Help me with my cold damp garage

[nickinnh]

Hey all, thanks for reading this. I’m a first time homeowner as of April! For reference, my garage is 2-car, attached, has a bedroom above it and the ceiling and attached walls are finished.

I’m finding in this cold NH winter that my garage retains high moisture levels even in the winter (humid in summer too and planned on installing dehumidifier next summer, but it’s still moist). I’ve noticed some mildew starting to develop on the outside walls. I’ve heard that humidity decreases when it stays cold but that is not the case for me. I placed a thermometer/hygrometer out there and it’s staying around 30-35 degrees and 70-85% humidity!

There’s not great airflow and some water comes in from snow on tires.

I’ve been reading some stuff and I think I need to both heat my garage and insulate the remaining two outer walls to remedy this problem. The problem is, I think I need to somehow dry or heat the garage first in order to fully remove the mildew, then probably paint with mildew resistant paint, BEFORE I can insulate the walls. My plan was to buy a wall mountable electric garage heater but I believe now I’m going To have to somehow heat with this to be able to clean the mildew before the insulation.

The second thing I’ve noticed is that water from the tire snow is running towards he back wall only on occasion, and running in between the floor slab and wall. This makes me think the floor doesn’t direct the water well enough to the central drain.

So do I:

1) proceed with my plan to heat and dry the garage, remove mildew and paint, then insulate, vapor barrier, Sheetrock and mount that heater to keep it temp controlled, or

2) pay someone to put down an epoxy floor that both insulated and directs water into the drain?

Thanks so much for your guys’ expertise, my area is limited in garage scorer resources.

 

[Pathfinders]

Welcome aboard.

 

[icthruu74]

Welcome to the forums, and congrats on the new home! For starters, can you skip parking in the garage for a while? Not bringing in more moisture is going to be a good first step. Secondly, relative humidity decreases as temperature raises (assuming you aren’t adding more moisture to the air), so if you could get the temp in the garage up a bit you may help reduce the mildew issue. With a humidity above 70% you’re in the mold and mildew range. I run a box fan on low in my garage that seems to help somewhat, but if you can get a dehumidifier out there that would probably be the best solution.

All that said, if you don’t do something about the floor slope, you may have bigger issues. You may want to look into garage under car mats that will help contain the water/snow from your cars. That will be the cheapest and easiest fix for that.

Finally if you’re going to heat the garage you’ll want to insulate the outside walls. But first you need to get the humidity down and I’d clean the walls with a bleach solution to help knock down the mildew that’s there already. I don’t think I’d paint the stud bays with mildew resistant paint, but I’d sure use it on finished walls. You can also buy mildew additive for regular paint.

Good luck!

 

[Vicegrips]

Hay Nick welcome and congrats to owning your home. I hope it’s not as bad as my first home which was a typical 4,000+ sf New England farm house built in 1850, with field stone foundation and no insulation except for the 8 layers of wall paper lol. There wasn’t any mold anywhere except for the parts of the home that were remodeled in the early 80s when they started using vapor barriers. We had about a month to work on the home before we moved in and didn’t even make a dent in all the things I had plan to do. We had a early winter like this year so moving in December was difficult. But living in a old home home through a NH winter can be exciting! Lucky me I do sprayfoam insulation, not really I had to go into the gates of hell into so of the worst crawl spaces I’ve ever been in. But after we were done we were only using one tank of oil with our old steam system and one to two cords of wood.

The garage in your place sounds exactly like the house I’m living in now with the garage in the first floor and walk out basement, it was built in the early 70s, 2x4s with a vapor Barrier every where. The whole place seemed like mold/mildew.

Like others have side, your going to want to stop water infiltration into the garage. If it’s not a leak, it could simply be moisture laden air hitting cold metal, concrete or plastic. One of the worst things you can do is open up your basement or garage when the humidity is high in the summer, people think they are airing or drying things out but really when really they are just introducing more moisture. My basement was a dark moldy nasty place, I stopped the leaks, treated the mold, properly insulated and now it’s a great space.

I’m central NH, let know if you need some help or a little direction

 

[matt_i]

I think a good step is to add a ceiling fan. Doesn't have to be flashy or super big. Let it run 24x7. This will keep air moving and should help with the stagnation that invites mildew growth.

Snowmelt's gonna happen, I squeegee it out when possible.

 

[nickinnh]

Welcome to the forums, and congrats on the new home! For starters, can you skip parking in the garage for a while? Not bringing in more moisture is going to be a good first step. Secondly, relative humidity decreases as temperature raises (assuming you aren’t adding more moisture to the air), so if you could get the temp in the garage up a bit you may help reduce the mildew issue. With a humidity above 70% you’re in the mold and mildew range. I run a box fan on low in my garage that seems to help somewhat, but if you can get a dehumidifier out there that would probably be the best solution.

