Can I first of all respectfully caution you about how you present your information in a public forum.
What you've posted here gives a very poor impression of the architect involved and on the face of it isn't clear what occurred.
Poor service during a job can arise from a number of legitimate factors, including pressure of work, a difficult builder or, the most unfortunate of all, a poor working relationship developing between the achitect and client, which can arise from time to time.
I'd say there are very few architects who aren't feeling the pinch right now and most are flying around like bluebottles trying to keep their practices together - those that still have them.
But it is not easy to see how an architect could have damaged your house.
Architects are primarily designers - they do not carry out the work themselves.
The architect may design the details, but its up to the contractor to build them.
The contractor's responsibility usually includes designing and installing any formwork, temporary works, propping or supports that may be required for new work, demolitions, opening up works, tie-ing in of structures, building-in of elements or extending the premises.
It is usually therefore the workmanship or working methods of the contractor that causes the physical damage during the building programme.
It is important to be clear on who has done what exactly, but I'm not suggesting you discuss this level of detail outside your solicitors office - certainly not here.
In relation to PI cover, Architects supporting the standards of the professional may carry Professional Indemnity Cover providing it is available at reasonable rates commercially.
Professional Indemnity cover generally covers loss or damages arising out of the design of the building, not damage due to works per se - one may follow from the other, but unless it can be traced back to the design, an architects PI cover may not come into play.
In relation to resolving this matter, an increasingly fraught exchange of solicitors letters may not be the best course to achieving a result to everyone's benefit.
When faced with distress like this people normally consider court action, but you should have due regard also to whatever method may be specified in any contract that may apply.
Could I respectfully suggest you also explore arbitration as well as mediation/conciliation, as time-and-cost-effective options.
Where the possibility exists of agreeing a solution, it is better to get people talking, and not have one chasing and the other furiously ignoring.
An independent Report, or the testimony of an inspecting professional may be required in order the present a legal action properly to a court, arbitrator or mediator.
Where this involves a review of the detailing, level of site inspections, photographic records, if any, and the competence of the architect, another architect may be required.
You may wish to consider contacting the RIAI or another architect directly with a view to asking someone to come in to inspect the damage and prepare a report, if your solicitor hasn't already suggested this possible course of action.
I trust the foregoing is of some use.