Modular / pre-fabricated buildings

[Stones]

I was watching an old episodes of 'Building Dream Homes' which featured a £350K mobile home. Whilst not exactly homes for the population at large given the price, it got me thinking about this subject again.

When looking at different building systems back in 2009, I looked for companies that could deliver factory fabricated units which could simply be craned into site, with minimal finishing required thereafter.

I was wondering if anyone else had looked seriously at pre-fabricated buildings as an option? There is clearly a market for ready completed garden rooms/studios, but currently less so for habitable housing. Modular construction in certain sectors will continue where large numbers of identical units/sections are required.

As far as I can see from a look online, it can be done cost effectively, although this may be more of a challenge for one off or bespoke designs. I did find an article about the MoD building prefab houses for servicemen - can't believe the MoD would pay a significant premium for the housing it has to provide. The UK and EU certainly seem to have more companies offering this type of build system (compared to 2009 at any rate).

Materials are going to cost what they cost, but one would have thought there were economies of scale available once output reached a certain size. The big plus for this type of factory controlled construction for me is the protection of the build from the weather allowing it to continue without weather related delays,quality control in terms of installation of insulation and air tightness depending on the type of construction, and speed of onsite installation.

Transport however is expensive, especially if you have large distances to cover, with width and height restrictions dictating the size of sections and roof types that could be built. Based on the kind of dimensions used by mobile homes, I reckon I would have needed 7 or 8 modules, or 4 lorries to build my house. Much I suppose would depend on distance from the production centre, although in some remote cases, paying a high transport cost could certainly offset having to pay high travel and time costs for tradesmen building conventionally. 

Is our reluctance to embrace this type of construction down to collective memories and experiences of holiday mobile homes and post war pre-fabs? Other countries, (I think Japan has a large factory orientated house building industry) seem to be comfortable with the notion so why not us?

[ProDave]

There is at least one member here building his own "portable building"

And there is a company local to me that builds low energy portable buildings built in their factory and transported as modules that get fitted together on site.  I did look at that as an option for our build but currently they can't do 1 1/2 storey buildings.

For single storey modular buildings up to a certain size, you can be exempt from building regulatiions as they are classed as "caravans" even if they don't have wheels. The Highland council have produced a simple fact sheet that you can download here http://www.highland.gov.uk/downloads/file/1346/bst_018_caravans_and_mobile_homes If your building fits within those limits then it can be exempt from building control.  The same rules should apply to all parts of Scotland.

England and Wales are allowed to have a larger sized "caravan" than we are, something to do with the caravan  act in England and Wales being updated at some point but Scotland never had the same update, but I have yet to find any English definition of what qualifies as a "caravan" for building regulations purposes.

And yes I have memories of freezing in a "Terapin" portable clsssroom at school.

[Jeremy Harris]

I think one of the limiting factors is that all the modules have to within the size limits for a normal load on a truck to make any pre-fab system viable.  Our build was pretty much a prefab, as all the twin stud walls panels were already fabricated in a factory, so the erection was mainly just fitting a lot of sections together (the whole ground floor, to first floor flooring, was done in a day).

I think there's a lot more scope for doing things like Huf, with completely finished and wired panels, but something has to be done about the cost.  When we looked at HufHaus the costs were around £4000/m², which is way over most self-builder's budgets, I think.

[Crofter]

Ah my ears are burning. Yes, my build is designed to fit within the definition of 'portable building' as ProDave linked to above.

The definition is clearly intended to apply to prefabricated units, which can be in up to two sections and capable of being removed intact from their foundations. The limits on dimensions exclude eaves overhangs, gutters, etc.

I have chosen this build path because it alleviates me of the need for a building warrant. This in turn means that I can be much more  'DIY' about the project. I do not have to persuade anybody other than myself that things are not going to fall down, and i have no delays for inspections. The single biggest downside is that it may be difficult to mortgage the property, which in my case is not an issue. There have also been some repercussions on my choice of foundation design.

 

If I were to ever move the building, I would jack it up where it stands and back a tractor-towed low loader in underneath, then transport it across the fields to the road.

[ProDave]

There is also the untested issue of getting a VAT refund. No building warrant = no building control completion certificate. You do still need planning permission so would a letter from the council saying it is completed according to the planning permission satisfy hmrc to issue a VAT refund?  I look forward to Crofter testing this in due course.

[Jeremy Harris]

The VAT one is where we could really do with Colin in here, as he knows the rules on this like the back of his hand, it seems.  There has to be a way of getting some evidence of completion that would satisfy HMRC, I'm sure.  My dealings with them have been remarkably positive, they really do seem to want to help if you call them.

[Crofter]

In my case I am probably ineligible for a VAT reclaim anyway, unless we make the decision to move into the new house and rent out the old one instead. We are retaining that as a possibility, though.