A flat roof installation designed for reliability: rails, membrane protection and waterproof path made by AirGreen
Project background
In a typical building in Southwest Montreal (flat gravel roof, low parapets and visible technical equipment), the occupants wanted to air condition and heat the main living area without losing floor space or altering the brick facade. Our recommendation: a latest generation Gree R-32 wall-mounted heat pump, with a condenser installed on the roof on rails to ensure stability , silence and durability . Objectives: four-season comfort , controlled consumption , secure maintenance and impeccable HVAC finish .
Site Analysis: Constraints and Opportunities of a Montreal Flat Roof
-
Bituminous membrane + gravel : need to distribute the loads and protect the waterproofing .
-
Prevailing wind overhanging the street: importance of anchors , anti-vibration pads and free height around the exchanger to avoid any air recycling .
-
Other equipment (extraction ducts, guardrails, vents): require precise positioning and minimum distances to maintain air flow in heating and defrosting mode.
-
Technical access : hatch/ladder allowing safe maintenance without disturbing occupants.
This reading guides us towards a compact installation on a raised frame , slightly set back from obstacles, with protected routing of connections to the roof penetration .
Equipment selected and capacity adequacy
The Gree R-32 wall-mounted range covers capacities from 9,000 to 24,000 BTU (and more depending on the series). We size the unit after load calculations taking into account insulation, sunlight, ceiling height and openness of the areas.
Why R-32? It provides high seasonal efficiencies , a lower refrigerant charge for the same performance, and better meets the efficiency requirements of assistance programs. Combined with an ultra-quiet indoor unit, the solution covers summer air conditioning and heating support down to the low temperatures of Greater Montreal.
Installation Details — What Makes the AirGreen Difference
1) Structure and load distribution
-
Installation on roof rails with white polymer pads under treated wooden joists : the load is distributed and the membrane is protected from punching.
-
Raised galvanized frame : the unit is above gravel and protected from melt water ; the space under the unit facilitates the flow of frost in winter.
-
Anti-vibration pads at the chassis feet: reduction of noise pollution and mechanical fatigue.
2) Positioning and clearances
-
Front and side clearances comply with Gree recommendations for free air intake and efficient defrosting .
-
Distance from visible kitchen/toilet extractors on the roof to avoid the suction of stale air and premature corrosion .
3) Refrigeration path and roof penetration
-
The UV insulated copper lines and the power cable run in a black technical conduit to a curved penetrant (red cap) ensuring a lasting seal .
-
Internally, the path to the wallhead is short and direct , limiting bends to preserve efficiency and fluid load .
-
Careful air/vapor barrier sealing at the crossing points to prevent infiltration and condensation .
4) Power supply and safety
-
Disconnect box near the unit, dedicated circuit to the panel, compliant grounding.
-
Waterproof and mechanically protected path against UV and abrasion.
5) Condensate and frost management
-
In air conditioning mode, the gravity drain of the interior head is provided with an adequate slope.
-
In heating mode, the defrost water flows freely towards the gravel without stagnating near the structure; the raised position prevents the formation of ice floes under the unit.
Commissioning: rigor and traceability
Our technicians carry out:
-
Extended vacuum draw in accordance with thresholds, circuit dehumidification control.
-
Leak tests and pressure verification.
-
Electrical controls (intensities, voltage, protection).
-
Blown/suction temperature measurements , validation of subcooling and superheat within the nominal range.
-
Setting of modes, speed and orientation of the shutters for uniform diffusion.
-
Customer training : best practices for use, filter cleaning , HVAC maintenance guidelines.
Observed results
-
Remarkable silence on the roof, no perceptible buzzing in the rooms.
-
Fast cooling during heat peaks; stable and comfortable heating when the temperature drops.
-
Technical aesthetics : discreet wiring and capping , clean penetration, aligned rails — an HVAC installation that inspires confidence during inspections.
Why the roof option is a winner here
-
No footprint on the ground or on the facade; ideal for buildings aligned with South-West street .
-
Less sound reverberation towards neighbors.
-
Easy maintenance : direct access through the hatch, total clearance around the condenser.
-
Winter protection : raised unit, efficient defrosting and natural water drainage.
AirGreen Best Practices for Flat Roofs (Montreal, Laval, Longueuil, North Shore, South Shore)
-
Use certified rails/pads to distribute the load and preserve the membrane .
-
Provide a minimum height under the chassis (≥ 20–25 cm) for frost drainage and service access.
-
Avoid areas of water accumulation and maintain a path to drains.
-
Anchor mechanically if required by wind exposure; add baffles as needed depending on the series and location.
-
Minimize the length and bends of refrigerant lines; protect the insulation from UV .
-
Install an accessible disconnect and identify the circuit on the panel.
-
Document the installation (photos of anchors, vacuum values , pressures), useful for guarantees and subsidies .
Grants and Eligibility
High-efficiency R-32 wall-mounted heat pumps may be eligible for assistance programs when the selected series meets the required SEER/SCOP/HSPF and a low temperature range (down to −25°C/−30°C depending on the model). We:
-
validate the conformity of the chosen Gree series;
-
provide traceability (product sheet, photos, statements);
-
We support the preparation of the file for Montreal , Laval , Longueuil , North Shore and South Shore .
Pitfalls to avoid on roofs (feedback)
-
Feet placed directly on the membrane: risk of sanding and infiltration ; always use pads and load distribution .
-
Insufficient clearances around the appliance: air recycling, ineffective defrosting .
-
Poorly sealed penetrations : source of infiltration and condensation ; use compatible penetrants and sealants.
-
Non-UV cable/insulation : premature aging; use resistant sheaths and tapes .
-
Frost flow directed towards a frequented low point: risk of ice ; orient the unit for safe discharge.
HVAC maintenance recommended
-
Every 3 months during the usage season: cleaning of the inner head filters .
-
Annually : gentle washing of the condenser coils , checking of the chassis fixings , inspection of the penetrant and the condition of the pads .
-
Before winter : check free flow under the unit and the integrity of the UV insulation.
-
Before summer : start-up test, checking intensities and adjusting comfort settings .
In short
-
Gree wall-mounted heat pump ( R-32 ), condenser on flat roof ;
-
Galvanized frame on rails/skids to protect the membrane ;
-
Protected refrigerated path , sealed penetrating ;
-
Rigorous commissioning and complete documentation;
-
Ideal solution for buildings in Greater Montreal where floor space is limited.
Are you thinking about a rooftop HVAC installation ?
We size, install and maintain durable , quiet and aesthetic systems in Montreal, Laval, Longueuil, North Shore and South Shore . Let's talk about your roof and your priorities.