Installing an outdoor unit on a shingle roof: the five constraints imposed by shingles
A shingle-covered sloped roof is not a floor. It has neither the flatness of an elastomeric membrane, nor the load-bearing capacity of a patio slab, nor the tolerance of a gravel surface. It drains in one direction, expands, and the slightest obstacle placed across its drainage path eventually makes itself known through a ceiling leak.
At Sainte-Marie-Madeleine, the only viable location for the outdoor unit of the Freematch R32 system was precisely there: on the low-slope roof of an addition, against the second-storey wall, beneath the roof overhang. Here is how we addressed each of the constraints imposed by this configuration.
Why this roof and not the yard
The owner had initially considered a ground-level installation against the rear wall. Three factors ruled it out:
- The wooden deck occupied the entire width of the rear façade, and dismantling a section would have cost more than the roof support.
- Ground-level snow accumulation in this open agricultural area of Montérégie regularly reaches one metre by the end of winter. A ground-mounted unit would have required a support more than 60 cm high and would have remained exposed to wind-formed snowdrifts.
- The piping length to the two areas to be conditioned would have doubled if routed through the basement.
The addition's roof was only a few metres from the two indoor units, partially sheltered by the roof overhang and out of reach of snowdrifts.
Equipment: GREE Freematch R32 GWHD(24)ND6MO
| Feature | Value |
|---|---|
| Connectable indoor units | 2 to 3 (2 installed) |
| Rated cooling capacity | 24,000 BTU/h — modulation from 7,500 to 31,400 BTU/h |
| Rated heating capacity | 24,000 BTU/h — modulation from 7,500 to 31,400 BTU/h |
| SEER2 / HSPF2 | 21 / 10 |
| EER2 / COP | 12 / 3,9 |
| Heating guaranteed down to | -30 °C |
| Refrigerant | R32 (A2L), 1,700 g factory charge |
| Sound pressure | 58 dB(A) |
| Net weight | 51 kg |
| Dimensions | 964 × 660 × 402 mm |
| Electrical | 208/230 V — MCA 19.5 A — maximum protection 25 A |
| Piping | precharge 30 m — maximum 60 m |
| Certifications | ENERGY STAR, AHRI, cold-climate certification |
| Warranty | 10 years + 2 years compressor and parts |
The choice of 24,000 BTU is explained by the open-plan ground-floor area, which alone warranted a 15,000 BTU indoor unit, and by the owner's desire to retain some capacity for extended heat waves. The inverter compressor modulates from 7,500 to 31,400 BTU/h, avoiding chronic oversizing during the shoulder seasons despite this nominal capacity.
Constraint 1: distribute 51 kg across an addition's framing
An attached addition or garage is framed to support snow, not necessarily a concentrated point load. Fifty-one kilograms applied at four support points of a few square centimeters each creates considerable localized pressure on 1/2-inch plywood.
Our setup:
- A treated wood board installed perpendicular to the rafters, distributing the load across at least three of them rather than a single span of plywood.
- A strip of self-adhesive membrane under the board, protecting the shingles from friction and moisture retention.
- An aluminum support bolted to the board, leveling the unit despite the slope.
- Anti-vibration pads between the support and the unit.
The non-negotiable preliminary check: determine the direction and spacing of the rafters from inside before choosing the location. A support installed parallel to the rafters, between two of them, concentrates the entire load on the roof panel.
Constraint 2: never block water flow
A board laid across the slope forms a dam. Water accumulates uphill, seeps under the shingles by capillary action, and the problem appears two or three years later as a stain on the ceiling.
The board was therefore positioned as high up the slope as possible, against the wall, in the area where the volume of runoff is minimal, and raised to leave a clear passage for water descending from the wall and the roof overhang.
The appliance itself is approximately 35 cm above the shingles: air circulates beneath the unit, snow does not accumulate against the coil, and defrost water falls freely and then drains with the rest of the roof runoff.
Constraint 3: snow and ice falling from the main roof
This is the most underestimated risk for this type of installation, and the one that destroys the most appliances in Quebec.
A slab of hardened snow sliding off a sloped roof and falling three metres onto an aluminum coil destroys it instantly. Replacement is not covered by the warranty—it is damage, not a failure.
At Sainte-Marie-Madeleine, the appliance is placed directly beneath the roof overhang, in the overhang’s shadow zone, protecting it from falling vertically. We also checked:
- the axis of the downspout—no water discharge above or in front of the appliance, which would produce a column of ice in winter;
- the absence of a valley directing water toward this section of roof;
- the prevailing wind direction, to anticipate snowdrift accumulation against the wall.
When the overhang does not provide sufficient protection, we install a protective canopy above the unit. Here, the building’s geometry made this addition unnecessary.
Constraint 4: noise transmission through the structure
The appliance is installed against a wall behind which there is an occupied room, and a window is located less than two metres away. The unit’s 58 dB(A) at maximum output is not a problem in itself—it is the structure-borne transmission that is.
Two principles applied:
- The bracket does not touch the wall. It rests entirely on the timber, with no attachment to the siding or the wall framing. A wall-mounted bracket turns the entire structure into a sounding box.
- The refrigerant lines are installed with some slack, never stretched tight between the appliance and the wall penetration.
Constraint 5: the wall penetration and electrical connection
The white enclosure visible on the wall is the disconnect switch, which must be within sight of the appliance and powered by a dedicated circuit protected at 25 A, in accordance with the model’s 19.5 A MCA.
The wall penetration for the refrigerant lines and control cable follows three rules:
- Drill downward toward the outside so that water can never migrate inward.
- Drip loop—the lines descend below the opening before rising again, so water running along the sleeve falls to the ground instead of entering.
- Two-level sealing: closed-cell expanding foam inside the opening, and a vinyl-compatible elastomeric sealant on the outside.
On a vinyl covering, the material must also be allowed to expand freely. Sealant applied across the full width of a vinyl plank prevents this, and the plank buckles during the first summer.
Commissioning
- Pressurization with dry nitrogen and hold test.
- Evacuation to 500 microns with an isolation test using a vacuum gauge.
- Piping length measured and then compared with the 30 m precharged—no additional R32 required in this case.
- Superheat, subcooling, and amperage checks.
- Supply-air temperature readings on both indoor units.
- Warranty registration and delivery of the technical data sheet to the owner.
Job duration: one day, two technicians.
What we apply everywhere
We carry out this type of installation on sloped roofs in Montreal, Laval, Longueuil, the North Shore, the South Shore, and throughout Montérégie. The rules do not change from one job site to another:
- Survey the roof framing before choosing the location, never afterward.
- Position it with water in mind—water that runs off, falls from the upper roof, or comes out of the downspout.
- Mechanically decouple the unit from the occupied structure.
- Document the commissioning so that the 10+2-year warranty remains defensible ten years later.
For the installation of a wall-mounted heat pump, a wall-mounted air conditioner, or for HVAC maintenance, our team assesses the building on-site before recommending a model and location.