Preparing ground for summer house

[Jason Judge]

Okay, my next job: put up a summer house in the garden.

We have the house itself, one of the 7ft corner units manufactured by Solis= and sold by just about everyone at wilding varying prices and brand names.

I have a patch of lawn in a corner, and need a solid surface there to place= it on. I have nine square paving slabs and eight strips of paving edging (=

15cm x 90cm paving slabs) that can be arranged into the right shape and siz= e.=20

I would like to surround the summer house with a strip of gravel soak-away,= because water has been a bit of a problem lately, so I guess the foundatio= ns need to be "self-supporting", since they won't have lawn soil to push up= against it.

So - how would you recommend I go about this? I suspect I need something co= ncrete-based around the circumference, to keep it all in shape, but just sa= nd or gravel in the middle (under the paving slabs)? How deep would the soa= k-away need to be, so make any difference (and I know that is a "depends" a= nswer, and may depend on whether a layer of gravel under the whole thing se= rves as a big, wide soakaway, perhaps)? What kind of depth would I need to = go down to? I wouldn't have thought I need to go down too deep, as this is = now a big heavy thing.

And if I'm using the wrong terminology, it's because I'm not a builder - ju= st a home-owner.

More of the grass around the summer house may (or probably will) be paved o= ver in time, so this is one reason I need to be careful about water. The ga= rden is enclosed by a wall, and rain water does not leave the garden onto p= ublic land or other people's property.

Thanks.

-- Jason

[The Natural Philosopher]

and sold by just about everyone at wilding varying prices and brand names.

on. I have nine square paving slabs and eight strips of paving edging (15cm x

90cm paving slabs) that can be arranged into the right shape and size.

because water has been a bit of a problem lately, so I guess the foundations need to be "self-supporting", since they won't have lawn soil to push up against it.

concrete-based around the circumference, to keep it all in shape, but just sand or gravel in the middle (under the paving slabs)? How deep would the soak-away need to be, so make any difference (and I know that is a "depends" answer, and may depend on whether a layer of gravel under the whole thing serves as a big, wide soakaway, perhaps)? What kind of depth would I need to go down to? I wouldn't have thought I need to go down too deep, as this is now a big heavy thing.

a home-owner.

in time, so this is one reason I need to be careful about water. The garden is enclosed by a wall, and rain water does not leave the garden onto public land or other people's property.

for a lightweight shed, simply level, lay a ring of slabs around the shed exterior and stick a brick on each and shove that under the main floor joists.

[Phil L]

It sounds like you've already designed something in your head, but it's not gone down in print too well.

What do you mean 'self supporting foundations' Are you intending having the summer house raised up higher than the rest of the garden?

Remove the grass - just the grass - no soil, to a depth of about 2 inches. rake over sharp sand and level, add to this a bag of dry cement and rake this into the sand. Lay paving on this. erect summer house. once flags have set in place (after a few days or so) dig a spade's depth and width trench around perimeter and infill with gravel

[Jason Judge]

No, the intention is not to raise it above ground level. I would like to su= rround it with a small trench filled with gravel - partly as somewhere for = rain water to go, and sink away. In my head, gravel would not support any s= ideways pressure, so I am assuming if the foundations (or whatever is there= ) is not prevented from squeezing sideways like a sandwich full of chutney,= then it may sink. Maybe with the weight spread out, this is not a problem?

Cool. That sounds straight-forward :-)

Is that depth of two inches from the top of the flags or the bottom of the = flags? I'm guessing it would be the depth of just the sand/cement mix, othe= rwise the sand layer would only be half an inch thick once the depth of the= flags are taken into account, which does not seem like much to me.

