Properly insulating old buildings, but how?

Hello everyone,

I am currently looking for a single-family house for my partner and me + upcoming child.

Therefore, in the past few weeks, we have looked at about 30 houses. There was everything from built between 1860 and 1980. The range goes from sandstone to rubble masonry to brick, numerous extensions, conversions, additions, partly renovated in the 70s or 80s, with wood / aluminum / plastic windows, Eternit roofs, oil / coal / coke / electric / night storage / wood vaporizer / low-temperature gas condensing heating systems up to pellet stoves.

Preliminary conclusion: due to the current interest rate situation, the market for (for us) affordable houses is practically swept clean, there are only the expensive showpieces from 300K€ upwards or houses at the lower price end around or under 100K€, thus heavily in need of renovation. The "middle" mostly consists of totally overpriced houses that actually belong to the previously mentioned league.

Therefore, it currently seems that we will buy a more or less heavily renovation-needing house. For those we have looked at in that category, it is always the same:

Uninsulated walls, ceilings, and roof (windows, of course).

Now, one usually only knows about retrofitting insulation from the outside with styrofoam boards or similar.

However, since in almost all the houses we looked at, a complete overhaul of water pipes and electrical system would be necessary, and in that process I would also install network and possibly KNX cables, now my idea is:

Instead of chipping dozens of meters of masonry to lay the cables anew + insulating the exterior walls, it might be more sensible to completely install wooden stud walls with insulation wool (rock wool?) inside and lay the cables at the same time.

Now my questions:
- Does this idea make sense in any way, or does retrofitting insulation only help from the outside?
- Is there perhaps something different to consider with different masonry types, meaning ventilation to prevent mold?
- To what extent does it make sense to insulate (intermediate) ceilings? For example, I would insulate all ceilings where the rooms above are mostly cold (bedrooms, hallway, storage room, attic).

That's it for now, I think more will follow.

Thanks in advance for your answers.

Hello,

Partition walls are not usually insulated for thermal protection but for soundproofing. The idea of using timber frame/drywall construction instead of chasing the walls is basically not wrong; you can do that. But then the question arises which walls are affected and what exactly you plan to do there? Do you want to take out the old walls and rebuild them in timber framing? First of all, you have to consider which walls are load-bearing and which are not, so be careful! An alternative would be to set up a drywall in front of the interior walls and lay the cables between the drywall and the actual wall. Whether this makes sense depends on the condition of the house. You have to think about that. Such a drywall also costs some money and is not negligible work either. As a rule, for example, it is double boarded to achieve a certain stability for shelves, pictures, etc.

Insulating ceilings because a bedroom is above, well, some do it, others don’t. I would consider whether that makes sense. A bedroom is usually heated a bit anyway, so why separate it from the rest? I can’t say whether that is a sensible measure.

Insulating exterior walls... I can only advise everyone to carry out as many insulation measures as possible on the outside of the exterior wall. Inside you only lose living space and then all the "nonsense" with vapor barriers etc. is no fun. Exterior insulation measures are more forgiving, and interior insulation is only done if there is no other way. By the way, one should generally be skeptical about insulation measures on walls and only make a decision after a more detailed examination (possibly with an independent expert) and recalculation. Personally, I consider wall insulation a task that I would rather push back in such a large project because I believe the savings are not as high as you might expect.

Roof insulation usually makes sense, as always, it depends on the condition of the roof. If the house is 50 years old or older, the question usually arises whether you want or must reroof it. In this context, you can consider whether you want to insulate on the roof, from inside, or a combination of both. Of course, there is also the question whether you want to insulate the roof itself or the top floor ceiling.

PS: Since I recently did a similar project myself, I can only say that it takes an insane amount of time and work. Don’t rely on friends; they won’t help forever (simple fact). Also note that the costs are not negligible, even if you do a lot yourself. I claim that if you want to renovate/refurbish an old building to the level of a new build, you will not end up significantly cheaper than with a new build. The idea of buying a cheap old building + renovating & refurbishing = cheaper than new build is therefore only true to a limited extent. Definitely take an expert with you for your preferred houses and have the place thoroughly inspected. After that, it is easier to estimate what it will cost and how much time it will take. If I hadn’t gotten the old building under the circumstances, I would have clearly bought a new building.

Thank you for your detailed response.

"The idea of using wooden stud/drywall construction for the walls instead of chasing them is basically not wrong, you can do that. But the question then arises which walls this concerns and what exactly you plan to do there?"

Thermal insulation, so mainly the inside of all exterior walls.

I would not tear down partition walls and rebuild them with wooden studs, but rather additionally insulate the walls that separate warm from cold rooms, for example between the living room and the stairwell.

If necessary, a ventilation system with heat recovery could also be installed directly into the wooden stud walls.

Well, I personally bought my house back then and renovated it almost entirely myself, so here are a few tips as a very interested layperson: If you have to have everything done by companies during a renovation, the location and/or size of the property is (almost) the only reason to buy an old used property. And it depends on the state of the technology. Since it will be a property under 100k€ for you, a complete overhaul really needs to happen. That starts with insulation. The top floor ceiling and roof should definitely be done. Basement ceiling, if present, as well. I am also an advocate of facade insulation because it’s not just about costs, but also partly about comfort.

Next comes water/electricity. Check the condition here and redo it. For example, I had a short circuit in the kitchen supply line a month after the renovation was completed and then had to tear up a lot again. Stupid mistake on my part.

Then comes the heating. Also check if the old one is too old. With oil, also consider the tank system.

Creating an installation level is relatively easy. Because of crumbling plaster in the dining room, I covered the walls with drywall. That made it easy to lay cables. I advise against interior insulation at first, as it must be 100% executed to avoid mold.

Well, that was just a brief overview of the work involved. I don’t want to discourage you, I would do such a project again at any time, but it costs an infinite amount of nerves. My parents supported me intensively back then, and I believe there was not a single day when it wasn’t said: it doesn’t work the way we imagined. I was also only 24 and am not from a trades background.

And generally about mold: new windows and a “tight” house require a lot of care with ventilation. That’s the main problem why mold keeps recurring.

We have, for official purposes, a building from 1979, relatively large, over 450 sqm of area, retrofitted. The condition: built in 1979, asbestos roof, facing brickwork, uninsulated air gap, lightweight concrete block, wooden windows, oil heating from 2000, wooden doors. The procedure: had an appraisal done by an engineer for energy/energy consultant. The result: no new technology, not worth it. Upgrading the roof insulation/side insulation, leave asbestos alone, do not touch it, then it does no harm, blow perlite into the cavity, double up all windows that were in good condition with slats and triple glazing, new sealing profiles, then repaint the windows fresh. Cost 25k. Savings: instead of 9000 liters of oil per year, 6200 liters of oil per year. Maybe this helps you. Karsten

When are you turning off the heating now in spring? At the end of March, I wanted to turn it off because of the summer-like temperatures, but now it’s freezing cold again, especially in the evening. Now it’s too warm during the day and too cold in the house in the evening. No idea how to best manage that... any tips?