Fireplace & Chimney Work
Masonry quantities for planning around the work — bricks, blocks, mortar and render — with the safety-critical scope left where it belongs.
The honest version first: fireplace and chimney construction and alteration is safety-critical, and it is regulated in most countries. Flue sizing, hearth construction, combustion air and the structural support of a chimney breast are not planning arithmetic — an undersized or badly built flue can put carbon monoxide into a living room. None of that is a calculator's job, and this hub doesn't try to make it one.
What this hub does cover is the masonry that surrounds that professional work. Even when every trade is hired, the quantities are genuinely useful to understand: how many bricks a chimney breast or surround consumes, how much mortar those bricks need, what a render or plaster coat takes for making good after the flue work is done, and the concrete behind a hearth base. Knowing those numbers means you can sanity-check a materials schedule, order the masonry yourself where that makes sense, and hold your own in a conversation with the trades.
The sequence below assumes the professional scope is settled first — installer, and where structure is touched, an engineer — because that scope decides what masonry exists to count. It's the one order of operations this hub is strict about.
The Plan
- Settle the professional scope first. A registered installer determines the appliance, flue size, hearth requirements and ventilation; an engineer covers anything structural — removing a breast, supporting what remains. Their spec decides the masonry, not the other way round.
- Measure the masonry. Chimney breast, surround, any new blockwork: net wall areas with openings deducted. A standard metric brick with 10 mm joints covers roughly 60 bricks per m² — the calculator applies it.
- Count the units. Bricks or blocks from area, single or double skin, with a 5% waste allowance typical for cut work around openings.
- Total the mortar. Wall area converts to mortar volume, then to cement and sand at the ratio the job needs — 1:3 to 1:6 by volume covers the common general-purpose bands, with the guide explaining the differences.
- Plan the hearth base. Where concrete sits under a hearth, it's a volume job at the thickness the specification calls for — the concrete mix ratios guide covers what goes into the pour.
- Make good. After flue and structural work, walls get rendered or plastered: net area times coat thickness and coat count, converted to cement and sand.
Calculators for This Project
Guides Worth Reading
What This Hub Doesn't Cover
Fireplace and chimney construction and alteration is safety-critical and regulated in most countries. Flue sizing, hearth dimensions and combustion air are set by qualified professionals working to local rules — an undersized or wrongly built flue can put carbon monoxide into the room. This hub covers masonry quantities for planning around that professional work, nothing more. Never build, alter or size a flue from a website.
Specifically absent: flue and chimney design, firebox construction, appliance installation, and the structural engineering behind removing or altering a chimney breast — all of it is registered-trades territory, usually with permits and inspection attached. Specialist materials sit outside these calculators too: firebrick and refractory mortar are a separate discipline from general brickwork, and mixing the two up is exactly the kind of error the regulations exist to prevent. Use this hub for the masonry arithmetic; use a professional for everything that carries smoke.
Frequently Asked Questions
Can I work out the flue size myself?
No. Flue sizing, hearth construction and combustion air are regulated in most countries and depend on the appliance, its output and the building. They are set by a qualified installer or engineer — this hub exists to plan the masonry quantities around that professional work.
How many bricks for a chimney breast?
Wall area times the per-m² count. A standard metric brick with 10 mm joints covers about 60 bricks per m², so a 3 m² breast is roughly 180 bricks plus 5% waste — order about 190. The brick and block calculator does any size, single or double skin.
What mortar mix should fireplace work use?
For general masonry around the fireplace, ratios from 1:3 to 1:6 by volume cover the common applications — the mortar mix guide explains which suits which. Fireboxes, flues and linings are different territory: they need specialist refractory materials and professional installation.