Hi,
I have followed some of the threads about 'surface foundations' vs 'traditional foundations' with interest and take the point that there is no substitute for digging down a metre or so.... but, what would you suggest as the best/cheapest/greenest way to proceed?

My logic is that SIPs for the floor, walls and roof of a building 11M x 5M are heavier than a 'caravan' but lighter than a 'house', so should need less than 'house' foundations.

I am tempted by the following ideas:

> thin concrete slab like a static caravan site and buy a chassis from http://www.bankside-patterson.co.uk/chassis/ng.aspx

> bury one layer of recycled wooden/concrete railway sleepers and put 2 to 3 layers of wooden sleepers on top (leave gaps for air circulation.

> minipiles of the concrete or screw in type with wooden or steel beams on top (6 piles for the size stated).

I like the sleeper solution the best, on cost grounds.... but what do you think?

rgds

Graham

Hi Tony,
ground type is neither solid rock or pure clay. I am looking for an answer for 'normal' soil conditions. My expectation is that it would have to pass building regs but not insurance backed guarantee (i don't need a guarantee if I am looking to live there rather than sell it).

thanks

Graham

SIPs are not really recommended for floors, but might be ok (ish) if very well supported and lightly loaded.

As for foundations, it depends on ground conditions and what ground floor structure you go for. Perhaps piles with a concrete ring beam infilled with timber joists suspended above the ground.

Posted By: glerwilla SIPS 'box' with a flat roof and MHVR seems fine to me?

I like that idea too, keep it simple.

Posted By: Peter_in_Hungarybuild something that is saleable

Does that not come down to future land values. A building plot without anything on it may be worth more than one with something on it that has to be torn down and removed.
Begs the question 'is it the plot or the building that adds value'

Posted By: TimberLong term creap performance of SIPs used in a horizontal situations is not good

Think we covered shrinkage in SIPs somewhere else, it is my only worry about it.

Posted By: TimberSIP flat roofs can be complex, and it is far better to use a timber joisted warm flat roof system when compaired with a cold SIP roof with ventillation requirements

How so? I can't understand the difference between the condensation risks of different insulation types apart from how the absorb moisture and where they absorb moisture, but maybe I keep missing something

Looking at the chassis pictures on the link in the first post, I don't personally think that there would be any problem at all with using SIPs for the floor. The support from the galvanised steel frame looks to be far better than that you'd get from ordinary floor joists to me.

Posted By: TimberSIP roofs are classified as cold roofs

Ah

Though I am not sure why they have to be, probably price.

Is cost a factor, I suspect that cast in situ concrete ring beam with strategically placed mini piles would work out cheaper than the chassis and metal screw pipes

You're right, J. At a push (no pun intended) you need to be prepared for a challenge to prove it can actually be moved, even an inch. And the inverted commas in the thread title won't exempt you from that requirement.

Posted By: JSHarrisI believe you need to retain the chassis and vestigial wheels in order for the building to be classified as mobile, and hence free from some of the regulation that applies to permanent dwellings.

I was reading a website about timber garages. It said that an advantage of building a garage from timber rather than block is that it is then classed as 'temporary' by the planners, with a claimed advantage in terms of getting permission. Does anybody know whether that is true? And would it have any bearing in this case?