Foundations for The Hide

[G and J]

Dangerous things, days away from site, it turns out.  I’ve got me notebook out and for a variety of reasons I’m considering the merits and costs of bringing forward the plans for the hermitage (aka the Hide, or Pigpen) at the far end of our garden.  

 

It’s planned as roughly 5m by 5m with a very shallow pent roof, timber framed and timber clad to match the house, but in my notebook I’m not even out of the ground.  Soil conditions are a base of silty sand with some gravel, which apparently is fine for strip foundations except that base doesn’t start till 1.2m down below some lovely soft, silty sandy soil.  It’s just over 60m from the road with no other access available.

 

Between the road and the Hide are some lovely trees and shrubs and to preserve that it’s wheelbarrow access only.  

 

So I either dig by hand an awful lot, hand mix some concrete (I’ve recently learnt what a starter bar is and no, it’s not something on a very early combustion engine), block up lots and top that with beams and blocks; or I dig a raft and pay out lots (I’m told) on a pump to move concrete from a lorry as trying to mix a raft by hand is not likely to end well.

 

Or something else?  It will be a combined workshop and gym, but not accommodation.  I’m not keen on wooden bases as I’ve concerns on longevity and inadvertently creating a rat hotel.

 

What am I missing? Are there any other options I should plan/cost out?

[JohnMo]

Why bother digging down at all. Just do the same as a garden room. Plastic grids filled with gravel, or slabs set on concrete are options. As well posts set in postcrete. Then build up from there. Pre designed and supplied as a kit garden rooms are great value, the 70mm thick ones are very robust. Just add insulation.

[G and J]

Hmmm.   Each time I look at garden rooms on the net I get depressed.   There’s so much glossy sales and I’ve convinced myself I can build cheaper and more solid than I can buy.   We’ve gone panelised timber frame for the house, and I guess this is my chance to actually put together a building from base components.  
 

Rereading that it does sound like a recipe for more work than really necessary.  Sigh.

[Redbeard]

Post and beam. Search Segal Method. I have built from small sheds to a garage/workshop with the floor plan of a fair-sized bungalow. Some just sit on pads (conc slabs on a concrete-filled pit for each post for heavier buildings; slab only if the building is light and you are sure of the density of your soil. But if the building is too light do you need to hold down? Could be as simple as some threaded rod or perforated strap embedded in the 'pit' footing and fixed up to the post. May not be as quick as stud-frame but it's such fun!

[JohnMo]

This is how I did mine

https://forum.buildhub.org.uk/topic/31017-summer-house-insulation/

[Iceverge]

I did something similar to what @Redbeard mentioned above. 

 

Dug 4 holes, used car tyres as formwork for concrete pads, set some 225mm corrugated pipe in the tyres and cut them level  Inserted 24mm (I think) threaded bar in the centre of the pipes and filled the pipes and tyres with concrete. 

 

Used this for a base for my office.Worked fine. 

 

 

Wouldn't do it again, too bouncy (and I like bouncy floors!) .

 

Next time DIY passive raft from EPS I think or else strip foundations with a double layer of OSB floated on the insulation.

 

 

[G and J]

8 hours ago, Redbeard said:

Post and beam. Search Segal Method. I have built from small sheds to a garage/workshop with the floor plan of a fair-sized bungalow. Some just sit on pads (conc slabs on a concrete-filled pit for each post for heavier buildings; slab only if the building is light and you are sure of the density of your soil. But if the building is too light do you need to hold down? Could be as simple as some threaded rod or perforated strap embedded in the 'pit' footing and fixed up to the post. May not be as quick as stud-frame but it's such fun!

If I’ve understood that means a suspended wooden floor, with less concrete.   I can easily imagine the merits of such an approach in building terms.  
 

Rightly or wrongly I’ve got my heart set on a solid base.  Solid meaning concrete or, as a second choice, bnb.  
 

Trouble is what’s there right now is a crater, just over 1m in the centre where I dug out a three stemmed conifer root.  And I’ve two 25’ but very weedy silver birches to come out at the edges of what will be my building too.  In combination with the light soil I think it makes a solid floor impossible.  Likewise a paved sub floor methinks.  
 

Hence the block and beam option.  

[G and J]

6 hours ago, JohnMo said:

This is how I did mine

https://forum.buildhub.org.uk/topic/31017-summer-house-insulation/

Thank you for that @JohnMo .

 

Very interesting read.  If we weren’t cladding to match the house it would be very tempting.  Sadly I don’t think I can replicate your solid paved subfloor. 

[G and J]

3 hours ago, Iceverge said:

I did something similar to what @Redbeard mentioned above. 

 

Dug 4 holes, used car tyres as formwork for concrete pads, set some 225mm corrugated pipe in the tyres and cut them level  Inserted 24mm (I think) threaded bar in the centre of the pipes and filled the pipes and tyres with concrete. 

 

Used this for a base for my office.Worked fine. 

 

 

Wouldn't do it again, too bouncy (and I like bouncy floors!) .

 

Next time DIY passive raft from EPS I think or else strip foundations with a double layer of OSB floated on the insulation.

 

 

Love the idea of DIY passive style raft.  I think you need fairly solid ground to base that on which would mean greater than a 1m deep layer of polystyrene - 25m3 of that would cost  and take some doing and I think that means I’m back to pumping lots of concrete for the raft.  
 

The floating double layer wooden floor is definitely part of the plan though.   I’d go for caberdeck type over OSB, partly as I won’t be carpeting.  

[Alan Ambrose]

Well tamped MOT3 only? Also, Dunster House-style ‘log cabins’ are pretty good and quick to put together.

[JohnMo]

2 hours ago, G and J said:

don’t think I can replicate your solid paved subfloor

Just use this then, your way over thinking.

https://www.ecodeck.biz/plastic-shed-bases/

[JohnMo]

2 hours ago, G and J said:

If we weren’t cladding to match the house it would be very tempting

That's easy, you do external insulation and clad. In fact that is way easier than what I did. 

 

 

[G and J]

14 hours ago, JohnMo said:

That's easy, you do external insulation and clad. In fact that is way easier than what I did. 

 

 

I’ll cost up my ‘stick built’ plans and contrast.  Once I’ve worked out how to build my nuclear war proof, 30 year expected life, base.