My garage suffered very badly with condensation on the inside of the roof during frosty weather, this year i'd like to try and minimise the condensation as much as possible.

Now the garage has a couple of problems allowing water to enter the garage:
a) from leaks where the corrugated sheets are fixed to the supporting beams
b) water from the raised ground level at the back of the garage
bi) the water from the roof runs of directly at the back of the garage so this makes (b) even worse.

Am i right in thinking if i eliminate the leaks themselves this should minimise any condensation i experience, or should i be looking at improving ventilation and adding insulation aswell etc....

Stopping the leaks is essential, then you need to increase ventillation.

You can increase ventillation by fitting some air vents. I fitted two at the top of my garage door and they helped.

If after doing the above you still get bad condensation then you will have to look at insulating the roof.

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DIY | Donnas dream house

Thanks for that.

Am i right in thinking the best location for ventilation is front to back or side to side (i can't do one side as it ajoins next doors garage.

The side has a window (which i leave the sidelight open anyway), the front is pretty well ventilated as the garage door has pretty large gaps around the side and bottom, although i might punch a hole in a couple of the gaps around the edges of the roofing sheets which are currently blocked with render.

So i think i mainly need to add ventilation to the rear of the garage, do i need to add ventilation at different heights? For example i can add ventilation at the top in the same manner as the roofing sheets, but is it worth adding some ventilation lower down too?

Just add a couple in the easiest position and see if it improves things, if not you can always add another couple in another location.

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DIY | Donnas dream house

Condensation on the inside of a metal roof, is caused by a warm moist wind that meets a cold steel garage roof.
You see this about 200 times a year in the garden, as frost or dew, where the warm air meets the cold ground.
What you need to do is, seal all the gaps, cracks and holes in the garage to stop the warm wet air getting in, adding more ventilation will only allow more warm wet air to enter the garage and enable more condensation.
Another solution is to line the roof with waterproof plywood covered with a blanket, the blanket will collect the drips, then it will dry out when the sun shines.

I dont think thats the case Perry.

Is'nt is that fact that the garage is by and large sealed therefore the air inside is warmer than the air outside, so the warm air (already inside) condensates on the coldest item in the case of frosty weather this is the roof of my garage.

And yet there is still frost and dew in the garden?
And by coincidence?
And is your garage still warm at 7am from the day before?
Does the heat from your garage not disipate during the evening and over night?

I once sealed my garage completely, by fitting seals to the doors and filling the gaps between the roofing sheets and garage sides with expanding foam etc.

This made the condensation 10 times worse, so I removed the seals and fitted vents and now the condensation is barely noticable.

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DIY | Donnas dream house

It is a fact that that the water vapour in the air is attracted to the nearest cold object and the nearest area of low pressure.
This is the reason why we have ground frost and dew and why our homes, garages and green houses get covered in frost on cold nights, when warm moisture laden air moves in and meets a cold object.

Water vapour has an incredibly small molecular structure, it is capable of entering most things found in a building, wood, concrete, mortar, plaster, soft furnishings etc;

As you may well realize water vapour created in the home by our washing, cooking, breathing finds its way through solid walls to the outside.

I believe you when you say your solution worked up to a point.

I will also write that the quantity of moisture in the air is not a specific and it varies, dry at 0C and below, to 30 grams per cubic metre with saturated air at a temperature of 30C.

Different nights, temperatures, moistures.