ᐅ Insulation of Basement Ceiling with Mineral Wool – How to Install

Hello. I have a house with a full basement.
Currently, there is no insulation applied, so the boards are directly visible.
I have now received quite a few stone wool boards with a thickness of 60mm (2.4 inches) as a gift.
These boards are coated on both sides with a firmer white material to allow the boards to be glued directly to the ceiling.

The problem is the ceiling height.
60mm (2.4 inches) is too thick for me. I would have to cut the boards in half, so to 30mm (1.2 inches), to still be able to walk around (unfortunately, very low ceiling height).

However, after cutting them in half, the white coating would be removed, so I would have to glue the stone wool directly to the ceiling.

I would cut them with a pruning saw with a good guide to keep the cut surface even.

Does anyone have experience with this?
Best regards, Herbert

Halving should generally be possible, as they can also be cut crosswise and glued together.
The prepared surface will be lost, so I would additionally use dowels to ensure stability.
What is the construction year of the house, or do you have any information about the existing screed?
For any building from 1978 onwards, I wouldn’t worry about adding more than 3 cm (1¼ inches) of insulation from below.
In older buildings with only 0-2 cm (0-¾ inches) of insulation thickness (of which little remains after 40+ years), this can help, but 6 cm (2½ inches) is naturally better.

Hello, thanks for your message.

The house dates back to 1950. It has visible steel beams with concrete slabs placed between them from below. So the surface is anything but even.

On the ground floor, there is underfloor heating with tile flooring. In the coldest winter, you can comfortably sit in the basement wearing just a sweater. That is why I wanted to insulate from below.

The basement is also quite damp. The basement walls are made of natural stone—large broken granite stones with a lot of sand and a bit of cement mixture (but the house stands solid). Because of the moisture, I did not want to use polystyrene foam boards, possibly to avoid condensation? Maybe someone has experience with moisture issues here.

Currently, all ceilings are covered with wooden panels. However, there is no mold on the ceiling, so it is not that wet after all.

Best regards, Herbert

Herbert 80 schrieb:

Because of the moisture, I didn’t want to use styrofoam boards, otherwise the water might still condense? Maybe someone also has experience regarding moisture.

Regarding ceiling insulation below a concrete slab, you don’t need to worry about moisture. No vapor passes through from “above” the concrete slab, and none comes in from below either, since the slab is warmer compared to other walls or the floor, especially with underfloor heating.
EPS, often called “styrofoam,” does not have a higher thermal resistance than mineral wool. Only PUR/PIR insulation offers a slightly better effect, but it is 1) significantly more expensive, and 2) only fire rating class B, meaning it is not allowed or only allowed under certain conditions in garages with car parking spaces and rooms with gas or oil heating systems.
Therefore, mineral wool remains the best solution, especially if you have it available for free.
For underfloor heating, I would recommend using the full thickness of insulation over as large an area as possible. Heat loss through floor areas with underfloor heating is twice as high as through unheated areas.

Herbert 80 schrieb:

All ceilings are currently covered with wooden panels. However, there is no mold on the ceiling.

The basement ceiling? Then remove the paneling and install the insulation. The paneling is usually attached to a substructure anyway, so you will probably reach about 4–5cm (1.5–2 inches) thickness there.

Herbert 80 schrieb:

The problem is the ceiling height.
The 60mm (2.4 inches) panels are too thick for me. I would have to cut the panels in half down to 30mm (1.2 inches) in the middle so that there is still enough headroom to walk. (unfortunately very low ceiling height)

If 3cm (1.2 inches) is what decides between walking and not walking, in my opinion the perception is somewhat distorted. Please install the full 60mm (2.4 inches) panels and enjoy the insulated floor – and don’t get annoyed (how often does this really happen?) about having to bend down sometimes.

In terms of installation, it will also be quite challenging in my opinion, because you need to press the panels firmly against the ceiling, which won’t work as well if they are cut in half.

Thank you for the initial responses. I agree, free insulation that is also fire-resistant—what more could I want.

dertill schrieb:

The basement ceiling? Then remove the covering and install the insulation. The covering is usually mounted on a subframe anyway, so there will probably already be about 4-5 cm (2 inches) thickness there.

Yes, due to the uneven ceiling, there is a supporting batten and a cross batten. Then the wooden panels are installed on top. The wood should be reattached as well; that was my initial thought. Leaving out the two battens would definitely be a huge effort. But for a rustic basement bar, they belong there again. I have to think it over. Wood certainly has a good thermal insulation value. So, the insulation would go around the first batten, then another cross section cut out.
It might be better to leave it white...

Are there special anchors and adhesives for the insulation boards? Has anyone had good experience with a particular manufacturer and type?
I have attached a picture of the type of insulation.

Best regards, Herbert