Sectional concrete garage condensation

[nathfoley]

I have a 4 x 5.5 m sectional garage. It's sound, but in cold winter months (Jan/Feb) it suffers from significant condensation. I read that this is a common problem on concrete garages.

Last year, all my tools got very damp in these months.

I would like to stop the condensation as much as possible. I'm not so much interested in it being warm, but more I don't want my table saw and planer/thicknesser getting ruined come the winter.

There is conflicting info about the best approach here. I am considering this approach, anyone who has any experience or advice would be much appreciated:

- Liquid DPM the concrete slab, lapping up wall
- DPM polythene up walls and under roof, with an air gap
- 50mm PIR in between roof's steel joists
- batten walls using clips attached to the bolts joining the sectional panels, finishing flush with the ribs of the sectional panels.
- 50mm PIR round the walls up to the ceiling insulation, taped at joints, creating a sealed envelope
- some form of insulation on the up and over, probably PIR.
- 6mm ply or 8mm OSB; board up the walls, but leave ceiling insulation exposed.
- Some form of ventilation in the external ply between the top of the sectional panels and the roof (both sides of the garage) to create air movement on the external side of the DPM polythene.

I could go 25/30 mm PIR if it would achieve the same reduction in condensation. Any thoughts on the PIR thickness?

Is tanking the concrete slab with liquid DPM sufficient? Or would it will need insulating/raising? This would fit down on the already short ceiling hight.

Ideally, I'd knock it down and build a timber framed workshop, but don't have the time to spend on that right now (prob not next few years with other jobs that need doing)... So just looking to extend the use of the garage.


Any thoughts/comments much appreciated

 

[accelerator]

I think you will need some form of heating in the garage to make all of this effective.

The key thing to consider is how you control humidity levels.

 

[nathfoley]

I think you will need some form of heating in the garage to make all of this effective.

The key thing to consider is how you control humidity levels.

Its a standalone at the bottom of the garden, so an oil filled rad or similar? How does this work in practice? Is there a certain temp it should be kept to and is it a case of warming it up to the desired temperature once a day? Just thinking how expensive it could be to have it heated 24/7.

Alternatively, could the humidy be controlled.with an extractor fan? Perhaps attached to a humidity sensor?

 

[big-all]

do NOT burn oil or gas as they give out masses off water
if you are not heating no point in insulating
on a sunny winters day the heat gain through the window and the concrete structure can be useful
if you think off it with an average say -5 degrees day and night your well insulated garage is a fridge without the solar gain through the structure as its insulated out
my suggestion is airflow sufficient to remove excessive moisture and observe the roof areas where the moisture will condense on and avoid putting tools in those areas
i would also experiment with bits off say hardboard or 5.5mm ply covering and angled on you table saw or other stuff to keep drips off this will both protect and through long winter days any falling drips will stain the board surface so help you trace the source

i would avoid plastic covering over your tools or covering in like a tent because iff the dampness is caused through hot machines through use attracting the moisture possibly your hot breath raising the moisture level around the saw or other tool and you throw plastic over it you can then have a mini rain forrest

you can also get dampness from the floor adding to the moisture level under the plastic iff tent like

 

[nathfoley]

Yep, meant an electric oil filled rad, not oil fired. I have power to the garage.

Your point on the solar gain in winter makes sense though.

TBH, the garage has gaps at the ceiling and top and bottom of the up-and-over door. I'm struggling to see how I could improve ventilation, save for using a fan or something.

My understanding is that the primary cause is likely sudden shifts in temperature/humidity... E.g. -5 dry to +10 raining. The warmer humid air condenses on the cold ceiling/walls. In a frost, this seems to be exacerbated with frost/ice forming on the inside of the corrugated roof.

With the roof being the assumed main culprit, wonder if running a DPM under the ceiling would help solve this? That being said, I assume any warm humid air hitting the bottom of the cold DPM would condense anyway.

As you can probably tell, I'm clueless about condensation/ventilation.

If I were to seal and heat the garage, for the purpose of stopping condensation, is it a case of ensuring the internal temperature is no less than the external temp?

