To test this theory, I searched for similar properties in the same road that I found offered for sale on Zoopla. Zoopla’s search facility has a neat little option to include key words in your search (such as Cabin) to narrow down your search. By using this tool you can compare properties and prices with and without a Garden Cabin. The results were staggering.
A few years ago I built a 3m x 4m cabin at the end of a garden in Surrey. It had a lofted sleeping area for a double mattress, a small shower room, WC and under floor heating which cost the owners £18,000.
The property was recently sold for £521,000. A few doors away is an identical property that I found on Zoopla in roughly the same condition but without extra living space at the end of the garden being offered for sale at £479,950 (that's £41,000 less).