A Simple Guide to The Structural Integrity of Conservatory Roofs
A conservatory roof is a complex piece of engineering, and this guide attempts to explain the various forces acting on it in simple terms. I am not a structural engineer - this is a guide only and should not be used as the basis for any calculations. As always, if in doubt seek professional advice before deciding if a design is structurally sound.
There are several major forces acting on a roof:
In order to determine if the roof is suitable for its site location we need following information:
The site specific information is often looked up from a location map - contact your roof supplier for more details.
A conservatory will begin to fail for a number of reasons:
If the given design is found to be insufficiently strong there are a number of remedies, including:
As the weight supported by the ridge increases (because either the span is large or the ridge length is long, or both), there will be a large force pushing the ridge down and the rafters outwards. When this load exceeds safe limits, the ring beam will start to be pushed outwards, which in the worst case could result in a roof collapse. A tie bar will prevent this outward movement by "tying" the rafters together. Note that the vertical element of a tie bar is simply to keep the bars level - all of the work is done by the horizontal members. Very large roofs may require two or more tie bars.
Use of a tie bar is illustrated below:
A portal frame provides a structural support upon which the roof sits. Typically portals are made of a steel or aluminium tubing, which is either welded or mechanically jointed. The portal is designed to transfer the calculated loads to fixed concrete footings. As a result the entire structure will by much stronger and capable of supporting a larger roof. A simple portal frame is shown below:
The roof would sit on this portal as shown here:
Resolving some of these structural issues manually can be very time-consuming and often requires the services of a structural engineer. Better software systems can recommend solutions automatically for many designs although complex designs will still need to be referred to an expert. In some cases there can be several ways of solving specific structural issues, and this is where the experience of a qualified engineer is invaluable.
All versions of roofwright provide for structural checks, but this data needs to be configured for your roof system. To find out if this information is available for your roof system, contact us or your roof system supplier.
Senior Support Engineer