I have a 20 year term and want to do some improvements, should I increase my term to 25 years or borrow the money in a different fashion?

My suggestion is that you must not increase your term but borrow from other source.That way you will be able to have extra funds at your disposal.

But would not extending my term mean i could get the extra funds that are at a lower rate than a loan?

Both of you have a valid point.  My view is that if you can extend the loan at a fixed rate (which will definitely be lower than a renovation loan) then do it.  But if you still have many years to pay off the loan, it is highly unlikely that the rate (for the extended term) will be known - then I think you should take a short term renovation at a higher but certain interest rate.

Good luck in your home improvement efforts :)

Well it all went a bit pear-shaped as when I approached my vendor they said I could not extend my mortgage as i was on a fixed term, that does not end for another three years!