Building Envelope, Weather Barriers & Exterior Insulation

Building Envelope Upgrades Behind Your New Siding

New siding is the one time in a house’s life when the outside of the wall is open, and in Calgary that is the cheapest moment to fix what is behind it. This page explains the four layers we can add or repair during a re-side, how they work together, and how to decide which ones your wall needs.

A house wall covered in plain rigid insulation boards with vertical wood furring strips fastened over them at regular spacing.

How These Systems Differ

The building code treats a wall exposed to weather as two lines of defence. The first plane is the cladding itself, with its trim, flashing and fasteners. The second plane catches the water that gets past the siding and sends it back outside. In Calgary that second plane is usually a breather-type sheathing membrane over the sheathing, lapped at least 100 mm with upper sheets over lower, plus flashing at windows, doors and every horizontal junction. The City of Calgary advises having the weather-resistive barrier inspected, repaired or replaced whenever siding is replaced. House wrap and weather barrier work is therefore the one envelope service that belongs on almost every re-siding job.

The other three services are choices. Exterior rigid insulation adds a continuous layer of foam or stone wool over the sheathing, which covers the studs that interrupt the insulation inside the wall. It comes with a rule: foam boards thick enough to act as a vapour retarder must be thick enough, relative to the cavity insulation inside, to keep the sheathing warm. In Calgary the outside layer needs at least 30% of the insulating value of what is inside it, so a thin layer of foam over a 2×6 wall can be worse than none. Stone wool boards such as ROCKWOOL Comfortboard 80 are vapour permeable and non-combustible, which changes that calculation. Rain screen siding adds furring strips that hold the cladding off the wall so water can drain and the back of the siding can dry.

Window and door capping is the fourth service, and the one most often done badly. Bent aluminum over old wood brickmould protects the wood and matches the new siding, but capping is a cover, not a flashing. If water gets behind it, it stays there. So we check and repair the wood first, form caps so each piece laps over the one below and sheds onto the siding, and seal between siding and frames as the code requires. None of these four layers is visible when the job is finished, which is exactly why they need to be decided before the siding is ordered.

Envelope & Insulation Services

The side of a new house covered in tan rigid insulation boards with vertical wood furring strips fastened over them, ready for siding.

Continuous Exterior Rigid Insulation (CI)

Rigid foam or stone wool over the sheathing to stop heat escaping through the studs.

How it works

A house wall covered with plain white house wrap in horizontal layers, upper layers lapped over lower ones and seams taped.

Weather-Resistive Barrier (WRB) & Housewrap

Tyvek, building paper or self-adhered membrane, lapped, taped and flashed.

How it works

Grey horizontal boards fastened to vertical wood furring strips over white house wrap, leaving an open drainage gap behind the cladding.

Rain Screen & Cavity Ventilation Systems

Furring or drainage mat leaving a drained, vented gap behind the cladding.

How it works

A window surrounded by smooth white bent aluminum capping with crisp folded edges, set into beige lap siding.

Custom Window & Door Aluminum Capping

Bent aluminum over wood brickmould and bucks, lapped and sealed to shed water.

How it works

Choosing Between Them

Always inspect the weather barrier: Treat house wrap and flashing as the baseline for any re-side. If the existing membrane is torn, brittle or missing at windows, it is replaced; if it is sound, it is repaired and re-flashed around openings.
Add a rain screen for specific claddings: Calgary’s dry climate means the code does not force a rain screen cavity on a house here. We still recommend one behind cedar and some metal systems, and some products require one regardless, such as HardiePanel vertical siding and synthetic housewraps whose evaluations call for an air space.
Add exterior insulation on older, colder walls: Exterior rigid insulation makes most sense on older homes with thin walls, or where the owner is already planning an energy upgrade. It adds depth at every window and door, so trim and capping details change with it.
Cap windows only over sound wood: Choose window and door capping when the frames are staying and the wood beneath is solid or repairable. If the frames are rotten through, capping hides the problem instead of solving it.

Why It Matters in Calgary

Calgary falls in climate zone 7A, with 5000 heating degree-days, while Okotoks, at 4920, sits in zone 6 and uses a lower 0.20 insulation ratio for exterior foam. The City of Calgary says houses whose building application was submitted on or after November 1, 2016 must meet the code’s energy-efficiency section for new renovations, while older houses do not, although every renovation must use components that perform as well as or better than those replaced. Older stock such as 1950s Killarney and Richmond bungalows and 1960s and 1970s homes in Varsity and Lake Bonavista is where exterior insulation is most often worth a serious look.

Permits change with the scope. For a straight replacement we confirm with the City. For a re-clad that adds exterior insulation, Calgary’s Land Use Bylaw exempts it from a development permit and lets the added insulation and cladding project up to 0.3 m into a required setback, but building-code approval is a separate question, and buildings on the City’s inventory of evaluated historic resources are not exempt.

Envelope & Insulation: Common Questions

Do I need exterior insulation when I re-side?

Usually not: for most homes it is an upgrade you choose rather than something a like-for-like re-side forces, and we check your house’s code history before saying so. It is worth considering when the house is older, the walls are thin, or you are already paying for tear-off, because the wall is open and the added layer covers the thermal bridging at every stud. It is not worth doing badly: a thin foam layer over a thick insulated wall can put the sheathing at risk. We size the insulation to the wall, or recommend skipping it and doing the weather barrier properly instead.

Which envelope upgrades matter on a straight re-side?

On a like-for-like re-side, the weather barrier and flashing matter most, because they decide whether water that gets past the new siding can get back out. Window and door capping follows if the frames are staying. A rain screen depends on the cladding: some products and membranes require an air space, and we recommend one behind cedar and some metal systems. Exterior insulation is the upgrade to add only if you want better energy performance and are ready for the deeper window and door trim it brings.

Can envelope work turn a siding job into a permit job?

It can. Under Alberta’s Permit Regulation, replacing siding with a similar type, for maintenance or appearance and with no structural change, is generally exempt from a building permit. Changing the cladding type, adding exterior insulation, altering openings or repairing structure can take a project outside that exemption. Rules also differ between Calgary, Okotoks, Airdrie, Cochrane and Chestermere, each of which is the authority having jurisdiction for its own projects. We confirm with the municipality before work starts.

Other Siding & Exterior Services

Talk to Us About Envelope & Insulation

Tell us about the house and what is going wrong with the walls. We will recommend the system that fits, including when a cheaper one will do.

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