Edit: just to add, last winter, everything was damp, not a specific area where the roof was "raining"

 

[accelerator]

I'd say think powered ventilation first. The key is moving warm moisture laden air out before external temperature drops.

You don't necessarily want to be drawing much air in, as this could be bringing damper air in.

If you cover metal surfaces with better insulated materials, this will mean less very cold surfaces and less condensation.

To keep your smaller tools condensation free, you can put them in sealable plastic boxes.

 

[big-all]

iff you are adding heat then yes insulate
i have an all wooden shed with 3" loft insulation all round [4" compressed]
i have a wood burner and an electric fan heater[[12ftx10ftx 6ft9[average roof height]
12 and 6mm ply walls inner cladding and roof not sealed on purpose as it can breath so no condensation other than the glass
i try and keep the minimum to around 6 degrees by bursts from the fan heater or wood burner
i have found what ever is the outside temperature if i bring the inside to around 5 degrees above with the fan heater [then turn it off]my presence [breath and body heat ] fairly sedate motions will maintain the +5 degrees with any machining wood adding slightly to the overall heat input iff i go in for dinner for around an hour it will drop perhaps 1.5 to 2 degrees and take say 2 hours to claw back the .5 to 2 degrees drop

i have many thousands £off powertools open tools mains table saw pull saw table router
then 54v dewalt table then 18v and 12v none in kit boxes

now the reason i mention kit boxes i used to check and organise the kit in boxes being me the box would not include much wasted space with say a bosch 10.8[now called 12v]mini router drilldriver buzzy toy and rotary tool and jigsaw to fill the space
any way the point i am making is when i would check the kits in the garden on a hot sunny summer day before putting away in shelve space i didnt realise [i should have known lol]that a plastic kit box closed on a very hot humid summer day will trap moisture and out off 5 kit boxes checked in the late autumn 3 had substantial water droplets in them fortunately no damage other than motors needing to run to clean the commutators
all main tools now stored in the open around the shed/workshop in purpose built areas

now the shed does get air damp and somtimes near to say 3 degrees for perhaps a couple off days but the normal minimum will be perhaps 6-8 degrees with perhaps at really cold times the burner up to 25-30 degrees every few days to drive out the damp
its worth pointing out i have near to zero airflow[sealed box] so the burner helps draw out the damp with a window diagonally oposit giving airflow

in general no problem at all with tools and damp over the sheds now 21 years

i also have a fan in the wood burner area to circulate the warm air

sorry to rant iff its not relivent to you please egnore...thank you

 

[nathfoley]

Thanks for the replies so far, upon further research, and speaking to people who have effectively removed condensation from their garage... I think how ill proceed with this is to seal/insulate the thing, add ventilation and heat it for the months it gets very cold.

As this is a temporary solution, which I'll probably replace in 3/4 years when I have completed all the other projects in the house, I'm seeking to keep costs low. So am pricing up - 25 mm PIR for floor (to not loose too much ceiling height), 30 mm PIR for walls and 50mm for the roof.

To seal, I'm thinking DPM membrane, PIR, OSB (chipboard for floor).

For the walls, Ill add timber studs to it finishes flush with the inside ribs, then I can create a continual layer of insulation, taped at the but joints). Up and over, I will leave in place, build a stud wall inside to form a new wall. I very rarely use the garage door, but nice to have the option to use it again in the future.

I do need to raise the ceiling as the pent roof finishes on top of the panels (2000 height), so add loosing
45 mm of that after insulating the concrete floor is not ideal.

I'd like to raise the brackets by 100-150 mm, however the brackets are Maxed out in the higher end of the garage (see pic below). Would it be possible for me to get some brackets made up to extend the brackets to raise each of the joists up 100-150 mil? Or perhaps build a frame from box section/angle bracket/timber fixed to top of the sectional panels, then fix the steel joists to that?

Another option is I could raise the joists up to the max height, then add timber to the top of the joists to create a 60:1 fall. I wouldn't gain any additional ceiling height, but would probably be OK. The preferred option would be to raise them all to gain a bit of height though.

Once the height is raised, I would then OSB the top of the joists, 50mm PIR, DPF, corrugated panels directly on top and fix down.

Any thoughts on all of that appreciated

"High" section:

Low side :