Your working drawings, whilst being a how-to manual for your builder, will not encompass absolutely everything. Let’s look at external suppliers who will add their own technical specifications to your build. In addition to the technical detail you’ll be specifying on plan with your architect, your working drawings might also need to dovetail with technical designs from these external suppliers.
There are usually six potential suppliers whose technical design will need to be accommodated for in the working drawings in order to design:
- Kitchens
- Bathrooms
- Fitted Wardrobes
- Staircases
- Air conditioning systems
- Heating systems
Kitchen technical specification
When it comes to kitchens, you will make arrangements in one of two ways:
- Leave it to the builder to measure up the space and supply a kitchen design from their go-to joinery
- Opt for the design route and head over to a kitchen showroom/supplier yourself
With the former, there are no specific inputs to the working drawings, as implementation takes place on-site during fitting.
With the latter, you will visit showrooms in advance of the build, armed with your extension plans. In this scenario, the kitchen designer will work with the dimensions you supply to design a bespoke scheme you’ll (hopefully) love. Based on this design, your builder will know which points to run utilities to. These runs should be marked on the working drawings, and the kitchen designs placed as an addendum to your master plan, for easy reference.
Bathroom design
It is largely the same story with bathrooms. The loo takes centre stage when designing a bathroom, as it must be connected to a rigid four-inch stack pipe, and this can have substantial bearing not only on the design of the bathroom, but on the new space as a whole. Because the stack cannot bend or twist or be made smaller, it is the anchor point around which the rest of the bathroom fixtures and fittings must fit. Macerators can provide flexibility and thus additional configuration options. But they come with drawbacks, most notable of which is the introduction of a mechanical point of failure to the drainage system. Features like wall-hung toilets, powered cabinetry, heated mirrors and the depth of the shower tray are a few things that will require pre-work before installation is possible. Wet rooms will require a lot more preparatory work.
Fitted wardrobe design
Thankfully, there is less dependancy on the design of fitted wardrobes, and the only essential detail to capture on plan is where in a room any wardrobes will be located. This is to ensure that the new (reduced) floor space can be recentred for the location of light fittings, power sockets aren’t lost behind units, cupboard doors can swing open, and that power has been supplied where it’s needed for the fitters.
Staircase manufacture
Next, it is imperative that the staircase manufacturers get early sight of the extension plan, and that your architect makes any necessary adjustments the scheme to accommodate the installation. Like the soil stack, the staircase is a feature that needs billeting, without compromise or deviation, on account of the strict building regulations governing its design.
Air conditioning installation
In the main, air-conditioning units can be installed under permitted development, save the usual exemptions. However, it is not uncommon for councils to ask for the technical details of the proposed unit, to satisfy any noise pollution concerns. An external unit will need to be cited appropriately, and the internal unit will need to be housed somewhere sympathetic to the new space; and both will need to be worked into the drawings.
Heating systems
Finally, in a similar vein, conventional heating firms and green energy companies (solar, ground source heat pumps, etc) will also need to install internal and external units. The size, spacing, utility connections and maintenance requirements of these should be marked on the drawings if any preparatory works need to be carried out by the builder, or indeed by the structural engineer if structural openings or reinforcements are necessitated.
There are other suppliers whose work may overlap with the production of your working drawings, but their services are less commonly retained for a classic home extension. These include audio-visual, home automation, green roof installers, interior designers and landscaping.
In summary, you may find yourself working with external suppliers who produce their own technical detail. You do not need to import their design to your working drawings, but you should make adequate allowances. That way they can plug into the scheme with minimal friction, and your builder will have foresight of any preparatory works required before the suppliers rock up to the job. Externally supplied designs should be addended to the rest of your plans, for ease of reference.