SettingsSettings for this calculationUS
From the head of the new opening up to the top of the wall, or to the next support.
Measure to whatever actually stops the load coming down — the underside of a slab that spans elsewhere, a ring beam, or the top of the gable. Where there is nothing above but more wall, measure the lot.
The thickness of the masonry being held, excluding any leaf that is not being supported.
A one-brick solid wall is 215 mm (about 8.5 in) and a single leaf is 100 to 102 mm (4 in). On a cavity wall, needle each leaf separately unless the ties are genuinely carrying the outer leaf on the inner one, which on an old wall they are usually not.
The bulk unit weight of the wall being held, mortar included.
Clay brickwork and dense concrete blockwork sit around 1900–2100 kg/m³ (119–131 pcf). Aerated and lightweight aggregate blockwork can be half that, and rubble stone with a wide core can be more. Where the wall is rendered or has a heavy plaster coat, allow for it.
The clear width of the opening being formed under the supported wall.
Take the structural opening, not the finished one — the width the masonry is actually removed over, including the end bearings that get cut back to seat the beam.
Centre-to-centre spacing of the needles through the wall.
Closer spacing means smaller loads per needle and more holes through the wall. The spacing also has to suit the coursing, because each needle hole cuts a bed joint and a hole in the wrong place turns two courses into a hinge.
The combined permanent and imposed load of any floor framing into this wall.
A domestic timber floor with its finishes and furniture runs around 3 kPa (about 63 psf) combined; a screeded concrete floor is several times that. Enter zero only if you are certain nothing bears — joists running parallel to the wall still often have a trimmer on it.
How much floor this wall carries — normally half the span of the floor either side of it.
For joists spanning onto the wall from one side only, this is half that span. Where floors land from both sides, add both halves. Where a floor above and a ceiling below both bear, both count.
What the surface the props stand on can take without settling or punching through.
This figure has to come from the temporary works designer, who will look at what is actually under the prop: a ground-bearing slab, a suspended floor spanning between joists, or hardcore. 100 kPa (about 2090 psf) is a common starting figure for a sound domestic slab and it is not a substitute for the check.
Load carried by each needle
3.63 kips
Needling and propping is temporary works. This gives the loads to design to; it does not select the props, check them for buckling at their extended length, or confirm that what the props stand on can take them. All three belong to a temporary works designer.
- Load carried by each prop
- 1.81 kips
- Needles across the opening
- 4 needles
- Combined line load along the wall
- 1,208.77 lbf/ft
- Masonry share of that line load
- 707.52 lbf/ft
- Floor share of that line load
- 501.25 lbf/ft
- Sole plate bearing area required beneath each prop
- 0.87 ft²
They open the calculator with your figures already in it
Needle and Prop Load Calculator (Temporary Masonry Support): 3.63 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Statics of a propped needle: the masonry above the opening is taken as a full rectangle of wall (height above opening × thickness × unit weight), any floor bearing on the wall is added as a line load, and the result is shared between needles on their spacing as a tributary width
- BS 5975, Code of practice for temporary works procedures and the permissible stress design of falsework — needling and propping is temporary works and requires a designer, a design brief and a check before any load is transferred
- The full rectangle above the opening is the CONSERVATIVE assumption and is used deliberately. Arching action in masonry can carry part of that weight around the opening, but it cannot be relied on where the wall is short above the opening, where another opening is nearby, or where the mortar is poor
- Masonry unit weight is entered by the user. The default of 2000 kg/m³ (about 125 pcf) sits inside the range normally taken for clay brickwork and dense concrete blockwork; lightweight blockwork is far lower and must be entered as such
Inputs used
- Height of Masonry Above the Opening
- 8 ft
- Wall Thickness
- 8.5 in
- Masonry Unit Weight
- 124.86 pcf
- Opening Width
- 10 ft
- Needle Spacing
- 3 ft
- Floor Load Bearing on the Wall
- 62.66 psf
- Floor Tributary Width onto This Wall
- 8 ft
- Allowable Bearing Pressure Under the Sole Plate
- 2088.54 psf
Intermediate steps
- Load carried by each prop
- 1.81 kips
- Needles across the opening
- 4 needles
- Combined line load along the wall
- 1,208.77 lbf/ft
- Masonry share of that line load
- 707.52 lbf/ft
- Floor share of that line load
- 501.25 lbf/ft
- Sole plate bearing area required beneath each prop
- 0.87 ft²
Confidence note: Needling and propping is temporary works. This gives the loads to design to; it does not select the props, check them for buckling at their extended length, or confirm that what the props stand on can take them. All three belong to a temporary works designer.
What this calculation does not cover
- Takes the full rectangle of masonry above the opening. That is deliberately conservative — arching can carry some of it away, but only in sound masonry with enough height and no nearby opening.
- Does not check the prop itself. A prop's safe working load falls sharply with extension and with any eccentricity at the head, and the manufacturer's chart is the only place that answer lives.
- Does not check the needle. Bending, shear and bearing on the masonry at the needle hole all need sizing against the load this page gives.
- Assumes props each side of the wall share equally. A single-sided scheme, or props at different extensions, does not.
Add the equipment this sizes
This result is a specification — 3.63 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0
Regulatory standards & verification citations4
- Statics of a propped needle: the masonry above the opening is taken as a full rectangle of wall (height above opening × thickness × unit weight), any floor bearing on the wall is added as a line load, and the result is shared between needles on their spacing as a tributary width
- BS 5975, Code of practice for temporary works procedures and the permissible stress design of falsework — needling and propping is temporary works and requires a designer, a design brief and a check before any load is transferred
- The full rectangle above the opening is the CONSERVATIVE assumption and is used deliberately. Arching action in masonry can carry part of that weight around the opening, but it cannot be relied on where the wall is short above the opening, where another opening is nearby, or where the mortar is poor
- Masonry unit weight is entered by the user. The default of 2000 kg/m³ (about 125 pcf) sits inside the range normally taken for clay brickwork and dense concrete blockwork; lightweight blockwork is far lower and must be entered as such
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