Garage de-humidification

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mdf

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#214610 20-May-2017 14:46

My garage is too humid. A big part of the problem is (I think) sometimes parking a wet car in it, with the moisture having no where to go except rusting up my tools. There's no ceiling cavity so a DVS/HRV/Smartvent style system isn't going to work (much less be able to be justified cost wise to Mrs MDF). Instead I am thinking about adding some bathroom style fans at each end on the gables.

Questions:

1. Will this help? Enough that it actually is worthwhile investigating further?

2. How should I run the fans? Both blowing outside air in, both blowing inside air out, or one of each? I was inclined toward the latter to get air flow going but clearly that will only help to the extent that the outside air is dryer than the inside air. So perhaps some kind of humidity differential monitoring will be required?

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#1785160 20-May-2017 14:56

Perhaps describe the construction of the garage first.

timmmay

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#1785164 20-May-2017 15:10

Isn't there enough airflow already around the door? Is it practical to protect the tools? I put a wet car in my shed, I haven't had any rust problems - I have DIY quantity and quality of tools

Bathroom fans you get at a hardware store are small and noisy. I got mine through a bathroom firm, it's quieter and moves a lot more air. I'd probably put the fan sucking air from the inside out, and I'd have it as far away from the door as possible.

BlinkyBill

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#1785189 20-May-2017 16:21

Open the garage door.

nickb800

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#1785192 20-May-2017 16:23

Is there any dirt built up against the outside of the garage walls?

Have you tried wiping your tools in a cloth that has been dabbed in oil?

You may find that passive options can also reduce humidity e.g. a vent on each gable, or whirlybird on the roof

mdf

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#1785323 20-May-2017 20:31

nickb800:

Is there any dirt built up against the outside of the garage walls?

Have you tried wiping your tools in a cloth that has been dabbed in oil?

You may find that passive options can also reduce humidity e.g. a vent on each gable, or whirlybird on the roof

Thanks for this. Passive vents are probably a much better place to start.

I've started oiling my tools now that I've noticed a little bit of surface rust, but it's easier on some things than others. I've actually got a bucket of sand and oil mix that I use for the gardening tools (plunge the tool in and out a few times; the sand will clean off gunge and dirt while it gets oiled). Ironically, they now seem in better nick than a couple of other tools that I try and look after. The cast iron bench saw is going to need a full recondition (though a good chunk of that is neglect; I can't claim that one is entirely recent environmental issues).

I'm considering re-roofing it. I'll look at a whirly bird then. But has anyone used the Colorsteel Dridex? Idea seems to be colorsteel backed with a layer of fleece to absorb evaporated moisture. Though it's not entirely clear to me where it goes after that.

nickb800

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#1785331 20-May-2017 21:27

I figure that with the passive gable vents that cutting the hole (especially if its cement board) is the hard bit - and you've gotta do that for motor-fan driven or passive vents.

Re the fleece backed roofing - I'm guessing it holds the moisture from releasing as droplets when the dew point is low, and lets the moisture out slowly to evaporate. Personally I'd just go with whatever roofing I want and lay roofing underlay/building paper/building wrap underneath - it's just the standard way of doing things, and probably cheaper than a special product like that

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illicit

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#1785405 21-May-2017 09:51

Soffit vents an option?

Peamsable

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#1785408 21-May-2017 10:06

My grandad wrapped his tools in oily rags. Can't remember what he used. Kerosene perhaps. Whatever it was, it was a fire hazard.

RunningMan

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#1785422 21-May-2017 11:03

How is the garage constructed? Internal access? Lined? Cladding? Insulation? Weather tightness? Airtightness? Type of door(s) and how well are they sealed?

Without knowing this, it's difficult to suggest solutions. It's quite possible it already has enough natural ventilation, depending on construction, so forced ventilation is a waste of time and money. Forced ventilation is usually only required when there is insufficient natural ventilation due to the building being almost completely airtight, which is unlikely for a lot of garages.

