Value is not only the estate-agent number
The immediate value may be the room you stop sacrificing inside the house. A dedicated office can give a bedroom back. A gym can remove equipment from the garage. An entertainment room can make the main living space calmer.
That day-to-day usefulness is real even before the property is sold.
Quality and permanence affect buyer appeal
A properly insulated, serviced and well-finished garden room is more likely to be seen as usable extra space than a lightly built summerhouse. Buyers will notice condition, access, heating, electrics and whether the building feels maintained.
Poorly proportioned or deteriorating structures can have the opposite effect, particularly if they dominate the garden or look expensive to remove.
Why we avoid percentage promises
Property value depends on location, the house, the garden, market conditions and what local buyers prioritise. A blanket claim that every garden room adds a certain percentage is not something Goldridge can substantiate.
If resale is an important part of your brief, design for broad usefulness and a finish that sits comfortably with the property rather than an extremely personal niche.
Build it because the space solves a real problem
The best starting question is whether the room improves how the household lives now. If it also broadens future buyer appeal, that is a useful additional benefit rather than the only justification.