A pitched roof for old buildings and extensions – experiences?

Hello,

the old building (built 1959) is being extended by an annex. The old building is being completely renovated from the basement to the roof (new roof covering with insulation) (only the shell and roof truss remain).

The annex will have a basement; the basement will rest on a well-founded slab foundation / base slab to minimize uneven settlements or settlement differences between the annex and the old building due to the larger area.

The old building and the annex would basically be separate buildings from the basement to the upper floor.
Between the old building and the annex there would be an expansion joint from the basement to the upper floor (therefore no cracks).

The old building has a gable roof. Now the question: is a unified roof design with a gable roof sensible and feasible?

The idea see sketch

[*]to extend the living area of the attic also in the annex by extending the gable roof
[*]and to use the south side of the annex for a photovoltaic system.

Old building and annex are separated, have an expansion joint, up to the upper floor this can be well imagined.
These are two structures. But how can there be ONE roof above them?
The ridge of the annex would slope diagonally from the annex to the middle of the old building.
If no solution is developed: the attic apartment would later have cracks, etc. in the sloped roof.
The roof truss (if old and new are connected) could be permanently stressed.

Is there a solution proven in practice over the years for this? Or better to take another approach?

The development plan is being observed. A structural engineer will be commissioned later.
Preferably feedback beforehand from several construction experts.

Do most construction experts say this is solvable with normal effort, no consequential costs, low risks
or high costs to meet requirements, later high consequential costs, risks, etc.?

Thanks for experience reports.

Best regards,
Matthias

The old building (built in 1959) is being extended by an annex. The old building is being completely renovated from the basement to the roof (new roof covering with insulation) (only the shell and roof truss remain).

That sounds very much like the concept of a naive calculation to me. You seem to imagine it much simpler than it can actually be realized. I strongly recommend that you hire an architect for this project who can save you a lot of money. If you approach any companies with the ideas shown here, you will find some that say "yes, sure, we can do that" – but from then on it will go downhill.

Your old building comes from a very critical construction period; the post-war era extends historically up to about 1963. For solid advice, you would need to show significantly more here (floor plans and sections preferably from the original building file, photos of the existing building fabric from several perspectives). Your idea that the "old building" roof truss will remain is already a solid basis for further incorrect assumptions. With a T-connection of the secondary ridge to the main ridge, you will rarely if ever see such a connection resolved; typically, the secondary roof is lower, which here, due to the wider gable, is even more unfavorable than usual.

Normally, in a symmetrical gable roof, the opposing sides contribute to stability; due to the construction year, there is a justified suspicion here that the ceiling of the upper floor basically "belongs to the roof truss." I could very well imagine that the most likely recommendation after closer analysis will be to change the ridge direction and really give the house a SINGLE gable roof as indicated in the headline. But that would probably also require a new ring beam. There are reasons why this type of annexes are often – even if not the most beautiful solution – designed with a lower pitch or with a shed roof. Therefore, I already suspect conceptually here that you might be dreaming of the method “get approval and companies, let’s do without an architect.” Of course, a carpenter will also build exactly what is shown in your drawings – but then get ready to print money ;-)

I strongly recommend hiring an architect for this project ... If you approach companies, you will find some who say "yes sure, we can" - but from then on it goes downhill

Thanks for your feedback! I am looking for several photos of the existing condition.

That is exactly why I am asking here for experience reports. I have the statement from architects, carpenters, construction companies "we will find a solution" but that is not sufficient for me, then I am stuck in it and cannot get out.

[*]Changing the ridge direction of the old building is not possible according to the development plan, etc.
[*]Correct: ceiling of the upper floor of the old building basically “belongs” to the roof structure
[*]the main ridge of the old building is about 3m high from the attic floor, inside there is a sloping roof up to the ridge without another attic ceiling beneath the ridge. Now the question is how much lower the secondary ridge would have to be, as described it gets worse because of the wider gable width.

Thank you for your feedback! I am looking for several photos from the inventory.

You can also gladly take fresh ones, and don't forget the old plans.

the statement from architects, carpenters, construction companies "we'll find a solution there"

... translated into German means: "we'll empty your account - no problemo" :)

Rotating the ridge direction of the old building is not possible according to the development plan etc.

So far, I do not consider an exemption impossible, and it would even be cheaper. So add far-reaching site images as well.

Now the question is how much lower the secondary ridge would have to be; as described, it becomes less favorable due to the wider gable width.

The exact height cannot be estimated from a crystal ball. From "generally lower" results a shallower roof pitch as soon as the extension does not have a narrower gable than the existing building – with even more width, this only worsens.

So far, I don't see a waiver as impossible, and it's cheaper on top of that. So add extensive situation reports.

Preliminary survey has shown that the appearance of the old building with the roof must remain (no prospect of a waiver).
Attached are pictures.

Thanks for experience reports on whether the side ridge being lower could be something useful for a bit more usable space in the attic...

The simple secure solution to use the extension roof for photovoltaics would probably be separately as a shed roof?

Preliminary survey has shown that the appearance of the old building with the roof must remain as it is (no prospect of exemption).

Nonsense. With this argument, it is exactly the template from which one can make a goal :) Unpack more information from the development plan (you can also do this via private message in the Green section – under no circumstances here with an external link). Don’t be so stingy with the illustrations. The house is not a "dame without a lower body," you can do little with just one upper floor, and an aerial photo / cadastral extract or the like should, as said, reach far.

Thanks for the experience as to whether lowering the secondary ridge could make sense for a bit more usable area in the attic ... The simple safe solution to use the extension roof for photovoltaics would probably be separately as a shed roof?

With a flatter pitch, the roof would probably also reach the range of a higher efficiency for photovoltaics, but a separate shed roof, no, see your introduction.