Insulating Walls (Block Shed)

[Mark-J]

I have a problem with mould growing on the inside shed roof. Weirdly, it isn't all over, and is only growing in two spots; the opposite corners of the roof. The pic attachment shows the worst of the mould and the area it covers. The other mould spot is fist-sized growth and isn't growing.

The roof is fibreglass on 18mm OSB, then a 25mm gap for airflow, then Kingspan 75mm insulation panels, and finally, plywood as can be seen in the pic.

The shed walls are single skin breeze block and ventilation is via two small windows above a larger window. Unless I leave the door open, that's the only ventilation the shed gets.

In January I'll be buying a Dehumidifier (Desiccant) and in spring I'll be insulating the walls (as mentioned earlier in this post).

For heating, I have a calor gas fire and the temperature in the shed is always between 9 degrees and 14 degrees (I'd say it levels out at around 12 degrees).

Is there anything else I can do to combat the mould? It's starting to worry me.

 

[Woody2Shoes]

I have a problem with mould growing on the inside shed roof. Weirdly, it isn't all over, and is only growing in two spots; the opposite corners of the roof. The pic attachment shows the worst of the mould and the area it covers. The other mould spot is fist-sized growth and isn't growing.

The roof is fibreglass on 18mm OSB, then a 25mm gap for airflow, then Kingspan 75mm insulation panels, and finally, plywood as can be seen in the pic.

The shed walls are single skin breeze block and ventilation is via two small windows above a larger window. Unless I leave the door open, that's the only ventilation the shed gets.

In January I'll be buying a Dehumidifier (Desiccant) and in spring I'll be insulating the walls (as mentioned earlier in this post).

For heating, I have a calor gas fire and the temperature in the shed is always between 9 degrees and 14 degrees (I'd say it levels out at around 12 degrees).

Is there anything else I can do to combat the mould? It's starting to worry me.

Be aware that the gas fire will be adding significant amounts of moisture - and this may in itself explain the mould growth (is the mould near where the heater(s) is/are?). https://sciencing.com/burning-propane-w ... 35338.html

Cheers, W2S

PS ventilation is always good!

 

[Mark-J]

That's another oddity, the gas fire is nowhere near the larger mould patches.

I've got two humidifier monitors and on average, the humidity levels are around 85% to 95%. That's way too much (I think it needs to be around 55%). I'm hoping the Dehumidifier will sort that out.

Would having a large fan on when I'm not in the shed help with the humidity? I'm thinking more air circulation. I could buy a timer so the fan isn't on all the time.

 

[Woody2Shoes]

That's another oddity, the gas fire is nowhere near the larger mould patches.

I've got two humidifier monitors and on average, the humidity levels are around 85% to 95%. That's way too much (I think it needs to be around 55%). I'm hoping the Dehumidifier will sort that out.

Would having a large fan on when I'm not in the shed help with the humidity? I'm thinking more air circulation. I could buy a timer so the fan isn't on all the time.

I think you'll find that the propane heater is putting excess moisture into the space. There would seem to be little point simply circulating air with a fan - the moisture is still carried in the air until it finds somewhere cooler to condense. You would be better with an electric heater than the propane heater, and possibly also instead of a dehumidifier e.g. a couple of these, maybe: https://www.dimplex.co.uk/product/ecot- ... thermostat

 

[Woody2Shoes]

That's another oddity, the gas fire is nowhere near the larger mould patches.

I've got two humidifier monitors and on average, the humidity levels are around 85% to 95%. That's way too much (I think it needs to be around 55%). I'm hoping the Dehumidifier will sort that out.

Would having a large fan on when I'm not in the shed help with the humidity? I'm thinking more air circulation. I could buy a timer so the fan isn't on all the time.

I think you'll find that the propane heater is putting excess moisture into the space. There would seem to be little point simply circulating air with a fan - the moisture is still carried in the air until it finds somewhere cooler to condense. You would be better with an electric heater than the propane heater, and possibly also instead of a dehumidifier e.g. a couple of these, maybe: https://www.dimplex.co.uk/product/ecot- ... thermostat

PS you might even solve the problem with no additional heating, but simply (better) cross-ventilation

 

[Woody2Shoes]

That's another oddity, the gas fire is nowhere near the larger mould patches.

The mould patches are simply telling you where the condesation is worst. The mould is showing you where the excess moisture from the propane fire is ending up and it is also effectively showing you the coldest surface - relative to the warmest and dampest air (which will nearly always be high up, since heat rises). So - fire creates warm wet air, which rises and finds the coolest surface on which to give up some of its moisture.

 

[Mark-J]

Thanks for the advice Woody.

The calor gas heater cost me almost £80 a couple of months ago, but if it's causing moisture build-up, I'll gladly get rid of it.

Do those lights actually work? I did read they are only good for small greenhouses and the inside of my shed measures 6m x 5m x 2.2m in ceiling height.

Ideal if they do work because I'd imagine they'd be cheaper to run.

 

[Mark-J]

That's another oddity, the gas fire is nowhere near the larger mould patches.

The mould patches are simply telling you where the condesation is worst. The mould is showing you where the excess moisture from the propane fire is ending up and it is also effectively showing you the coldest surface - relative to the warmest and dampest air (which will nearly always be high up, since heat rises). So - fire creates warm wet air, which rises and finds the coolest surface on which to give up some of its moisture.

This is the best explanation I've had concerning the mould patches.

Thanks Woody!

 

[Mark-J]

PS you might even solve the problem with no additional heating, but simply (better) cross-ventilation

Not sure if I have the know-how to fit vents into the breeze block walls (for cross ventilation) because I'll be fitting a timber frame and OSB over insulation panels on the interior walls later on.

Would I just have to cut out an opening in the OSB to access the exterior vents?

 

[SammyQ]

W2S got it spot on re propane heater/ condensing on cold spots, but you also need circulation. I recently installed a PIV system and banished previously sodden (with condensate) surfaces.
I suggest, ventilation and a dryer heat source. You can pick up oil- filled rads second hand and also small (1kW or so) air heaters for £20 'ornearenuff' from the big sheds. I have used both and they are a good combo; oil-filled as frost protection, air heater to boost when you are present..
Alternatively, diesel caravan/boat heaters are gaining popularity- they vent externally, but heat internally. Someone on here has one and published details.

Sam

 

[Mark-J]

I may be overthinking this. I've found that after about 5 to 10mins working at the bench, I am warm to the point I have to remove my hoody. If remove the gas fire heater and that slows down (stops) the mould growth, I'd be happy with just me being warm. For the rest of the workspace, I'll be timber framing and insulating the walls in spring.

Perhaps then, a standard 1.5kw halogen heater placed close by will be enough for me. Or one of those infrared heaters. Seeing as the temperature has never dropped below 4 degrees in winter, I can't really say it gets very cold - just, cold.