mineral wool on top of wood shavings

[svante.a]

Hello!

I recently got a tip that you shouldn't mix sawdust and mineral wool because it could trap moisture between these layers.
Could that be true, or what do you think?

In two rooms, I have supplemented the insulation in the crawl space, which consists of wood chip insulation (house from the early 1940s), with a 50 mm mineral wool since the sawdust has settled. Was this incorrect or what??

Svante

 

[matsmats]

As I have understood, what you describe is correct. This is because mineral wool lacks hygroscopic properties, i.e., it cannot absorb and release moisture in the same way as sawdust or other cellulose-based materials. This means that moisture released from the sawdust is not absorbed by the mineral wool but remains in between the insulation layers.

 

[jon_h]

It is not the mixture of materials itself that could cause issues, but rather in some rare cases, shavings with their hygroscopic properties may work in areas where a mineral wool would have led to too high a moisture concentration. That is to say, if you have so much moisture in, for example, a floor structure that you encounter problems with a mixture, you would likely have had problems even if you had only used mineral wool insulation.

I would not worry at all if I were in your shoes.

 

[svante.a]

Thanks for the responses.

I'm not particularly worried about problems arising in the crawl space, but I did have a thought regarding the additional insulation done in the late '70s up in the attic (by previous owners). The humidity varies quite a lot more there than in the house itself, especially here on the west coast. They laid a mat on top of the chip insulation, but with a paper-lined one. In my eagerness, I took a look there this morning and didn't find a trace of any change. So, all in all, I don't think anything will happen, it's been there for almost 30 years.

Svante