ᐅ Assessing Building Structure – External Wall Insulation

Hello everyone,

This concerns a semi-detached house built in 1980 that will undergo extensive renovation soon. The planning process is still at a very early stage. I am currently focusing on insulation. It’s easy to spend a lot of money on this without it being economically worthwhile.

Here are some details from the building description:

Basement exterior walls: MZ150 III, partly precast concrete
Upper floor exterior walls: 24 cm (9.5 inches) pumice hollow block masonry with an air gap and brick cladding
Insulation of the existing exterior walls: approximately 4 cm (1.5 inches) mineral wool batts in the air gap, covered on the outside with a sealing membrane
Gable walls: insulating aerated concrete backup wall, externally covered with black slate attached to a sealing membrane
Damp-proofing against soil moisture: insulating coating on the concrete slab as well as two layers of sanded felt within the layers of the exterior walls

The gable wall (only one, as it is a semi-detached house) can easily be insulated from the outside since the slate cladding will be removed anyway. How would you assess the other two exterior walls? The rear exterior wall is flush with a covered terrace.

Additionally, is it worthwhile to insulate the basement walls or the basement ceiling?

I also have values from an energy demand calculation. The following K-values (nowadays U-values) are listed:

FB: 0.80
AW: 0.54
ED: 2.36
TR: 1.00

I assume AW refers to exterior walls? However, I am unable to interpret these values.

Anyone have an assessment of this?

Remote diagnoses by non-experts are always difficult ;-)

I would guess that removing the brick veneer is not effective. I would consider having an inspection to determine to what extent the insulation between the masonry and the brick veneer is still intact.

What is planned to replace the slate? You could of course simply use external wall insulation systems (EWI) here (although it’s unclear whether that would look odd?!).

Regarding your U-values: an external wall (EW) U-value of 0.54 is not that bad. What do FB (floor heating?), ED (?), and TR (?) stand for?

Here’s a simplified calculation model:
Our external wall accounts for 28% of the surface area and 20.6% of the heat loss. In your case, it might be closer to around 15% (semi-detached house, no ventilation system) – but I’ll leave that aside. Our external wall has a U-value of 0.186 W/m²K (not great for a new build, but not terrible either) – about one-third of yours. Our predicted heating demand is 8,400 kWh – 1,730 kWh. At 7 cents per kWh for eco-friendly gas (whatever that means 😀), that results in 121 € for the external wall.

In your case, that would correspond to a maximum of about 360 € per year (depending on the share of total heat loss, see above), meaning a potential saving of 240 € per year.

Of course, this is a very rough approximation since I don’t know your building’s geometry or other components – but the point is that any investment over 5,000 € for a complete façade renovation (including the brick veneer part) is probably not cost-effective.

Thank you very much. That roughly matches my assumption.
So that I only have a maximum check done to see the condition of the insulation.

Slate is to be removed purely for aesthetic reasons. Plaster combined with wood is planned for the gable wall.