Roofs and roof coverings
What does a stock house plan really cost, and when is it the right choice?
The catalogue price of a house plan covers only part of the cost of the documents you need to build. Check whether the design suits your plot, what it will take to adapt it and which changes you want to make. A stock plan helps you choose a building shape and a room layout; it does not guarantee that you can build that house on your site without changes. Before buying, look at the roof, the structure and what the proposed details will cost to build. Check which documents and licence the offer includes. A rendering shows what the house might look like, but it is no substitute for floor plans, sections and specifications. Find out what you will receive and which site-specific drawings and documents still need to be prepared.
In this guide
What exactly do you get with a catalogue plan?
Check which area the description quotes. Usable floor area, building footprint and total floor area measure different things. In a loft, compare the actual headroom and how the figures were measured. Two houses advertised with a similar number of square metres may leave very different amounts of space for furniture and everyday activities.
Why does the plot need a separate assessment?
Check the design against local planning rules and site conditions. The permitted building shape, its position, road access and utility connections all matter. Ground conditions can affect the foundation design. A house shown on a wide, level plot may not suit a narrow sloping site or one with poor exposure to sunlight.
Adapting a plan involves more than filling in an address. The proposed details must be checked and the documents prepared for the actual site. A designer establishes what needs to be changed or drawn up separately. Get a preliminary assessment before buying. It reduces the risk of paying for a plan that later needs substantial redesign.
Which changes can drive up costs?
Moving a loadbearing wall or changing a roof span or support can mean new calculations. Raising the knee wall changes both the appearance and the structure. Larger windows affect energy performance and the risk of overheating. A change that looks simple on a rendering may therefore involve several design disciplines.
Changing the building envelope means checking the junctions again. Replacing a designed wall with sandwich panels is more than changing an item on a materials list. Check the supporting structure, fire protection, sound insulation and how doors and windows are installed. Switching the insulation to PIR likewise requires a review of the facing, fixings and layer arrangement.
How should you assess the roof before choosing a plan?
Count the roof slopes, valleys and dormers. A simple roof is generally easier to draw, build and maintain. Complex geometry adds junctions and cuts. You need not rule it out, but price the whole roof before committing to a plan that depends on it.
Cut-to-length metal tile sheets and modular metal tiles need different laying plans. With T18 or T35 trapezoidal sheets, check the actual profile data and supports. Minimum roof pitch varies by product. Choose a covering for the roof slope using its documentation rather than the colour shown in the illustration.
Allow space for future roof equipment as well. Solar panels, a roof hatch and the access route to the chimney should work together. Spare space in a rendering is not evidence of sufficient load capacity or suitable fixing points.
How do you compare a stock plan with a bespoke design?
Add up the catalogue purchase, site adaptation, modifications and any additional coordination. Compare that total with a bespoke design covering a similar level of detail and access to the designer. A low price for the first stage tells you little about the final cost of a complete set of construction documents.
A stock plan can work well if the layout already meets most of your needs. If most rooms, the roof and the structure have to change, the time advantage may disappear. Separate essential changes from preferences on a short list. This makes it easier to decide whether the plan is a useful starting point.
What should you ask before ordering?
Find out when the plan was drawn up, which updates are included and how changes can be made. Ask what detail drawings are available and whom to contact if something is unclear. Check the licence restrictions and which permissions are needed for modifications. These points, the delivery format and the delivery date should be clear before payment.
Take a site plan, the main planning conditions and your list of requirements to the discussion. Include a budget for the whole project. A design that cannot be built within that budget is no bargain, however little it costs to buy. The most useful plans fit the site, your needs and the way the house will actually be built.