Building Control rarely rejects drawings for minor errors. Rejections typically happen when fundamental compliance or coordination is missing under the Building Regulations 2010. In reality, approval usually depends on how clearly the design demonstrates compliance. Drawings often stop at planning-level detail. Building Control expects construction-ready information—junctions, build-ups, and specifications that demonstrate compliance. Drawings without notes on materials, performance standards, or compliance references reduce confidence in the proposal. From experience, drawings are rarely rejected because a project is “too ambitious.” In most cases, it’s not about complexity—it’s about lack of technical resolution. 1. Insufficient Structural Information (Part A) When walls are removed, openings widened, lofts added or extensions built, structural implications matter immediately. If drawings do not clearly address beams, load paths, foundations or support strategy, building control will often ask for revisions or structural calculations before progressing. A layout can look attractive on plan, but it must also work structurally. 2. Fire Safety Strategy Missing or Incorrect (Part B) This is particularly common in loft conversions, HMOs and altered layouts. Escape routes, fire doors, smoke alarms, protected stair enclosures, separation between floors and material performance all become important. If these points are not resolved on drawings, delays are common. 3. Inadequate Insulation & Thermal Details (Part L) Part L requirements have become increasingly important, and England has issued further 2026 updates as part of the Future Homes and Buildings Standards programme. If drawings do not adequately show insulation build-up, thermal upgrades, glazing performance or compliant specifications, approval can stall. 4. Ventilation Not Addressed (Part F) Modern homes are becoming more airtight, so ventilation matters more than ever. Kitchen extract, bathroom extract, purge ventilation, background ventilation and overall air quality strategy need proper thought. This is one reason Part F has continued to evolve. 5. Non-Compliant Staircase Design (Part K) Very common in loft projects. A staircase may fit visually on plan, but if pitch, headroom, width or landing arrangements are poor, redesign is often required. Many late-stage changes happen here. 6. Drainage & Services Missing (Part H) Extensions with kitchens, utility rooms or bathrooms often trigger drainage complications. Connections, falls, access chambers, venting and below-ground runs need practical solutions. Ignoring drainage early usually creates site problems later. 7. Incomplete or Ambiguous Drawings This is one of the most underestimated issues. The Building Safety Regulator has publicly highlighted that a large proportion of rejected applications lacked sufficient detail to demonstrate compliance. While that data relates to higher-risk buildings, the principle applies everywhere: vague information creates delay. If a drawing leaves too many questions unanswered, expect queries. 8. Existing Conditions Are Measured Poorly Many problems begin before design even starts. Incorrect surveys, wrong wall thicknesses, inaccurate roof geometry or missed level changes can undermine an entire technical package. Good compliance starts with accurate existing information. My View After Years of UK-Focused Work Building control rarely rejects drawings because the authority wants to be difficult. Usually, they need confidence that the proposal is safe, buildable and compliant. That confidence comes from clear technical drawings. Planning may secure permission. But it is technical quality that determines whether a project can actually move forward—on site, on programme, and within budget. What causes more delays in your experience — unclear drawings, late structural changes, or compliance issues discovered during construction?