Keeping garages dry in winter

[Oldmogman]

Could anyone offer advice on keeping garages damp free and, more particularly, keeping their contents dry?

My sectional concrete garage is old but watertight. I’ve insulated the cement board roof with polythene and wood, and fitted a floor-level vent in the back door as well as leaving the rear window ajar for good ventilation. The car sits on a sheet of polythene.

However, I’ve noticed that when the weather warms after a cold spell, my car is covered with condensation for a while.
I understand that this is caused by the temperature differential, so I wondered if further insulation would help.

I’m thinking of lining the walls with polystyrene covered by plywood, adding polystyrene to the inside of the roof and covering the floor with lino.

Has anyone else tried something similar? Or have a better solution? Are there any tame builders among our members who could advise on this?

Thanks all!

[les]

You can line the walls with slabs of insulation and then use 3/8 board over that. It's my understanding that concrete is the worst material for condensation, a friend of mine is a builder and I think I recall him telling me that the softer brick or block material the less of this problem you get as it absorbs some of the moisture.

[Trickydicky]

I think the only realistic option is a dehumidifier but that would be expensive. I have the same problem as yourself, to try and help I fitted a vent low in the door and two vents in the gable ends (both ends of the garage) to try and keep the air flowing. Before I installed the door vent I found that there was little air movement low down and It now seems to have helped.
As Les says concrete is the worst for soaking up moisture.

[kevin s]

What is happening is the dampness in the air is condensing onto cold surfaces like the car as the temperature changes.

You have 2 choices, keep the temperature constant or get rid of the damp. Insulating will slow the effect down but not fix it, a damp proof membrane behind the ply lining would also help.

I have a similar garage, in mine I have a de-himidifier running which takes around 4 or 5 litres of water out a week in wet weather, Parts of our minor has been in bare metal for several months now with no rust. The cost of this would be much the same as insulation and ply.

Kevin

[Matt Tomkins]

couple of sacks of kitty litter would act as a cheap dehumidifier if funds are tight

[beero]

It must be an insulation thing. My garage is very well insulated, almost to house standards, I have virtually no air movment, just the gaps around the up and over doors and I have no damp at all.

[Mulli]

If your garage isn't to large (or you don't want an electric one) you could use several of these:

http://www.ebay.co.uk/itm/Streamline-Ko ... 417a1aedc6

but buy the crystals in bulk otherwise it gets expensive:

http://www.ebay.co.uk/itm/5kg-Moisture- ... 20d55909d0

I brought two 10KG sacks, cant remember the proper name of the stuff but it tells you on the box of the dehumidifyer.

Helps in my small garage I use 6 of them and empty every 2-3 weeks.

[bmcecosse]

The usual de-humidifying agent is Silica Gel. Heat it in the oven to regenerate it. You can either go for good air-flow, or try to completely seal the garage - and run the dehumidifier.... this is most likely to be successful. Helps too if the garage can get the benefit of any sunlight through windows during winter..

[dalgrae]

I have a concrete secrional garage and as far as I am concerned it is damp free,it recently had a new roof fitted the same type as B & Q and other tin type sectional buildings .I installed standard roof felt under this prior to puttng the roof sheets on ,I have left this felt overhanging slightly under the guttering on the side that the wind blows from but trimmed it back on the other side and this seems to create some positive ventilation,all the machinery in the garage is all rust free so I assume my plan works .We used to run a dehumdifier in the house and yes it removed a lot of water but it also consumed a large amount of electricity as I believe they are rated quite high in electrical consumption also unless a permanent drain is used you have to daily empty the tank

[kevin s]

My dehumidifier uses a small fridge pump and uses about the same amount of electicity, the tank needs emptying once a week (4 litres). you can get much bigger units which will take a gallon a day of water out but my small one keeps a 20 x16 garage dry.

The other problem with concrete garages is if you have the concrete corrugated roofing( looks like the old asbestos), the drips can attack paint, I had the paint on the bonnet of a xjs I used to have ruined by this.

[MarkyB]

As long as the roof is good and water isn't finding it's way in else where I'd say ventilation is the way to go.
Nothing to remember, or pay for are the highlights
Maybe a solar powered fan somewhere to aid circulation?

