# Extension over the garage cost



## imalwayshappy (25 Jan 2021)

Hi,

I am considering building an extension over the garage in my home. Its a standard 3 bed semi. I am told (without foundation by someone) that building an extension over the garage is very expensive (I don't know why) far more than a similar sized extension that would be build on the back of the house for example. Has anyone had any experience with this? Is this actually the case? 

Thanks


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## Leo (25 Jan 2021)

What's there will need to be surveyed to assess what the options are. It may be cheaper knock the garage and build a new two story extension. That would bring the benefit of better insulation below the ground floor. 

Even if there is a foundation under the garage, it may not be sufficient to support a two story extension, so expensive underpinning would be required.


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## RedOnion (25 Jan 2021)

It can be expensive.
Firstly, you're making an assumption that the foundations & walls of garage can support the structure. That might not be the case.

You'll be taking off the existing roof of garage before you start. Leads to internal replatering, etc.

The other part is it depends on the existing roof structure of the house. Say for example you've a hipped roof, you're going to be rebuilding quiet a bit of the existing roof structure to bring it out over the extension. To get roof to 'blend', it's also common to strip the tiles from back of house to put on front, and recover the back completely.


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## imalwayshappy (25 Jan 2021)

All good points. Many thanks for the responses.


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## DublinHead54 (4 Jan 2022)

@imalwayshappy did you progress this any further?

I am starting to look into rough costs of extending over the garage and attic. With all the commentary on rising construction and material costs over the last 12 months I need to figure out if it is a non starter. Standard Semi-D 1960s build with a hipped roof. 

I know this question is equivalent to 'how long is a piece of string'. I have seen estimators at 2-3k per sqm, therefore a 30sqm extension at 3k would come in at 60-90k, is that a reasonable estimation?

I am really trying to figure out is this going to be a 100k job, 150k job or a 200k job for the basics before factoring in finishes and ensuites etc.


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## cremeegg (4 Jan 2022)

RedOnion said:


> Firstly, you're making an assumption that the foundations & walls of garage can support the structure. That might not be the case.


You are not alone in making this assumption, see all Irish TV architects.


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## cremeegg (4 Jan 2022)

Dublinbay12 said:


> @imalwayshappy did you progress this any further?
> 
> I am starting to look into rough costs of extending over the garage and attic. With all the commentary on rising construction and material costs over the last 12 months I need to figure out if it is a non starter. Standard Semi-D 1960s build with a hipped roof.
> 
> ...


Knocking and building from scratch should cost under €2k per sq m. That does depend on location and site access of course.


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## lucky1!! (7 Jan 2022)

hello, we are also extending above our garage. A builder dug a hole and engineer has certified that foundations will support a second story. You coould do this, it wasn't that expensive.


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## DeeKie (10 Jan 2022)

lucky1!! said:


> hello, we are also extending above our garage. A builder dug a hole and engineer has certified that foundations will support a second story. You coould do this, it wasn't that expensive.


Interested to know the rough cost of the engineer test please?


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## jim (17 May 2022)

Also interested to know cost for this please?  @lucky1!!


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## DeeKie (15 Aug 2022)

Considering building over the garage and an attic conversion at the same time. Has anyone here done that? Also if anyone has costings on any of this it would be appreciated. Whether costs or recommendations for engineers or builders who do a lot of this work. We are based in Dublin


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## Salvadore (21 Aug 2022)

DeeKie said:


> Considering building over the garage and an attic conversion at the same time. Has anyone here done that? Also if anyone has costings on any of this it would be appreciated. Whether costs or recommendations for engineers or builders who do a lot of this work. We are based in Dublin


Did this some years ago. Definitely worth doing the attic at the same time.

The advice at the time was that it would cost about half as much to build while the house was a virtual building site, relative to trying to convert it in an otherwise complete property- issues with access etc.


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## DeeKie (21 Aug 2022)

Salvadore said:


> Did this some years ago. Definitely worth doing the attic at the same time.
> 
> The advice at the time was that it would cost about half as much to build while the house was a virtual building site, relative to trying to convert it in an otherwise complete property- issues with access etc.


That’s what I was thinking. I was hoping to get a specialist attic crew in and then get a normal builder to do the first floor. Is that how you did it?


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## Salvadore (21 Aug 2022)

DeeKie said:


> That’s what I was thinking. I was hoping to get a specialist attic crew in and then get a normal builder to do the first floor. Is that how you did it?


No. The builder did it in conjunction with the over-garage extension (which extends to attic level as well).

Doing it this way allowed for an integrated staircase to the attic area (albeit much narrower than a regular staircase) rather than the pull-down attic ladder from the landing option.


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## DeeKie (21 Aug 2022)

Yes. It seems to make sense from a layout and staircase point of view. I’m getting an architect to price the redesign of the top floor and attic I think. I’m trying to do it as simply as possible.


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