How the two differ in kind
Both footings answer the same soil question in different units. A pad takes one concentrated column load and spreads it over enough area that the pressure on the ground falls below what the ground will accept: load divided by allowable bearing pressure gives the area, and a square root gives the side. A strip asks the identical sum per linear metre — the load each metre of wall delivers, divided by the same allowable pressure, gives a width — and then repeats that one cross-section along the entire run. That difference in units is the whole comparison in miniature — but not for the reason it first appears. Do both sums on bearing alone and the total area of ground you end up covering is the same on each side, because both reduce to the building's load divided by the allowable pressure however you slice it. What actually separates them is that a strip is almost never permitted to be as narrow as bearing alone would allow: it has to be wide enough to build a wall on, wide enough to dig cleanly, and wide enough for the minimum in your code. Its concrete is therefore set by the perimeter times that buildable minimum, not by the load — while pad concrete is set by the load and barely notices how many posts you divide it between.
So the first question is not about concrete at all: what is between the posts, and does it need holding up along its length? In a post-frame barn or a carport the honest answer is often nothing — the walls are cladding hung on girts, spanning post to post, carrying their own weight and the wind and no more. Pads are the correct element and a strip would be paying to support air. A garage or an addition usually answers differently, because things quietly accumulate on that line: a masonry or brick skin, a stud wall with joists bearing along a plate, a lintel over a wide opening that can land anywhere it likes, a slab edge, a door threshold, and a perimeter that has to be closed against draughts, water and vermin. Every one of those wants a continuous bearing surface, and the strip is already that surface.
The second question is how much you trust the ground. A pad has no redundancy — it is alone on the patch of soil beneath it, so a soft pocket under one shows up as that corner dropping while its neighbours stay put, and whatever spans between them has to absorb the difference. A strip averages soil variability along its length and, with continuous top and bottom steel, can span a local soft spot and share the load with the lengths either side. The same continuity buys forgiveness in construction: a post set slightly off along the run is still fully on footing, whereas a pad is sized on the assumption the load arrives in its middle, and a column set off-centre tips the pressure diagram and overloads one edge. That forgiveness is also what makes the strip the cheaper thing to change later — a post added next year needs no new excavation at all.
The factors that actually differ
| Isolated pad footings | Continuous strip footing | |
|---|---|---|
| What the soil sum asks | An area. Load divided by allowable bearing pressure, then a square root for the side — every pad is its own calculation sitting on its own patch of ground. | A width. The load each metre of wall delivers, divided by the same allowable pressure — one cross-section, repeated along the whole run. |
| What the quantity scales with | The total load, not the post count. Divide the same load between four posts or twenty and the plan area you must cover is identical — wider bays simply mean fewer, larger and (because punching shear worsens) thicker pads. | The perimeter, times a width that is usually a minimum rather than a result. Bearing alone would often permit a strip far narrower than anyone could dig or build on, so every metre of wall line becomes a metre of trench at buildable width, occupied or not. |
| Soft spots and differential settlement | No redundancy. Each pad settles on the soil directly beneath it, so a soft pocket under one corner is expressed by that corner alone. | Averages and spans. Continuous longitudinal steel lets the run bridge a local soft pocket and hand the load to the lengths either side of it. |
| Tolerance for being out of position | Unforgiving. Sized on the assumption the load lands at the centre; a column set off-centre skews the pressure under the pad and loads one edge hard. | Forgiving along its length. A post landing anywhere on the run is fully supported, and one added later sits down on concrete that is already there. |
| Closing the gap between posts | Open ground until you close it. A grade board, a rat wall, a skirt or a thickened slab edge is separate work running along exactly the line the strip would have occupied. | The footing is that line. Perimeter closure, the wall above, the slab edge and the threshold all bear on one continuous, level surface produced by one operation. |
| Frost depth | Depth multiplies each hole, not their number — but a slender pier is the shape most vulnerable to adfreezing, where frost grips its sides and lifts it regardless of what is on top. | Depth applies to the entire line, so hard-frost country is where a strip's excavation and volume grow fastest, and where a frost-protected shallow design is worth designing for properly. |
| The pour | Many small independent placements. They divide into weekends, happen in whatever order the digging allows, and each hole is small enough that mixing on site is genuinely on the table. | One continuous placement, with truck-and-crew economics. Any stop is a construction joint that has to be planned and have steel lapped through it, not a place you simply ran out of day. |
| Uplift and overturning | Resisted post by post, by the pad's own weight plus the wedge of soil above it — which is why a light barn's pads are frequently sized by wind uplift rather than by bearing at all. | Resisted along a continuous mass tied together by the wall above, so no single point carries the whole event — provided each post is genuinely anchored to the concrete rather than sitting on it. |
| What governs the thickness | Punching (two-way) shear usually decides it: the column tries to push a plug straight through the pad, and that check has nothing to do with bearing pressure. | One-way shear and the cantilever moment about the face of the wall — the projection each side of the wall is a cantilever, and the width you chose sets the moment it must carry. |
Which one, and when
Choose isolated pad footings when…
- The loads genuinely arrive at posts and nothing between them needs support — a post-frame barn or carport whose walls are cladding hung on girts.
