Manual Load Takedown with Pen and Paper

How to trace loads by hand from roof to foundation, with realistic UK domestic values.

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Understanding load paths, and being able to carry out a load takedown calculation quickly and reliably, is a fundamental skill for every structural engineer. Tracing loads through a structure, from roof and floor areas down to beams, walls, columns and foundations, underpins both manual checks and software analysis.

At the early stages of a project you do not want to open a full analysis package just to check whether your walls and foundations are in the right ballpark. A quick manual load takedown, literally with pen and paper, is often enough to test the scheme, confirm tributary areas and build confidence before committing to detailed calculations.

This post walks through a takedown for a simple two-storey house, with the numbers you would actually use in the UK.

What is load takedown?

A load takedown is the process of examining a structural form and working out how applied loads are transferred to the supports, usually at ground or foundation level. You start at the top of the structure and work down through beams, walls and columns until the loads reach the foundations.

It breaks into three steps:

• Assess the load paths. Identify which elements support which loads: floor to beams, beams to walls, walls to foundations.
• Calculate the tributary areas. Work out the loaded widths and contributing areas that define the forces on each supporting element.
• Reduce the loads to the supports. Combine tributary loads with self-weight to get the reaction at each vertical element, and finally at foundation level.

Start with a marked-up plan

Print the architect's plan and draw on it. Span directions first, then supports, then the tributary strip for the wall you are checking. This markup is the calculation: the arithmetic that follows is trivial once the geometry is on paper.

Three things earn their place on the markup:

• Span direction on every floor zone. A one-way floor only loads the two walls it bears on. W4 and W5 in the plan above run parallel to the joists and pick up almost nothing from the floor, which is exactly the sort of thing that gets missed when you work from a schedule instead of a drawing.
• A reference for every vertical element. W1, W2, B1 and so on. Numbers without a reference are useless to a checker.
• The tributary strip, shaded. Half the span each side for a simply supported floor. If you are unsure how the strip is set out, the tributary regions article covers the geometry, and loaded width covers the cantilever and continuity cases.

Loads worth carrying in your head

For UK housing these values will get you to a defensible first-pass number. Check them against the relevant national annex before they leave your desk, but they are the right order of magnitude:

• Tiled pitched roof on trusses: 0.75 to 0.9 kN/m² permanent, 0.6 kN/m² imposed (snow, UK lowland).
• Timber joisted domestic floor: 0.5 to 0.8 kN/m² permanent, 1.5 kN/m² imposed plus 0.8 kN/m² for movable partitions.
• 150 mm RC slab with screed and finishes: 4.8 to 5.2 kN/m² permanent, 1.5 to 2.0 kN/m² imposed.
• Cavity wall, brick outer leaf and block inner leaf, plastered: about 3.5 kN/m² of elevation.
• 100 mm dense blockwork, plastered both sides: about 2.4 kN/m² of elevation.

The example below uses a concrete floor at 5.0 kN/m² dead + 2.0 kN/m² imposed = 7.0 kN/m², and a roof at 0.9 + 0.6 = 1.5 kN/m².

Turn an area load into a line load

Pick one wall and one floor. Everything in a takedown reduces to this single step, repeated.

The front zone in the plan spans 6.0 m between W1 and W3. The floor is simply supported, so half of it goes each way:

Loaded width to W1 = span / 2 = 6.0 / 2 = 3.0 m
Floor area load   = 5.0 + 2.0 = 7.0 kN/m²
Line load to W1   = 3.0 × 7.0 = 21.0 kN/m

That 21 kN/m is the floor's contribution to the top of W1. The roof, spanning the same 6.0 m, adds:

Roof line load to W1 = 3.0 × 1.5 = 4.5 kN/m

Two assumptions are buried in there and both should be written on the sheet: the floor is treated as simply supported, and no imposed load reduction has been taken. Both are conservative, which is what you want at this stage.

Add the wall, then work down the storeys

Floor loads alone will flatter the foundation. Masonry self-weight is often a third of the total at the bottom of a two-storey wall, and it is the part people forget.

W1 is a cavity wall, roughly 5.4 m from eaves to the underside of the ground floor:

Wall self-weight    = 3.5 × 5.4 = 18.9 ≈ 19 kN/m
Total at base of W1 = 4.5 (roof) + 21.0 (floor) + 19 (wall) = 44.5 ≈ 45 kN/m

Now do the internal wall, W3. It takes floor from both sides, so its loaded width is 3.0 / 2 + 6.0 / 2 = 4.5 m, and it is a 100 mm dense block wall over the same height:

Floor to W3         = 4.5 × 7.0 = 31.5 kN/m
Roof to W3          = 4.5 × 1.5 = 6.8 kN/m
Wall self-weight    = 2.4 × 5.4 = 13.0 kN/m
Total at base of W3 = 31.5 + 6.8 + 13.0 = 51.3 ≈ 51 kN/m

The internal wall carries more than the external wall. That is the usual result for this arrangement, and it is the reason internal walls so often need a wider footing than the perimeter. A takedown that only looks at the external envelope will miss it.

