In short and in plain language
Lower Saxony has a rule for roofs. It is in the building code. If a roof gets a new cover, a solar system can be required.
This applies from 50 square meters of new roof. Then at least half of it must carry solar panels. Small repairs do not count.
There are exceptions. Some roofs cannot carry panels. Sometimes the system does not pay off. After a storm, the duty can also fall away.
The duty is on the client. That is usually the owner. The roofer explains the rule. But the roofer does not check each case like a lawyer.
The roofer's website explains the rule in short. In the form, the customer gives the size of the roof. An electrician connects the power.
A gable roof from the 1970s, the tiles porous, the underlay brittle: the owner asks for a quote to re-roof. Since early 2025, a second question comes with it in Lower Saxony, and many owners only hear it during the conversation: does a solar power system now have to go on the roof as well? The answer is in Section 32a (2) of the Lower Saxony Building Code (NBauO), and it depends on the renewed area, the scope of the work and the exemptions. For a roofing firm, this is more than a legal question. Firms that explain the rule clearly on their website receive inquiries in which the roof area is already stated, the owner has decided whether they want a system, and the electrical partner is known. Firms that stay silent explain it on the phone, one inquiry at a time. This article shows what the provision requires, which exemptions paragraph 4 lists in full, who is responsible, and how a roofer's service page and inquiry form can handle it without giving legal advice.
Key takeaways
- Since January 1, 2025, Lower Saxony has required that when at least 50 m² of roof covering is renewed down to the water-bearing layer, at least 50 percent of that area must carry PV (§ 32a (2) NBauO).
- The building ministry reads a renewal of the roof covering as a fundamental renovation in which the waterproofing or roof covering is completely removed and replaced, even if the old tiles are reused.
- The duty lapses to the extent that it conflicts with other public law, is technically impossible or economically unreasonable, or solar thermal panels go on the roof, and also when work after storm damage is unavoidable (§ 32a (4) NBauO).
- The client is responsible (§ 52 (1) NBauO). The roofer's website explains the rule in general terms; a legal review of an individual case is a legal service and does not belong in page copy (§ 2 (1) RDG).
- The inquiry form asks for the type of work, roof shape, approximate area per roof side and existing solar systems, and calculates whether the renewed area reaches 50 m²; next to it sits a neutral note, not a ruling.
- Behind the service fuse, the system is connected by an electrical contractor listed in a grid operator's installer register (§ 13 (2) NAV). The page names the partner and the joint workflow from survey to registration.
What § 32a (2) NBauO requires for a roof renovation
The Lower Saxony Building Code has contained a solar requirement for roofs for some time, initially staggered by building type and by the date of the planning application. The new version was announced in December 2023 and has applied since January 1, 2025; clients therefore had a one-year transition period for their planning (Lower Saxony building ministry). Paragraph 1 covers new buildings: when a building with a roof area of at least 50 m² is erected, at least 50 percent of the roof area must be fitted with a solar energy system that generates electricity (§ 32a (1) NBauO). What is new is paragraph 2, which extends the same duty to existing buildings.
If an existing building is altered by 1. adding a story, 2. an extension or 3. renewing the roof covering down to the water-bearing layer, then, where a roof area newly built or renewed in the process amounts to at least 50 m², at least 50 percent of that roof area must be fitted with a solar energy system for generating electricity.
For a roofer, number 3 is the core: renewing the roof covering. Adding a story and extensions affect roofers as well, but the planning there usually sits with an architect or a carpentry firm. According to the wording, what counts is the roof area renewed or newly built in the process, not the whole roof of the house. If only one side of the roof is re-covered, that side is what matters. And in the ministry's reading, the duty begins when construction work starts (Lower Saxony building ministry), not with an application, which a simple re-roofing job rarely involves anyway.
