Hi Eyeball,
This depends on what you actually want from the extension.
The primary mistake people make is in extending to put in a bathroom or kitchen and placing it in the extended bit, taking light away from the resulting interior space.
Service areas that don't need view windows should be kept internal where possible and the foul water, waste water and ventilation pipes run to the outside, taking account of any stack venting required.
There is no greater waste of space than a toilet block with a small frosted window sticking out into the garden, blocking light, views and access from the kitchen/dining family room.
Kitchens OTOH have a claim on the light and visual connection because the home-maker may want to "keep an eye" on the kids if they're playing in the back garden.
An L-shaped extension with the kitchen to the side in a galley form with a big window from a family space, both enclosing a paved area just outside for barbies, etc. can work wonders on the usability of a back garden.
The toilet can be kept behind the kitchen, perhaps accessed via a vented utility enclosure.
You may also need to bear in mind compliance with Part M for people with disabilities or older persons - yourselves in years to come perhaps - who cannot climb stairs any more.
(looks up)
There's a bit more to "doing an extension" than you might think.
The cost of designing an extension competently is separate from the cost of making the planning application.
It usually takes a minimum of two weeks to-ing and fro-ing to even get the clients to properly address the brief and develop a concept, perhaps do a model.
The appication proper will require, at minimum; -
- An Ordannce Survey Map set ~ €50
- A site notice ~ €50 - €150 printing and materials / erected by, say, Site Notices Ireland.
- A newspaper advertisement ~ €20 - €250 depending on the paper and the area
- A survey of the house including plans sections and elevations - POA
- A set of drawings to a stated scale showing the existing and proposed development - POA
- Completed APplication form and supporting documentation as required.
But long befoer you get there you should discuss the proposed development with your neighbours and the Planning Officer.
Out-of-sorts neighbours are a difficulty you can try to avoid and your architect can advise on the best party wall agreement.
There are people supposedly going around saying they can make applicatons for under €1,000 or less - you get what you pay for.
€2-4,000 is a more eralistic price to include for designing the concept, pre-planning discussions, neighbours briefing, etc.
Good luck with it and I hope the foregoing has been of some use.
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 persons should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
My best advice is that you should retain a competent building professional to advise you on these matters.