[Trickydicky]

I should have added in my original post that on dry days I leave the side door of my garage open for an hour or so which also helps air movement.
As Kevin rightly points out too, drips from the roof are a problem, to try and counter this the car has a cover, it's amazing just how much rubbish gets blown in through the eves.

[MikeNash]

Alas, Oldmogman, the trouble is the weather. In winter we get cold snaps which are dry (below freezing, air holds little water) interspersed with mild wet weather, often stormy, in which the humidity is high. So your garage gets cooled down in the frost only to be hit by mild damp intervals when the damp air gets into your garage and cause condensation on everything. If you're lucky and your garage is attached or built into your house you've no problem - its always just warmed enough to keep it dry. But separated, its real problem. (Especially for me 'cos I live in a frost pocket - we had minus 15C one night last winter.)

I think you need to minimise ventilation and only open it up on dry days and insulate as best you can. Don't what ever you do open it up or ventilate on warm moist days after a frost. Keep a cheap thermometer in there to check that the garage is warmer than the outside before you open up. And if you can add a little heat then so much the better. Regards, MikeN.

[bmcecosse]

Fortunately my garages are attached to the house - and double brick wall construction with air gap. The doors face south - so any sun is gathered by the steel doors and transmitted in to the garages. I agree with above - better to NOT ventilate after cold weather. Best you can do with a separate garage is to build a sealed room within the garage - and dry it with a dehumidifier - maybe just a couple of hours each day - and/or trays of silica gel.

[philthehill]

Whilst my Minor is kept under a breathable cover in a dry garage (attached to the house) and where I do not suffer much with condensation the anti condensation trap filled with Calcium Chloride crystals and placed inside the Minor soon fills up with condensation even in good weather. So not only does the surrounding air need to be considered but also the inside of the Minor.
When placing the moisture trap inside the car I place it in a seed tray which does not have holes in the bottom to catch any overflow or spills.

[Oldmogman]

Thanks guys – that’s certainly food for thought, if not the definitive solution (which would probably involve replacing my garage with a wooden one, or moving house...).

However, while there seems to be some disagreement of whether to ventilate or not to ventilate, the subject of absorption seems to be a common thread.

I’ve noticed that my wooden shed seems drier, which is either because the wood doesn’t retain the cold or absorbs the moisture – or both.

So perhaps the answer is to line the garage walls with wood to absorb the moisture on the days when the temperature changes, while keeping some silica gel/salts, etc, inside the car. I was thinking of 6mm ply - or should I go thicker?

Since the garage is separate from the house and unheated, it would seem that insulation is pointless – what would I be insulating it from? Or is it that I’m insulating the car/wood lining from the cold concrete walls?

As for the ventilation, I’m tempted to think a good draught blowing through the gaps in the up-and-over and out of the vents and back window will keep the garage drier than trying to seal up everything. I wonder if it’s possible to test this?

Has anyone tried lining their concrete garage with wood?

[bmcecosse]

Ventilation just brings in more moisture! You need to make a sealed inner room with the car inside - and then de-humidify it. Ventilation is good - on a dry day - if for example you drove the wet car into the garage - then you need to ventilate to dry off the excess moisture.

[MarkyB]

It should be possible to rig up a fan with an inside and outside humidity sensor such that the fan only runs when it's more humid inside than out.
Someone here can probably come up with a circuit.

Insulation has to be a good idea to moderate temperature extremes and reduce condensation.
Even if it was possible to hermetically seal a garage it would be defeated when the door is opened to use the car and counter productive when the car is wet.

[philthehill]

If you are concerned about condensation effecting the car and are going to spend money it may be far better to buy a Carcoon Car Bubble for example:

http://www.frost.co.uk/carcoon-car-plastic-bubble.html

[bmcecosse]

I assume these carcoon bubbles must dry the air before pumping it in? Otherwise it's just pumping more moist air over the car. And yes - the 'sealed' inner garage would be only for over-winter storage - to maintain dryness over a long period. A timber frame with poly sheeting stretched over would do it - with an easily removable front piece to allow the car to be rolled out. A wet car should never be put away in a garage !