Garage ventilation/extraction strategy
Discussion
A post on the 'best garages' thread reminded me that I really must get on and do something about ventilation for my new garage. It's a shed type T&G construction with an open pitched roof. No insulation.. 9x6m and 3.7m to the ridge. Three pairs of barn doors on the west face which (if it's relevant) is generally the direction the wind blows from.
I'd like to keep some air flow going and will likely control that from a humidistat. Is one 6" extractor going to do the trick? Or could I consider one on each gable on the assumption they won't be trying to work against each other?
How key is vent location in all this?
I'd like to keep some air flow going and will likely control that from a humidistat. Is one 6" extractor going to do the trick? Or could I consider one on each gable on the assumption they won't be trying to work against each other?
How key is vent location in all this?
Control of ventilation via a humidistat is intended for those spaces where humidity is being created within the space itself (bathroom, utility room, laundry room etc) and wants exhausting to outside to prevent damp/mould etc. Using extract fans in an (assumed) unheated garage will ultimately achieve very little, as (during the winter months at least), you will simply replacing the internal air with damp / cold air from outside - you could potentially make the situation worse by creating a continuously colder/damper room. In fact, depending on set point, you could end up in a situation where the fans run continuously through the winter, without really achieving anything, except maybe removing odours/exhaust smell etc.
Is the space heated at all? If so, some strategic passive vents should be sufficient to keep RH low and provide improved air movement. If not, perhaps a better use of your money/effort would be to keep the space 'closed up' and use a dehumidifier instead (by recycling the air) and keep RH as low as possible. Construction of the shed alone sounds like natural infiltration through the doors/fabric will be sufficient for a 'turn over' of air in this instance.
Is the space heated at all? If so, some strategic passive vents should be sufficient to keep RH low and provide improved air movement. If not, perhaps a better use of your money/effort would be to keep the space 'closed up' and use a dehumidifier instead (by recycling the air) and keep RH as low as possible. Construction of the shed alone sounds like natural infiltration through the doors/fabric will be sufficient for a 'turn over' of air in this instance.
Edited by MattyD803 on Wednesday 6th November 08:36
Baldchap said:
I've bought a dessicant dehumidifier (work better in cold environments) for mine that exhausts outside.
Is there much maintenance to do with one of those?I’m just building a new garage for my dailies and have been wondering what to do about water/moisture removal too.
Was going to put a large inline fan to deal with fumes but don’t really see it as a good solution for the moisture.
LooneyTunes said:
I’m just building a new garage for my dailies and have been wondering what to do about water/moisture removal too.
Was going to put a large inline fan to deal with fumes but don’t really see it as a good solution for the moisture.
It depends if the space is heated. If it's an unheated garage and your bringing cold/wet cars in, it'll be just as wet in the morning as when you drove it in the evening before. (Particularly mid winter when ambient is low and RH is high).Was going to put a large inline fan to deal with fumes but don’t really see it as a good solution for the moisture.
If it's a heated space, then an extract fan at high level to pull the remnant of exhaust fumes out as well as the damp/moist air would work well.
Edited by MattyD803 on Wednesday 6th November 09:49
Unless an I heated garage has actual damp issues then the time when humidity is higher than outside will typically be when a wet car is parked in it and while that car dries.
I would assume that drawing air from the front doors, over the car and out the back via an extractor would be of some use to aid in the drying of the car.
If it were me I'd not bother with typical domestic fans but instead consider proper 12" fans such as catering extraction and simply set it via something like a multi hour timer that you hit when leaving the garage if a car is wet.
I wouldn't see any benefit to either a small fan or running a fan continuously. Just a system to drive air flow over the car when it's wet.
At my previous house my solution for a permanently damp Gloucestershire was to just not have doors on three bays which were used for the every day cars. Made life much simpler.
Also helped with exhaust extraction.
More valuable offroad dailies could then be stored in closed bays (these did have insulated ceilings and the wooden sides had also been insulated as this does stop 'sweating'.
If it's plausible, just leave a door open when parking up a wet car as this was always the original solution since the advent of the motor car.
I would assume that drawing air from the front doors, over the car and out the back via an extractor would be of some use to aid in the drying of the car.
If it were me I'd not bother with typical domestic fans but instead consider proper 12" fans such as catering extraction and simply set it via something like a multi hour timer that you hit when leaving the garage if a car is wet.
I wouldn't see any benefit to either a small fan or running a fan continuously. Just a system to drive air flow over the car when it's wet.
At my previous house my solution for a permanently damp Gloucestershire was to just not have doors on three bays which were used for the every day cars. Made life much simpler.
Also helped with exhaust extraction.
More valuable offroad dailies could then be stored in closed bays (these did have insulated ceilings and the wooden sides had also been insulated as this does stop 'sweating'.
If it's plausible, just leave a door open when parking up a wet car as this was always the original solution since the advent of the motor car.
There will be a couple of open bays, but definitely need the doors closed on the main part when not entering/exiting (otherwise I’ll forget to close them!).
I’ll figure something out when I see how the space actually gets used as it could turn out that the open bays do indeed see the most use.
I’ll figure something out when I see how the space actually gets used as it could turn out that the open bays do indeed see the most use.
