Clay soil and garden room foundations

[Larry1990]

Hi Guys,

I'd like to build a garden room now the weather is starting to improve and I'm somewhat undecided on foundations. I thought due to sloping ground and tricky access ground screws would be better than anything requiring large amounts of concrete (access to back garden is through the house and the garden room site is up some steps and over 100ft from the kerbside so barrowing not an option and possbily pumping but I havn't spoken to any providers yet).

I spoke to one of the ground screw providers and they said they were fine for clay soil and 750mm should be sufficent for my plans (5x3M SIPS) but they do a 1100mm option if I wanted.

I've dug a hole and its at nearly 600mm before I reach the lighter more firmer type of ground (not sure what this is). Would I be mad to attempt this with ground screws? The area I live is a former Ganister mining area, I had a mining survey done as part of buying the house and there were no concerns, but there are a lot of rocks when digging in the ground (did some fence posts last year and had to remove a number of football sized rocks).

The neighbours have a garden room (timber framed and uninsulated) and its on a concrete slab, they don't know the specs and the guys used a mixer for it, with how soft the top clay is pouring a 100-150mm slab feels like it might go for a ride over the years.

Should I avoid the screws and just concrete or am I just overthinking things?

Cheers

Larry

 

[KenGMac]

As for the ground under your feet, suggest you check out "I Geology" a web based App, works very well on an I pad that will allow you to get a better grip on the strata.

As for something like [say] Shire piles, in your situation I would go for it. a lot better than trying to get rid of a load of soil over that distance.

Ken.

 

[Larry1990]

Hi Ken,

Thank you for the suggestion, I don't have anything apple based to install it on but I managed to take a look elsewhere on the BGS site and it suggests its alluvium where I am.

I spoke to the ground screw centre (I'm looking to DIY as much as I can) and they told me they even have mortgaged houses built on their foundations, its great to get a thumbs up from an independent source as well (and I didn't fancy lugging a lot of sand, stone and cement).

Cheers

Larry

 

[Leejay]

Hi Larry,

Could I ask who you used for ground screws please?
In building a summer house and have very clay soil.
Ground screws would be ideal.
I've looked at The Ground Screw Centre and they do 750mm screws...

 

[Leejay]

Sorry, just reread your reply above and see you asked ground screw centre.
Did they say their 750mm screws are okay in clay soil?

 

[KenGMac]

Leejay, good afternoon.

Several companies in this field.

Check out "ground Anchors " and screw piling.

As far as i know "Shire piling" may ?? be market leader, no idea about costs.

Ken.

 

[Larry1990]

Sorry, just reread your reply above and see you asked ground screw centre.
Did they say their 750mm screws are okay in clay soil?

Hi Leejay,

They were really helpful and said 750 should be fine for clay soil, they also said they could do a longer screw (1100 IIRC) for not much more money but I'd have to use their pro ratchet installation tool.

In the end I was offered another job which I will not be working from home for do I didn't build it after all!

Good luck with your project.