All that said, if you don’t do something about the floor slope, you may have bigger issues. You may want to look into garage under car mats that will help contain the water/snow from your cars. That will be the cheapest and easiest fix for that.

Finally if you’re going to heat the garage you’ll want to insulate the outside walls. But first you need to get the humidity down and I’d clean the walls with a bleach solution to help knock down the mildew that’s there already. I don’t think I’d paint the stud bays with mildew resistant paint, but I’d sure use it on finished walls. You can also buy mildew additive for regular paint.

Good luck!

Thanks for the welcome and input! I had no idea about garage mats so I’ll look into those which will at least stop the runnage problem. I’m gyessing they’ll stay wet in there until I get the garage heated.

From what I understand, I would have to get a special dehumidifier for any significant dehumidification at 30 degrees, to have it work well and avoid freezing in the winter. My original plan was to put in one for the summers. Would heating the garage to 50-60 or so plus a fan and reducing snow moisture get it dry enough to get the wall cleaning done prior to insulation?

 

[Barnabas]

I keep a humidifier going in my garage all year. It's just a regular one you get at an appliance store. I keep it on top of my full-sized freezer and the water drains down and out through a hose.

Heating with gas, like propane can add lots of humidity. Your idea of electric is better for controlling humidity, but costs more to operate.

Can you add a vent from your house furnace to the garage?

 

[nickinnh]

I keep a humidifier going in my garage all year. It's just a regular one you get at an appliance store. I keep it on top of my full-sized freezer and the water drains down and out through a hose.

Heating with gas, like propane can add lots of humidity. Your idea of electric is better for controlling humidity, but costs more to operate.

Can you add a vent from your house furnace to the garage?

Hey Barnabas,
I’ve thought of that but I’m worried about freezing. It gets pretty cold up here-been about 15-25 for a week now and not even winter. I’m going to put my portable one out there for the day today to see what happens. Maybe running it once a day will do enough to clean the mildew and get the project started.

My house is hot water heater with propane and the garage is an add on ten years ago. I think the cost of adding the garage to my heating may be a lot up front and still more expensive than electric. Plus my propane costs are much higher than electricity so there’s that. We’ll see what the dehumidifier does today!

 

[finn]

Your dehumidifier won’t work at low temperatures, and vented propane heaters don’t ad humidity to the heated space.

Get some airflow, but, just as importantly, insulate and raise the temperature. Moisture laden air condenses when it hits a cold surface, like an uninsulated wall.

I also question the suggestion to put a mat under your wet car. It will probably act like a sponge, sopping up snow melt, and will remain wet.

Better to park outside until you insulate and solve the moisture and humidity issues.

 

[glentre]

Welcome to the forum, Nick. To resolve your situation, might want to think about a window type heat pump to give you both heat and cooling. Also, look at the Bard heat pumps. These are mounted on the outside wall and all you see inside are the supply and return grilles and they are much more quiet than window units. I had the same problem in early Spring with warm and moist days outside and overnight cold garage floors and everything inside including tools and cars. I foolishly opened the doors and got a flash of condensation and subsequent mold over everything. Installing a 7 ft ceiling fan running 24/7 fixed that problem.

Good luck and please keep up posted when you get the problem resolved.

Glen

 

[nickinnh]

Thanks for the replies everyone.

Vicegrips- thAt first house sounds like a lot of work!! I stayed away from really old New England houses because I didn’t think I wanted to handle stuff like field rock foundations! I’m also central NH, western part.

So what I’ve decided so far - I took a look online at the outside Bard pumps and while they look awesome, they are probably too much for what I do in my garage. I’m more DIY guy, never going to have a lift in my garage, etc. I don’t think I mind about cooling the garage so much in the summer, mostly just on a mission to reduce the humidity.

Dehumidifier- I ran it today out there for 4 hours. Too cold. Not a drop, didn’t work. Will have to forget this for the winter and install a automatic pumping dehumidifier for the summer.

I moved everything sitting on the floor of the garage to the peg board or the basement to increase air circulation.

I put a utility fan on the floor and am running that, will keep that on daily.

Planning on parking the vehicles outside for awhile to let the floor dry.


Next steps- I’ve gotten a couple quotes from electricians to get a 240v plugin out there for a walls mounted electrical heater. As others mentioned, propane will probably increase the humidity and as the garage is an add on and the house hot water heat with pricey propane, this plan may still be cheapest?

Going to get a heater put in, dry it out a week, clean the mildew, and insulate and then see where I’m at.

