Planning Drawings, Working Drawings, Building Regulation Drawings, Construction Drawings, Structural Drawings – Which do I need for my proposed Home Extension!?
2nd January 2024.
This subject can be very confusing, but it is important to have an appreciation of. Many homeowners who have built extensions will have a least one story about their builder taking a sharp intake of breath as they utter the words ‘I think we have a problem here’, and often this is related to this subject.
There are many different words used to describe the typical, normally black and white documents that are commonly associated with architecture and planning permission. So it is no wonder that many people who are not familiar with these, get very confused and sometimes frustrated.
This is a wide-ranging subject, but for the purposes of the majority of home extensions built, the terms plans and/or drawings are often used to mean the same thing, which are the black and white 2D scaled line drawings that show your existing property and also your property with the proposed extension added.
This initially sounds straightforward, but as with most things, the devil is in the detail, and the detail is often very important when it comes to your planned home extension. It is therefore worth understanding the key differences, so that you can ensure your Home Extension Designer (Design Professional) will deliver the plans/drawings that you require.
Planning Drawings
These are the scaled black and white line drawings that most people are familiar with, which show the existing and proposed home, from an elevation (horizontal plane) and plan (vertical plane) perspective. The main drivers for such drawings are often submission into the local council for planning consent or for presentation to builders for quotations.
When submitted to a local council planning department for planning permission, or a certificate of lawfulness, these drawings are often modified appropriately for this specific need. For example, the planning department in the council doesn’t need to be made aware of the technicalities of construction methods, so this is often not shown to avoid confusion. Therefore, planning drawings are often the drawings that are produced for this specific purpose.
However, in less complex home extensions, which many are in reality, then these planning drawings can also be used as a strong foundation for the drawings which are used for all related purposes (e.g. builder quotes, structural plans).
Working Drawings
When a home extension is being discussed, designed and planned, it is possible to lose control of decisions along the way. The more complex the extension becomes, the more likely it is to lose this control. There can be different plans/drawings produced for different purposes (e.g. planning submissions, technical design, builder quotes, structural design), so it is possible to become confused as to which is comprehensive and correct. The idea of working drawings is to overcome this problem by having version-controlled drawings, which are aimed at being the latest, most accurate and comprehensive, so they are the best representation of the proposed home extension at the current time. Therefore, working drawings capture all inputs, so they represent the comprehensive design as it evolves. Some more-complex home extensions suffer from having different drawings and inputs at separate times, which are not then all brought together again to assess the overall impact of the changes that have or are being made. This can inevitably cause problems during the build!
Construction drawings are those which add the technical detail to the drawings of how the planned extension will be built. For more complex extensions, this detail is obviously important, as the build detail/method might vary from the everyday construction methods which most builders are familiar with. Also, there may be elements which are better considered and defined during the design process (e.g. soil pipe runs from bathroom to existing connections, electrical placements, boiler placements, bespoke additions (e.g. balconies, overhangs), bespoke construction methods (e.g. Structural Insulated Panels) and so on.
This is always a balance though, as it may be perfectly viable to have final drawings/plans for your extension, which just show the way your property is now and the way it will look when your proposed extension will be built (e.g. planning drawings). It is possible also, for a good and frequent builder to use such drawings to quote for your extension, as they will be using their in-depth knowledge to compensate for the missing construction detail on the drawings. Please read the following analogy.
Cooking Analogy
A simple analogy would be showing an experienced chef a picture of a meal, and asking to quote you for making it. As the chef is experienced and makes meals frequently, they should know exactly how to make this one without any instructions? Their quote is likely to be accurate and the end-result is likely to be good? However, there is a risk here too, of course. Perhaps the chef has different ideas about how this meal is made, or perhaps they have certain preferences which aren’t yours? Maybe the chef looked at your picture and got the wrong idea about one or more things? Perhaps you have preferences which you didn’t make clear?
Or perhaps you showed a picture of a meal to the chef, which in reality, had a lot more complexities involved than a simple picture can express? In such cases, the simple picture is no longer sufficient, so a more complex picture and supporting information is needed to get the end-result you want.
