The blaze broke out at the large home off the Headley Road, just beyond St Luke's Church, at around 1-30 pm.
It was believed to have started in the roof space of the recently refurbished home where builders were understood to be working on an extension.
At the height of the fire there were eight fire appliances on the scene and up to 45 fire fighters, many wearing breathing apparatus. They fought against the thick, acrid smoke of the roofing felt, to bring the fire under control.
It took all afternoon and until the early evening and firemen remained on duty well into the night to damp down the fire.
They returned the following morning along with fire investigation officers.
Although a large salvage operation had been carried out at the house, the fire severely damaged more than 60 per cent of the first floor and roof space and the ground floor was also badly affected by smoke and water.
No one was hurt but one man had to be treated by paramedics for slight smoke inhalation.
Special units came from as far away as Eastleigh, Basingstoke and Winchester, joining firefighters from Grayshott, Haslemere, Liphook, Bordon, Petersfield, Godalming and Guildford along with ambulances and police.
Headley Road was closed to traffic and police set up diversions along Beech Hanger Lane, Beech Lane and School Lane from around 2-30 pm until the road was reopened at 10 pm.
One of the largest fires in Grayshott for many years, it happened on the day national fire brigades' strike had besen due to take place.
"Maybe it was fate," said Grayshott Fire Station sub officer Peter Norman whose retained fire crew were first on the scene.
The owners of the home did not wish to be named.