Masonry house and chimney
Walls of fired brick or stone in lime mortar, a roof that does not burn, and a chimney that takes every trace of smoke out of the house.
Everything for this step
- Field guide
- Stone and earth building → 18 sections
- Builds
- Fireplace and chimney
- Reference sheets
- 10 sheets in Stone and earth building
- Sciences it rests on
- Engineering
- Track
- Dwellings, level 2 of 5 · next: Framed and glazed building
Why this matters
An earth house lasts about thirty years if its roof and render are kept up. A brick or stone house in lime mortar lasts for centuries, does not soften in rain, and does not burn, so houses can stand wall to wall along a street. This is where Brick and tile and Lime become a building.
The other change is the chimney. Smoke from open fires indoors kills an estimated 2.9 million people a year (WHO, 2021), and only a chimney that draws removes it: a smoke hole in the roof moves it around the room. A tiled roof finishes the job, because in a dense settlement roof fire is what destroys a whole street. The fireplace and chimney build gives every dimension of the chimney.
The shape of it
- Footings to firm ground and below frost, wider than the wall, and a damp-proof course of slate or hard brick at least 150 mm above the ground outside.
- Lay in lime mortar, 1 part putty to 3 of sand, weaker than the brick, in a bond that ties the wall through: Flemish or English bond, or a header course every fifth or sixth course.
- Build the corners first and lay to a line: level every course, plumb every corner, and gauge four courses of brick to 300 mm.
- Carry every opening on an arch or a lintel bearing at least 100 mm into the wall at each end, with a relieving arch over any timber lintel spanning more than about 0.9 m.
- Build the fireplace and chimney with the wall: a shallow firebox, a narrow throat, a smoke shelf and a lined flue rising at least 0.6 m above the ridge, with no timber touching it.
- Roof in fired tile at 35° or steeper, rafters tied at their feet, and flash the chimney where it passes through.
- Keep fresh lime work above about 5 °C and damp for the first week or two, and dry the house with small fires raised over a week.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Footings below frost, and a damp-proof course above the splash
Masonry is heavy, and it cracks where one part settles more than another. Dig through topsoil to firm, undisturbed ground, and in cold climates below the depth frost reaches, as for any building in the building guide.
- Footing about 1.5–2 times the wall's thickness: roughly 0.45 m under a one-brick wall, stepped in a quarter-brick each course up to the wall's width.
- Lay the footing in the hardest bricks or large flat stones, bedded full in mortar.
- A damp-proof course at least 150 mm above the ground outside: two courses of slate in mortar, or two courses of the hardest, least absorbent brick. Ground damp rises through brick and lime; the damp-proof course stops it.
✓ Check: The footing rests on ground a steel bar will not push into by hand, its top is level to within 5 mm along its length by the water level, and the damp-proof course sits at least 150 mm above the ground outside.
2 · Choose the wall thickness, and a bond that ties it through
A wall stands because each brick or stone overlaps those below it. Bricks stacked joint on joint are a pile, not a wall.
- Break every vertical joint by at least a quarter-brick (about 56 mm); half a brick is normal.
- Tie the wall through its thickness. In Flemish bond every course alternates a header (the short end, showing) with a stretcher; in English bond whole courses of headers alternate with courses of stretchers. A face laid all in stretchers needs a course of headers every fifth or sixth course to bind it to the brick behind.
- One brick (215–230 mm) is the least thickness for the outside wall of a small house.
- Stone walls are thicker, because the stones are irregular: set a through-stone reaching the full thickness every 1.2–1.5 m along the wall and every 0.45 m of height.
- Bond every corner and cross-wall in, course by course. A wall butted against another with a straight joint is two walls that will part.
- In earthquake country, add a continuous ring beam at the top of every wall and keep the roof light, as the building guide sets out.
✓ Check: Along any course no vertical joint sits over the one below it; headers show in the face at least every sixth course, or in every course in Flemish bond; every corner and cross-wall is bonded, not butted.
3 · Mix lime mortar weaker than the brick
The mortar is the sacrificial part of the wall. It must be softer and more permeable than the brick or stone, so damp and salts leave through the joints, and frost damages joints that can be repointed rather than bricks that cannot be replaced.
- 1 part lime putty to 3 parts sharp, well-graded sand, by volume: the mix in the lime guide.
- Joints about 10 mm. Four courses of 65 mm brick with 10 mm joints rise 300 mm. Mark a gauge rod every 75 mm and check the wall against it.
- Dampen the bricks in hot, dry weather, so they do not suck the water out of the mortar before it can work.
- Non-hydraulic lime mortar keeps for weeks if covered, and can be beaten back to a workable paste. Mortar containing cement or hydraulic lime cannot: use it within the hour.
Never lay or point soft brick in hard cement mortar. The joint becomes the strongest and least permeable part of the wall, and the faces of the bricks take the frost and salt damage instead. That spalling can only be repaired by replacing bricks.
✓ Check: Lift one freshly laid brick: its bed is covered with mortar edge to edge, not in patches. A week later the joints can be scratched with a nail but do not crumble.
4 · Corners first, then lay to the line
Build each corner first, racked back course by course, and plumb it as it rises. Keep no corner more than about 0.9 m above the rest of the wall. Then stretch a string line between the corners at the top of each course and lay every brick between them to the line.
- Level every course with a spirit level or a water level.
- Plumb every corner and every opening with a plumb line, or a straightedge and level.
- Gauge the height against the rod at every corner, so the courses meet at the same height all round.
- Fill every joint, bed and vertical. A hollow joint lets water into the wall and weakens it.
- Level uncoursed stone work every 0.4–0.45 m of height, so the courses do not wander.
