How detailed should our architect’s plan be?

We are planning an extension to our property with renovation works included. Our architect has produced drawings of the proposed works. However, we note that the detail included is not comprehensive. What level of detail should we go into at this stage so that the builder on site knows what is required?

It is typical when planning an extension or any building works that the information will be developed in stages. The first stage is generally basic and is largely to facilitate clarity in terms of size and layout of the extension. In this respect, the drawings would include key details such as size, layout, positioning of windows and doors etc.

When the principle is agreed, further information can then be added to include a description of the basic type of construction, for example slates or tile finishes on a roof, or PVC or timber windows etc. This level of detail is normally sufficient to get a good flavour of what is intended and in fact more often than not satisfies the planning process as the planner’s main concerns relate to appearance and as to how a building fits into the environment. Clearly planners will also have specific concerns such as nature/use of the space, the local infrastructure in terms of road access, drainage services etc, all of which would normally be covered in a planning application.

However, assuming that the extension either does not require planning permission or that planning permission is now in place and you want to proceed to having the extension built, then a whole lot more information is required. This is typically referred to as the specifications. So, for example, if you take any building element, for example the floor – let’s say it is a concrete floor – then one needs clarification as to the mix/strength of the floor, the depth of the floor, the type and depth of any thermal insulation, damp-proof membranes and radon barriers etc. All of this information needs to be specified in detail. The same principal can be applied to all building elements including the walls, roof, windows and external doors. The level of detail also needs to include all the internal elements such as skirting boards at floor/wall junctions. Similarly, clarification would be required in respect of the services, for example the number and location of general power sockets.

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In the absence of clarity, it is inevitable that builders will have to make their own assumptions as to what they are pricing for and they could very well be pricing on totally different proposals. It is for this reason that you often get significant variations in builders’ quotations and while at first it might appear that a contractor’s price is very expensive, when this is checked out in detail it might transpire this represents better value than a lower quotation that has excluded many items.

So, in short, the more detail provided at the start, then the less chance there is for arguments at a later stage. The information can be included on the drawings – though this tends to overcrowd the drawing – or, more often , provided as a separate specification or schedule of works which should be read in conjunction with the drawings. This would normally form part of a tender package that should be issued to contractors for pricing.

Val O'Brien is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie