Green Building Forum - Suitable foundations for a 'park home' made of SIPS

Suitable foundations for a 'park home' made of SIPS

glerwill — Tue, 05 Jun 2012 15:31:41 +0100

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

Suitable foundations for a 'park home' made of SIPS

tony — Tue, 05 Jun 2012 16:08:43 +0100

Depends if you can handle it moving a bit or not and if it has to pass building regs/new homes insurance backed guarantee etc

Foundations are not deep because of the weight but so that they dont move.

If you build on rock you dont need any foundations, what is your ground type?

Suitable foundations for a 'park home' made of SIPS

glerwill — Tue, 05 Jun 2012 16:54:45 +0100

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

Suitable foundations for a 'park home' made of SIPS

woodcutter — Tue, 05 Jun 2012 17:28:09 +0100

Hi The wood railway sleepers will rot if they have any exposure to air and moisture no mater how much they are treated.

Suitable foundations for a 'park home' made of SIPS

Timber — Tue, 05 Jun 2012 17:33:30 +0100

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.

Suitable foundations for a 'park home' made of SIPS

glerwill — Wed, 06 Jun 2012 07:24:05 +0100

Thanks woodcutter - certainly 'treated' fence posts rot.... but I have some treated hardwood sleepers in my garden now - they have probably done 60 years in the ground and seem mostly still good.... I'm not necessarily looking at a 300 year house - I could be jack and say I'm 53, and just something that uses minimum energy and would see me out would be good.... but that doesn't really qualify as 'green'. I would be content with another 60yr+ lifespan.

Timber,
is there any information available about 'SIPS not reccomended for floors' - a SIPS 'box' with a flat roof and MHVR seems fine to me?

Suitable foundations for a 'park home' made of SIPS

SteamyTea — Wed, 06 Jun 2012 07:27:11 +0100

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

I like that idea too, keep it simple.

Suitable foundations for a 'park home' made of SIPS

Peter_in_Hungary — Wed, 06 Jun 2012 08:27:51 +0100

Glerwill - I accept that you want to live in the place and not sell it, but IMO you should build something that is saleable because you can't predict the future. I can see building regs. having a problem with railway sleepers. I would side with Timber - concrete piles with a concrete ring beam. The whole thing would be cast in situ as one entity with the pile re-bar tied in to the ring re-bar.
Concrete ring beam is common practice over here for both new build and for repairing / tying together stone/rubble buildings when re-roofing (to stabalise the walls and prevent the roof pushing the walls apart.) The construction can be DIY or ready-mix.

Suitable foundations for a 'park home' made of SIPS

SteamyTea — Wed, 06 Jun 2012 08:44:09 +0100

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'

Suitable foundations for a 'park home' made of SIPS

Timber — Wed, 06 Jun 2012 12:14:56 +0100

glerwill - Long term creap performance of SIPs used in a horizontal situations is not good. Over time the SIP sags. Talk to SIP manufacturers about it and see what they say, but I understand that the use of SIP for floors is fairly unanimously agreed to not be viable.

As for a SIP box with flat roof - not as simple as you might think. SIP 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 etc.

Suitable foundations for a 'park home' made of SIPS

SteamyTea — Wed, 06 Jun 2012 16:09:10 +0100

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

Suitable foundations for a 'park home' made of SIPS

Timber — Wed, 06 Jun 2012 16:42:12 +0100

Not shrinkage, deflection creap.

SIP roofs are classified as cold roofs, and so need suitable ventillation below the waterproof roof membrane, above the SIP. In large span situations, the use of cold flat roofs are normally probited due to ventillation problems, plus we all agree (i think) that warm roofs are better.

Suitable foundations for a 'park home' made of SIPS

JSHarris — Wed, 06 Jun 2012 17:15:04 +0100

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.

Suitable foundations for a 'park home' made of SIPS

Timber — Wed, 06 Jun 2012 17:42:16 +0100

Ah, I must confess that I didn't click through the link to the chassis.

Looks like a good lot of support for the SIP, so should work, but SIPs don't span well as floors generally speaking.

Suitable foundations for a 'park home' made of SIPS

SteamyTea — Wed, 06 Jun 2012 17:45:18 +0100

Posted By: TimberSIP roofs are classified as cold roofs

Ah

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

Suitable foundations for a 'park home' made of SIPS

glerwill — Thu, 07 Jun 2012 08:01:05 +0100

Thanks for all the comments - you have given me a lot to think about.

So - ok - dump the sleepers idea.... dump the concrete slab idea..... and the concrete minipiles idea....

Keep the idea of the Chassis and the SIPS floor and walls and consider 'metal screw piles' to allow stability and adjustment for the building. I would guess you would need about 6 for an 11 x 5M building....

http://www.gtl-partnership.com/what-are-helical-piles.html

So - what about the roof - some park homes have a pitched roof and use SIPS with a large central beam for support. How do they deal with the cold roof (ventilation required + heat losses) VS warm roof?

rgds

Graham

Suitable foundations for a 'park home' made of SIPS

Peter_in_Hungary — Thu, 07 Jun 2012 08:17:15 +0100

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

Suitable foundations for a 'park home' made of SIPS

JSHarris — Thu, 07 Jun 2012 09:03:02 +0100

Posted By: Peter_in_HungaryIs 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

I 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.

Suitable foundations for a 'park home' made of SIPS

Joiner — Thu, 07 Jun 2012 09:10:00 +0100

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.

Suitable foundations for a 'park home' made of SIPS

glerwill — Thu, 07 Jun 2012 11:28:03 +0100

Thank you - yes, cost is a factor. Cheap and simple to build. Cheap bills Save money on land via a long thin plot that would be unattractive to others.

Any chance of a link with pictures for the concrete beam and concrete piles? I can't quite visualise how it would support the floor of the building at the moment..

rgds

Graham

Suitable foundations for a 'park home' made of SIPS

djh — Thu, 07 Jun 2012 13:36:36 +0100

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?