Window replacement in modernized old buildings

Hello everyone,

we recently bought an old building (built around 1920) that has already been partially modernized. The previous owner had an energy consultant create a renovation plan, including a roadmap. One important and, in our opinion, economically sensible measure is the replacement of the windows. These have been partially renewed over the years and therefore are all in different conditions, but they are already quite old (between 15 and 30 years). We have already read up on the topic a bit and have also had a glassworker come to prepare a quote. The longer we delve into the subject, the more questions arise. Perhaps someone here in the forum already has experience with this and can answer the most important ones for us.

[*]According to the renovation plan, the exterior walls have a U-value of 0.265 and the roof 0.128. According to our research, triple-glazed windows are possible here (and also sensible?). What is the experience with mold in this regard? Does it develop much faster now, or can it be managed without problems with sufficient ventilation?
[*]The house used to contain three small apartments and a staircase that is not heated. In the staircase, there are partly really old windows (wooden frames, uninsulated) installed. Is it sensible from an energy and economic point of view to replace these as well? The previous owner replaced almost all the windows, except these. Could there be a construction-related reason for this? As far as we can judge, the staircase is not insulated everywhere either (e.g., on the exterior wall under the stairs).
[*]Is there anything else one should pay attention to?

Thank you in advance for the answers. If further information and/or pictures are needed, I can provide them.

Best regards

We recently bought an old building (built around 1920) that has already been partially modernized. The previous owner had an energy consultant prepare a renovation plan, including a refurbishment roadmap. An important and, from our point of view, economically sensible measure is the replacement of the windows. These have been partially renewed over the years and therefore all have different conditions, but are already quite old (between 15 and 30 years).

Please show photos of the house as a whole, the floor plans with a section, and this refurbishment roadmap.

Hello,

thank you for your reply. I have attached a few pictures of the outside, the attic conversion, the staircase, and a very old window (the toilet). Additionally, the floor plan and the relevant parts of the renovation plan are also attached.

Best regards,
Danny

I meant more the floor plans and a section from the building file or a survey. The floor plan sketches - at least of somewhat above-average real estate exposé quality - are not sufficient for a renovation roadmap, and to put it mildly, mine would look different. A brick wall thickness of 20 cm seems odd to me, especially for BW; that rather makes me suspect brick formats from Benelux / F. But you also say that the renovation roadmap was created by the previous owner - how have the goals shifted since then, and what is your approach anyway?

Unfortunately, no further documents are available, as they were burned in the war. I also cannot really trace where the data from the renovation plan come from, but the general insulation is correct (the wall was opened), although I have doubts about the brick thickness.

But you also say that the renovation plan was created by the previous owner – how have the goals shifted since then, and what is your approach anyway?

Unfortunately, I do not know the goals of the previous owner, but from what I can judge, a very energy-saving house was targeted, completely independent of the economics of the implementations. One measure is, for example, rafter insulation for almost €50K. We already knew before moving in that the windows needed to be renewed, which is completely independent from the renovation plan (at that time, we did not know there was one). Our approach is to implement economically sensible measures, and the first measure is window replacement. That it is also listed in the renovation plan is completely independent of that. Other measures in the renovation plan partly cost so much that implementation simply does not economically make sense for us or only becomes worthwhile when other things need to be done anyway. If it is perhaps easier for you to answer my questions without the renovation plan, then just ignore it. Here I only have the U-values, assuming they are roughly correct.

I don't care at all about your renovation plan; what matters is that it is important to you. I have formatted your response accordingly:

Old goals (previous owner)	NEW goals
A very energy-saving house was aimed for, completely independent of the economics of implementation; One measure is, for example, a roof insulation above the rafters for just under 50K €.	Implement economically sensible measures; the first measure is the window replacement.

That is already a clear difference. You can work with that:
Pick out all measures from the old renovation plan, prioritize and price them. Priority "Z" = "not required and not important to us," Priority "A" = "required with a deadline," "B" = "important but without obligation," and so on for the levels "as soon as possible but saving / credit required," "only if there is too much money and time," or similar.
Normally one would proceed by trade, but other groupings (by rooms or the like) would also be conceivable. You spoke of different types and conditions of windows: I would specify individually what should be done with each window. Where is a seal replacement, adjustment, or the like sufficient, where is a glass replacement indicated, where must an entire sash or even the whole element sash and frame be replaced.
As pure remote coaching, this is difficult, and I will not be at my base in the south anytime soon. So you would first have to implement this advice on your own or with an (experienced in old buildings) architect on site.

The general insulation is correct though (the wall was opened), but I also have doubts about the brick thickness.

If I understand you correctly, the wall insulation is already done, and above all that counts. Whether there are 20 cm bricks in the wall (or the more likely 25 if they are from Germany) does not concern us here. If the exterior walls are now "finished" like this, we no longer need to consider them (for example, with regard to the roof overhang when it comes to ETICS).