Arches with more than two centres form ellipses, oval outlines or shapes that are more complicated. These arches are less common but are still required for period renovation or extension. As with Semi-circular arches and Gothic arches, you may need to consider support for the full thickness of the wall including the inner leaf. You may require cavity wall or solid wall lintels.
The Three Centred Arch works alongside and in the place of, the Semicircular Arch when the height of a semicircle over a wide span widow or other opening is too great for the storey height. This arch style is a strong structure, and is often found in bridges and aqueducts. The strength of the design as with the semicircle and the Segmental arch comes from the regular consistent shape of the voussoirs, as each is identical in taper to its neighbour.
As with all curved arches adequate clearance is required between the striking points (or span) of the arch to allow a frame to fixed, 3mm all round will normally suffice. Joint width is also a key consideration in the design of a semicircular arch as this affects the lintel position on the jamb.
With cavity work, careful thought should be given to the support for loads the inner leaf of masonry or structural frame, which is often load bearing. Does the inner structure require support as a Three Centred Arch? This is a frequent oversight and can be easily resolved at the initial enquiry.
These arch types may feature a profiled hood around the extrados called the Label Course, which often projects from the face brickwork. This feature is a weathering over an opening and can sometimes have a lead work dressing over.
To specify a three-centred arch you will need the following information. When measuring period property it is useful to measure the work, using the system in which it was built. Typically, before 1970 in the UK work was built using Imperial dimensions E.g. 4 courses per foot or in metric, 4 course per 305mm:
- Brick type colour & finish (sand face or rubbed).
- A digital image of similar arches on the property or nearby
- Opening span, (the brickwork opening).
- Camber rise to the centre of the arch at the soffit. Typically half the span unless the jamb starts with special bricks as part of the feature.
- Face height, (measured along any long joint line radiating from soffit to head)
- Joint width
- Number of voussoirs (complete tapered sections from Intrados up to Extrados counted across the arch).
- Bond pattern, (the horizontal joint pattern across the arch)
- Soffit depth (from front to back)
- Brick finish (rubbed or sand faced)
We will also need to know whether the arch will have any special features such as a keystone or carved soffit. If you are not sure call us on 01787 269132 for advice or email your enquiry to firstname.lastname@example.org