Hi there, 

We are having a single story new extension built. 

The block work was completed and a separate large company came to measure up for the window and bifold doors. 

A building contractor has the contract for all the work but windows and door are supplied and fitted by a big well reputable local company separate to them that we found who had done the work on the rest of the house.

They mismeasured twice and had to be turned away causing delays (we didn't mind as we'd rather it be correct).

The third time they came, the main builder was off sick (Monday) and just the plasterers were in. The fitters have gone in, realised the window and doors were too big and instead of going back, they have hacked away 3 inches around the perimeter of both openings to fit them and left. 

When the builders have been there Tuesday morning they have noticed this straight away and the damage is as follows:

1. Damage to DPC needing more to be taken away to ensure it's sealed. 

2. The cuts are all not straight and the check reveal (no idea what this is) has to be corrected. 

3. Distance between the window and door is now less than 665mm meaning it doesn't comply with building regs and a structural engineer, support beams/steels may be needed. 

The builders are furious as no one contacted them to allow this damage. No one contacted us before it was done. 

It's created lots of extra work and subsequent expense for builders and us. Delays in work finishing and also, although the builders say they can correct a lot of the damage, they can't give a full guarantee the dpc won't have issues in the future due to the damage meaning potential issues in the future.

They have advised us not to pay the fitters until they have corrected the work/know how much it is going to cost.

My question:

1. How do I best form a written complaint about the work.

2. I feel we should be compensated/the fitters should pay for work to be corrected and also the extra costs with structural engineer and steels etc.

3. Even if it is corrected, we could potentially have massive issues going forward with the build re:damp etc so is there a way to get compensated for future work?

4. This has all caused big delays meaning we may not be able to move into the house for an extra month (expenses would mean putting things into storage as they need to take away bits of the ceiling for beams etc, I'm not technical so no idea what's involved).

We have paid £2k deposit and owe a bill of £3.5k to the fitters for the windows so far.

Photos attached.

Wales: Window and door fitted by company whilst building contractor not present. Sized wrong and frame of extension hacked away exposing DPC and leaving insufficient space between the 2 to comply with building regs. How do I best form a complaint to fitters for corrections needed and future issues?