Floor plan: New construction on existing bungalow basement, 1.5-story

I also spoke with a friendly representative from Streif Haus Haus. In the past, renovations/extensions were carried out in cooperation with Renopan, but by now there is apparently a new (partly in-house) company name, which he did not know. Our plans from the 80s are no longer available at Streif Haus Haus, but inquiries like mine are common and they are familiar with them. They now have the documents and will get back to us shortly. He was basically open to your suggestion of a split (shell construction: Streif Haus Haus, finishing: regional).

That makes me happy, that sounds good. Regarding the plans, I don’t understand the house manufacturers: retired designers are usually overjoyed if someone asks them again how the stuff was constructed back then. The ax in the house saves the carpenter, and the retired designer the beam-finder device ;-)

I wanted to PM you about that too, but I probably haven’t posted enough yet to be allowed. From when is that unlocked?

That is the best kept secret ever, suspected to be: from 200 posts. However, I have the same name at gmx de as in the forum.

It was not about social status, but because the OP has two very contrasting house manufacturers to choose from. Like Dacia and Porsche.

It's about a new Dacia vs. a 15-year-old Porsche (at 30 years old it would be a collector's item again). It's definitely a matter of taste, one wants the "perfection," the other the "modern navigation system."

Looking at the plot, if building new is the decision, I would consider excluding the basement from consideration. The east side seems to have a view, at least into greenery and unbuildable land. It makes sense, just like with new builds in the north, to plan the living side—meaning terrace and garden—there.

Are there already 2-story buildings in the neighborhood?

Show us some pictures of the house.

Attached are pictures of the existing building.
In the immediate neighborhood, there is a colorful mix of different house types (2-story with hipped roof, 2-story with flat roof, 1.5-story with gable roof and dormers).

If I look at the plot and new construction is the decision, I would definitely consider removing the basement from the consideration. The east side seems to have a view, at least into greenery and is unobstructed. It makes sense, as with the new buildings in the north, to plan the living side, i.e. terrace and garden, toward that side.

Exactly, the east side is unobstructed and offers a nice view. Therefore, we would also orient the living room there. At least we want to keep the basement even in the case of new construction.

Current status new build vs. renovation:

[*]Feedback from the local carpentry after inspection: The statics of the exterior walls and the floor ceiling between the ground floor and attic will probably be critical for an extension. The installed 12 cm wooden studs (outside) and 9 cm (inside) are probably too small for the expected additional loads. The ceiling joists are probably too narrow at 6 cm width as well. The prefabricated house was statically just designed to function as a bungalow.
[*]A building technician confirmed this in a further inspection.
[*]I am still waiting for feedback from Streif Haus to see if they can work some magic.

Attached are excerpts from the original static calculation from Streif Haus, in which the wall structure is well illustrated. In the picture from the attic, you can make out the sizes of the wooden studs. The rafters on the left correspond in width essentially to the ceiling joists of the attic. On the right side of the picture you can see the 12 cm exterior wall beams.

Was the house that cheap?

It really was: gift/advanced inheritance within the family.
We apparently seem to be the "wrong" family for the property, as our space requirements are simply bigger and therefore we want to add an additional story. A two-family household could probably renovate and use the existing footprint more easily (and with less invasion).

The tendency is therefore increasingly toward (partial) demolition up to the top of the basement ceiling and new construction as a 1.5-story building. However, a local energy consultant advised me to at least declare the whole thing as renovation in the building application, which in his opinion should generally be possible.

Attached are pictures of the existing building.
In the immediate neighborhood, there is a colorful mix of different house types (2-story with hipped roof, 2-story with flat roof, 1.5-story with gable roof and dormers).

Exactly, the east side is undeveloped and offers a nice view. Therefore, we would also orient the living room there. At least we want to keep the basement even in the case of a new building.

Current status New construction vs. Renovation:

[*]Feedback from the local carpentry after inspection: The statics of the exterior walls and the ceiling structure between the ground floor and attic will likely be critical for an extension. The installed 12cm wooden studs (outside) and 9cm (inside) are probably undersized for the expected additional loads. The ceiling joists with a width of 6cm are also probably too narrow. The prefab house was statically just barely designed to work as a bungalow.
[*]A construction technician confirmed this in a further inspection.
[*]I am still waiting for feedback from Streif Haus whether they can work some magic.

Attached are excerpts from the original structural calculation by Streif Haus, in which the wall structure is well illustrated. In the picture from the attic, the sizes of the wooden studs can be guessed. The rafters on the left basically correspond in width to the attic ceiling joists. On the right side of the image, you can see the 12cm exterior wall beams.

That was indeed it: a gift/advanced inheritance within the family.
We seem to be the "wrong" family for the property, as our space requirements are simply larger and we therefore want to add a story. A two-family household could probably renovate and use the existing floor area more easily (and minimally invasive).

The tendency is therefore again leaning more towards (partial) demolition down to the top of the basement and new construction as a 1.5-story house. However, a local energy consultant advised me to at least declare the whole thing as a renovation in the building application, which in his opinion should basically be possible.

