ᐅ Construction of a multifamily house or two semi-detached homes built to KfW40+ energy efficiency standard
Created on: 22 Feb 2020 05:38
S
superzapp
Dear Community,
The plots have just been purchased, and the floor plans are quite finalized.
Now we are at the very beginning of the rest of the planning for this new build. I still have many questions regarding construction details and building services that have not yet been sufficiently clarified. I would like to present the project as planned so far and explain our ideas. Due to the size of the plots and the development plan, there are unfortunately quite tight limits regarding the size (which affects, for example, the need for a separate technical building, etc.).
The following key data have already been decided:
Two plots (two owners = one is my brother, one is me).
Border construction is mandatory, resulting in two semi-detached houses (one per plot, each with two residential units). The building will be two stories (eaves height limited to a maximum of 4.5 m (15 feet)).
Gable roof with a pitch of 30-45°, maximum height 9 m (29.5 feet) (all maximum heights measured from the top of the finished floor level). No basement. The upper floors will be accessed via external stairs.
Left half: 2 units each approx. 65 m² (700 sq ft), right half: 2 units each approx. 45 m² (480 sq ft) (each upper floor unit is naturally about 4-5 m² (43-54 sq ft) smaller than the ground floor unit).
The ridge runs west to east, meaning the roof surface for photovoltaics is precisely south-facing.
The ground floor faces south with many windows and doors; the upper floor rooms each have a roof window. The attic is insulated but only accessible via an emergency staircase. Balconies on the upper floors are oriented west or east.
Three residential units will be rented, and I will move into the small 45 m² (480 sq ft) ground floor unit.
A separate technical building of about 8 m² (86 sq ft) is detached from the house by about 1.5 m (5 feet) (for heat pump, storage tank, water, and electrical connections). Due to the necessary space requirements for the technical equipment and boundary setbacks, this is hardly feasible in any other way.
Our wishes and technical/building details as far as feasible:
Solid wood construction. The wall and roof build-up has already been roughly calculated by an energy consultant based on our initial design drawings and considered okay for KfW40 Plus standard. Some details for windows and precise thermal bridge calculations are still missing.
Wall construction from interior to exterior (U-value: 0.11 W/m²K)
1.25 cm (0.5 inch) gypsum board Thermal conductivity: 0.25 W/mK
10.00 cm (4 inches) solid wood wall Thermal conductivity: 0.13 W/mK
26.55 cm (10.5 inches) wood fiber insulation Thermal conductivity: 0.039 W/mK
6.00 cm (2.4 inches) wood soft fiber insulation boards Thermal conductivity: 0.040 W/mK (plaster base)
1.20 cm (0.5 inch) exterior plaster Thermal conductivity: 1.00 W/mK
Total thickness: 45.00 cm (17.7 inches)
Roof construction from exterior to interior (U-value: 0.13 W/m²K)
A Inhomogeneous layers: 10% structural wood
1.5 cm (0.6 inch) gypsum board Thermal conductivity: 0.25 W/mK
2.25 cm (0.9 inch) air layer Thermal conductivity: 0.16 W/mK
24.00 cm (9.4 inches) structural wood Thermal conductivity: 0.13 W/mK
8.00 cm (3.1 inches) wood soft fiber insulation boards Thermal conductivity: 0.042 W/mK
B Inhomogeneous layers: 90% insulation between rafters
1.5 cm (0.6 inch) gypsum board Thermal conductivity: 0.25 W/mK
2.25 cm (0.9 inch) air layer Thermal conductivity: 0.16 W/mK
24.00 cm (9.4 inches) structural wood Thermal conductivity: 0.13 W/mK
8.00 cm (3.1 inches) wood soft fiber insulation boards Thermal conductivity: 0.042 W/mK
Total thickness: 35.75 cm (14 inches)
Ground slab from inside to outside (U-value: 0.14 W/m²K)
7.0 cm (2.8 inches) screed Thermal conductivity: 1.40 W/mK
12.00 cm (4.7 inches) impact sound insulation board Thermal conductivity: 0.032 W/mK
24.00 cm (9.4 inches) reinforced concrete with 1% steel Thermal conductivity: 2.30 W/mK
10.00 cm (4 inches) EPS (expanded polystyrene) Thermal conductivity: 0.035 W/mK
Total thickness: 53.00 cm (21 inches)
(The 10 cm EPS is planned to be replaced by foam glass gravel; thickness will be determined once windows are finalized and the building recalculated.)
