Advice on SIP floor and foundation (garden building)

28 Mar 2014
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United Kingdom
I'm looking at putting a SIP building in my garden. Planning and building regs exempt however I want to build it to last, but to keep costs down where possible.

Dimensions 7m * 4.2m

Can anyone with experience of SIPs recommend the best way to do the foundation and flooring? I'm struggling to find appropriate technical guidance as most of it relates to housing and I don't plan to build that level of foundation.

I'm currently considering two options: concrete slab or plinths.

Main downside of concrete slab is lack of access to my garden, pumped cement would be needed, adding to the cost. There is also a slight incline in the garden that would require levelling, approx 1:20 slope.

Plinths would add to the overall height of the building, which is not ideal due to keeping eaves height below 2.5m for planning rules.

I am very aware of the need to ensure the OSB on the SIPs is protected and ventilated.

Are there other factors for or against the two methods that I have missed?

With either method can anyone suggest best practice construction, in terms of battens, ventilation and DPM?

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I am no expert in any shape or form but find SIPs interesting.

From what I have read today it seems to get the airtightness benefit you have to insulate the foundations and it all sounds like big money in the sense that you are only building a small one storey garden room. I'm thinking the complexity involved might make it uneconomic for your project.

Have you considered timber frame atall?

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