 

[nickinnh]

It’s making me have 5 posts before I post a link, this is five

 

[nickinnh]

These are the two heaters I’m considering right now

http://https://www.amazon.com/NewAir-G56-5600-Garage-Heater/dp/B009NJ6K8K/ref=mp_s_a_1_1?ie=UTF8&qid=1543686545&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=newair+5600+watt+garage+heater&dpPl=1&dpID=61NSNSEw1QL&ref=plSrch

http://www.amazon.com/gp/aw/d/B01ANZHULI/ref=psdcmw_510182_t2_B000TK2SWO

 

[Jakemedic]

Hello! Personally, would stay away from electric heat. I installed a King heater in my old shop last winter. ONE weekend raised my electric bill 40.00. Now I’m in Iowa and thank goodness I sold the house before this winter. Propane, if vented outside, should not raise your humidity (although I have only had natural gas besides electric). I would let my vehicles be outside for a little while. That, obviously, is a main source of your humidity in my opinion. Best of luck with your problem!

 

[e-tek]

So I have a very similar set up to what u describe in my attached garage (finished, bedrooms above, snowy vehicles inside). I use garage mats to contain the water, heat the area about 10degree above freezing and run a 4"vent fan through the window. This not only keeps the humidity to about 30, but even dries the melted snow from mats.

Good luck!

 

[nickinnh]

Hello! Personally, would stay away from electric heat. I installed a King heater in my old shop last winter. ONE weekend raised my electric bill 40.00. Now I’m in Iowa and thank goodness I sold the house before this winter. Propane, if vented outside, should not raise your humidity (although I have only had natural gas besides electric). I would let my vehicles be outside for a little while. That, obviously, is a main source of your humidity in my opinion. Best of luck with your problem!

May I ask, was that electric heated shop fully insulated? My house is already sucking up the propane so much that I don’t know if I want to add more to that bill. What were you keeping the temps at? I was hoping that once insulated, keeping the garage at 50 wouldn’t be too bad?

I grew up in SE Iowa (MP) so I’m familiar with your neck of the fields.

 

[BillK]

Can you add a vent from your house furnace to the garage?

Illegal and VERY dangerous

 

[BillK]

I would bet that one of those 1500 watt oil filled radiator type heaters would make a big difference. Not sure what it would cost to keep it on 24/7 during the cold spells.

 

[Showkey]

1500 watts likely would run continuously........so at avg national electric rates $108 per month.

 

[nickinnh]

1500 watts likely would run continuously........so at avg national electric rates $108 per month.

Hey showkey, mind me asking how you calculate that? The wall heaters I posted above are 5600W or so, so I’m betting they’d run less.

 

[Pluribus]

Hey showkey, mind me asking how you calculate that? The wall heaters I posted above are 5600W or so, so I’m betting they’d run less.

When I run the #'s, I get a different cost.

1500 watts = 1.5 kilowatts.
Hours per day = 24.
Average days in a month = 30.42
National average electricity rate is 13.01 cents per kilowatt hour. ($.1301/kwh)

1.5 kilowatts x 24 hours/day x 30.42 days x $.1301/kilowatt hour = $142.48

I use the little 110v, oil filled heaters in my outbuildings to "heat" them. Basically, I have the switches set for 600 watts, then set the knobs at low, which is 2.5 or 3. When it's cold, it runs constantly. This keeps the temperature 15 or 20 degrees above the outside temperature on the colder days. For example, when we were in the mid-20's this week, it was in the high 40's in one of my shops. I figure this costs me about $50/month in the coldest months per heater. (My rates are cheaper than NH.)

During the summer, I keep the heaters going on low to control the condensation. My location is in the woods & shaded. The shops will stay very cool, and when a bunch of warm, damp air comes in through open doors, condensation can form. They don't run all the time during the summer though. I was using a dehumidifier for a while, but it croaked, so I need to do some troubleshooting or get another one.

I have a bunch of the 220v heaters like you show, but I don't dare run them due to cost. It doesn't need to be THAT warm for me. The guy that gave them to me used them and paid big bucks for power, but he did keep it warmer than I do.

 

[nickinnh]

When I run the #'s, I get a different cost.

1500 watts = 1.5 kilowatts.
Hours per day = 24.
Average days in a month = 30.42
National average electricity rate is 13.01 cents per kilowatt hour. ($.1301/kwh)

1.5 kilowatts x 24 hours/day x 30.42 days x $.1301/kilowatt hour = $142.48

I use the little 110v, oil filled heaters in my outbuildings to "heat" them. Basically, I have the switches set for 600 watts, then set the knobs at low, which is 2.5 or 3. When it's cold, it runs constantly. This keeps the temperature 15 or 20 degrees above the outside temperature on the colder days. For example, when we were in the mid-20's this week, it was in the high 40's in one of my shops. I figure this costs me about $50/month in the coldest months per heater. (My rates are cheaper than NH.)

