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Damp workshop - Improvements ideas

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Noho12C

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Hello,

we moved in a new house 2 months ago, with a pretty nice double garage. After repointing the walls and painting the walls and floor, it starts to look good.
However, I have a humidity issue : humidity level is between 80 to 95%.

It is a cold roof garage (non insulated), with an old up-and-over door, with big gaps on top of bottom.

I'm getting quotes at the moment to replace the door with a sectional garage door with insulated panels. And when installed, this type of doors are (normally) draught proof. Also, I plan to invest in a good quality dehumidifier (desiccant type).

My concern now is that the roof will still let moisture get in. The roof is fairly old and will need to be replaced at some point, but i'd like to wait couple of years for that.

What are your thoughts ? Any opinion/past experience ?

Chris.
 

mikej460

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It's possible that moisture in the damp air is condensing on your cold roof and dripping onto the garage floor. You could put some PIR Insulation in between the rafters (even 25mm will help but leave a 50mm gap between insulation and roof) then a vapour barrier (Screwfix) and if your budget will run to it make a ceiling out of 9mm OSB3 moisture resistant panels. All that could stay on if you only replace the roof covering, if the whole roof structure needs to be removed then just make sure you screw the boards on so you can take them off. When you put a new roof on take a look at MikeG's How to Build a Workshop in the Workshop section.

Hope this helps
 

Noho12C

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Thanks Mike. I don't see any condensation, nor water dripping.
And I had a look at insulation panels , but it's gonna be expensive for something that would stay just couple of years at most.
I think when replacing the roof we will go for a fully insulated roof (I think it's required now to have at least some of it insulated anyway)
 

Chippymint

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I built my workshop about 10yrs ago. My good friend owns his own insulation business. At the time I pondered over what best to do for achieving, well as best you can, a constant temperature with minimal heat exchange. His simple advise was to insulate, insulate and insulate and that I use 2 inch thick polestirene 1m sq panels (cheap). We just doubled these (4inch thick) for the side walls and trippled them for the roof. The floor was 6 inch concrete. The exterior was metal cladded (no membrane between the metal and insulation).
Was his advice correct? after 10 yrs of use, it was spot on. My workshop is 12m by 8m. All I have is a small oil heated radiator which is on 24/7 on a very low setting. The room temp is about 14/16 degrees in winter and summer. Humidity is non existent - proof is that my cast iron machines tops and tools do not have a trace of rust. Also my wood for making furniture is below 10% moisture content. It's great to work in - warm in the winter and cool in the summer; even in this year's high temperatures.
Was it expensive? well it's not cheap when doing any insulation work but over the long run you get your money back in many ways. Hope this helps.
 

Noho12C

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I will get some proper insulation once the roof has been changed. Might put something temporary in the meantime.
I just hope a new garage door with draught proofing will improve the situation.
 

mikej460

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I used 100mm polystyrene slabs under my new inner 100mm concrete slabs for my outbuilding as I needed to raise them due to occasional flooding, it worked like a dream (you could do the same by laying a floating floor over it when you have the roof done?). Just to add to Chippymint's post I put a new uninsulated roof on the same outbuilding but it did have sarking over it which stops condensation. The walls are existing 150mm thick concrete blocks again with no insulation and I built new solid framed T&G doors. Two thirds of the building consists of two loose boxes I use as lambing pens (hence no insulation in the roof as they need a whole gable vented) the other is my toolshed which is sealed off from the loose boxes by a concrete block wall, the toolshed shows no damp and no rust yet is unheated. The only thing I could think of with yours is that cold, damp air is getting in through the door so I would get your door fitted, use a heater and see how it goes. However, my 'shop' is an old 1970s garage that is so damp the floor has a permanent water stain over half of it all through winter and I daren't leave my best tools there. It's coming down in a couple of months ready for a spring/summer rebuild 😁
 

Noho12C

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What do you mean by sarking ? The OSB board under the felt ?
I think I'll get the door fitted and see if this improve the situation. If not I might add some insulation between the joists.
Doesn't have to be perfect, but never nice to see your tools & machines rusting like crazy :confused:
 

mikej460

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Sarking is laid over the rafters in some roof designs, not so common here but is in the US where they often use felt shingles as the roof covering. It can be anything, osb, ply or in my case treated t&g as I liked the effect when exposed as mine is. In my case I was laying a cedar shingle roof with no ceiling and this is what it looks like inside
Tool shed ceiling.jpg

I did it this way to have a warmish roof that prevents condensation and dripping but I didn't need it insulated. It works very well and looks good but it's not the cheapest method. I won't be able to do the same in my new workshop as that will need insulation.
 

Jameshow

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I have a roof like this but 50 yes older

I've not had a damp issue even though it's occasionally flooded until sorted done wayward guttering.

Cheers James
 

Noho12C

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Well, I guess a new door might help then...
Any experience with a dehumidifier ? Considering getting one to reduce the overall humidity.
 
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