Does the homeowner have to pay the full 20% VAT rate for work carried out and then claim the remaining 15% VAT back?
No, the sash window company will handle the VAT rates, the final amounts will be listed on the customers invoice.
Check out rates of VAT here https://www.gov.uk/vat-rates
How long will this reduced rate of VAT last for?
As it stands in 2021 there doesnt seem to be a date in place for the reduced rate to end but that could change at any point.
What is sash window refurbishment and draught proofing?
Click here for the full description https://www.sashrepairs.com/refurbishment-draftproofing/
The best advice we can give is to take advantage of the reduced rate of VAT now and get your window work booked in before it disappears.