During the summer, I keep the heaters going on low to control the condensation. My location is in the woods & shaded. The shops will stay very cool, and when a bunch of warm, damp air comes in through open doors, condensation can form. They don't run all the time during the summer though. I was using a dehumidifier for a while, but it croaked, so I need to do some troubleshooting or get another one.

I have a bunch of the 220v heaters like you show, but I don't dare run them due to cost. It doesn't need to be THAT warm for me. The guy that gave them to me used them and paid big bucks for power, but he did keep it warmer than I do.

Hm that’s interesting. Another person recommended trying those 110v oil filled stand up heaters in the garage. The reason I was hoping to do the ones I posted is because they are able to save floor space by being mounted.

I wish I knew how much they’d cost. It shouldn’t be the 220v part of that that costs more, that just changes the amps, as the Watts is what actually gets the charge in kwh if I’m not mistaken. The fact that the heater is 5500W is why it may cost more. It has a thermostat on it, and I’m assuming a 5500w unit would run much less time than a 1500w heater, so I’m wondering If I set it to 2000w max, how much it’d actually cost more.

Do you feel safe with those stand up oil heaters running automatically without you there?

Thanks

 

[nickinnh]

I think it’d be like this, math-wise.

5.5kw x 6.5 hours x 30.42 days x $0.13 = $141

So basically if the larger unit ran 6.5 hours/day it’s cost the same as yours running 24hrs

 

[nickinnh]

E-tek, what do you use to heat your garage?

 

[Jakemedic]

Sorry didn’t know how to quote...
May I ask, was that electric heated shop fully insulated? My house is already sucking up the propane so much that I don’t know if I want to add more to that bill. What were you keeping the temps at? I was hoping that once insulated, keeping the garage at 50 wouldn’t be too bad?

I grew up in SE Iowa (MP) so I’m familiar with your neck of the fields.


Hello! Yes, the garage was insulated. To be fair, it was insulated by the previous homeowner, possibly not to the level that I would have done. My next shop will be well insulated, and will be using natural gas. The last house was in NW Iowa, colder and more snow than where we are now. I hope that helps!

 

[Pluribus]

Hm that’s interesting. Another person recommended trying those 110v oil filled stand up heaters in the garage. The reason I was hoping to do the ones I posted is because they are able to save floor space by being mounted.

I'm a big fan of them, especially the ones I picked up at thrift stores for $10 or $15 apiece. As for floor space, I've put them on top of workbenches before. They are all on casters, so they don't need to be on a fireproof surface.

I wish I knew how much they’d cost. It shouldn’t be the 220v part of that that costs more, that just changes the amps, as the Watts is what actually gets the charge in kwh if I’m not mistaken. The fact that the heater is 5500W is why it may cost more. It has a thermostat on it, and I’m assuming a 5500w unit would run much less time than a 1500w heater, so I’m wondering If I set it to 2000w max, how much it’d actually cost more.

Figure electric resistance heat (with no fans or pumps) is 100% efficient. You can balance time vs. wattage, but there's no "efficiency" improvement going up or down unless there's some weird voodoo I'm not aware of.

Do you feel safe with those stand up oil heaters running automatically without you there?

Absolutely. I figure the heating element is encased in metal, and surface temps of the units are nowhere near combustible to whatever might touch it.

Thanks

See colored text below paragraphs.

 

[nickinnh]

Hey all,
After keeping the snowmelt and cars out of the garage the humidity has dropped from above 80 to about 75.

I bought an oil filled radiator space heater since it was on sale. I ran it about 18 hours and it increased the temp from 33 to 41 but was afraid to leave it on while not home. This increase didn’t change the humidity at all.

My next thoughts are to somehow try to get the heat up to 50-55 for a few days vs opening the windows to see if it’s a ventilation issue(however not too excited about that as the bedroom is above the garage and a 25 degree garage below doesn’t sound great).

Trying to get ahold of a garage contractor for opinions but would like to do the work myself

 

[Abeo]

Just to clear up the idea of humidity in the winter...
Warm air has more capacity to hold moisture. Air at freezing and 100% humidity (ie, all the air can hold at 32 F) is the same amount of water in the air at 85 F with 15% humidity. So if you warm up air without taking any moisture out of it, you will reduce the % humidity but will still have problems with it condensing on cold uninsulated walls (because the uninsulated walls have a temperature that's less than the dew point, ie the temperature where 100% humidity is reached).