Half sounds like a lot, but the figure is deliberately rough. The 50 percent already allows for edge zones, areas for rooftop structures and equipment, walkways and parts facing an unfavorable northern direction (Lower Saxony building ministry). The ministry derives the 50 m² threshold from the assumption that systems with an output from about 3 to 5 kWp can be considered economical (Lower Saxony building ministry). Small roofs on garages or garden sheds therefore generally stay out of scope.
Why the question now lands in the quote
Solar on buildings no longer grows by itself. According to initial figures, 16.4 gigawatts of solar capacity were added in Germany in 2025, slightly less than the year before (Bundesnetzagentur). Just under half of that went to building-mounted systems and the other half to ground-mounted systems; the year before, the capacity added on buildings was still twice that added on open land (Bundesnetzagentur). To reach the target of 215 gigawatts in 2030, an average of 19.6 gigawatts would have to be added each year from now on (Bundesnetzagentur).
In Lower Saxony, § 32a (2) moves part of this decision to a moment when the owner already has a tradesperson on the roof: the renovation. That puts the question of a solar system on the roofer's desk, possibly before an electrical contractor has even been asked. A roofer who knows the rule and can explain it clearly becomes the first point of contact for a project that involves two trades, and can plan roof and system together instead of one after the other.
The search for answers starts online. 94 percent of trade businesses in Germany with at least one employee use their own website (Bitkom 2025), so having a site barely sets anyone apart. What makes the difference is whether a roofing firm's page answers the questions owners have before a renovation, and the solar mandate is one of them. How a service page for roofers is structured in principle is shown on the page web design for roofers. Why a separate page per service carries more weight than a combined page is explained in the article on service pages instead of one combined page.
When a renovation triggers the duty
Everything hinges on the term “renewal of the roof covering down to the water-bearing layer.” The law does not define it further. The building ministry interprets it in its question catalog on the building code as follows: it means a fundamental roof renovation in which the waterproofing or the roof covering is completely removed and reinstalled. This is meant to apply even when material is reused, for example when waterproofing and insulation are renewed and the old tiles are laid back on (Lower Saxony building ministry).
This interpretation binds no one. The ministry itself writes that its answers are not legally binding and that in individual cases the competent lower building authority decides on its own responsibility (Lower Saxony building ministry). It still works as orientation for page copy, as long as the copy says so openly. The following overview classifies typical roof work.
| Work on the roof | Para. 2 no. 3 affected? | What the website says about it |
|---|---|---|
| Replacing individual tiles after a storm, re-mortaring the ridge | generally no, not a complete renewal | repair, no solar question |
| Insulating from inside, covering stays in place | no, the covering is not renewed | no solar question; a note on § 35c EStG is possible |
| Re-covering one roof side with new underlay | yes, if that side measures at least 50 m² | settle the solar question in the quote |
| Re-covering with old tiles, new insulation and waterproofing | yes, in the ministry's reading | reuse does not change the question |
| Flat roof with completely renewed waterproofing | yes, from 50 m² of renewed area | raise structural load early |
| Re-covering because a storm destroyed the roof | duty may lapse under para. 4 sentence 2 | refer to the storm damage page |
The roofer measures the area during the survey anyway. For new buildings, the ministry takes the entire roof area from gable to gable and from eaves to ridge, not the building's footprint (Lower Saxony building ministry); for alterations, the threshold applies by analogy to the area being altered or added. A worked example: a gable roof with an eaves length of ten meters and a rafter length of six meters has 60 m² per side. If only the south side is re-covered, it is above the threshold, and at least 30 m² would need modules. If both sides are renewed, at least 60 of the 120 m² would need modules.
The exemptions in para. 4, read in full
Sentence 1 of paragraph 4 lists four reasons for which the duty lapses, and sentence 2 adds a fifth that applies only to renewing the roof covering and to parking lots (§ 32a (4) NBauO). A roofer's page should list all five, not just the one that suits its own business. Mentioning only the storm case gives the impression that the duty is the exception. Leaving the exemptions out gives the opposite impression. Both mislead the reader.
