ᐅ Is a low-pitched shed roof practical, or is a flat roof a better choice?

Hello dear forum,

For our newly planned house with two full stories (floor-to-ceiling height 3.25m (10.7 feet)) on a 14 x 12m (the house is positioned “crosswise” on the plot, so the 14m (46 feet) side runs parallel to the street), we still need a roof. Visually, we like a flat roof. However, there are also some drawbacks. Mainly, we want to install photovoltaic panels across the entire roof (south-southwest orientation), and a flat roof is said to require more maintenance and be more prone to problems. As a second option, we are considering a single-slope roof (shed roof) slanting from the street side to the back. I find the single-slope roof interesting because its construction is simpler (no complex waterproofing, for example), and since we need a tilt angle anyway for the photovoltaic system, we wouldn’t have to elevate the panels as much. The big disadvantage is the appearance—or rather, that the front of the house would have to be much higher than the back. We want to achieve a clear ceiling height of 2.8m (9.2 feet) on the upper floor and would lower the ceiling anyway, so we wouldn’t gain any extra space.

Even with a 5-degree slope, which according to what I’ve read does not really offer advantages over a flat roof (no “self-cleaning,” water or snow — if it comes again — cannot drain as well), there would already be a height difference of more than 1m (3.3 feet) over 12m (39 feet).

Here are my questions, and many thanks in advance to everyone who takes the time to think this through:

- From what roof pitch does a single-slope roof actually offer advantages?
- Is my “concern” about a flat roof justified?
- Doesn’t a flat roof also require a certain minimum slope?
- How much photovoltaic capacity (kWp) would I “lose” by elevating panels on a flat roof?
- What is the cost difference between a flat roof and a single-slope roof?

I’m very grateful for any (partial) answers. I’m a bit stuck.

As far as I remember, we still don't know anything about your building project, which is inconvenient because then we'd basically have to talk about colors as if we were blind. Your approach looks to me like a perfect example of starting off on the wrong foot.

The basic disadvantage of a shed roof is the increase in height due to the absence of a slope reversal at the ridge. Its advantage lies in its economical size, although even a truss roof, such as a hip roof, is affordable for a villa-style building. A flat roof is the cheapest option, as long as airtightness is not required ;-)

What does the local building plan / planning permission say about your roof ideas?

If you want to continue with your awkward approach, your next step would be to ignore the “stone mantra” and look for the “philosopher’s stone” (Godot is already waiting).

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@11ant It took me a while to decipher "Amfalschenendeanfangerei."

The house will be built according to Section 34 of the Building Code ("similar to neighboring development"), and on this street, you really find *every* type of roof. We have already completed a floor plan design, which is now with the general contractor’s architect. We will refine the floor plans with them or be told what is not possible. We also already know the construction method (aerated concrete), the heating system, and so on. I’m not sure how helpful all this information is in deciding on the roof type, but I’m new to the forum. The options are basically a shed roof or a flat roof. I wouldn’t want anything else. From my question here, I hope to get information to possibly counter any bias from the general contractor or architect, or at least not blindly follow their preferences, like the attitude “we always build a 3-degree shed roof, it never causes problems,” or similar. Everyone has their own reasons, of course.

A flat roof is the cheapest, as long as you don’t want it to be watertight

Is this meant as a general warning against flat roofs? Or only that it becomes poor quality if built cheaply?

bauhonk schrieb:

@11ant It took me a while to decipher "Amfalschenendeanfangerei."

The house is being built under Paragraph 34 of the Building Code ("like neighboring development"), and on this street there really *is* every kind of roof.

Just slightly off-topic:
Ultimately, how Paragraph 34 is interpreted is decided by the authorities. Do the houses within sight count? Houses within a certain distance? Only the immediate neighbors?

What exactly is taken into account? Number of stories? Height? Building line (even if only planned)? Facade? Roof?

Unless you are very close to the immediate neighbors, I would consider submitting a preliminary building inquiry.