Then let us hope that the energy consultant is otherwise knowledgeable on his subject, because no building authority will approve a demolition down to the basement as a renovation.

The tendency is therefore moving more strongly again towards (partial) demolition down to the top of the basement and reconstruction as a 1.5-story building.

After more detailed clarification on my part now as well. However, I would leave the basement ceiling standing and only do a "demolition" regarding the walls above it, i.e. dismantle the entire house, regarding the roof structure as a dismantling with a view to material preservation. I have just realized a knowledge gap here: my Rolodex does not yet include companies that dismantle "prefabricated" houses. If anyone knows any, please get in touch!

I believe I already said that I would be glad to advise on this project; it is not quite trivial. I would build much more contour-following on the basement than in the form outlined in the opening post. And probably a "one-and-a-half-story," possibly even in hybrid construction.

A local energy consultant advised me, however, to declare the whole thing at least as a renovation in the building application, which in his opinion should basically be possible.

Then let’s hope that the energy consultant is otherwise knowledgeable in his field, because a demolition down to the basement will not be approved as a renovation by any building authority.

There is news to report again here:
As already mentioned, we will place a 1.5-story new building on the existing basement.
After initially planning with a prefab house company (post #1), we are now working with a freelance architect who has provided us with the first floor plan draft after a conversation and an on-site visit.
The draft tends to be headed in the right direction for us, but the devil is still very much in the details.
To facilitate the evaluation, I will fill out the profile again (changes to the profile from post #1 in blue).
I also have concrete questions again (highlighted in purple), but I am basically open to any feedback!
Thanks in advance.


Development plan/Restrictions
Plot size: 615m²
Slope: North/South: <0.5m over 18m, West-East: approx. 2m over 33m (see elevation profile in post #1)
Site coverage ratio: No development plan (§34 Building Code). In the immediate neighborhood, there are partly very generously built plots. We do not want to change the footprint of the existing building but want to add a double garage (not existing so far).
Floor area ratio: No development plan (§34 Building Code)
Building envelope, building line and boundary: No development plan (§34 Building Code). Plot boundaries and existing property see aerial photo in post #1
Edge development: The garage of the southern neighbor directly borders (9m). We would like to place our garage there
Number of parking spaces: none, double garage planned
Number of stories: 1.5 stories
Roof shape: Gable roof
Style: Modern single-family house
Orientation: see aerial photo in post #1, entrance: north
Maximum heights/limits: No development plan
The surveyor recently measured the existing building as well as the direct neighbors:
- Existing building (bungalow with gable roof): eaves height: 4.1m, ridge height: 6.6m
- Southern neighbor (2 full stories + hip roof): eaves height: 7.8m, ridge height: 11.9m
- Northern neighbor (2 full stories + shed roof): eaves height: 5.4m, ridge height: 6.8m
Planned house (basement protrudes about 70cm above ground): eaves height: ~7m, ridge height: 9.20m. (All boundary distances are observed)
I am unsure how well our house fits into the street according to §34 Building Code. Can it be assumed that the building authority will have no objections since the southern neighbor also builds higher? The architect is at least relaxed about this so far.
Immediate neighborhood: Northern neighbor: 2 stories with flat roof. South: 2 stories with hip roof, West: 2.5 stories with gable roof

Client requirements
Style, roof shape, building type: We want to convert the existing bungalow into a classic 1.5-story single-family house with a gable roof and a shed dormer to the south.
Basement, stories: Usable basement (existing, concrete basement), ground floor (living), attic floor (sleeping), roof peak
Number of people, age: We are a family of 4 (ages: 32, 30, 2, 0), one more child planned
Space requirements on GF, UF:
Ground floor: living room, kitchen (with pantry/utility room), room for home office or guest room, guest WC with shower, wardrobe
Upper floor: master bedroom, 3x children's bedrooms, bathroom
Office: Family use or home office: home office (100% for me)
Overnight guests per year: few, <5 persons/nights
Open or closed architecture: tends rather closed. Option to separate dining area and living room would be desirable (e.g., by sliding or folding wall).
Conservative or modern construction: modern
Open kitchen, cooking island: Cooking island not a must. Partly open kitchen: possibility to separate from living room would be good. Currently planned with cooking island.
Number of dining seats: 5-8
Fireplace: only if budget permits, not a must. Currently planned.
Music/stereo wall: no
Balcony, roof terrace: Balcony on upper floor facing south desired, if later a separate dwelling unit is made.
Garage, carport: double garage
Utility garden, greenhouse: no
Further wishes/special features/daily routine, gladly also reasons why this or that should or should not be: Technical room should be accommodated in the existing basement (e.g., in the previous room for the oil heating). A sensible routing concept is important to us: front door/upper floor stairs/basement stairs. Ideally short routes between garage and apartment as well as good accessibility of rooms within the apartment.

