{"id":652303,"date":"2026-08-23T14:06:21","date_gmt":"2026-08-23T14:06:21","guid":{"rendered":"https:\/\/www.europesays.com\/ie\/652303\/"},"modified":"2026-08-23T14:06:21","modified_gmt":"2026-08-23T14:06:21","slug":"planning-an-extension-heres-what-can-send-the-cost-soaring","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/ie\/652303\/","title":{"rendered":"Planning an extension? Here\u2019s what can send the cost soaring"},"content":{"rendered":"

\u00a0IN OUR NEW series, The Big Reno Clinic, Houses to Restore QS Shay Lally provides answers and solutions to the big (and little, but important) questions you may have about making the most of your home.<\/p>\n

Send your question to reno@thejournal.ie.\u00a0<\/p>\n

This week\u2019s question:<\/p>\n

We had our extension designed 16 months ago \u2014 3m x 7m off the kitchen-diner, flat roof, glazed on two sides, a couple of roof lights, and a large steel to open up the back wall. Our site\u2019s on a slope, so we wanted it built on our upper patio level rather than disturbing the whole garden. We went with a recommended architect, but it\u2019s dragged on \u2014 flip-flopping on planning, two failed submissions, endless promises that never materialised. 16 months later we have a \u20ac6,000+ bill from him and a first quote of \u20ac130,000 plus VAT plus glazing, against the \u20ac100,000 we were told to expect. The builder says the slope means heavy groundworks and possibly pulling up the whole garden. Is this just where extension costs are now, or has this gone wrong somewhere?<\/p>\n

\"renovationprojects-buildingofextensionoftheexistinghouseunfinished\"
\n Site conditions, structural work and glazing can all add substantially to the final cost. Shutterstock<\/p>\n

Shutterstock\n<\/p>\n

Shay says:<\/p>\n

Short answer: both.<\/strong> The number itself isn\u2019t mad for what you\u2019re building \u2014 but there\u2019s a lot in your 16 months that should have been flagged a long time ago.<\/p>\n

Let\u2019s take it in three parts: the architect, the budget and the slope.<\/p>\n

The architect.<\/strong> Hiring one was the right call. But 16 months is a long time, and it sounds like they were either overloaded or not prioritising you. Here\u2019s the trap people fall into: once you engage an architect, it\u2019s tempting to hand over the whole process and stop checking in. Don\u2019t. You still need to set deadlines, follow up on decisions, and know exactly what service you\u2019re paying for \u2014 some architects just design, others manage the whole build through to sign-off. Get that scope agreed at the start, in writing, with a timeline attached.<\/p>\n

The budget.<\/strong> \u20ac100,000 was set 16 months ago \u2014 and costs haven\u2019t stood still since. Materials, labour, waste and transport have all gone up, partly due to wider geopolitical pressures affecting fuel and transport costs. A budget that was tight then is tighter now, and no one revisited it with you along the way.<\/p>\n

This is where a quantity surveyor earns their fee before a single block is laid: getting realistic costs for your actual scope tells you straight away whether your budget matches your ambition, or whether something needs to give. If it doesn\u2019t match, you defer what you can \u2014 wardrobes, decorating rooms you\u2019re not using yet, landscaping \u2014 and value-engineer the rest.<\/p>\n

The slope.<\/strong> This is the part that should never have been a surprise.\u00a0A sloping site can push groundworks costs to two or three times those of a flat site \u2014 it\u2019s labour- and plant-heavy no matter how you slice it. Stepping down into the extension instead of levelling the ground can bring that cost right back down, though not everyone wants a step in their house. Either way, this should have been priced and discussed the day you were quoted \u20ac100,000, not 16 months later in a builder\u2019s site visit.<\/p>\n

So what should this actually cost?<\/p>\n

Based on what you\u2019ve described, here\u2019s roughly where I\u2019d land:<\/p>\n

That \u20ac4,400\/m\u00b2 rate is on the higher side to reflect the glazing you\u2019re planning \u2014 the final number could climb further depending on the roof finish and glazing spec. In other words: your \u20ac130,000 quote isn\u2019t the world gone mad. It\u2019s close to where this project should sit \u2014 the problem is nobody walked you to that number gradually, so it landed as a shock. Worth noting, I didn\u2019t allow for any works other than the knock to the existing house \u2013 any works you intend to do would be in addition to the above<\/p>\n

Key takeaways<\/p>\n