One assumption there deserves a note on the sheet: the roof has been taken as bearing on W3 as well as on the external walls. Trussed rafters normally clear-span the full 9.0 m, in which case W3 picks up no roof at all and its total drops to about 45 kN/m. Check the roof arrangement before you rely on either figure.

Those totals are characteristic (unfactored) loads, which is what you want for a bearing pressure check against a presumed allowable pressure. To size the masonry or the footing to the Eurocodes, factor them. For W1:

Permanent = 2.7 (roof) + 15.0 (floor) + 19.0 (wall) = 36.7 kN/m
Variable  = 1.8 (roof) + 6.0 (floor) = 7.8 kN/m
ULS       = 1.35 × 36.7 + 1.5 × 7.8 = 61 kN/m

Keep the two sets of numbers clearly separated on the page. Mixing factored and unfactored loads in the same column is the single most common error in a hand takedown, and it is invisible to anyone checking your work.

Sanity check the number at the bottom

A line load is not the answer. The answer is whether the ground can take it. Assume a 600 mm wide strip footing under W1:

Bearing pressure = 45 / 0.6 = 75 kN/m²
Plus footing and backfill, roughly 20 kN/m² → about 95 kN/m²

Against a presumed allowable of 100 to 150 kN/m² in firm clay, that is comfortable, and a standard 600 mm strip is a reasonable starting assumption. Run the same check on W3 at 51 kN/m and you get about 105 kN/m², which is closer to the limit and tells you to widen the internal footing or wait for the ground investigation before committing. The foundation load worked example takes this step further into footing sizing.

That is the whole value of the exercise: two divisions turn a set of line loads into a foundation decision.

Where hand takedown breaks down

The method above assumes one-way spans, simple supports, and a continuous load path straight to the ground. Real buildings depart from that, and it is worth knowing exactly when your sheet of A4 stops being reliable.

Two-way spanning slabs. Once the aspect ratio drops below about 2:1, an RC slab spans both ways and the tributary regions become trapezoids and triangles, not rectangles. You can hand-calculate it with the 45 degree yield line split, and for a preliminary number that is fine, but it is fiddly and easy to get wrong on an irregular panel. If you take the one-way assumption anyway, you will overload one pair of walls and underload the other, so state clearly which way you have erred.

Transfer structures. A wall that stops at first floor and lands on a beam breaks the vertical chain. The takedown above it is still valid, but everything below the transfer has to be re-thought: the beam reactions become point loads, and the columns or piers under them need a pad, not a strip. Transfer beams also attract deflection and robustness requirements that a takedown says nothing about.

Point loads from beams. B1 in the plan spans a 3.5 m opening in W3 and carries the same 4.5 m loaded width the wall would have:

Load on B1        = 31.5 (floor) + 6.8 (roof) = 38.3 kN/m
Reaction each end = 38.3 × 3.5 / 2 = 67 kN

That 67 kN is floor and roof only. The masonry sitting over the opening has to go on the beam as well, either the full panel or the triangle above it if you are taking arching action, so the real reaction is higher again. Either way it arrives as a point load on a short pier, not as a line load. Smearing it along the wall, which is what a purely line-load takedown does, understates the pier and the foundation beneath it by a wide margin. Whenever an opening appears in a load-bearing wall, stop and calculate the reactions properly.

Continuity over supports. Real joists and slabs run over internal walls rather than stopping at them. Continuity increases the reaction at the internal support, typically by 10 to 25 per cent, and reduces it at the ends. If your internal wall is already marginal, use a continuity factor rather than the simply supported split.

Other things a gravity takedown ignores. Wind uplift on light roofs, notional horizontal loads, out-of-balance loads during construction, and any load applied through the frame rather than through the floors. None of them appear in a takedown, and all of them can govern.

When two or more of these show up on the same plan, stop hand-calculating the whole building and hand-calculate only the elements you need to sanity check the model.

Keep the record in one place

The arithmetic is not the hard part. Keeping track of thirty walls across three levels, each with its own loaded width, is the hard part, and it is where hand takedowns quietly go wrong. Once the same three multiplications are being repeated forty times, put them in a structured template so the loaded widths and load cases are visible in one place.

A few habits that keep a takedown checkable:

• Record spans, area loads and assumptions next to the results, not on a separate sheet.
• Round sensibly. 132.7 kN/m becomes 133 kN/m. Precision you did not earn reads as confidence you do not have.
• Keep factored and unfactored figures in separate columns and label them.
• Note which walls you assumed carry nothing, and why. Those are the assumptions that get overturned.

For a fully worked version of this method on a two-storey house, from plan markup through to foundation loads, see the load takedown worked example.

When the plan gets bigger

Hand takedown scales badly. It is excellent for one wall, good for one house, and painful for a block of flats where a change to the floor build-up means recalculating everything. At that point the geometry is better held by software that can re-run the takedown when the plan moves, while you keep the judgement: span directions, load cases, and which assumptions are conservative.