Padstone Notes and Specifications

A padstone is a hard, level bearing element placed under a steel beam to distribute the concentrated load at the beam end into the masonry below. Getting the right padstone in the right position matters: an undersized or incorrectly specified padstone can lead to local masonry crushing or a Building Control inspection failure.

Padstone Specification on Your Drawings

Padstones are specified on your PorthouseDean drawings in the format LENGTH × WIDTH × HEIGHT. For example, `450 × 215 × 100` denotes a padstone 450 mm along the wall, 215 mm through the wall depth, and 100 mm tall.

Key rules:

– Minimum width is 200 mm through the wall — this is a standard brick course or block width
– Width must not exceed the wall thickness — a padstone wider than the wall would project into the cavity or beyond the external face
– Minimum length is specified per design — this is the dimension along the wall and is calculated from the applied load
– Height is typically one or two brick/block courses

All padstones on PorthouseDean projects are specified in C35 concrete minimum (concrete Class RC35 or better).

How Padstone Dimensions Are Described

It is a common source of confusion on site. Always confirm with your supplier which dimension convention they are using. At PorthouseDean, dimensions are always given as:

Length along wall × Width through wall × Height

If in doubt, cross-reference with the wall thickness shown on the architectural drawings.

If You Cannot Find the Padstone Off the Shelf

Pre-cast padstones are typically available from builders’ merchants in standard sizes. However, if the specified padstone size is non-standard or your merchant cannot source it, there are two acceptable alternatives:

1. Cast In-Situ

Cast the padstone in position using C35 concrete. Shuttering is required to form the shape. This is often the most practical solution where access is difficult or the size is unusual.

2. Stack Lintels Vertically

Standard concrete lintels (sold for spanning openings) can be stood on their narrow edge to create a padstone. When doing this:

– Stack lintels vertically (on edge) — never side by side
– Stacking side-by-side means the joint between them sits directly under the beam flange, which creates a weak line and risks splitting under load
– Stacking on edge stacks the lintels like books on a shelf, with the joint away from the bearing face

3. Mild Steel Spreader Plate

A mild steel plate of equivalent bearing area is an acceptable alternative and may be more practical where headroom is tight. This is typically only used where specified or explicitly approved by the engineer.

Beam Parallel to Padstone

Where the beam flange runs parallel to the padstone’s length (rather than perpendicular), the bearing contact is along a narrow line rather than spread across the full padstone area. In this case:

Shims are required between the beam flange and the padstone surface to distribute load evenly. Discuss this with your steel fabricator — shim packs are inexpensive and easily specified.

Never Use the Wrong Size

If the padstone you have procured is different from what is specified, do not use it without checking first. A padstone that is too short will result in a bearing stress that exceeds the masonry capacity. A padstone that is too wide may bridge the cavity or extend beyond the wall, both of which are non-compliant.

Raise a Change Request or contact us before proceeding if you are unable to source the right padstone and are unsure which alternative is appropriate.