[GJim]

> most mould is caused by buildings.

An honourable mention to fitting Cavity Wall Insulation, heavily sold and encouraged by UK government energy saving schemes thorough the 1990's and 2000's.

Except by stuffing the wall cavity, you provide a nice moisture bridge to outside whilst simultaneously stopping air circulating in the cavity and whipping away moisture; thus an explosion of mould.

The policy was a disaster, as getting the stuff removed costs a small fortune.

[zrail]

I think this depends on the construction of the rest of the house. A typical stack built house in the US will have extensive insulation in the exterior walls, but it's paired with a number of different layers intended to expel moisture.

As a retrofit without those things I guess I can see it being problematic.

[skyberrys]

Maybe everyone here can help me. I bought a house with an accessory addon already built, but it's walls and roof are very cheap aluminum. It's a constant source of mold. I'm at the point where I want to demolish it and rebuild properly. Some contractors I've spoken with instead encourage me to just frame out inside the existing aluminum box and get double pane windows instead. I don't think that will solve the problem though, these cheap aluminum panels are so full of mold now how would putting fresh wood over the panels solve anything, in 4 years I'll just have more mold growing over the interior frame out if I don't demolish and rebuild the whole thing with proper moisture barriers on the exterior and underside of the accessory room.

[IIsi50MHz]

The walls are getting below dew point when they cool and/or the humidity is too high for extended periods. And the walls have dust or other surface accumulations conducive to mold. Insulating the exterior and keeping the interior humidity low will help. Thoroughly clean and dry the interior walls, removing all mold and all other surface accumulations. Keep the interior above dew point.

[sidewndr46]

The walls are aluminum? Where do you live?

[skyberrys]

Trailer park in California. It's a prefab kit built accessory room. The main part of the trailer is normal, just this accessory room is built out of aluminum panels (about 3' x 9' per panel) and then plenty of single pane windows.

[zrail]

Mold growth is a moisture problem which can either be because of condensation or because of leaks. I agree with the contractors, properly framing out and insulating the interior would probably help a lot with condensation on the inside of the aluminum, as would double pane windows. Ventilation is also important for stopping mold growth.

[amluto]

Or it could just hide the mold behind the insulation if done poorly. In cold weather, when cavity insulation, the inner surface of the metal will be cold. If warm, humid interior air that can sneak behind the insulation and get to that surface, it will condense. And metal is impermeable to moisture, so it can’t dry to the exterior.

One technique to mitigate this that does not require extraordinary care on the part of the installer is “flash and batt”: apply a thin layer of spray foam to the exterior wall and then fill the cavity with fiberglass, mineral wool or some other fluffy insulation. The spray foam adheres to the wall and leaves no space for humid air to reach, and the inner surface of the spray foam will stay warm enough to avoid condensation.

[IshKebab]

Who has cavity wall insulation removed? The effect on your heating bill is going to be much worse than a small amount of mould, and I'm unconvinced that it makes it worse anyway - one of the main causes of mould in my experience is poor insulation! It makes the walls cold, which means you get condensation on them, and if you have poor ventilation in the rooms then you get mould.

If you have this problem, then the only thing I found which helps is fungicidal wash, and keeping furniture away from the problem walls (especially north facing corners of the house). I suspect wallpaper would also help but I never tried it.

[EliRivers]

Who has cavity wall insulation removed? The effect on your heating bill is going to be much worse than a small amount of mould

Some of these houses have been transformed into being unfit for human habitation due to the damp and mould. In some cases, the botched insulation has resulted in an increase in heating costs (along with the damp and mold). Some have suffered structural damage due to the botched insulation, costing tens of thousands to repair.

[IshKebab]

How did they botch it? Definitely a [citation needed] here...

[amluto]

Here’s an extremely snarky take, from an author who is very much an expert in the field:

https://buildingscience.com/documents/building-science-insig...

[GJim]

> The effect on your heating bill is going to be much worse than a small amount of mould

A small amount of mould?

Oh you sweet summer child! You really need to see the damage it can do.