Why do people think it will take 10 years?
They are not building a new palace. They are only removing asbestos, rewiring and updating the plumbing. They have already started. The asbestos was removed from areas in the basement so any wiring, plumbing and painting was probably also updated at the same time.
They will have multiple teams of people working not just a few people.
They have not decides how the work will be done but they will probably work in sections.
Example:
1.) A team of movers remove all the furniture, carpets and drapes from a few rooms.
2.) The asbestos team will remove asbestos from these rooms.
3.) Then the rewiring team and the plumbing team will come in do their work.
4.) Followed by the plasterers and painters.
5.) While all this work is being done, the carpets and drapes will be cleaned and repaired and the furniture would be repaired and upholstered.
6.) Return carpet, drapes and furniture to each room.
Step 5 would only apply to the nineteen State Rooms. (and maybe the Queens & Philip's private quarters.)
The articles I read stated the Palace would be closed for one year, which makes sense since the family and most of the staff would not be at the palace during the renovations.
IIRC, the State Rooms are on the second level, the Queen's & Philip's rooms are on the second level, the family bedrooms are on the third level. The staff rooms are probably on the fourth level and in the basement. Staff offices are probably on the ground level.
If BP is closed for a year, then three floors are empty or near empty of people.
If BP is closed for a year, why would most of the staff stay at BP?
The staff that is needed would move to Windsor.
The staff that can be placed at Balmoral, Sandringham or with other members of the RF will move to their new positions temporarily or permanently. The staff that cannot be placed will be made redundant.