At the same time, to put things into perspective: this also makes it difficult to predict which roof styles will be approved. For example, if the closest neighbors have gable roofs and flat or shed roofs only appear five houses down the street, it will be challenging under Paragraph 34.

The building volume usually also suggests which roof shape is more suitable. The floor plan plays a practical role in this as well. (For example, a shed roof might provide storage space that a flat roof does not.)

Is this meant as a general recommendation against flat roofs? Or just that it will be poorly done if built cheaply?

From what I recall, flat roofs are generally considered the most cost-effective roof type to construct. Unfortunately, they’re also the most prone to problems, and repairing those issues can be very complex, so building them too cheaply can quickly lead to trouble. However, spending more money on construction is never a guarantee of quality.

bauhonk schrieb:

Does a flat roof not need to have a certain slope?

Yes, it can range from 2 degrees up to 10 degrees.

bauhonk schrieb:

following their preferences based on the motto "We always build 3-degree shed roofs, never any problems" or otherwise. Everyone has their own reasons.

Their priority is to provide the homeowner with a house that does not have defects later on, avoiding constant calls or defect claims. They naturally want to prevent that because it costs them money.
So if they say, "We always build 3-degree shed roofs, never any problems," believe them. They gain nothing from doing the opposite or from building something unproven.
Of course, you can present them with amateur ideas and forum knowledge as with the floor plan design. If they are one of those who build anything just to make quick money with a homeowner who is temporarily happy and flattered during the construction process, and knowing that your contract exempts them from many liabilities anyway, then feed them forum opinions. This might sound blunt, but it’s the truth. I would choose the proven way unless I am building freely with architects and can afford a better execution.

bauhonk schrieb:

With them we will then refine the floor plans or get told off about what is not possible.

They won’t do anything like that. They will keep you in a good mood and build exactly what you have drawn there. Of course, they will make adjustments—if, for example, you accidentally dragged and dropped the toilet into the shower, they will correct that. But I wouldn’t expect much more. They are basically a general contractor who just lets things be drawn in.
Regarding your questions: whether flat or shed roof is mostly an aesthetic matter and a decision unless the building permit / planning permission or the local regulations restrict it. Usually, you know the roof type during planning because it influences the house style. So you have the goal in mind. You also recognized there are height differences.
All other questions should be discussed with a professional—already several tall trees can affect the photovoltaics. Raised mounting structures must be acceptable visually, as they simply don’t look great. For all other questions: "it depends." There is no general answer.

Papierturm schrieb:

How the regulation Par34 is interpreted is ultimately decided by the authority.

Actually, Par34 is clearly written. Most mistakes are made by homeowners who read something else into it or see it as a free pass. I assume that at least every third homeowner who is new to house building completely misinterprets the first three lines.

Thank you for your replies. I realize my initial post may have come across a bit too casual compared to the reality (hopefully). First of all: Of course, I’m a layperson, building for the first and probably the last time. The architect asked what I had in mind, and I drew something based on my living experience—what I know I want—plus a few features inspired by other houses. Overall, nothing extravagant. The architect first checks whether the design is fundamentally feasible (structural stability), answers my questions, and shares his opinion or experience. The roof options currently being discussed are a slightly pitched shed roof and a flat roof, with a preference for the shed roof. Why is it so frowned upon to want to understand this independently from the general contractor and architect? Of course, when it comes to the sea and construction, at some point you just leave it in God’s hands.

And the general contractor likely won’t care much if I have to go onto the roof every year to remove standing water or leaves that accumulate. That’s not a defect, but simply a consequence of the roof shape and its low pitch. Hence my question about the slope. I just wanted to find out whether there are (negative) experiences with slightly pitched shed roofs or flat roofs. From the “passive-aggressive” comments about the flat roof, I gather that it really might be as problematic as people say. 😉

Regarding Section 34: According to a verbal agreement between the general contractor and the authorities, I can build almost any roof, including flat and slightly pitched shed roofs explicitly. My neighbor on the left has a very long lean-to roof running transversely; on the right side, there is a hip roof with some "turrets." Next to them are classic gable roofs, and then comes the first flat roof.