The challenge/special feature in our floor plan is the fixed existing basement. The outer contours are fixed. The position of the basement stairs is fixed (an alternative stairwell should not be chiseled at another location).
After consultation with the energy consultant, the basement will be excluded from the thermal envelope of the new building. Accordingly, the basement exit on the ground floor (door and surrounding basement stairwell) must be sufficiently thickly insulated. Additionally, we are preparing the house for 2 dwelling units (possibility of later separation of GF and UF). Therefore, kitchen connections and a separate entrance (at the end of the staircase to the UF) must be prepared upstairs. This fixes the positions of the front door and the stairs to the UF as well. The goal is an as energy-efficient as possible house. According to our energy consultant, "KfW40 possible, KfW55 certain." Is that realistic? Does anyone here in the forum have experience with "KfW40/55 new build on non-insulated existing basement"?

House draft
Who planned it: First CAD draft by an architect after several hours of joint sketching
What do you particularly like? Why?:

[*]All desired rooms are planned
[*]Relatively spacious wardrobe area due to "cantilevered slab" (expansion of entrance area by concreted basement ceiling extension)
[*]Separation of UF and GF dwelling units possible
[*]Basically, we like the ground floor quite well, especially the nice kitchen facing southeast with great view
[*]Washing machine integrated in UF bathroom (less laundry carrying)

What do you not like? Why?:

[*]Knee wall of 0.65m (clear height) is too low: this causes us to lose 2m² in the bathroom and in the children's room the bed cannot be placed against the wall. The knee wall is probably also so low so that the window sill height of the dormer windows remains still acceptable. However, as I understand it, measures should be taken to pull the dormer windows deeper into the roof (e.g., by metal flashing).
[*]The roof peak is very small at 1.70m due to the low knee wall and the very generous UF room height (less height would also do). Especially the space-saving staircase (instead of the pull-out staircase, actually a nice idea) makes no sense here because the exit "rippled away" can only be done in a bent-over manner
[*]The balcony (client wish, not the architect’s fault) might steal too much space from the children’s rooms and could worsen our energy balance
[*]The shed dormer roof is very flat at 22°, we had hoped more for 30° (appearance and better suitability for photovoltaics), the connection of the dormer to the collar beam would have to be changed. Currently, there is a lot of facade area between the dormer window and the dormer roof gutter.
[*]Wall recesses at the showers on GF and UF: actually a nice idea, but on the GF the recess of 30cm is so small that furniture cannot be placed sensibly in the adjacent office. On the UF the wall recess is too big again, here a ~1.1x1.1m shower (closed) would also suffice for us.
[*]Wardrobe area (client’s wish) still suboptimal integrated in bedroom. Possibly we have to revert to a classic bed-facing closet here
[*]Preparation for kitchen connection in child 2 instead of child 1 (kitchen of UF apartment planned later in child 2).
[*]Stairs GF-UF / hall GF: the first step juts out as a tripping hazard in front of the entrance door room. Possibly the concreted basement ceiling can be extended another 1.5m to the west (one basement window must be closed anyway), so that the stairs can also be further north.
[*]Terrace: one terrace is enough for us, but larger. Here we prefer the street-facing away terrace 1 and would delete terrace 2 including doors to the house.
[*]3x north-facing roof windows in bathroom, stairwell and child’s room 1 could be useful to improve the lighting situation, possibly with a skylight above the upper floor hall door.
[*]Floor-to-ceiling (instead of normal) windows in dining room and bathroom are not necessary, here we value privacy and expect sufficient brightness in combination with dormer window (dining room) or possibly additional roof window (bathroom)
[*]The decision on construction method (wood or solid) is still pending, but there is a tendency towards solid construction. The plan is therefore based on 42.5cm aerated concrete blocks as exterior walls. These overhang the basement ceiling contour by 4cm all around. According to consultation with the local solid construction expert, the blocks can probably statically overhang the basement by 12cm without problems. That could give the floor plan some breathing room again and facilitate the transition to planned subsequent external insulation of the basement.
[*]No concept yet to separate living and dining areas on the GF

Price estimate according to architect/planner: Not yet determined. What expensive items still to come: photovoltaics, water/water heat pump, centralized controlled residential ventilation. We are currently planning with no brakes applied and all wishes articulated, the red pencil will probably come later.
Personal price limit for the house, incl. furnishings: 700,000€ (rough estimate: demolition down to top of basement ceiling: 30,000€, house: 530,000€, incidental building costs incl. basement statics: 50,000€, double garage: 30,000€, kitchen/furniture: 40,000€, landscaping: 20,000€)
Preferred heating technology: Heat pump with underfloor heating. If budget permits: brine/water heat pump with deep drilling.

If you have to do without, which details/extras
-can you do without: Reluctantly, but in decreasing order: fireplace, balcony, walkable roof peak with fixed stairs, pantry/utility room
-can you not do without: Home office

Why did the draft turn out as it is now?
Several hours of joint development of ideas with the architect using pencil and tracing paper. Before that, phone calls and an on-site visit (incl. energy consultant).