Basement wall interior insulation

Hello everyone,

we have a heated basement. During the inspection with the energy consultant, he said he wouldn't do anything to the interior walls as long as it is not going to be a permanently used living space.

One room is now supposed to become a study/office. It won't be used permanently, but maybe something can still be improved.

The room is heated with a regular radiator. Can I simply use insulating plaster here to gain an advantage, or would you rather use insulation boards?

Hello "roadrun87". In a so-called "internal insulation," thermal insulation and vapor retarders must be coordinated in their construction. Simply attaching insulation boards to a cold wall can lead to condensation water formation (namely behind the thermal insulation boards) in a used room. So you need to know what you are doing! Without knowing the exact local situation in detail, it would be irresponsible to give a concrete construction recommendation in response to your question. Why? Well, you would bear the damage – not the person who gave a non-binding answer. Already because of the risk (which you bear), it is definitely worthwhile to be clear about the necessary system construction before execution! ---------------- Regards: KlaRa

I have lined my basement with 50mm Multipor, it is a mineral insulation and can therefore absorb and release condensation water.

Regards Christoph

@ "roadrun87": Although a single opinion was requested by you, it alone must not be considered as conclusive for a conversion measure. So let's simply calculate a case! We take a room of 5m x 5m with a ceiling height of 2.30m. This is an example for your new office in the basement. You work at a temperature of 23°C and make sure (by short ventilation through the basement window) that the relative humidity does not exceed 65%. You have glued so-called thermal insulation boards to the wall, without taking a vapor barrier into account. If you now calculate the amount of water that accumulates on the (here realistically assumed) 12°C cold backside of the thermal insulation boards, this already results in a condensate amount of over 170ml. Since the insulation (as "Egos89" explained in his case) is open-pored, it absorbs a certain amount of water. That is correct so far. However, warm air (and thus additional humidity) from other rooms will be drawn into your basement through air movements. Also, do not underestimate the moisture emission of a human body. This means that moisture will condense on the wall again in a relatively short time. At some point, the mineral insulation will no longer be able to absorb these amounts of water. That is logical. Then it runs down the wall (behind the insulation boards) as a trickle, into the room. The condensate kindly takes along all mineral, water-soluble components from the wall plaster. And that then crystallizes as a white layer on your floor. ---------------- This scenario addressed by me is not impractical or far-fetched, but rather one of the (unfortunately) "usual situations" that I encounter from time to time in my professional work in improperly internally insulated residential buildings! Which variant you ultimately apply in your basement rooms is for you alone to decide. ------------------------------- Regards: KlaRa

Sounds not illogical but where exactly does the condensate run down if the dew point is, for example, in the adhesive mortar of the internal insulation? At the interface between the internal insulation and the mortar? Wouldn't there then have to be condensate in every exterior wall at subzero temperatures and, for example, 60% indoor relative humidity in the wall and... where exactly does it run?

It could, for example, run down in the open-pored insulation. In exterior walls without interior insulation, there is usually no dew point undershoot, regardless of the outside temperature.