house-spec/specs/03-baufritz-coordination-spec.md

Baufritz Builder Coordination Specification

1. Overview

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.

---

2. Technical Room Requirements

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.

2.1 Minimum Specifications

Parameter	Requirement
Floor area	4–6 m² minimum (ideally 6–8 m²)
Ceiling height	≥ 2.4 m
Access	Full-width door (≥ 900 mm), no obstructions
Floor	Waterproof, drainable (steam humidifier condensate)
Electrical	3× dedicated 230V/16A circuits (MVHR, humidifier, controls)
Lighting	Bright, shadow-free (filter inspection)
Location	Central in building footprint (minimizes duct runs)
Noise isolation	Sound-insulated walls/door (MVHR generates 35–45 dB)

2.2 Equipment Layout

block-beta
    columns 3

    block:row1:3
        A["G4/M5\nPre-filter\nHousing"] B["F7\nIntermediate\nHousing"] C["Activated\nCarbon\nHousing"]
    end

    block:row2:3
        D["H13 HEPA\nCassette Bank\n(600×600mm panels)"] space:1 E["MVHR Unit\n(Drexel & Weiss\nor Swegon)"]
    end

    block:row3:3
        F["Steam\nHumidifier\n(Condair/Hygromatik)"] G["Control\nPanel\n(KNX Gateway)"] H["Supply\nDuct\nManifold"]
    end

    style D fill:#1a5e1a,color:#fff
    style E fill:#1a3d5e,color:#fff
    style F fill:#1a5e5e,color:#fff

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

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.

4.2 Radon Protection

Item	Specification
Radon membrane	Continuous radon-proof membrane at foundation/ground slab
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
Bypass	Summer bypass with motorized flap	Automatic
Controls interface	Modbus	KNX native
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
Fire safety	Fire damper at wall penetration

---

8. Electrical & Wiring Coordination

8.1 Technical Room Electrical

Circuit	Rating	Purpose
MVHR dedicated	230V / 16A	MVHR unit power
Humidifier dedicated	230V / 16A (or 400V / 3-phase)	Steam humidifier (high wattage)
Controls	230V / 10A	KNX power supply, gateway, sensors
Backup/spare	230V / 16A	Future expansion

8.2 Building-Wide Wiring

Item	Specification
KNX bus cable	To every zone (MVHR dampers, sensors)
Cat6a shielded	To every room (sensor data, future-proofing)
230V at sensor points	USB power for sensor units
Outdoor sensor cable	Weatherproof, north wall
ΔP sensor cabling	5× runs from filter housing to control panel

All wiring for the air system 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.

---

9. Construction Phase Checkpoints

9.1 During Construction

Phase	Checkpoint
Foundation	Radon membrane installed and sealed at all penetrations
Framing	Duct routing voids verified, vertical risers in place
Framing	Ceiling void dimensions verified for Plafotherm + MVHR trunk
Pre-close	First blower door test (target ≤ 0.6 n50)
Pre-close	All duct runs installed, mastic-sealed, pressure-tested
Pre-close	All KNX/Cat6 wiring installed and tested
Interior finishing	Plafotherm ceiling suspension and panels installed
Interior finishing	Ceiling heating circuit pressure-tested
Interior finishing	Raised floor pedestals installed, subfloor leveling verified
Interior finishing	Under-floor services (ducts, wiring) installed and pressure-tested
Interior finishing	Floor panels and WOODline parquet tiles installed
Interior finishing	Verify no ducts compressed or kinked by finishing work
Completion	Final blower door test
Completion	Commission MVHR, set airflows, balance dampers / AirHybrid panels
Completion	Commission ceiling heating/cooling, verify surface temperatures
Completion	Commission sensors, verify readings, connect to Home Assistant

9.2 Commissioning Verification

Test	Acceptance Criteria
Blower door (n50)	≤ 0.6 ACH
Duct leakage	Passivhaus class
Room-by-room airflow	Within ±10% of design spec
House positive pressure	+3 to +5 Pa vs. outside
CO₂ decay test	< 800 ppm within 30 min of occupancy end
PM2.5 indoor vs. outdoor	Indoor < 10% of outdoor
Noise at diffusers	< 25 dB(A) per diffuser

---

10. Timeline Integration

Baufritz Phase	Air System Action	Lindner Floor/Ceiling Action
Initial design	Specify MVHR unit, technical room size, duct routing	Confirm raised floor + Plafotherm, specify cavity heights and floor-to-floor height (≥ 3000 mm)
Detailed planning	Approve duct routing on drawings, specify all penetrations	Lindner layout drawings for floor and ceiling, coordinate with MVHR plan
Pre-fabrication	Confirm radon membrane spec, duct void dimensions	Verify subfloor level tolerance and ceiling anchor points in prefab panels
Factory build	Verify duct voids in prefab wall/floor panels	No impact (Lindner systems installed on-site)
On-site assembly	Supervise duct installation, first blower door test	Install ceiling system, then floor pedestals and cavity services
Finishing	Sensor wiring, diffuser installation	Parquet tile installation, floor and ceiling commissioning
Handover	Full commissioning, sensor calibration, HA setup	Heating/cooling commissioning, AirHybrid airflow verification