Kieran McCarthy: How to start planning a house extension

Confused about when to contact an architect, and if you need a quantity surveyor, and when to contact builders for quotes? 

Kieran McCarthy: "The first thing I would do is consult an architect who will sketch up some draft drawings and comment on any planning permission requirements (if your new extension is to the side of your house you will certainly need planning permission)."

Hi Kieran I’m in a bungalow by the coast considering an extension (living room with mezzanine and maybe an extra bathroom at the back).

I’m wondering where to start... builder or architect first — or do we need an architect, then planning, then building quotes? Is it worth getting a quantity surveyor?

Thanks, Eve, West Cork

Hi Eve, thanks for your question.

It really is a poor reflection on the building industry that you even need to ask me this. This is the problem with the industry in general, it consists of silo expertise and you are left to piece through and work out how to do it. And, let’s face it, this means you will undoubtedly end up managing the project yourself. As an engineer and project manager, let me talk you through how I would approach this and this will hopefully guide you.

So, the first thing I would do is to get an architect to call to your house. They can review your house in its current form and advise on how best to extend it. Certainly advise them of your budget but in truth you will need a QS to cost out your project later to check if it is on budget. The architect will sketch up some draft drawings and comment on any planning permission requirements (if your new extension is to the side of your house you will certainly need planning permission).

I would not advance too much with the plans, just enough so that you are broadly happy with them.

Next you could consult with an engineer. They will need to visit your house and inspect the current structure. They will advise what key structural adjustments need to be made. If you have wide spans (doorways/windows/open plan) you will likely need some structural steel. They will also look at the existing roof and the condition of your masonry and drainage. They will need to tie in with these and upgrade where necessary.

Now you could engage with a QS to do a quick budget check (estimate) to see how much the plans would cost to execute. What the QS is doing here is using market rates and some general provisional allowances where they feel there might be unknowns and certainly a
contingency (always prudent when extending an existing house). They use the architect’s drawings and the structural guidance from the engineer.

This budget cost will give you a sense of how much the extension will cost to build and may in truth be a cost range plus or minus but it will inform you as to how the proposed plans align with your budget. If you are above, you can ask the QS how you could save some money, if it’s below then you can spend a little more on your prime cost sums (windows, tiling, flooring).

Kieran McCarthy: "If you don’t have contacts in the building area you could seek prices from a couple of builders — but if you get a price that looks too good to be true it usually is. I would be slow to award a project to a builder who just looks at it and gives you a cost per square foot or a ballpark. You need to ensure they have done their due diligence and have everything included."

Now you can circle back to the architect and inform them of what the state of play is with respect to the design v budget match. You have a lot of work done at this point so now the architect is well informed on how best to proceed. It is likely that the architect will adjust the drawings and advance them for the likely planning permission, which they can lodge for you in due course.

Once planning permission has been attained, now you are ready to look for a builder. The engineer can now take over and advance engineering
construction drawings, These are drawings fully detailed with all the required engineering analysis and detailing and these are ready for a builder to price.

(A lot of people send their planning drawings to builders to quote but this is not advisable. There is not enough detail and there will be
numerous extras on site).

When it comes to looking for a builder there are two ways to do this:

• Seek out a trusted builder based on family or friend recommendations and ask the builder to price the project. His price should approach the QS’s estimate but invariably will be a little above or below as slightly different assumptions may be made. This is now the time to negotiate with the builder to align his price with your budget.
• If you don’t have contacts in the area you could seek prices from a couple of builders but if you get a price that looks too good to be true it usually is. I would be slow to award a project to a builder who just looks at it and gives you a cost per square foot or a ballpark. You need to ensure they have done their due diligence and have everything included.

If you have a trusted builder in mind and the project is relatively simple you could in fact negotiate with the builder from the very start of the
project and possibly avoid the need for an external QS (as this is a relatively straightforward project assuming the existing house is in good condition) but this is clearly reliant on a professional and trustworthy contractor.

The simplest way of all to execute a project such as this is to seek the services of a design & build company who will manage everything for you and keep the project on budget.

These companies tend to be located in urban centres so I am not sure if any operate in your locality but well worth checking at the start of your quest.

• Send your home build queries to [e-mail]

Kieran McCarthy is a building engineer and director of KMC Homes who specialise in designing and building luxury new homes for busy people in Cork. He is also presenter of the RTÉ TV show Heat My Home showcasing deep retrofits in Irish homes.

kmchomes.ie

Kieran is on Instagram @kierankmc for more home building
information, tips and Q&A advice.

You can also follow Kieran on the Built Around You YouTube channel.