greg]

Try a heavy plastic sheet for a vapor barrier that should help. Install it as best that you can to cover the ground under the home. You will need to make cuts for plumbing & supports but it should help a lot.

Greg

[Greg S]

By using the fans you determined what your problem is. You do not have sufficient ventilation for the space and conditions you experience.
We are also in Canada (Ontario) and feel that large screened openings (2-3 feet square) are required at a minimum on each corner as well as intermediate along the side of the home. This seems to work better than the equivalent ventilation in numerous smaller openings. Depending on the surrounding area there is sometimes not enough cross draft to adequately ventilate and in those cases we install a dehumidifier under the home with a drain to the outside. In this case we close all the ventilation openings so we are not dehumidifying the great outdoors.

[frosty2013]

Thanks for the reply's guys.Been away for a bit and wasn't able to reply..
Greg as I stated I already have a continuous 10 mil plastic on the ground and sealed at bottom of skirting.There are no breaks in it and seams are taped. As for adding more ventilation I would rather wait until next year to do this as the heating season is drawing near.Last weekend I closed off all vents and I have and decided to install a dehumidifier down there as a test... With the dehumidifier constantly running I can get the RH down to 61. Isn't that still pretty high for a completely sealed area? I have to dump the bucket everyday and if I am late and the unit cuts out the humidity creeps up to about 70-75. also I have the exhaust fans running. I must have another problem somewhere that I am not seeing..

Also I forgot to mention last winter after I did insulate the skirting/vapor barrier ground my windows frosted up for the first time as well. So even the living space is getting more moisture than normal. I may have the house too tight?

[Greg]

Sorry, I just reread your post & I missed the plastic.
What are you heating with? We had a major humidity problem also a few years ago and I brought home a large dehu from work (220 CFM/15gal/day) and let it run for a week to get the humidity down. After we got it down it seemed to stay down and we could manage with a small unit.

It there any way to put an auto drain attachment to it? Also check to see if your's is one of the 2 million units recalled due to a fire hazard.
http://www.cpsc.gov/en/Recalls/2013/Gre ... midifiers/

Greg

[frosty2013]

Hi Greg,

Thank you so much for posting that link about the fire causing dehumidifiers, MINE WAS IN THE LIST!!. Unplugged it right away.

When you say you got your humidity down to a normal level, do you know what the RH% was? Also my home is heated with forced Air Oil Furnace. Do you have vents in your crawl or just dehumidifier? I forgot to mention that I also replaced the whole underside belly material which was in rough shape, Removed the bad insulation and put new and used home wrap(Typar) to keep it up.

thanks

[Greg]

When we had the problems (before we moved the home) I had 4 2'x4' panels in the skirting that I would remove for warm weather and put in a screen panel. Before we started we had 80% humidity with the big dehu going for a week we got it down to around 40%.
We heat with wood pellets now but we did have a monitor kero. unit at the time. Propane is notorious for adding moisture to the air, that is why I asked.

Since we have moved last summer I really don't know what the winter will bring, but I have a feeling that since the area is wet there may be a problem.

Greg

[frosty2013]

So on the weekend I did a few tests. outside temp during day was 13-18 degrees C overnight drops to around 5 degrees
Friday night - Saturday Night Vents open - 2 exhaust fans going
RH 80

Saturday night - Sunday night
Vents closed
dehumidifier going - 2 exhaust fans going
RH 68

As soon as I take that dehumidifier out of the picture it shoots right back up, Exhaust fans seem to do very little.. Also RH in house is 45.. I have no idea what to do with this situation, Even though the RH is 80, it doesn't feel damp.. Add more vents..? frustrating.. Rather not keep dehumidifier going all the time
- there is no water under the place, none visible under plastic, temp in crawl pretty consistent at 10-11 degrees.. Should I add conditioner air from house?

[Greg]

OK so if the house humidity is 45% and the humidity under the home is 80% the moisture has to be coming either from the bottom of the home itself or from the ground/outside air.

You could try shutting off the water overnight at the main and see if holds pressure overnight. That would help eliminate the possibility of a water leak causing the humidity.

Greg