Hi,
You would only need to register for VAT as an NETP if you are making taxable supplies in the UK. If you are renovating houses and selling them then this would be a an exempt supply and would therefore not require registration.
If you renovate a property which has not been lived in for 10 or more years and then sell it this would be a zero rated supply. This would prompt a requirement to register for VAT although you could request an exemption from registration for this type of supply. You can see guidance here:
Who should register for VAT (VAT Notice 700/1)
Thank you.