Other public law
Para. 4 sentence 1 no. 1: the duty lapses to the extent that it conflicts with other public-law obligations. The ministry names zoning plan provisions, building energy law, green roof requirements and heritage protection (Lower Saxony building ministry).
Technically impossible
Para. 4 sentence 1 no. 2: for example thatched or glass roofs, or an existing roof whose load capacity is not enough even for very light modules (KEAN). A missing option to feed power into the grid can also count (Lower Saxony building ministry).
Economically unreasonable
Para. 4 sentence 1 no. 3: when a well-planned system would not pay for itself within 20 years (Lower Saxony building ministry). The calculation should be prepared by a qualified person.
Solar thermal on the roof
Para. 4 sentence 1 no. 4: area on which a solar thermal system stands or is planned is deducted. For the rest of the required area, photovoltaics still apply.
Storm damage
Para. 4 sentence 2: when the roof covering is renewed, the duty also lapses if the work is unavoidable due to special external circumstances, in particular after unforeseen storm damage.
“To the extent,” not “whether”
The reasons in sentence 1 only apply as far as they reach. If the system fits on only part of the roof, the duty remains for that part.
The Climate Protection and Energy Agency of Lower Saxony works through two cases. If a 100 m² roof already carries 12 m² of solar thermal panels, a further 38 m² would need photovoltaics (KEAN). If the grid connection allows only 30 kWp while the roof would call for 40 kWp, enlarging the connection is probably not economically reasonable (KEAN). A 30 kWp system would still have to be built (KEAN). Both examples show why page copy that just says “lapses” falls short.
For economic viability, the ministry assumes a service life for solar systems of at least 20, more likely 25 to 30 years (Lower Saxony building ministry). No official decision is needed for the duty to lapse: the explanatory memorandum to the law, which the ministry cites, requires neither a deviation decision nor a separate notice from the lower building authority (Lower Saxony building ministry). Anyone relying on an exemption must still be able to show economic unreasonableness in a traceable way, and the evidence should be kept together with the contractor's declaration (KEAN).
Who is responsible and who checks
The duty falls on the client. The client is responsible for ensuring that the construction work they commission complies with public building law (§ 52 (1) NBauO). In a roof renovation, that is generally the owner or the owners' association, not the roofing firm doing the work.
In a typical re-roofing job, the building authority usually does not check anything. Replacing roof coverings without changing the existing external dimensions is exempt from procedure (Annex to § 60 (1) NBauO, no. 13.5), as are solar energy systems on the roof surfaces of buildings that are not high-rises (Annex to § 60 (1) NBauO, no. 2.3). Exempt from procedure does not mean exempt from rules, though: even procedure-free construction work must comply with public building law, and the building authority can enforce compliance under § 79 NBauO (Lower Saxony building ministry).
For extensive changes to the roof structure, the ministry recommends a structural stability report, even though it is not mandatory for procedure-free projects (Lower Saxony building ministry). Once a solar system is added, the question of load capacity arises anyway. For a roofer's page, this means structural capacity and load belong in the described workflow, not just on the construction site.
And the roofer? The roofer is not the addressee of the duty, but the one who raises it with the owner first. This is exactly where a website should draw the line. A legal service is any activity in specific matters of others as soon as it requires a legal review of the individual case (§ 2 (1) RDG). Page copy that explains the provision in general terms does not review an individual case. Whether a remark in a consultation counts as a permitted ancillary service to the trade depends on its content, scope and factual connection with the main activity (§ 5 (1) RDG). The website therefore explains what the rule says and leaves open what it means for a particular house.
The website does not decide individual cases
What belongs on the roofer's page
The right place is the service page for roof renovation, not a hidden paragraph in the notices or a PDF download. A dedicated section with a fixed order makes sense, one that an owner can read in a few minutes and then knows whether the question may concern them.
- The rule in three sentences, with legal reference and review date: what § 32a (2) NBauO requires, from what area and since when.
