This document specifies requirements that must be communicated to and coordinated with Baufritz during the design and construction phases. Baufritz builds with excellent low-emission materials (no formaldehyde, no synthetic glues, tested for 300+ pollutants) and designs for airtight envelopes — this is the ideal foundation for our clean air system.
**The air system is not a retrofit. It must be designed into the structure from the beginning.**
**The house includes a reinforced concrete cellar** housing a home datacenter (4x 42U racks, 10 kW cooling) and goods elevator. The cellar is built first; the Baufritz timber-frame is erected on top. See 06-datacenter-spec for full cellar, elevator, and datacenter specifications.
A dedicated technical room is required for the air handling equipment. This is not a utility cupboard — it needs standing access for filter changes and equipment maintenance.
**All filter housings must be accessible from the front** with tool-free opening for filter changes. Minimum 800 mm clearance in front of each housing.
---
## 3. Duct Routing Requirements
### 3.1 Design Principles
| Requirement | Detail |
|------------|--------|
| Duct material | Rigid galvanized steel or aluminum — **no semi-rigid flex** |
| Exception | Final 0.5 m to each diffuser: flex for vibration isolation |
| Sealing | All joints mastic-sealed (not tape only) |
| Testing | Pressure-tested to Passivhaus duct leakage class after installation |
| Velocity: main trunk | ≤ 2.0 m/s |
| Velocity: branches | ≤ 1.5 m/s |
| Velocity: diffuser connection | ≤ 1.0 m/s |
| Main trunk diameter | 200–250 mm round (or equivalent rectangular) |
| Branch diameter | 125–160 mm round |
### 3.2 Routing Constraints
- **No ducts in exterior walls** — condensation risk and thermal bridging
- **Dedicated vertical risers** for multi-story distribution — coordinate with structural plan
- **Acoustic silencers** at MVHR outlets and before each room diffuser
- **Inspection/cleaning access points** at all bends > 45° and every 6 m of straight run
- **Fire dampers** at all floor/wall penetrations per DIN 4102
### 3.3 Duct Space Requirements
```mermaid
flowchart TD
subgraph Ground["Ground Floor Ceiling Void"]
GT["Main Supply Trunk\n200–250mm"]
GB1["Branch: Living Room\n160mm"]
GB2["Branch: Kitchen\n125mm (exhaust only)"]
GB3["Branch: Office\n125mm"]
end
subgraph Upper["Upper Floor Ceiling Void"]
UT["Main Supply Trunk\n200mm"]
UB1["Branch: Master Bedroom\n160mm"]
UB2["Branch: Leo's Room\n125mm"]
UB3["Branch: Bathroom(s)\n100mm"]
end
TR["Technical Room"] --> GT
TR --> UT
style TR fill:#1a3d5e,color:#fff
```
**Baufritz must allocate ceiling void depth of ≥ 300 mm** in areas where main ducts run, or provide dedicated duct boxing. This must be shown on construction drawings.
**Note**: The ceiling void is shared with the Lindner Plafotherm radiant ceiling system (see 04-flooring-ceiling-spec Section 4). On the ground floor, branch supply ducts may route through the raised floor cavity instead (see 04-flooring-ceiling-spec Section 6), potentially reducing ceiling void requirements. However, the main supply trunk and Plafotherm pipes still require adequate ceiling void depth. **Floor-to-floor structural height must be ≥ 3000 mm** to accommodate both the raised floor and ceiling system while maintaining ≥ 2500 mm usable room height (see 04-flooring-ceiling-spec Section 2).
---
## 4. Building Envelope Requirements
### 4.1 Airtightness
| Parameter | Requirement |
|-----------|-------------|
| Blower door test (n50) | ≤ 0.6 ACH (Passivhaus standard) |
| Target | 0.3 ACH if achievable |
| Testing | Blower door test during construction (before interior finishing) AND after completion |
Baufritz typically achieves excellent airtightness. This is critical — the air system only works if 100% of air passes through the filter stack. Every uncontrolled leak bypasses the entire system.
| Membrane type | HDPE or bituminous, radon-tested per DIN/ISO |
| Sealing | All penetrations (pipes, cables) sealed with radon-rated sealant |
| Sub-slab ventilation | Provision for passive sub-slab depressurization (can be activated later if needed) |
| Monitoring | Radon sensor in lowest habitable room, connected to Home Assistant |
**Note**: The Bremen/Grasberg area is generally low radon risk per BfS (Federal Office for Radiation Protection) maps, but radon protection is inexpensive at construction stage and expensive to retrofit. Specify it regardless.