Is there excess moisture getting in somewhere that should be addressed?

EDIT: Spelling

froob

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#1785423 21-May-2017 11:08

How exposed is the garage to the wind? Cutting a ventilation hole in each gable end might create a bit of a wind tunnel through the garage.

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mdf

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#1785427 21-May-2017 11:22

It's a free standing double garage. Basically a box with an open gable roof. Half is for a car, half for me. Galvanised iron roof and walls over a timber frame. No internal lining (though that is on the to do list). Double roller doors. It's most definitely not airtight, with big enough gaps around doors and windows that you can feel a breeze. There's one spot where the rain can get in in a driving southerly (again, on the to do list) but it doesn't _seem_ consistently wet.

The building paper on the roof is clearly ancient and basically crumbling to pieces. Part of the problem might be water evaporating then condensing again on the roof? The building paper is over the top of the rafters so that will be a stone cold bachelor of architecture to replace unless I did the roof anyway.

When I drive the car in wet, there will still be a puddle on the floor up to 24 hours later, so there's either not enough ventilation and/or enough ambient humidity that there's nowhere for the water to go.

I reckon passive vents would be a good starting point. The garage runs north to south, so would get plenty of breeze with a vent in each gable. Another option might be to have low vents on one side and high on the other and get a nice wee convection current / stack effect going.

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RunningMan

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#1785433 21-May-2017 12:01

If you can feel a breeze around the doors, then I'd suggest there is already plenty of natural ventilation, and adding more vents isn't really the solution. As long as that breeze gets in one end and out the other, then you probably have pretty good ventilation already. Puddles on the floor 24 hours later is unlikely to improve with ventilation, it probably needs more warmth to evaporate better - the same thing would happen if you poured a few litres of water on the bathroom floor - it will take a long time to evaporate.

A metal roof will get a lot of condensation on the underneath when cold - building paper should stop this from getting inside, or allow drops to drain away, as long as it is in good condition! If the slab doesn't have waterproofing underneath then you may have moisture coming up through that as well. You'll also get condensation on the inside of the metal walls. Lining and insulating may help to get the warmth up, but particularly with metal walls and roof this needs to be done correctly to prevent build up of moisture in the cavities.

The tin shed type construction can be very susceptible to moisture inside though.

neb

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#1785684 21-May-2017 22:38

mdf:
My garage is too humid. A big part of the problem is (I think) sometimes parking a wet car in it,

And there's your problem. Why would you put a car inside your garage? Garages are for your workbench, a beer fridge, exercise equipment, the spare mattress, storage boxes, and shelves full of screws in glass jars. There shouldn't be any room for silliness like a car in a well-managed garage, that goes out on the street.

mdf

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#1785693 21-May-2017 22:45

neb:
mdf:

My garage is too humid. A big part of the problem is (I think) sometimes parking a wet car in it,

And there's your problem. Why would you put a car inside your garage? Garages are for your workbench, a beer fridge, exercise equipment, the spare mattress, storage boxes, and shelves full of screws in glass jars. There shouldn't be any room for silliness like a car in a well-managed garage, that goes out on the street.

@neb - this made my day! Well played sir, well played.

Aredwood

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#1785702 22-May-2017 00:47

My suggestion - a ceiling fan. Switch it on for a few hours after you park the car. The residual heat from the car engine will warm the garage and help to evaporate the water. As for the tools, get some old fridges that still have good door seals. And use them to store the tools in. Don't plug them in, you are only using them as airtight boxes. I know someone who has good success with this method in a garage that is close to the beach, to help keep salt spray off the tools.

Does the garage get any sun? As you need to figure out if the problem is higher humidity inside the garage than outside. Or is outside also really damp? Meaning the inside will also be damp as ventilation alone can't reduce humidity to lower than outside levels. As if it is the second, Then you will instead need to make the garage airtight and run a dehumidifier.

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