Lots of people around my parts have good luck with a bathroom fan that vents outdoors, hooked up to a humidity switch. Without an air exchange or warming up and using a dehumidifier, I don't think you'll have much luck. Since there is a living space above, I'd insulate and add a gas furnace to keep it around 50, as well as run a dehumidifier.

 

[Daniel Dudley]

Do a search on Radon Seal. It might help with your moisture problem.

 

[nickinnh]

Just to clear up the idea of humidity in the winter...
Warm air has more capacity to hold moisture. Air at freezing and 100% humidity (ie, all the air can hold at 32 F) is the same amount of water in the air at 85 F with 15% humidity. So if you warm up air without taking any moisture out of it, you will reduce the % humidity but will still have problems with it condensing on cold uninsulated walls (because the uninsulated walls have a temperature that's less than the dew point, ie the temperature where 100% humidity is reached).

Lots of people around my parts have good luck with a bathroom fan that vents outdoors, hooked up to a humidity switch. Without an air exchange or warming up and using a dehumidifier, I don't think you'll have much luck. Since there is a living space above, I'd insulate and add a gas furnace to keep it around 50, as well as run a dehumidifier.

Thank you for the input. I'd insulate right now, but due to mildew on the walls, I somehow need to fix the humidity and dry everything out in order to mitigate t\he mildew BEFORE I insulate. This is the tough part :/

 

[nickinnh]

So what I've attempted so far:

Keeping vehicles and snow melt out of the garage: 83% down to 75%

Tried 1500W oil filled radiator heater at this point, which couldn't get the garage past 42 degrees. Humidity stayed at 73-75%.

Turned off the heater, opened up the doors for an hour and then left the windows open. Humidity dropped 10% but staying at 65%.


The floor is now entirely dry and there's ventilation. I feel I should be in the dry winter air range and definitely under 60%. There has to be moisture coming in from somewhere. There's a drain in the middle of the floor and a small 1/4-1/2" crack around the concrete. The garage is an add on, no basement under and is a slab. Is the moisture coming through the floor? The floor appears dry.

My next thoughts are:
contact a garage flooring person to see what they think about moisture from the floor and epoxy coating it.

vs

install the wall mounted hardwired space heater and see if this warms it up enough to run a dehumidifier.

heat pump? know less about this.

thanks

 

[nickinnh]

To all that followed this, thank you. It was a 6 month process, but my cold, damp, garage that I used to shovel ice out of is now warm and dry at a constant 40% humidity

 

[MetalBuildingFun]

Thank you for the input. I'd insulate right now, but due to mildew on the walls, I somehow need to fix the humidity and dry everything out in order to mitigate t\he mildew BEFORE I insulate. This is the tough part :/

When hurricane harvey came to town I needed to find out how to get some mildew out of a few things for an elderly lady and my ceiling where I had some water damage and this stuff worked fantastic. It dries the mold and mildew. It can be used on clothing, furniture, walls etc. It won't take away any stains, but you wipe away the dried mold and mildew, then paint over the stains to cover. It could take a few treatments to complete the process depending on how bad the mold is.

We used it on patio furniture, dresses she made and didn't want to get rid of, pillow cases she made. It all came out no problem. Just follow the instructions, it is quite easy to use and don't let the price scare you.

https://www.lowes.com/pd/Concrobium-128-fl-oz-Liquid-Mold-Remover/1001073964

 

[Bent Handle]

What did you end up doing?

 

[nickinnh]

The major issues was rot through the frame next to the garage door, letting water in, and whomever added the garage on, they did not put a vapor barrier under the slab, allowing the moist gravel under to seep moisture through the slab. A concrete specialist said I needed a new slab and graciously wanted to do it for $13k- no thanks.

It was quite the process, in relative order I:
-put a strong dehumidifier in there
-fully rebuilt the bottom wall frame next to the doors so water can’t run in
-installed gutters to get water further away from the front of the garage
-in full protective gear, I cleaned the mould and mildew off all walls
-painted all walls with mold killing primer
-hand scraped the slab wit a metal brush
-chemical stripped the entire slab
-used grinder on slab all to take off prior cheap treatment
-applied Ghostshield densifier to slab
-applied ghostshield concrete sealer to slab to prevent moisture coming through
-filled all slab expansion joints
-closed cell spray foam insulation to all walls
-drywalled entire garage and primed and painted
-insulated my garage door
-installed raised threshold bump across garage door openings
-installed hardwired electric space heater to climate control garage

Did it all myself other than the spray foam and was certainly cheaper than a new slab