Prefabricated Extension

Catbells
Catbells Posts: 849
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I had two quotes for refashioning two rooms into one in my kitchen.  Both were double the estimate the architect gave at the planning stage.  I can't afford £100k.  He has suggested a prefabricated alternative which is cheaper.  I\ve looked at the website and the results do indeed look impressive for £50k.  A post on this board 7 years ago featured a builders assessment that they were NOT good alternatives to traditional materials (which are now very expensive). Does anyone know if this has improved.   I need to find out what the materials used.  It would be helpful to know which you think are the best for prefab building and if you have experience.  Thank you.
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  • TELLIT01
    TELLIT01 Posts: 16,260
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    What size is the area involved?  Can you provide plans of the existing building and proposed new layout?
  • Around 30sq m. I can't put the plans on here but it is combining a kitchen which is part of the main house and has an outside wall. The conservatory was added later on the other side of this outside wall.   The work would involve knocking down this wall to combine with a conservatory and making one room out of two.  Thanks.

  • FreeBear
    FreeBear Posts: 14,271
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    Catbells said: The work would involve knocking down this wall to combine with a conservatory and making one room out of two.
    A conservatory requires an external grade door/windows between it and the main house (or any extension). If you knock through an external wall to make a conservatory part of the main living space, it needs to comply with building regulations (and possibly planning). Most conservatories fall well short in terms of insulation and standards of construction (e.g. insufficient foundations). If you are looking at one as a cheap extension, you are going to be very disappointed and could well have trouble selling the property in the future.

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  • greensalad
    greensalad Posts: 2,524
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    edited 14 November 2022 at 1:24PM
    Not much to add except to chime in with a plea to not remove external grade doors or solid walls from your conservatory to access the house! We have this in the house we purchased earlier this year, it is not at all pleasant. It makes the entire kitchen subject to about the same temperature as the outdoors. 6 degrees in the kitchen was our lowest in March this year. We were aware of the issue before purchase and will rectify it in the future but I would strongly advise you not to do this. 
  • Currently the kitchen is definitely warmer than the conservatory. Insulation is key as you both say.   Here is a link to the prefab company - you have to admit they look great.  https://www.vita-modular.co.uk/extensions.  Only 10 year guarantee which isn't that long in my mind.  Thank you for your thoughts on this.
  • Doozergirl
    Doozergirl Posts: 33,723
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    edited 15 November 2022 at 2:04AM
    Catbells said:
    Currently the kitchen is definitely warmer than the conservatory. Insulation is key as you both say.   Here is a link to the prefab company - you have to admit they look great.  https://www.vita-modular.co.uk/extensions.  Only 10 year guarantee which isn't that long in my mind.  Thank you for your thoughts on this.
    A new build only has a 10 year warranty on it.  You won't get better than that.  Most traditionally built extensions don't come with an insurance backed warranty at all.  

    There are "Modern Methods of Construction" available and they will build a property as good as any other, often with superior thermal capabilities.  Because they are mainly fabricated off site, there is less margin for error when it comes to the 'Wet Friday Afternoon' quality test on the builder.  


    Having built our house from an MMC (SIPs)  and now pricing up a garden room system in the same fabric that meets full
    building regulations spec to sell, I don't really believe that they're a cheaper product when being built to regulations.  

    Any extension price has to be bespoke.  It's not the same as a free standing building with nothing but the foundations to worry about.   No website price is going to include any works in or to the existing building, be that knocking through, or work to make good after matching floor levels or provide electrics for a kitchen, for example.   

    Have they given you an actual quote?    

    They're asking you to produce planning and building control drawings - bit odd if it's their build system being used - I would expect them to be able to produce the BR drawings for one of their standard spec extensions. 

    They're also saying that their extensions meet the building regs, but the u-value quoted don't appear to meet the regs introduced in June.  

    And yes, they look lovely, but everything looks good on a CGI.  Case studies are missing - not a single photo of a finished job.  

    It's only a website, however.  The answer is yes, MMC is a viable building option but garden rooms and extensions aren't usually built using the exact same specification, particularly when it comes to insulation because most garden room companies like to fly under the radar like conservatory companies do.   This website isn't doing a great job of explaining what those differences might be and the prices don't fill me with hope of being realistic, especially with a lack of real world examples.  