✓ Check: Every course is level, every corner is plumb over its full height, and the number of courses at each corner matches the gauge rod.
5 · Span openings with arches, and protect every timber lintel
Masonry is strong in compression and weak in tension, so an opening is spanned by an arch, which stays in compression, or by a lintel.
- Segmental or round arches of bricks on edge, built over a timber centre that stays in until the mortar has stiffened: at least a week in lime.
- Keep openings back from corners, so there is solid wall beside each arch to take its outward thrust.
- Lintels run about 200 mm longer than the opening, bearing at least 100 mm into the wall at each end.
- Over any timber lintel spanning more than about 0.9 m, build a brick relieving arch bearing on the wall beyond the lintel's ends, so the wall still stands if the lintel rots or burns.
✓ Check: When the centring is struck, the arch does not drop and no crack opens at its crown or haunches; every lintel shows at least 100 mm of bearing at each end.
6 · Build the fireplace and chimney as the wall rises
The chimney is built with the wall, never added afterwards, and every part of it has a dimension. The fireplace and chimney build draws it in full. The rules that decide whether it works, from the USDA bulletin and Rumford:
- A shallow firebox with splayed sides. Rumford's rule is a back about one-third the width of the opening, with the sides at 135° to it, which throws heat into the room.
- A narrow throat 150–200 mm above the bottom of the lintel, as long as the opening is wide, with an area no less than the flue's. Rumford's throat is 4 inches (100 mm) front to back.
- A smoke shelf behind the throat, and a smoke chamber whose sides lean in at 30° to the flue, plastered smooth.
- Flue area at least one-tenth of the fireplace opening, lined with fired clay. One-twelfth is enough only if the chimney is at least 6.7 m tall from the hearth.
- The top at least 0.6 m above the ridge, or 0.9 m above a flat roof. Through thatch, 1.8 m.
- No timber touching the chimney. Leave 50 mm of air between the chimney and every joist, beam and rafter, filled only with loose incombustible material.
Carbon monoxide has no smell. A flue that leaks or does not draw fills rooms with it. Headache, dizziness and nausea in several people at once, easing outdoors, is carbon monoxide until proved otherwise; see the fire guide.
✓ Check: A smoky fire at the base with a wet blanket over the chimney top shows no smoke through any joint; with the blanket off, a fire lit from cold draws within a few minutes, and a lit taper at the fireplace opening leans inward.
7 · Roof in fired tile, and flash every junction
A tiled roof does not burn, which is what lets houses stand close together.
- Pitch 35° or steeper for plain clay tiles, each course lapping the one below by about a third, as in Brick and tile.
- Tie the rafters at their feet with tie beams or ceiling joists, so the roof pushes down on the walls, not outward.
- Project the eaves beyond the wall face, so water runs off rather than down the brick.
- Flash the chimney where it passes through the roof: an apron below it, stepped flashing up each side dressed into the brick joints, and a back gutter above. Lead is the traditional metal; where there is none, tile or slate fillets set in lime mortar do the same job and need renewing more often.
✓ Check: After heavy rain the roof timbers and the ceiling around the chimney are dry, and no tile has slipped.
8 · Cure the lime, dry the house slowly, sweep the chimney
- Keep fresh lime work above about 5 °C and damp for the first week or two, shaded from sun and wind under damp sacking. Mortar that freezes or dries before it has carbonated crumbles.
- Do not load new walls with the roof or floors until the mortar has stiffened: weeks, not days.
- Render or limewash the outside in wet climates, in lime, never cement. Renew limewash every year or two.
- Light the first fires small and raise them over a week or two, so the water in the new chimney and walls leaves without cracking them.
- Sweep the chimney before each winter. Creosote, a black tar, forms when a fire smoulders in a cold flue, and a chimney fire in it burns very hot. If one starts, shut off the air: hold a wet blanket or rug over the fireplace opening and get everyone out.
✓ Check: The first fires, raised over a week, leave no new cracks in the chimney breast, and a sweep's brush comes down without a crust of tar.
Build it
Dimensioned drawings, bills of materials and construction procedures for the things this step asks for.
How this fails
Hard cement mortar laid or pointed into soft brick: the joint becomes the strongest, least permeable part of the wall, and the brick faces take the frost and salt damage and spall away.
Timber built into or touching the chimney (a joist, a lintel, a mantel): it chars and ignites from a hot flue, often inside the wall where nobody sees it until the house is alight.
An unlined flue with open joints, which leaks smoke and carbon monoxide into rooms and the roof space; found only by a smoke test.
Straight joints at corners and cross-walls, so walls part as the building settles or in an earthquake.
Lime mortar that froze or dried out before it carbonated, which crumbles and has to be raked out and relaid.
In earthquake country, heavy unreinforced masonry with no ring beam and a heavy roof: this is what collapses on people. The building guide's earthquake rules apply to brick and stone as much as to earth.
How you know it worked
VerificationAfter the first winter of daily fires: a fire lit from cold draws without puffing smoke into the room once the flue is warm; a smoke test (a smoky fire at the base, a wet blanket over the chimney top) shows no smoke through any wall; no damp patches inside; walls within about 10 mm of plumb over a storey; and no cracks at corners or above openings.
What this unlocks
t2-barn
Barn and byre
House the herd and its winter fodder so that the bedding stays dry, the air stays below the ammonia limit, the hay cannot burn the byre or the house, and nothing from either reaches the well or the people.
t3-frame
Framed and glazed building
Frame a building in timber on a masonry plinth, brace it so it cannot rack, glaze its windows, and keep it dry, warm and ventilated.
t3-fire
Fire separation and the building code
Write and enforce a building code that stops a fire in one building from reaching the next, gets everyone out of the building it starts in, and puts enough water within reach of every building.