It all comes down to complexity really. Many home extensions are not that complex, but can still produce a great outcome. However, some extensions have complexities which need to be clearly explained and might render builder quotes worthless unless they are. Also, certain builders might not wish to, or might not be able to build more complex extensions.
Showing an experienced builder a simple 2D drawing of a proposed home extension may well be enough to get a reasonably accurate quote and get it built correctly. This is more likely to be the case, where the build is fairly standard, or ‘non-complex’ (e.g. block, render, standard roof construction, standard windows/doors, straightforward lighting/power, non-complex structural design, integration with existing house fairly straightforward). In practice, the majority of home extensions are ‘non-complex’ in my experience, so an accurate scaled drawing can be enough to get a good quote and end-result, as I have seen happen on hundreds of occasions.
There will inevitably be assumptions though, when a builder quotes from such a drawing, which may or may not prove accurate later. Naturally, it is useful to ensure that all assumptions made are documented, so these can be checked for accuracy and the impact understood if they are not accurate.
In summary, construction drawings are important to have for extensions which are more complex, or where you want all the detail documented beforehand to ensure no ambiguities or false assumptions later. Some construction drawings have every element of the build defined (e.g. light positioning/type, electric socket positioning/type, plumbing routes, wall treatments and so on), which will leave room for no assumptions of course.
Building Regulation Drawings
Building regulation drawings are similar in nature to construction drawings, and can be the same thing. In straightforward terms, building regulation drawings are whereby all the required information to meet mandatory building regulations is added to the final drawings for a home extension. Construction drawings, as before, should include all this building regulations detail, as it is all part of the construction process.
A key element in building regulations drawings though, are the details of any structural work that needs to be undertaken (e.g. steel beams and their supports) which must be calculated and defined by a qualified structural engineer only. There is a wide range of other factors that need to be met to achieve building regulations, but these are well documented and generic, whereas a structural design is often bespoke to the property involved.
Again, the prior ‘cooking analogy’ and the complex versus non-complex comparison applies. Many good and frequent builders will be fully versed with current building regulations and so do not need to be instructed on how to meet them. Also, with building regulations, there are council/private inspectors who must be appointed to oversee that building regulations are being met. So, for non-complex extensions, building regulation drawings can be superfluous unless something applies that is out of the ordinary. However, for more complex extensions, or for extensions where certain tolerances could be affected by using standard methods to achieve building regulations, then building regulations drawings become more important. Such an example of tolerances is where a loft extension needs to have a specific finished internal headroom, and the Design Professional has to be more creative with the design to achieve this and also achieve building regulations at the same time. Another example might be where large steel beams are required to support a removed wall, which would cause large protrusions from the walls and ceilings if left to the builder. Again, in this situation, the Design Professional should be aware of the potential outcome and work to achieve the finish required (e.g. flat ceilings and walls).
Structural Drawings
These are drawings which show the structural design/work necessary, to ensure the home remains safe during any build or renovation. These must be produced by a qualified structural engineer, and would show such detail as steel beams, wall supports, foundation requirements, padstones and so on. Often structural drawings can be planning drawings with the structural detail added. Sometimes they are separate. Whatever method is used, they need to be amalgamated with the other drawing types, depending on the process being used, to ensure clarity and accuracy overall.
Summary on drawings
So, isn’t it just best to demand construction and building regulations drawings in all cases, so you are covered for all eventualities? Well, my advice is to work with your chosen Design Professional to understand how important all this detail will be to achieve your final objectives, and how best to co-ordinate this.
The key reason for explaining all this is that I am often asked by clients to provide construction and building regulations drawings, but often they don’t understand what this really means. I have seen examples of building regulations drawings from Design Professionals, which are smothered in ‘cut and paste’ building regulation detail, but there has been no real point in listing any of this, as the builder will know it already, and the building inspector will enforce it too. I have also seen building regulation drawings where there is a real tension between the design and building regulations, but the drawings don’t highlight this at all.
So, my key message on this is don’t just tell the Design Professional that construction and building regulations drawings are needed; work with them instead to understand what the real need for these are, and any extra time and cost involved.