Home Additions near you

Each type of addition raises its own structural question. In every case, opening an exterior wall to join old and new rooms needs a beam and posts carried down to solid support, sized by an engineer or qualified designer, as our structural engineers page explains.

Before anyone draws an addition, the zoning bylaw decides how much you can build. Ontario's citizen's guide to land use planning explains that zoning bylaws control lot sizes and dimensions, parking requirements, building heights and densities, and setbacks from the street. Toronto's guide to small residential additions, for example, asks for a summary of the permitted and proposed zoning provisions, including lot area, gross floor area, coverage and grade elevations, as part of the permit application.

When a design doesn't fit exactly, Ontario's system lets you apply for a minor variance. According to the citizen's guide, the application must explain how the variance is minor and why it is needed, the committee of adjustment holds a hearing and decides, and anyone with an interest in the matter may appeal to the Ontario Land Tribunal, or a local appeal body where one exists, within 20 days. A minor variance doesn't change the bylaw; it excuses your property from one requirement so a permit can be issued. Other provinces have their own variance processes.

An addition needs a building permit; Toronto's permit guidance, for example, names second- and third-storey additions, sunrooms, porches and attached garages among the additions that require one. Its guide to small residential additions lists what the drawings must show: a site plan with property lines and setback dimensions, floor plans for each level with existing and proposed uses and the location of smoke and carbon monoxide alarms, elevations with roof slopes and window and door sizes, and cross-sections showing the floor, wall and roof assemblies. The architects, architectural designers and permit drawing pages explain who can prepare and sign that set.

Most leaks and drafts in additions start at the seam between old and new. The new roof has to be framed and flashed into the old one so water runs past the joint, whether it forms a valley where two roofs meet, a lower roof butting against a wall that needs step flashing, or a flat roof against siding. The addition's sheathing membrane and air barrier have to lap onto and seal to those of the house, and a new foundation next to an old one can settle differently, so the connection is detailed to allow for it.

Natural Resources Canada points out that new construction is a chance to install a continuous air and vapour barrier and high levels of insulation efficiently, so the addition will usually outperform the house it joins.

A furnace and ducts sized for the original house may lack capacity for the new rooms, and long duct runs often leave an addition colder in winter and warmer in summer. Ask the HVAC contractor for a room-by-room heat loss and heat gain calculation that includes the addition, and let it choose between the options below. Gas piping, refrigerant and wiring are for licensed trades only.

Many families stay home through a ground-floor addition, but a second storey usually means the roof comes off above the bedrooms, and many households move out for that stage. Go through the phasing with the contractor before signing: when the wall between old and new will be opened, when water or power will be off, and how long the kitchen or a bathroom will be out of use.