- The three triggers: adding a story, an extension and renewing the roof covering down to the water-bearing layer, plus one sentence on what sets a repair apart.
- All exemptions under para. 4: the four in sentence 1 and the storm case in sentence 2, with the note that they only apply as far as their reason reaches.
- The workflow with the electrical partner: who prepares the roof, who mounts the modules, who connects them and who registers the system.
- One sentence on responsibility: the duty falls on the client, and the section does not replace a review of the individual case.
- The way into the form, asking for the approximate roof area per side.
Be careful with overstatement. A sentence like “Every roof renovation now requires a solar system” is wrong because it ignores the threshold, repairs and the exemptions. A commercial practice can also be misleading through untrue or deceptive statements about the need for a service (§ 5 (2) no. 5 UWG), and an exaggerated claim of obligation that pushes owners to buy a system can fall under this. Conversely, a sentence like “The solar mandate probably does not affect you” does not help either. Factual copy names the rule, the threshold and the exemptions and leaves the assessment to the quote.
Sample copy for the service page
The review date is not decoration. Laws and their interpretation change, and the article on the new heating law shows how quickly a correct statement of obligation goes out of date. Adding the section to website maintenance means it comes up at every review and gets updated as soon as the ministry revises its question catalog or the state parliament amends the building code.
The roof area in the inquiry form
Many questions about the duty can be settled before the site visit if the form collects the right details. Five fields are enough, and none of them requires expert knowledge. The basic rules for trade inquiry forms are in the article on how many fields an inquiry form can take.
- Type of work as a choice: repair, re-covering one side, re-covering the whole roof, flat roof waterproofing, added story or extension, damage after a storm.
- Roof shape: gable, hip, mono-pitch, flat or other, ideally with small pictograms.
- Approximate area in square meters per roof side, or eaves length and rafter length in meters, plus an “I don't know” option.
- Existing installations: photovoltaics, solar thermal, roof windows, dormers.
- Interest in a solar system: yes, no or advice first, so the quote takes the system into account from the start.
The form asks for the area only roughly, on purpose. Many owners do not know it, but eaves length and rafter length can be taken from building documents or estimated in the attic. The form can calculate the area per side and show whether the renewed area is likely to reach 50 m². It then displays a neutral note, not a ruling. For hip and mono-pitch roofs the calculation is rough, but it is enough for a first assessment.
<fieldset>
<legend>Which roof area will be renewed?</legend>
<label for="eave">Eaves length in meters</label>
<input id="eave" name="eave_length" type="number" min="1" step="0.1" inputmode="decimal">
<label for="rafter">Rafter length in meters</label>
<input id="rafter" name="rafter_length" type="number" min="1" step="0.1" inputmode="decimal">
<label for="sides">Number of roof sides renewed</label>
<input id="sides" name="sides" type="number" min="1" max="4" value="1">
<p id="area-note" aria-live="polite"></p>
</fieldset>
<script>
const fields = ['eave', 'rafter', 'sides'].map((id) => document.getElementById(id));
const note = document.getElementById('area-note');
fields.forEach((el) => el.addEventListener('input', () => {
const area = fields[0].value * fields[1].value * fields[2].value;
note.textContent = area >= 50
? 'Probably 50 m² or more. The solar mandate under § 32a NBauO may then apply; we will clarify this in the quote.'
: '';
}));
</script>Two things belong next to the fields. First, a sentence saying that the details are used only to prepare the quote. Second, a field for photos of the roof, if the customer has any. For older houses, the construction year belongs in the same form as well; the reason is explained in the article on the construction year in the inquiry form.
Name the electrical partner, separate the workflows
A photovoltaic system is a project for two trades. The roofer prepares the roof, fits roof hooks or the mounting structure and seals penetrations. An electrical contractor handles the connection: apart from the grid operator, work on the electrical installation behind the service fuse may only be carried out by an installation company listed in a grid operator's installer register (§ 13 (2) NAV).