LooneyTunes said:
There will be a couple of open bays, but definitely need the doors closed on the main part when not entering/exiting (otherwise I’ll forget to close them!).
I’ll figure something out when I see how the space actually gets used as it could turn out that the open bays do indeed see the most use.
I found the open bays ideal for the cars used regularly. So much easier than doors etc. Bays with doors for the storage side and less used or seasonal cars also superb. For me, the ideal scenario having now lived with it is to have both. I’ll figure something out when I see how the space actually gets used as it could turn out that the open bays do indeed see the most use.
Stuff gets from 'wet' to 'dryish' in an open shed quite easily, but sometimes you still get dew on cars etc.
If you want really dry, then close everything up and install a dehumidifier and maybe some heat
Ventilation in your house is a lot more effective, because your house is heated.
Of course parking a hot car in a garage is different from a cold wet car or other object.
There's enough heat in a car engine to do some drying.
Having an insulated roof and lots of 'thermal mass' so your garage doesn't cool so much at night also helps.
A lot depends on local climate and time of year.
When I put a bike away wet, I try to arrange ventilation for a while, but this time of year, once things are dry-ish, longer term I find a dehumidifier effective.
But if your are talking about everyday cars which get driven in the rain often, then going mad about optimal storage overnight may be a waste of time.
If you want really dry, then close everything up and install a dehumidifier and maybe some heat
Ventilation in your house is a lot more effective, because your house is heated.
Of course parking a hot car in a garage is different from a cold wet car or other object.
There's enough heat in a car engine to do some drying.
Having an insulated roof and lots of 'thermal mass' so your garage doesn't cool so much at night also helps.
A lot depends on local climate and time of year.
When I put a bike away wet, I try to arrange ventilation for a while, but this time of year, once things are dry-ish, longer term I find a dehumidifier effective.
But if your are talking about everyday cars which get driven in the rain often, then going mad about optimal storage overnight may be a waste of time.
DonkeyApple said:
I found the open bays ideal for the cars used regularly. So much easier than doors etc. Bays with doors for the storage side and less used or seasonal cars also superb. For me, the ideal scenario having now lived with it is to have both.
Makes sense, but this garage block is closer to the house and will have automated doors. The plan is that I can keep a daily and a couple of toys in it so that the latter get used more than if I have to walk down to the other garage and deal with additional manual gates and doors. LooneyTunes said:
Makes sense, but this garage block is closer to the house and will have automated doors. The plan is that I can keep a daily and a couple of toys in it so that the latter get used more than if I have to walk down to the other garage and deal with additional manual gates and doors.
Sounds nice. I have electric openers now at the current place but I still miss the ease of simply driving in. I reckon I'm the most impatient human as the electric seats and boots of modern cars drive me up the wall and keep reminding me of this: 
Thanks all.
The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
Gad-Westy said:
Thanks all.
The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
I suspect tools will rust just because the space isn't insulated. I found that as soon as I insulated a garage space the curbing of the diurnal temp differentials stopped things like tools getting that surface rust. The other thing I used to do was spray the tools with that WD40 grease. The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
I've just completed a garage build and the front is single skin but the garage is extra deep so it has a workshop and storage space at the rear which has 200mm celotex in the roof and 50mm on the walls. There is a dehumidifier in there but it's not yet kicked in despite it being pretty damp at the moment.
If you're doing a multi bay garage but have quite a few tools etc then could you contemplate one of the bays being an insulated room?
Gad-Westy said:
Thanks all.
The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
Could you not baton off and insulate? That'll make a big difference. The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
Baldchap said:
Gad-Westy said:
Thanks all.
The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
Could you not baton off and insulate? That'll make a big difference. The garage isn’t heated and not insulated. I have admit I’d assumed a little air movement might be wise but seems there is a bit more to consider here.
The goal here is really to avoid rusty tools and cars and generally make for a more pleasant environment.
I have to admit running costs have always put me off the the idea of dehumidifiers and heating but maybe I could be convinced.
Gad-Westy said:
I certainly could but costs are pretty huge to do it well and the slab underneath is neither insulated nor damp proofed. I've also read a lot of horror stories about insulating sheds causing far more damp issues than it solves. I'm certainly not an authority on that but I'm treading carefully.
It's arguably a DIY job for a shed style garage and with ventilation you generally wouldn't have to worry about the lack of dpm. However, you'd be doing it to just mitigate 'sweating' from temp changes and it really may not be worth doing depending on where you live etc. Keeping the tools in an old wardrobe/cupboard with a couple of 1kg silica bags on rotation could be a cheap solution for protecting them?
DonkeyApple said:
Gad-Westy said:
I certainly could but costs are pretty huge to do it well and the slab underneath is neither insulated nor damp proofed. I've also read a lot of horror stories about insulating sheds causing far more damp issues than it solves. I'm certainly not an authority on that but I'm treading carefully.
It's arguably a DIY job for a shed style garage and with ventilation you generally wouldn't have to worry about the lack of dpm. However, you'd be doing it to just mitigate 'sweating' from temp changes and it really may not be worth doing depending on where you live etc. Keeping the tools in an old wardrobe/cupboard with a couple of 1kg silica bags on rotation could be a cheap solution for protecting them?
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