[Phil L]

It shouldn't be a problem, there's not that much weight in a dozen flags and a summer house, but ISWYM, the end flag may 'creep' slightly if it's got somewhere to go and this does happen....you could use edgings, although the

150mm ones you've got probably aren't deep enough, I'd be tempted to use 300mm ones (half flags) concreted in 200mm deep and then pave up to these. Make your soakaway wider, about 18 in, but shallower, say about 6 inches, so as not to undermine the concrete or edgings

You want the finished surface to be slightly higer than the lawn, so take off 2 in of grass and soil, add 2 inches of sand/cement and 2 in of slabs and it shouldn't fill up with water

[Jeremy Nicoll - news posts]

Gravel resists sideways pressure reasonably well. I have a gravel drive and when I bring the car in, the gravel doesn't all get squeezed out to the side! Nor does it appear to move much when I walk on it. My shed stands directly on the gravel.

On the other hand, the gravelled area here covers what used to be a sloping down ramp from the street and a garage (now demolished)'s floor and the remains of its walls. The garage area was filled with hardcore before a weed control fabric and then gravel was laid on top. The overall area does have concrete edging on it, but it was put there not so much to stop gravel squeezing out (though I suppose it must do) but to make a neat edge where otherwise there'd be several inches depth of hardcore and gravel visible.

[Jason Judge]

Looking around the internet at descriptions like this, they tend to recomme= nd a mix of 1:8 (cement to sharp sand). Is that what I am aiming for?

With sand/cement 2" deep and a total area of 6ft x 6ft comes to 0.05m x 2m = x 2m =3D 0.2 cubic metres

At 600kg per cubic metre of raw material (source: Screwfix site), 0.2 cubic= metres is about 120kg of material (600x0.2), which is five bags in total (= at 25kg per bag).

Digging a little deeper than two inches, five bags of sand to one bag of ce= ment would do it, with a little cement left over to tidy up the edges.

If I wanted to do the edges down to 20cm deep and 10cm wide, with firmer co= ncrete, to keep everything together, then I would need to add that on (~8m = length x 0.2 x 0.2 =3D 0.16 cubic metres - another 3 or 4 bags - a surprisi= ng amount). Perhaps I can half that using old house bricks around the edge.

Sound about right? Or have I dropped a decimal point somewhere. 5 to 6 bags= of material for a 2m square area down to 2" with a dry mix, and half as mu= ch again for a deeper border, with some old house bricks in there, easily p= ulled out of skips in the area if I don't already have enough laying around= .

-- Jason

[Dave Liquorice]

Yeah, I don't know why people insist on solid concrete rafts or paved areas under sheds (summer houses). Nothing will grow under there, too dark and dry. The OP mentions he doesn't want to raise the summer house off the ground, I feel that is a mistake. Being timber it needs good ventilation to stop it rotting (treated or not), wether it is mounted above bare ground or a useless paved area.

Not sure about the french drain either. Does the roof have a gutter and down spouts or is this to provide a landing place and drain for rain running straight off the roof? For the latter you probably need something at least a foot wide maybe 18" and about 6" deep. Filled with 20mm or so "gravel". Pea gravel will be washed out by the momentum of the falling water.

[Jason Judge]

Okay, so steer clear of fine gravel. There is no gutter at the moment, but = no reason why I can't add one. The summer house is fitting into a corner of= the garden, with walls on two sides. The corner has an angle of about 108= =B0, so there is a wedge-shaped gap behind the rear two walls (remember, it= 's a corner unit). Once reason for the French drain (new name to me;-) is t= o fill that gap, since I don't want anything to be growing back there.

There will be similar wedge-shaped gaps at the front too.

The paving slabs I am using with the hope that they will not be wicking wat= er up from the ground. A neighbour was chucking them out, so it has saved h= im a trip to the tip, and me a trip to the DIY store. The ground here, near= the coast, is never dry. Ever.

The floor joists are quite thin - about 1.5" high and spaced about a foot a= part. They would need supporting over the whole floor area. I could put som= ething more substantial in and raise the thing a little, if more ventilatio= n would help.

-- Jason

[Jeremy Nicoll - news posts]

Indeed, but water may well pool on top of them.

One advantage of having a shed standing on gravel is that water drains away very easily.