Thanks ONQ,
I have read a lot of your advice on different threads and the key posts. Most informative I must say.
You're very welcome, as are all who find my comments useful or informative - that's what this forum is all about.
Sometimes I post too much, but I prefer to qualify my advice where I can. This thread of yours is exercising me greatly.
Firstly I should say that the current bungalow is inhabited and will continue to be for along time.
This may hugely complicate your health and safety file. Normally when people continue to occupy part of a premises which is being extended, it is possible to facilitate this by a vertical separation of the works from the accommodation.
Usually this can occur when the house is being extended to the side or the rear, and it is possible to use separate entrances for house and works, even if this may require temporary kitchen and toilet accommodation.
You OTOH appear to be proposing a horizontal segregation of house and works, but in reality this is not what's gong to happen. The works will be carried out at high level over the living accommodation and this carries significant risk to all concerned. Full perimeter access will be required if you intend to build off the existing walls and that implies full scaffolding too.
The only structural change to this house will be the removal of the roof not the existing ceiling. Just to reiterate, the current bungalow will not be touched (except the roof) and a new 120sqm house will be built on top. The roof of the new house will be the same as the old one, a parapet roof, not totally flat. So no eaves either.
I'm not sure I see the difference where a flat roof in concerned since the ceiling attaches to the roof in an intrinsic manner. I mean, what holds up the ceiling? Or is there a crawl space overhead and a roof above that again? Remember teh stub walls for the parapet may not be the same thickness as the walls lower down, and you may need to take these down to the "thicker" level and build up again. This may in turn require you to very the roof support detail.
I'm also unclear about the structural or services method here. You appear to be suggesting a clear span of up to 10M [recall the "square" plan of 10Mx12M to give 120sqm area]. Even is this is more stretched out, to say 8Mx15M, this is still a massive clear span and in normal domestic construction it would require a cross wall or line of intermediate supports coming up at intervals through the existing house to break the span into 2No. circa 4M lengths.
If you are going to span this in one go, you need to check your structural assumptions and calculations again. A steel frame is lighter to begin with but will generate point loadings and requires to be fire-proofed. This suggests a cradle or cage outside the existing house per Sconhome's suggestion.
A concrete wide plank system will need perimeter support and careful positioning of services cores for pipework, etc., in fact all the services need careful consideration and may need fireproofing including the waste outlets.. The plank system may be happy with a simple linear continuous wall or ring beam for support, but it seems that the overall weight on the existing walls will be significant without an intermediate spine wall to take half the floor and roof load.
It seems that you are proposing two separate residential units separated by what effectively seems to be a compartment floor. Whether this is directly above the existing ceiling or not I think it will act as a compartment floor, and even if you're proposing this as a granny flat to be used as family accommodation I'm not sure any lesser standard will apply. This may need FR 60 construction.
If this isn't a granny flat, then the proposed development seems to be effectively two separate houses - as in apartments - one atop the other. Although the units may have separate accesses and means of escape they are separated by a compartment floor, not a Separating Wall. This suggests that a Fire Safety Certificate may be required.
I have little direct experience of Duplexes and any granny flat I have provided has had interconnected fire Detection and Alarms Systems and minimum FR60 structural complementation and multiple alternate exits from upper levels. When in doubt ask the Building Control Officer or the DOE for a definitive comment. It all adds to the complexity and expense of what you are doing.
The fact that some people were suggesting that €100/sqft was attainable had lead me to hope that 130k was potentially possible. I have priced semi D’s in the area and a friend of mine recently bought one for 300k. The whole point of building on top of this house in the first place is that we could not afford a house in this area, an area where we have both lived all of our lives and would like to continue to live here for the foreseeable future.
Well I see where you are coming from MRTULES, but in terms of economical building practices, I'm sorry to say your proposal isn't a semi-D.
Semi-D's save in every way your development doesn't, including needing only three out of four walls to be external, and having a very good almost cube-like shape to minimise heat loss - the closer to a globe the better, whereas your proposed development seems strung out and flat, more like a cigar.
Standard Semi-D's benefit over bungalows in that they make more efficient use of their foundations, and they employ a cross wall to halve their major spans to allow them use lower stressed, low-embodied energy [and therefore cheaper] timber construction.
They also have no need for fire sealing apart from the party wall, which can be achieved by cavity barriers at the eaves and resilient Rockwool under the roof covering.
When you look back at all the issues raised above, you can see where the costs might arise in your build, which is why I took you along this little voyage of discovery.
Having said that, your proposal, Fire Cert and Fire Proofing notwithstanding, may lend itself to off site pre-fabrication in a big way, and once you decide to plump for the erection of a crane on site to assist with the build economies of scale in production and time on site may allow you to bring costs down again.
I think you'll need someone who knows how to design for off-site prefabrication and on-site dry trades assembly and this may in turn suggest one of the several system builders as opposed to a more traditional build route. Using the frame method suggested by Sconhome, you could end up with a very quick time to erection on site and minimal intrusion into the land with little or no effect on the existing house except perhaps for lateral support.
Be careful with wind bracing, the suction effect on large flat roofs and the wind loading on lightweight structures with large side areas.
Finally I'd just like to draw what I see as a clear distinction between "doing a course" and "Learning a trade".
People in offices, in marketing, public relations office management and the professions go on courses.
People who work their wonders with their hands and materials in the real world learn a trade.
Courses last for 6 months or a year at the end of which you get a cert.
Apprenticeships last for 4 years at the end of which you have a skill.
If you learn nothing else here "stick to what you're good at".
Work as a tradesman's mate if you like, you'll learn a lot.
Just don't think you can do what they do.
They make it all look so easy...
There's no doubt what you're doing is doable and to some the level of the detail above is just so much "stuff" [although you cannot build without it].
What I'd really be interested to see is how your architect dealt with the design of the new extension and how he expressed it.
Links to photos/.jpegs or pdf files of elevations. sections or plans would be appreciated.
HTH
ONQ.