    You'll have to do the research though.  Make the phone calls and let us know how you get on!  
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  • SJW1510
    SJW1510 Posts: 12
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    Hi there - we've actually just started a project to add an extension which is along the lines that @Doozergirl describes. Really excellent thermal values. From what I understand, these methods of construction are really common in Europe/the US - it's just us who are a bit behind in insisting on traditional brick builds!

    Our project is only just beginning - we've just had the pull tests and the ground team out to check for the prep etc. We are knocking through one wall and keeping two others. We're extending a main house and creating an annexe. 

    I actually spoke at length to the company you mentioned and I was really impressed by them. There are a number of others in the market but compared to them, VM seemed thorough and professional. They're happy to either use your existing CAD drawings or create their own, but they handle the full building control process. 

    As it happens, after all of that I didn't end up using them! I think they would have done a good job but I was slightly concerned that they'd only been in business for about a year. The directors also seemed to have a few companies listed under their names on Companies House., some of which had closed down. What can I say, I'm a super-cautious person haha! 

    We've ended up using another company and although I was actually really happy with VM, I feel that the company we've picked are even more thorough. VM sent me an email with figures on whereas this other company pulled together a full polished quote with a breakdown of what was included. One of their directors is also an engineer, which pleased me. They've been operating about 2.5 years so still relatively newish but have a six-month waiting list and have exhibited at Grand Designs etc. Just seemed a bit more professional. Similar price. Also, they had lots of good reviews on Google - reviews seemed to be authentic as they had photos of finished projects etc. VM didn't really have any reviews, again a concern. 

    The engineer for the company we've chosen came out to look at the property before the groundscrew team and he was really attentive, gave us advice on other elements too. It took me 6 months+ to choose a company while we were waiting for planning, and I feel really confident that we've made a good choice. I suspect that VM  would also have done a good job but I just had a couple of little niggling doubts. if they had more checkable reviews I probably would have gone with them because they were really thorough and seemed to have good attention to detail in the many emails I received from them. 

    The reason we picked a modular build is because a) it's cheaper than a traditional brick build (about £30k) difference - even though we haven't chosen the cheapest modular supplier b) the thermal performance is better and the build quality has the same guarantees c) the price won't increase - lots of people saying allowing 10-15% extra for traditional build - the modular price is fixed  d) the build time and hassle is reduced. For us d) was really important as I have disabled kids and I could really do with as least disruption as possible. 

    Happy to answer any questions you have - also happy to keep you updated with how the build goes if that helps. We're schdeuled to be built in Dec/Jan. 
  • aoleks
    aoleks Posts: 720
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    a 30sqm extension doesn't sound right at £100k. the whole myth around "today's prices" is just that, an exaggeration. did materials get more expensive? absolutely, significantly more expensive. but that won't triple the price of an extension several years ago, as most of the price is labour.

    find some reputable local builders and see what they say.
  • Doozergirl
    Doozergirl Posts: 33,723
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    edited 15 November 2022 at 9:56AM
    aoleks said:
    a 30sqm extension doesn't sound right at £100k. the whole myth around "today's prices" is just that, an exaggeration. did materials get more expensive? absolutely, significantly more expensive. but that won't triple the price of an extension several years ago, as most of the price is labour.

    find some reputable local builders and see what they say.
    A 30 square metre extension wasn't a third of the price several years ago either, so I'm not sure what your point is.  

    Before the pandemic, most of ours were coming in at around £2,500 a square metre.  This is 32%

     £3,300 was perfectly possible pre-pandemic, depending on spec and location, but if you add a kitchen into the most popular spec with a bit of wall bashing and it would be easy to hit £100k.   That's without taking hyperinflation into account.  
    Everything that is supposed to be in heaven is already here on earth.
  • stuart45
    stuart45 Posts: 3,836
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    aoleks said:
    a 30sqm extension doesn't sound right at £100k. the whole myth around "today's prices" is just that, an exaggeration. did materials get more expensive? absolutely, significantly more expensive. but that won't triple the price of an extension several years ago, as most of the price is labour.

    find some reputable local builders and see what they say.
    How much would you expect to be paying?
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