Outbuilding always wet inside

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DaveHhh1

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Hi all,

So I got a builder to build me an outbuilding. I use it for a gym. It has a power rack in it and my gym plates. It also has my Mrs sofa from her old property.

From what I gather I had 14x12ft concrete base and 2.5m height building. It has 2 French doors. Zero ventilation except for these. No insulated walls.

It has plasterboard on the walls now painted.

I put rubber type tiles on the concrete floor.

So, before I put the tiles down I had a severe issue in the building of water seeping in. It went up the walls and made a lot of damp. The builder came back and put membrane outside and this has definitely helped.

However, a couple of months later to today I get mold that I am staying on top of cleaning. I was convinced water must still be coming in as it is always at the back of the building, I pull the sofa our to clean mold behind it.

I thought that water must still be coming in or up through the concrete floor (it always feels cold). Anyway, today was very hot and yesterday too. I was not home to open the garage to give it an airing.

Just went outside and it was like a sauna and the windows were visibly wet. Definitely condensation. I pulled the sofa back and underneath it was what I described as a thin puddle across the rubber tiles. The bottom of the sofa which is off of the tiles by say 100mm was pretty wet.

I've mopped it up and let it air out a bit. Closed building now as its dark.

My question is, it appears to be condensation. What can I do? I have no air bricks, and what I should have done was get insulation etc. But hindsight.

What can I do now?

I'm attaching a pic of the water after I pulled sofa back and lifted up a tile. I'm not the best with diy I should add.

Thanks in advance. Dave.
 

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you need ventilation at the minimum
you don't mention how the roof is constructed
 
Hi,
Thanks. The roof is constructed with joists I believe. It has a grey roof and covered with bitumen(spelling). It's a flat roof with a slight slope forward so water runs to a gutter collected in a water butt.
 
You have a 'low end' building and it is behaving as such. Water vapour inside the building will be as much a problem as that from the outside.

Without proper insulation and ventilation you are always going to be fighting condensation related damp. All surfaces need consideration i.e. walls, floor and roof. You gets what you pays for.

Build an internal frame and insulate.

Was this built on a trench footing or on a concrete slab?
 
Last edited:
Hi it was built on a concrete base. He dug down, hardcourt and then did the concrete base.

Yes it seems my lack of knowledge stopped me asking the correct questions to the builder.

An internal frame that is insulated, could you give me a few more pointers?
 
The construction of the base alone means your building will be prone to floor level damp.

I'd be looking at lining the floor with DPM lapped 300mm up the walls. Foam fix 50mm foil sandwich PIR insulation to the walls and seal all joints with foam/foil tape/silicon. Fit same to the floor and float ply over it. Build an internal stud frame and insulate between studs. Fix foil back boards to the studs.

With the whole weights thing, you may want to consider a different approach for the floor, particularly if the increase in height is contentious.
 
I think I have enough height to sacrifice here. I can check this out.

In terms of ventilation what should I be looking at in addition to this?
 
If I did the insulation for the walls and ceiling but left the floor and instead used tanking slurry for the floor.
Would that suffice?
 
I think you have three problems which all overlap in "condensation" inside the building. The first thing, you said that your builder put a membrane on the outside, can you be more explicit please?
Prob #1 water soaking through the walls and floor, raising the moisture level in the air inside.
Prob #2 Condensation from the air inside, as it cools overnight, moisture appears out of the air as water droplets, like the dew on fields in the morning.
Prob #3 When you occupy the building and indulge in excercise, you breath out a lot of moist air.
The total cure is to heat the place so the moisture in the air does not condense, but this is expensive, so you insulate instead so less heating is required. It also will reduce the day/night temperature difference and so lessen the likely hood of condensation. Also ventilation so you can dump moist air outside but you are dumping hot air also. Also think about fields, they are well ventilated.
The no brainer is to investigate what insulation you have at present.
Frank
 
Thanks for the reply princeofdarkness here is more info.

Ok so the engineering bricks 3 high you can see from the outside and when I had walls completely damp from outside, it was lots of concrete under the soil round the edges that made the water run back towards the walls.

The builder tool all the earth back away from the wall and put a membrane (black sheet) covering at least one high engineering brick and threw shingle around it.

This has seemed to fix the the walls getting soaking wet.

Incidentally I just went into the garage and I moved the sofa from its new location. Under the sofa there was a film of water laying on the EVA tiles. This tells me that the air flow is so poor the sofa blocks moisture undrr it. Sofa is on legs around 300mm off floor I think.

In terms of what insulation I have at the moment there is none.

I am going to drill holes in a corner and put a vent over them from inside. And do same in opposite high corner too.
 
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