Cottage basement ventalation question

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eastern one

eastern one

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Hi everyone, I've been trying to solve a high humidity problem with my newly purchased cottage. Briefly, a 1920's cottage with addition in the mid 60's. 3 season not insulated except for 2" styrofoam over top pine planks and siding on top level. Bottom floor (basement) was dirt. Walls are small footing with cement block up to 3' in height.

I excavated the floor and put in a new concrete slab on 4" clear stone with drainage pipe around perimeter (inside and outside) I laid down a foil barrier and tuck taped joints. Poured roughly 4" cement. Exterior walls were changed for osb, added layer of bat insulation (r20), vapour barrier and finished interior walls with osb. Outside I sloped the ground away from cottage as much as possible, added drain pipe and clear stone, where i could I put tar and 2" styrofoam insulation. I have only one vent 6"x 10" roughly inside the basement. At this time my humidity level is close to 95% and temp is around plus 2 celcius. I realize new walls and a fresh floor will emit alot of moisture into the air but how could I keep the humidity level to the 50% or lower level that I am looking for. I have one space heater down there to keep temps above freezing but all it serves to do is create even more moisture. Does anyone have an idea how to bring my humidity level down without having to keep baseboard heaters running 24-7? Here are a couple pictures if I'm allowed to post them.

cottage by river (Medium).jpg

cottage renos 032 (Medium).jpg

cottage renos 038 (Medium).jpg

frisky and cottage renos 013.jpg
 
If your space heater is gas or propane and is not VENTED to the outside via chimney or exhaust pipe, this will add humidity to the basement. You'll need a heater that can be vented outside or an electric space heater or electric baseboard.

You should close the 1 vent to the basement, especially if it is vented to the outside. Even if it vents to the upstairs, it is still a problem. The basement is cooler than the upstairs because it is protected by earth and soil. It does not get any warmth from the sun as the upstairs rooms do so it will always be cooler. The cool air attracts humidity from upstairs or outside and is the source of your moisture. Keep all doors and windows to the basement closed, both summer and winter.

Run a dehumidifier with a drain hose connected to your sump pump. It needs to be able to drain on its own, whenever it needs to. Get one with a built in deicer because it could freeze up in the cooler temperatures. This site about dehumidifiers explains the idea.

The whole idea here is to isolate the air in the basement space from the outside or other areas in the home. Because the dehumidifier will have a limited amout of air volume to keep dry, it will automatically shut off when humidity levels drom to acceptable levels.

Your 95% humidity will attract mold and insects. I'd deal with this problem fairly quick if it were my home. Some people worry about running dehumidifiers because they use extra electricity but you'll find that the drier air is actually easier to heat so you'll save on your heating bills. Also, you'll find only 3 or 4 months in the year where the humidity levels are high enough to make it run more often. Right now, your humidity is high all the time because it has never been properly removed.
 
Robbie245 said:
If your space heater is gas or propane and is not VENTED to the outside via chimney or exhaust pipe, this will add humidity to the basement. You'll need a heater that can be vented outside or an electric space heater or electric baseboard.

You should close the 1 vent to the basement, especially if it is vented to the outside. Even if it vents to the upstairs, it is still a problem. The basement is cooler than the upstairs because it is protected by earth and soil. It does not get any warmth from the sun as the upstairs rooms do so it will always be cooler. The cool air attracts humidity from upstairs or outside and is the source of your moisture. Keep all doors and windows to the basement closed, both summer and winter.

Run a dehumidifier with a drain hose connected to your sump pump. It needs to be able to drain on its own, whenever it needs to. Get one with a built in deicer because it could freeze up in the cooler temperatures. This site about dehumidifiers explains the idea.

The whole idea here is to isolate the air in the basement space from the outside or other areas in the home. Because the dehumidifier will have a limited amout of air volume to keep dry, it will automatically shut off when humidity levels drom to acceptable levels.

Your 95% humidity will attract mold and insects. I'd deal with this problem fairly quick if it were my home. Some people worry about running dehumidifiers because they use extra electricity but you'll find that the drier air is actually easier to heat so you'll save on your heating bills. Also, you'll find only 3 or 4 months in the year where the humidity levels are high enough to make it run more often. Right now, your humidity is high all the time because it has never been properly removed.
Click to expand...

Thanks for the response, I'll clarify a couple more things. I have closed the vent and now humidity level is down to 80 or so, but could also be because the river is now frozen over. The space heater is typically left off since I spend very little time there, btw it is electric so no venting required. I would rather not leave it on, I find it creates more moisture in the air. I have no sump pump since my basement floor is only 4' above river level and the spring time brings water almost to floor grade. Unfortuneatly a hydro dam was built in the 60's which raised water levels by roughly 4'. I have no connection from upstairs to down stairs they are sealed off. To enter the basement I must come in from outside. Would it make any sense to spray between the floor joists with foam insulation to prevent further damage to the existing framing if I can't rid of the humidity? Thanks for helping out.
 
Robbie, I could not have said it better.Good to see someone around who understands homes, and building science.

Also until the lake freezes, you will have plenty of moisture around...there is no such thing as a sealed home. You cannot see it, but moisture is always moving around and through your home, no matter how much tape you use.
Follow the advice, and tell us how it turned out in a few weeks.
 
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