A wall plate is a horizontal timber beam that sits on top of a wall or ring beam and forms the connection between the wall and the roof structure. The roof rafters rest on the wall plate. It is the lowest support point of the roof structure.
Function
The wall plate distributes the weight of the roof evenly across the wall:
- Without a wall plate, the rafters would create point loads on the masonry, which can cause damage
- The wall plate also absorbs the horizontal forces exerted by the rafters (they tend to push the wall outward)
- When a ring beam is present, the wall plate is fixed to it with cast-in anchors
Fixing
On a ring beam (masonry building)
1. Threaded rods (M12-M16) are cast into the ring beam, protruding 10 cm
2. The wall plate is placed over the rods (pre-drill the holes)
3. Secured with washers and nuts
On a timber frame wall
The wall plate is effectively the top rail of the wall. The rafters are fixed directly to it with angle brackets or birdsmouth joints.
On a masonry wall without ring beam
For light structures (garden building, small shed), the wall plate can be fixed directly to the masonry with chemical anchors or coach screws. Less strong than a ring beam, but sufficient for light loads.
Dimensions
| Application | Wall plate size (indicative) |
|---|---|
| Garden building, light shed | 50 x 100 mm or 50 x 150 mm |
| Shed, garage | 63 x 150 mm or 75 x 150 mm |
| House | 75 x 175 mm or larger |
The width of the wall plate is usually equal to or narrower than the wall width (or the inner leaf in a cavity wall).
Wall plate vs. purlin
A wall plate *is* technically a purlin — it is the lowest purlin of the roof structure. The difference lies in the name and position:
- Wall plate = purlin on the wall (bottom)
- Ridge purlin = purlin at the ridge (top)
- Intermediate purlin = purlin halfway up
In self-build projects
The wall plate is one of the first roof elements you install:
1. Level it — The wall plate must be perfectly level, otherwise the entire roof will be skewed
2. Align — The wall plate sits on the inside of the wall (on the inner leaf in a cavity wall)
3. Fix — Anchors, bolts, or chemical fixings
4. Install rafters — The rafters are placed on the wall plate with a birdsmouth joint
Related terms
- Ring beam
- Ridge purlin
- Purlins
- Rafter
- Truss