Most self-builders aren't competent to assess the risk of building incompetently and no, there is no game being played here. If you don't build in accordance with the building regulations on what is likely to be your single biggest investment claiming "its your risk" you're talking from ignorance. It becomes the risk of anyone you sell you and could prove a serious liability as sufferers from Toxic Mould in America have discovered. In addition there is a significant risk of prosecution if people come to harm through your negligence.
In relation to costing a build, a main contractor's rates include for items that need to be done on site. The bare supply price will not include delivery to site, supply and deliver will not include fixing into place on site, so the whole labour cost thing is askew if you're only pricing building costs. Things that need to be done on site include supplying general operatives to perform attendances for specialist sub-contractors, erecting and maintaining safe operation of scaffolding installations, scheduling deliveries and co-ordinating their placement on site to minimize carriage within the site, safe and weathered storage, preparing and stoning the ground to allow for safe working conditions, etc. Most self-builders don't have a clue about such things, even when they have worked on building sites themselves, because they were working as a general operative, and not as a main contractor or one of his foremen.
More importantly, builders rates assume certain competences and efficiencies and skillsets are in place and applicable to the work on site. IMO builder's rates are not applicable to self-builder's where the level of competence and governance is much lower than with an experienced contractor. Self-builders seem to think that there is some sort of assumed entitlement to kudos merely for getting a house to stand upright and not leak, but a quick glance over this forum or the Construction forum on boards.ie will show the extent of the carelessness and casualties. Sites like the subject site, offering cut-down versions of professional services, run the risk of supplying just enough information to let the self-builder get himself in hot water, with the assumed safety line of one of their experts wading in to assist at that point.
Let me put it like this: I've studies sand-casting, carpentry and bricklaying at the School of Trades when it was in the Linen Hall as part of Bolton Street CDVEC. In my own house have laid a driveway a low random rubble retaining wall and a rear few steps, but I wouldn't undertake carpenter's work or bricklayers work on a building site despite my competent professional's knowledge of the trades in question. I simply don't have the necessary skill. There is a reason why serving time in a trade takes four years. Similarly I would not consider myself competent to act as a main contractor. Quite apart from the knowledge, there is a huge amount of time investing in learning how to DO the thing, just as a concert pianist spends far more time learning and practising than performing in his formative years. You don't just "pick up" the skills to become the main contractor on a site. In fact, where they have come up through the trades, it is often a qualified bricklayer or carpenter who - many years after completing his masters piece - may have acquired the necessary in-depth knowledge of running a site and safely co-ordinating work to take on board the job of main contractor...
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.