home improvements that are claimed for business use will be taxed as capital gains when you come to sell your house, there is a minefield about what you can claim and what you have to pay back on your property,
If you rent a house then run a biz from it and say use 2 rooms ( 1 bedroom and a dining room ) and use 1 bedroom and lounge for personal use you can claim 50% of the rent against the biz. ( kitchens, toilets, bathrooms don't count ) you can not claim any part of a repayment mortgage payment against the biz.
(Only a percentage of the interest of that payment)
Rent of the unit is 100% deductible cost against the biz - that's its sole purpose, just like diesel
Darran