I don't have that problem. And my clients don't have that problem.
The client is paying the builder. That's the control. If a client is not able to enforce his requirements then perhaps he should employ someone to do that function?
Not all builders are reputable and finding a good one these days is getting harder and harder. When you ask on Facebook, most traders recommend themselves while pretending to be a client, or the client has no idea if the work is good but recommend them anyway cause they were cheap or talk a good game.
Withholding payment isn't really a control though. It's not going to get the builder to admit they've messed up and they're certainly not going to come back and do a better job when you had to hold them to ransom before they'd come back. Like this mob, they're not even accepting they changed the terms of the contract after the fact, nevermind admitting they botched the job. And if the bill is big enough, they can easily pass that onto a debt collector, which has potentially major long-term consequences.
The only option I have if things continue this way, is a small claims court. To submit the paperwork is a £120 fee, plus whatever independent expert report, plus time off work, plus whatever else is needed. And max expenses claimable if you win is £150 as this claim is under £3,000. Considering the bill is around £400, is it really worth all that time and effort?
Probably not and the builder is likely counting on that.
And that, dear reader, is why it's always advisable to get a second, or a third, opinion in discussions on a major project.
It's not a major project thankfully, if it wasn't for the roof work, I would have done this myself. As the saying goes, want something done right, do it yourself.
I just don't want to pay full price for a job not finished or completed as agreed. Getting them to admit that is a challenge and they managed to get me doubting myself.
Duct need to exit roof with 500mm to avoid condensation issues , or move fan to roof exit so it pulls air thru .
The duct is vertical and goes through a cold loft space. Humid kitchen air is going to condense on the cold surface; pushing/pulling the air through isn't going to change that.
Just how bad the condensation is I plan to verify this weekend.