- The building is light and the perimeter is long. That is exactly where a strip's buildable minimum width is far more concrete than the load needs, and discrete pads stop paying for the metres in between.
- Deep frost, where taking the whole perimeter down to founding level would be the single largest item in the excavation.
- The work goes up in stages with a mixer rather than a truck — pads divide into afternoons, and a continuous footing does not divide at all.
Choose continuous strip footing when…
- Something continuous sits between the posts: a masonry skin, a stud wall with joists bearing along a plate, or a lintel over a wide opening that can land where it likes.
- The building is heated or sealed. The perimeter has to be closed, insulated and vermin-proof anyway, and the strip is already occupying that line.
- The ground is variable, or you have not proved that it isn't — averaging and the ability to span a soft pocket are the cheapest insurance available at this stage.
- The posts are close enough that the pads would nearly touch. At that spacing a continuous footing is the correct element rather than a compromise.
- The layout will move: posts added, a door relocated, a lean-to bolted on. Changing your mind on a strip costs nothing; on pads it costs an excavation and a cure.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Which one uses less concrete?
- Usually pads — but not for the reason it looks like, and it is worth knowing the real one. Size both on bearing alone and they tie exactly: total pad area and total strip area both come out as the load divided by the allowable pressure, which is the same algebra written two ways. What actually decides it is that a strip can rarely be built at the width bearing permits. On a light building that sum will hand you a strip a few centimetres wide; you will pour it at the narrowest width you can dig and stand a wall on, and that minimum, multiplied by the whole perimeter, is where the extra concrete goes. So the question to ask is how far your strip's buildable minimum sits above its calculated width — the wider that gap, the more the pads save, and if the load is heavy enough to need a genuinely wide strip the saving largely evaporates. Concrete is also only one line in the ledger, and the two sides carry different work. The strip's extra volume buys jobs you would otherwise do separately — perimeter closure, slab-edge support, a level bearing line for the wall — while the pads' saving shrinks every time you add a grade board or a rat wall back in. Labour differs in shape too: pads are many small hand-dug or augered holes, a strip is one machine-friendly trench and one placement.
- Can I mix them — pads under the posts and a strip only where a wall needs one?
- Yes, and it is a normal and sensible thing to do; plenty of buildings sit on exactly that hybrid. The detail that decides whether it works is settlement compatibility. Two footings side by side that carry very different bearing pressures will settle by different amounts, and the structure spanning between them has to tolerate the difference. Keep the pressures under the pads and under the strip broadly similar rather than sizing each in isolation, found them at the same level so they respond to the ground the same way, and be deliberate about the junction where one meets the other. The hybrid fails at the seams, not in the middle.
- Is a grade beam the same thing as a strip footing?
- No, and the difference matters even though the same volume arithmetic serves both. A strip footing bears on the soil beneath it along its whole length; that soil is the support. A grade beam spans between piers or piles and is deliberately designed not to rely on the ground under it — often with a void former beneath, so that heaving soil has somewhere to go instead of lifting the building. Same geometry, entirely different load path, and entirely different reinforcement: a footing's main steel is transverse and near the bottom, resisting the cantilever each side, while a beam is reinforced top and bottom to span. If your soil is expansive, or the competent bearing stratum is well below founding depth, the honest answer to this whole comparison is often neither — it is piers taken down to good ground with a grade beam spanning between them.
- How do I compare the two when one calculator sizes and the other measures?
- They deliberately answer different halves of the problem, so use them in sequence. The spread footing calculator answers how big each pad has to be, from the column load and the allowable bearing pressure on your geotechnical report. The continuous footing calculator answers how much concrete a given run takes, from dimensions you supply. To put the two options on the same page, size a pad first, then multiply its area by the thickness and by the number of posts to get a comparable volume. For the strip, do the same soil arithmetic per linear metre — the load each metre of wall delivers, divided by the allowable pressure — to get the width. Expect that width to come back unbuildably narrow on a light building; take it up to the narrowest trench you could actually dig and stand a wall on before you enter it, because the volume calculator will accept a few centimetres without complaint and hand you a fictional answer. Then feed that corrected width and your perimeter into it. Both results are preliminary sizing, not design: shear and moment checks still govern the thickness on either side.
- Do pads have to go as deep as a strip footing?
- Founding depth is a property of the site, not of the footing type, and both go to the same level — below the frost line, below topsoil and made ground, and below the zone of seasonal moisture movement if the soil is one that shrinks and swells. What genuinely differs is the thickness of the concrete element itself. Pads tend to be thicker for their footprint because the load arrives concentrated and punching shear governs; strips tend to be shallower for their width because the load is already spread along a line before the concrete sees it. Keep the two ideas separate when you enter numbers, because the depth field in the volume calculator is the element, not the hole.
- Will pads crack the wall between them?
- That depends on what the wall is, which is the real deciding question rather than a detail. Rigid masonry laid between independently settling pads is the textbook recipe for a stepped crack over the weakest support, because the wall has no way to accommodate one pad moving relative to its neighbour. Cladding hung on girts in a post-frame building absorbs exactly the same movement without complaint, since the whole assembly is articulated by design. So ask what the wall between the posts can tolerate before asking what each footing option costs — a strip under a masonry wall is not an upgrade, it is the thing preventing a defect.