Often the best new building is an extension to the one you already have. You reuse a wall, keep everything under one roof and avoid a second set of footings and services. Done well, nobody can tell where the old building ends. Done badly, it can leak at the join for the rest of its life. Just as common, the dimensions don’t match: a slightly different roof pitch or height makes the add-on look obvious and out of place next to the original. We work hard to make extensions marry in with the existing building. We extend buildings by other suppliers as well as our own.
Three ways to extend #
- Add bays to the end. The cleanest option for portal frame buildings: remove the end wall, add frames with the same profile, and re-clad the end.
- Add a lean-to. A lower, mono-pitch roof off one side wall, popular for open machinery bays and covered storage.
- Build alongside. A second building next to the first, sometimes linked by a canopy, sometimes sharing a wall.
Check the existing building first #
An extension can put new loads on the old structure. A lean-to hangs off the existing columns, and joining two buildings changes how wind acts on both. Attaching to an existing building relies on it having the capacity to take the join. That means the strength of the beams and columns you’re connecting to, and also whether the concrete foundations beneath them can carry the extra loads. An engineer should check that the existing frame, foundations and bracing can take it. On older buildings, the drawings may be gone, so we measure what’s there. If the existing building doesn’t have the capacity, it can be cheaper to put a new frame right beside the existing one, even with the existing wall removed, and build the extension off that. The new building then has its own foundations and structure.
Matching cladding and colour #
Roof and wall profiles need to match for a clean, weathertight join. Colour matching is harder than it sounds, because existing cladding fades with sun and age, so new sheets of the same colour can look different at first. Sometimes re-cladding a whole elevation looks better than patching. A Waipu customer told us our extension to their storage complex “matches the existing units perfectly” (Ralph, Waipu).
Watch the water #
The join between old and new roofs is where most extension problems happen. Valley and internal gutters must be sized for heavy rain, with overflows so a blocked gutter spills outside, not inside. Wherever possible, design the roof so water runs off the outside rather than collecting between buildings.
Fire, consent and planning #
- Extensions are building work and normally need building consent.
- A bigger building may trigger fire requirements near boundaries that the original didn’t.
- Site coverage and boundary rules apply to the total building, not just the new part.
Improving the old while you’re there #
An extension is a good time to fix roof leaks, upgrade gutters, add skylights or re-roof the existing building. Alongside the 36,000 m² of buildings we’ve supplied, Steelspan has maintained or repaired more than 100,000 m² of existing buildings. We offer maintenance and re-roofing across greater Auckland, Hamilton, Tauranga and up to Whangarei. Every job is different, so we come and assess your building on site before we price it.
Tax #
For businesses, improvements to commercial buildings can qualify for Investment Boost. See our Investment Boost post.
Talk to Steelspan #
Send us photos and rough dimensions of your existing building and what you want to add. Use our Easy Shed Quote or call 0800 787 726.
