Any experience with SIPS??

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I’m in the early planning stages of a single storey rear extension on my 3 bed semi. I’m going to be self building, pretty much from the ground up. It’s going to be the full width of the house, so about 6m and 4m out so within permitted development hopefully.

My main hurdle before I get architects/engineers involved is to get the plan straight in my head. I’m fine with a traditional block and brick build, but I can’t seem to shake off the idea of SIPS. Other than internet research and some YouTube vids, I have no practical experience with them. Can anyone advise on what foundations they require? My ground is firm clay, and there is a sewer running under where the extension will sit, which I will be getting buildover permission for. The appeal of potentially no traditional footings and speedy erection (ooo err) is massive! Also, the ubiquitous bi-fold doors will be required, so do they require steelwork above, or just a heavy duty lintel?

Any advice/constructive criticism appreciated
 
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The footings are determined by the ground not the structure. So same as whatever would be used for masonry walls.

Whether the doors are top or bottom hung will dictate the type and performance of the support above them.
 
My main hurdle before I get architects/engineers involved is to get the plan straight in my head. I’m fine with a traditional block and brick build, but I can’t seem to shake off the idea of SIPS. Other than internet research and some YouTube vids, I have no practical experience with them. Can anyone advise on what foundations they require

SIPs would be expensive for a small extension, if you want that sort of construction go for timber frame.

Foundations for your extension will be the same whatever you put on it. To expand on what Woody has said: it is mostly ground stability that determines foundation spec rather than weight of structure.

Foundations are normally mass filled trench footings, depth depends on load bearing capacity of soil, shrinkability of soil, influence of trees (esp leylandii, oak, hawthorn hedge etc). Bottom of trench must be 150mm below invert level of drain.

Note that if you have large bifolds resulting in a small brick return either side, lateral stability might be an issue and a calc needed.

Be very careful with permitted development rules -is the rear if the house flat across the 6m?
 
Be very careful with permitted development rules -is the rear if the house flat across the 6m?

There is a old kitchen extension already that comes out 1m halfway across the rear.

Thanks for the responses. As I said, I’ll be getting calcs done and building control involved. I just want to get as much of it clear in my own mind first. I might do timber frame. As has been said, brick and block would probably be cheaper. The speed to water tight stage is what appeals, but then you have to issue of cladding and the junction between new and old
 
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I had an idea of using SIPS when doing my self build extension for speed and ease. I concluded it was much more expensive for a small project than traditional brick/block. Comes into its own when you’re building a whole house as the base costs remain the same.
 
When I built my timber frame extension, I got the materials and knocked up the wall panels under cover and over a period of time and then just fitted them all together over a few days to form the waterproof shell. This is effectively the SIPS process and concept.

But if you are a customer, then you should be really telling your designer the criteria that needs to be considered, and let him determine what is best in terms of design and how it is built. Otherwise you could end up having a poor ill though out scheme due to building in problems, high cost and waste that really should all be designed out.
 
When I built my timber frame extension, I got the materials and knocked up the wall panels under cover and over a period of time and then just fitted them all together over a few days to form the waterproof shell. This is effectively the SIPS process and concept.

But if you are a customer, then you should be really telling your designer the criteria that needs to be considered, and let him determine what is best in terms of design and how it is built. Otherwise you could end up having a poor ill though out scheme due to building in problems, high cost and waste that really should all be designed out.

That’s kind of the line I was thinking. I can get hold of blank sips panels reasonably cheap, and then adapt to the design. I’d happily design and build it from scratch, but I’m aware of my limitations. Not having the experience/knowledge of the long term effects of weather and the required structural/insulation properties, means I need the input of a architect. I know an architectural technician who is going to do our drawings, so I suppose his knowledge is what we will have to go with. I suppose once it’s done, brick is aesthetically there and I don’t have to faff about with cladding, which works out expensive all in!

I’m essentially an impatient sole, so come here to try and build the thing on paper while I’m waiting for the more trivial things like permissions and drawings haha
 
There is a old kitchen extension already that comes out 1m halfway across the rear

Be careful of the side extension rules -maybe post a simple plan drawing / sketch on here for some feedback in case its not PD.
 

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