After commissioning, the operator must register the system in the core energy market data register within one month (§ 5 (5) MaStRV). Toward the building authority, however, this entry is not an intended proof of compliance with the solar mandate, according to the ministry (Lower Saxony building ministry). Both belong in the workflow on the page, so the customer knows what still comes after the scaffolding is taken down.
Survey and area
The roofer measures the area to be renewed, checks the covering, substructure and load reserves and notes whether an exemption might come into question.
Joint quote
Roof and system are planned together: module layout, penetrations, cable route and meter cabinet. The electrical partner checks the grid connection.
Roof and mounting structure
Re-covering or waterproofing, roof hooks or rail system, sealed penetrations. With in-roof solutions, the modules replace part of the covering.
Connection and registration
The registered electrical contractor connects and commissions the system and supports registration with the grid operator and in the market data register.
The roofer measures the area to be renewed, checks the covering, substructure and load reserves and notes whether an exemption might come into question.
Roof and system are planned together: module layout, penetrations, cable route and meter cabinet. The electrical partner checks the grid connection.
Re-covering or waterproofing, roof hooks or rail system, sealed penetrations. With in-roof solutions, the modules replace part of the covering.
The registered electrical contractor connects and commissions the system and supports registration with the grid operator and in the market data register.
The website names the partner with name and trade, ideally with a link to the partner's own site. If the electrical contractor links back to the roofer, both firms benefit. How the other side builds its photovoltaics page is shown in the article on websites for electrical contractors; what we build for electrical firms themselves is on the page web design for electricians.
Storm damage: the bridge to the emergency page
Sentence 2 of paragraph 4 links the solar mandate to the least predictable part of a roofer's business. If the roof covering has to be renewed because of special external circumstances, in particular to repair unforeseen damage from severe weather, and the work is unavoidable, the duty under para. 2 no. 3 lapses (§ 32a (4) NBauO). The ministry describes this as an involuntary renewal that the owner is directly forced to carry out (Lower Saxony building ministry).
For the website, this means two things. The storm damage page, as described in the article websites for roofers: storm damage as the trigger, gets one short sentence: if the roof has to be re-covered after severe weather, the solar mandate may lapse, and we clarify this in the quote. And the damage report asks for the date and type of event and requests photos, because the documentation of the damage later supports this question as well.
The line is drawn at the word “unavoidable.” A roof that was due for renovation for years anyway and finally gets done after a storm is not automatically a case for sentence 2. The website should not decide this but ask the question. A page that already separates emergency protection from planned renovation has laid out this distinction and only needs one more sentence.
What implementation costs
For a roofing firm that already has a website, the solar section is an extension: a section on the renovation page, a sentence on the storm page, five form fields with an area calculation and a partner block for the electrical contractor. Firms starting from scratch plan it in from the beginning, along with separate pages for gutters, insulation and flat roofs. The tax reduction under § 35c EStG is a second legal topic that belongs in the same renovation section.
A new website costs from 1,490 euros net at a fixed price with us, a relaunch of an existing website from 2,900 euros net. Website maintenance starts at 49 euros per month net, hosting in Germany at 15 euros per month net; both can be canceled with one month's notice to the end of a month, with no minimum term. Prices as of September 2026. The details are on our pricing page, and have a trade website built describes the steps to a finished site.
Related Articles
Websites for Stove Installers: Inquiries in Heating Season
Wood stoves, tiled stoves, built-in fireplaces: how stove installers build a website that settles stove type, chimney, room size and spot before the site visit.
Heating breakdown: the fault report form for winter
Heating off, phone ringing: how heating firms build their own fault report form with fault code, rating plate photo and callback window, apart from emergencies.
Skilled workers from abroad: the trade careers page
Around 86,600 recognitions in 2025: how a trade careers page explains the route via the chamber of crafts, in plain language, with help for settling in.