It is not a requirement to have a QS involved, but it is advisable, because they will not only advise on tenders returned, the QS will also prepare a budget cost exeimate based on the design of the building and its fit out and he will advise on the best form of contract to use and everyone's contractual obligations. Some architects may also offer a QS service on jobs of this size and they can be better and more affordable than a QS from a background in large commercial work.
Many people forget that the basic building is only a fraction of the total cost and services and fit out works and furnishing can be over two thirds the final cost. Add to that any landscaping works or unusual drainage systems like attenuation chambers or reed bed disposal and the "afters" costs skyrocket.
Architects someitmes don't like "their" budget being bridled by such considerations but if that's the position, either they change their way or you'lll have to llose the architect and get another. The architect's role is to advise on how best to balance all the clients requirements to best achieve their vision of the final result, even if this may need to be done in stages.
WIthout trying to multiply your costs please allow me to offer a couple of other suggestions for your consideration in relation to a one-off house project.
Is advisable to have a civil and structural engineer look at the soil and the bearing strata and design the foundations and superstructure. He may also comment on how to address any groundwater problems. He may also be the registered site assessor, although architects and surveyors can also offer this service.
You can read up on these at [broken link removed] but you may already be past this stage.
Is advisable to have a mechanical and electrical engineer look at any highly serviced house, in particular the siting and design of the MVHR system air inlets, exhausts and routes, in relation to both limiting fire propagation and sound transmission. He may also comment on the sizing of pumps and how best to run UFH systems if installed. It is specifically his role to examine and comment on the mechanical and electrical tenders and the issuing of nominated sub-contracts to the prospective tenderers.
Finally, since you are at tender stage, you should assure yourself of the competence of each contractor and nominated sub-contractor from which you are seeking tenders. I'm presuming this is your own private residence. All persons on the job still have to be competent at what they do.
Finally I strongly advise you to appoint a Main Contractor. If you have no-one acting as project manager, the task of managing the project falls to them. They are the one who must co-ordinate the site and ensure safe practices are followed and that all operatives have their safe site passes for the work they are doing, but no doubt your architect has advised on this.
If you don't appoint a main contractor OR a project manager all that mountain of work falls on your shoulders, and to be fair, most lay people simply aren't up to doing this per se, and those that are find its not easy to balance project managing their own site, doing their day job and having a home life.
Best of luck with the project and you might let us know how you get on.
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.