What is a pole plate?

A pole plate is another type of plate that is sometimes involved in the assembly of a roof. It is defined as a plate that is not sat directly on a masonry wall. In most instances, a pole plate sits on top of the joists, with the rafters pitched off of this pole plate instead of the wall plate. This offers more height to the roof in relation to the top level of the joists, increasing the usable space within the room. This is a desirable feature when carrying out a loft conversion, where the space inside the roof is to become a habitable space.  

A pole plate can also refer to a timber plate that is installed further up the inside of the roof, supporting the mid span of the rafters in a similar way to a purlin, though this is still sat on top of ceiling collars, where the ceiling is not sat directly on the wall plates. This is not very common in modern construction, as advances in engineering have created other methods of supporting rafters at their midspan. For the ease of explanation, we will solely look at pole plates that are positioned above roof joists.  

What are the criteria of a pole plate?

The pole plates must be positioned parallel to each other to allow for the successful pitching of the rafters upon them. They must also be parallel to the masonry, as well as centred within the roof. This is to ensure that the roof is installed centrally atop the building - also ensuring that the soffit and fascia can be kept the same on both sides of the building. The plates must be level, though this is determined mostly by the level of the joist below. We must also ensure that the pole plates are straight down their length, to ensure that the roof surface remains flat.  

How are pole plates installed?

Pole plates are a very easy timber component to install. The process is as follows. With the roof joists securely fixed to the wall plates, we can mark out the location for the pole plate on top of them. Typically, in order to keep a proportionate roof in relation to the span of the underlying wall plates, the pole plates are situated directly above the wall plates on top of masonry below. That being said, they can sometimes be set further in or out in relation to the wall plates. The location of the pole plates can also be determined by a measurement off of the drawings if applicable. By taking a plumb line up from the back of the plate up the side of one of the joists, the exact location of the plate can be marked on the top of the joist. From this, we can measure in or out a set amount to locate the position of the pole plate. By copying this on all 4 corners of the roof, a chalk line can be struck across the top of the joists to mark a perfectly straight line for the plate to follow. The plates can be laid across the joists in relation to the chalk line, being fixed with nails or screws along their length. With one plate fixed in place and perfectly straight, a measurement can be pulled to the other side of the building to ensure that the other pole plate is parallel. If so, fix the other pole plates.  

Any joints in the plates will be half lapped as usual. For pole plates installed as a part of a hipped roof, the pole plates may follow around the corners of the building to continue the pole plates at the correct height for the hip end.