The wall construction might still be adjusted to achieve thinner walls by using higher-performance insulation materials (e.g., 0.031 mineral wool instead of wood fiber boards with about 0.039). But only if a) summer heat protection remains effective and b) ecological compromises are not too great. Unfortunately, I am not yet very familiar with the advantages and disadvantages of mineral wool compared to wood fiber insulation boards.
The perimeter insulation of the slab is planned with around 40-60 cm (16-24 inches) of layer-compacted foam glass gravel (required insulation thickness will be calculated).
Overall, we want to build as ecologically as possible and achieve high living comfort. Of course, since I plan to live here for the next 30-50 years if all goes well. Our priority is not primarily the construction costs but what makes sense energetically and ecologically. However, there is a maximum budget. I believe economy and ecology can be reconciled at least with a good compromise. We also hope — thanks to the currently quite generous subsidies for KfW40 Plus buildings — not to have to exhaust this budget.
Our further wishes:
So, this is the first batch of information. I look forward to plenty of feedback.
Next week, we will visit the company with which we want to build and have our plans reviewed and adjusted where necessary. Only then can we get initial cost estimates for the building envelope.
The plots have just been purchased, and the floor plans are quite finalized.
Now we are at the very beginning of the rest of the planning for this new build. I still have many questions regarding construction details and building services that have not yet been sufficiently clarified. I would like to present the project as planned so far and explain our ideas. Due to the size of the plots and the development plan, there are unfortunately quite tight limits regarding the size (which affects, for example, the need for a separate technical building, etc.).
The following key data have already been decided:
Two plots (two owners = one is my brother, one is me).
Border construction is mandatory, resulting in two semi-detached houses (one per plot, each with two residential units). The building will be two stories (eaves height limited to a maximum of 4.5 m (15 feet)).
Gable roof with a pitch of 30-45°, maximum height 9 m (29.5 feet) (all maximum heights measured from the top of the finished floor level). No basement. The upper floors will be accessed via external stairs.
Left half: 2 units each approx. 65 m² (700 sq ft), right half: 2 units each approx. 45 m² (480 sq ft) (each upper floor unit is naturally about 4-5 m² (43-54 sq ft) smaller than the ground floor unit).
The ridge runs west to east, meaning the roof surface for photovoltaics is precisely south-facing.
The ground floor faces south with many windows and doors; the upper floor rooms each have a roof window. The attic is insulated but only accessible via an emergency staircase. Balconies on the upper floors are oriented west or east.
Three residential units will be rented, and I will move into the small 45 m² (480 sq ft) ground floor unit.
A separate technical building of about 8 m² (86 sq ft) is detached from the house by about 1.5 m (5 feet) (for heat pump, storage tank, water, and electrical connections). Due to the necessary space requirements for the technical equipment and boundary setbacks, this is hardly feasible in any other way.
Our wishes and technical/building details as far as feasible:
Solid wood construction. The wall and roof build-up has already been roughly calculated by an energy consultant based on our initial design drawings and considered okay for KfW40 Plus standard. Some details for windows and precise thermal bridge calculations are still missing.