**Raised floor compatibility**: The Lindner NORTEC Doppelboden pedestal system must be anchored with adhesive bonding only — no mechanical fixings that penetrate the radon membrane. Verify adhesive compatibility with the membrane material (see 04-flooring-ceiling-spec Section 7.5).
### 4.3 Thermal Bridge Prevention
Baufritz excels at thermal-bridge-free construction. Verify:
- No thermal bridges at window reveals, sills, lintels
- No thermal bridges at floor/wall junctions
- No thermal bridges at balcony connections (if any)
- Surface temperatures never below dewpoint at any point (prevents condensation → mold)
---
## 5. MVHR Specification for Baufritz
### 5.1 Unit Selection
Specify to Baufritz that the MVHR unit must meet:
| Parameter | Minimum | Preferred |
|-----------|---------|-----------|
| Available static pressure | 450 Pa | ≥ 500 Pa |
| Airflow capacity | 400 m³/h | 450 m³/h |
| Heat recovery | 85% | ≥ 90% |
| Fan motor | EC variable speed | EC variable speed |
| External filter box | Compatible | Designed for |
### 5.2 Baufritz-Typical vs. Our Requirements
Baufritz typically installs standard residential MVHR units (e.g., Zehnder ComfoAir Q350, Paul Novus 300). These are excellent units but designed for F7/F9 filtration with ~200–250 Pa system pressure.
**Our H13 whole-house requirement means upgrading to a higher-pressure unit.** This must be specified early because:
- The MVHR unit dimensions affect technical room layout
- Higher-pressure units may have different duct connection sizes
- Electrical requirements may differ (larger EC motors)
- Noise characteristics change — sound insulation may need upgrading
---
## 6. Garage Separation
If the house includes an attached garage:
| Requirement | Detail |
|------------|--------|
| Pressure separation | Garage at negative pressure relative to house |
| No shared air volume | No door directly from garage to conditioned space without airlock |
| Separate exhaust | Garage has its own exhaust fan with timer/CO sensor |
| Sealing | All wall/ceiling penetrations between garage and house fully sealed |
| CO sensor | In garage, interlocked with garage exhaust fan |
**Garage exhaust fumes (CO, NOx, PM, benzene) are extremely hazardous. Zero tolerance for garage air entering the conditioned space.**
---
## 7. Kitchen Exhaust Specification
| Requirement | Detail |
|------------|--------|
| Type | Ducted to outside — NOT recirculating |
| Backdraft damper | Motorized, closes when hood is off |
| Duct material | Stainless steel or galvanized (grease-rated) |
| Interlock | Activates MVHR boost mode for make-up air |
| Separation | Never connected to the MVHR system |
**All wiring must be specified on Baufritz's electrical plan before wall construction begins.** Retrofit wiring in a sealed timber-frame house is extremely difficult and expensive. The fiber and Cat6a backbone risers from the cellar must be coordinated with the elevator shaft and/or dedicated cable riser.
| Initial design | Specify MVHR unit, technical room size (8-10 m2), duct routing | Confirm raised floor + Plafotherm, specify cavity heights and floor-to-floor height (≥ 3000 mm) | Confirm POE RO location, municipal water entry, reject water drain | Cellar dimensions, elevator shaft location, main electrical sizing (3x80A) |
| Detailed planning | Approve duct routing on drawings, specify all penetrations | Lindner layout drawings for floor and ceiling, coordinate with MVHR plan | 316L pipe routing in ceiling void, riser locations, fixture drop-down points | Cellar structural drawings, elevator spec, cooling condenser location |
| Pre-fabrication | Confirm radon membrane spec, duct void dimensions | Verify subfloor level tolerance and ceiling anchor points in prefab panels | Confirm ceiling void can accommodate water pipes alongside MVHR and Plafotherm | **Cellar construction begins** (concrete, waterproofing, elevator shaft) |
| Factory build | Verify duct voids in prefab wall/floor panels | No impact (Lindner systems installed on-site) | No impact (water system installed on-site) | Cellar complete, slab cured, ready for Baufritz erection |
| On-site assembly | Supervise duct installation, first blower door test | Install ceiling suspension, route Plafotherm pipes | Install 316L supply mains in ceiling void (same phase as Plafotherm) | Elevator installed, main distribution board installed |
