To ask for money off (shoddy works)

[letmeeatinpeace]

I've posted already on Property but got no replies and need some guidance.

We’re nearing the end of renovation works, and have come across some snagging. The builders have corrected most of the snags, however this one is tricky -

We've had additional radiators installed in the lounge. We noticed that when the rads are coming to temperature if you walk around the lounge you can hear a loud metallic rattling under foot. Basically, one of the CH pipes is not properly supported and is rattling against the floorboards when there’s movement in the room. This happens for a 15-20min window each time the rads are either heating up or cooling down.

We have also just laid BEAUTIFUL new engineered wood floors. Fixing the issue would require bringing up the floors, which I really really don't want to do, but the noise is noticeable, even when our tiny toddler walks around...

The floor was laid by another company. The boards are glued down, not floated, so would likely break upon coming up. Flooring company has quoted £3k+ to re-do the lounge.

I’ve sent the quote to the builders and said I’d like to hold the £3k back for 2-3 months so we can properly assess whether we can live with the noise, or if it needs fixing.

If we decide to live with it can we ask for £ off the final invoice to compensate for the noise / shoddy installation? And if so, how much is fair? The builders were not cheap - they were similar in price to other builders that came via personal recommendations (sadly those were too busy), so I expect a level of quality.

It is a shame as the builders have generally been very communicative and responsive, which I have appreciated, however the attention to detail has been lacking.

The kitchen had to be re-fitted three times due to calculation errors on their part, causing damage to a corner post which they mostly repaired but the finish is not ideal (can’t be replaced at this point due to position under worktop). They installed the kitchen extractor vent in the wrong place, so now we have two vents sticking out of the new roof (visible from loft extension).
One of their team used our flat roof as a chopping board, creating gashes that caused leaks in the roof and then took weeks to fix it. They got paint on many areas of our new wood floors. The whole job took twice as long as scheduled (typical, I guess).