Wall construction from interior to exterior (U-value: 0.11 W/m²K)
1.25 cm (0.5 inch) gypsum board Thermal conductivity: 0.25 W/mK
10.00 cm (4 inches) solid wood wall Thermal conductivity: 0.13 W/mK
26.55 cm (10.5 inches) wood fiber insulation Thermal conductivity: 0.039 W/mK
6.00 cm (2.4 inches) wood soft fiber insulation boards Thermal conductivity: 0.040 W/mK (plaster base)
1.20 cm (0.5 inch) exterior plaster Thermal conductivity: 1.00 W/mK
Total thickness: 45.00 cm (17.7 inches)
Roof construction from exterior to interior (U-value: 0.13 W/m²K)
A Inhomogeneous layers: 10% structural wood
1.5 cm (0.6 inch) gypsum board Thermal conductivity: 0.25 W/mK
2.25 cm (0.9 inch) air layer Thermal conductivity: 0.16 W/mK
24.00 cm (9.4 inches) structural wood Thermal conductivity: 0.13 W/mK
8.00 cm (3.1 inches) wood soft fiber insulation boards Thermal conductivity: 0.042 W/mK
B Inhomogeneous layers: 90% insulation between rafters
1.5 cm (0.6 inch) gypsum board Thermal conductivity: 0.25 W/mK
2.25 cm (0.9 inch) air layer Thermal conductivity: 0.16 W/mK
24.00 cm (9.4 inches) structural wood Thermal conductivity: 0.13 W/mK
8.00 cm (3.1 inches) wood soft fiber insulation boards Thermal conductivity: 0.042 W/mK
Total thickness: 35.75 cm (14 inches)
Ground slab from inside to outside (U-value: 0.14 W/m²K)
7.0 cm (2.8 inches) screed Thermal conductivity: 1.40 W/mK
12.00 cm (4.7 inches) impact sound insulation board Thermal conductivity: 0.032 W/mK
24.00 cm (9.4 inches) reinforced concrete with 1% steel Thermal conductivity: 2.30 W/mK
10.00 cm (4 inches) EPS (expanded polystyrene) Thermal conductivity: 0.035 W/mK
Total thickness: 53.00 cm (21 inches)
(The 10 cm EPS is planned to be replaced by foam glass gravel; thickness will be determined once windows are finalized and the building recalculated.)
The wall construction might still be adjusted to achieve thinner walls by using higher-performance insulation materials (e.g., 0.031 mineral wool instead of wood fiber boards with about 0.039). But only if a) summer heat protection remains effective and b) ecological compromises are not too great. Unfortunately, I am not yet very familiar with the advantages and disadvantages of mineral wool compared to wood fiber insulation boards.
The perimeter insulation of the slab is planned with around 40-60 cm (16-24 inches) of layer-compacted foam glass gravel (required insulation thickness will be calculated).
Overall, we want to build as ecologically as possible and achieve high living comfort. Of course, since I plan to live here for the next 30-50 years if all goes well. Our priority is not primarily the construction costs but what makes sense energetically and ecologically. However, there is a maximum budget. I believe economy and ecology can be reconciled at least with a good compromise. We also hope — thanks to the currently quite generous subsidies for KfW40 Plus buildings — not to have to exhaust this budget.
Our further wishes:
- KfW40 Plus standard
- Air-to-water heat pump (alternatively ground-source heat pump if it offers significant advantages). There is not enough space for trench or surface collectors.
- Photovoltaics (approx. 13-14 kW peak capacity possible), possibly split into two systems
- Li-ion battery storage (approx. 13 kWh, possibly Tesla PowerWall or are there more ecological alternatives?)
- Controlled mechanical ventilation with heat recovery
- Additionally, we would like to have cooling if possible. Various options are being considered, each with different pros and cons:
- Cooling via the underfloor heating system (done by the heat pump) with low efficiency
- Cooling via separate ceiling or wall cooling (cost/benefit?)
- Ceiling heating/cooling as an alternative to underfloor heating
- Cooling via the ventilation system with downstream cooling coils per dwelling unit (disadvantage: condensate hard or impossible to control?)
- Air conditioning units
- Idea: to install a kind of earth collector to feed permanently cool air into the ventilation system, using a bypass when cooling is needed.
So, this is the first batch of information. I look forward to plenty of feedback.
Next week, we will visit the company with which we want to build and have our plans reviewed and adjusted where necessary. Only then can we get initial cost estimates for the building envelope.
S
superzapp22 Feb 2020 19:06Hello, good idea... but we have already considered that :p. The apartments can be connected later by installing a spiral staircase. In the appropriate areas, for example, the underfloor heating is omitted...
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