Howdy! Another garden room selfbuidler here needs early advice on foundations.

[dai jinks]

Howdy, 
Like others i want to build a man cave livable room and the end of the garden.
Its gonna be 2440 x 2440 x 2500 plus a small side extention same hieght for toilet and shower to the right. (very cramped i know but doable).

Currently my dying shed is there but thats all to go.

I share a solid rear boundary brick wall 215 with some extra piers my side in it. ( it used to be a cavityless factory outer wall)
Its has pertruding double flat tile drip and a soldier coarse on across the top. Total 2650 high from ground. My side, there is damp on 1/3 because the niegbour has build up all sort on the other (a small high disused fish pond ).

I'm to make up off this wall a standard timber frame and flat roof.
My question is this so far;

I already have 175mm poly slabs for floor insulation.
I want the threshold of doors and the floor to be say 25 mm up from level with outside ground on completion.
I don't want to pour one big slab but rather build a 215mm block perimeter on a footing, then infill with the insulation slab to levelish with the blocks and my floor cover on top of that.
What do I need to additional do to make this level floor water and damp proof from the outside ground ( and underneath i guess) before I build my frame work on top.

Anyway thats me and my dream for this years nice weather. Any tips and guides be great.
Thanks

[Canski]

You'll probably need to be higher than 25 mm to floor level off ground level. See Oakwood Garden Rooms on Youtube for ideas for foundations. 

[Temp]

6 hours ago, dai jinks said:

I share a solid rear boundary brick wall 215 with some extra piers my side in it. ( it used to be a cavityless factory outer wall)
Its has pertruding double flat tile drip and a soldier coarse on across the top. Total 2650 high from ground. My side, there is damp on 1/3 because the niegbour has build up all sort on the other (a small high disused fish pond ).

I'm to make up off this wall a standard timber frame and flat roof.

 

Not sure I would do that. I think I would buy a garden buildng/kit an erect it close but not touching the wall.  Or build your own "kit" and erect it rather than building onto the wall. Eg build and clad a wall on the slab and lift it up. The roof/verge that side will also need planning in advance 8f you want it too close to the wall to stand and swing a hammer in the gap. 

 

You could try tanking your side of the wall but it's unlikely to work well because the wall is already wet and the water pressure is pushing the tanking off the wall. Tanking should be on the other side really. The damp wall may even appear to get worse when your building stops the water evaporating away.

 

6 hours ago, dai jinks said:

What do I need to additional do to make this level floor water and damp proof from the outside ground ( and underneath i guess) before I build my frame work on top.

 

What I did was make the top of my slab above ground a few inches. Then I put a course of engineering bricks around the edge inset slightly. The building structure rests on a DPC on the brick course. I arranged for the cladding to overhang the edge of the slab so rain running down the outside drips onto a gravel filled trench around the slab not onto the top of the slab. The cladding stops 1" or so above the slab. Any water that gets blown under the bottom of the cladding onto the top of the slab is prevented from getting inside by the brick course. My roof overhangs the door like a stable so I didn't need a step up to prevent water getting under the door. 

 

I might be able to find a sketch drawing I did somewhere.

 

 

 

 

 

[dai jinks]

OK yes please to the sketch you have would be great to visually get your system. Thanks.

As the niegbour is an elderly council tenant, one day, all that will be removed back to level.

But I'm tempted to ask them if I can go and dig it out and just bag it up and leave it there neat for that time.

I like the idea of making up the entire rear timber wall ( as it has to be insulated later anyway and needs to be 95 mm deep timbers plus external covering - what do you recommend as the skinnest final sheeting to use under the breather membrane)?

 

im gonna have the rear wall slightly stepped off for ventilation from both sides. but I will fix the top roof timber flush to the wall to just under the existing tile coarse as its dry as a bone up there and it acts well to move any rain waters away from the soldier coarse etc on the roof.  (proberbly just below it, a bevelled 2 x 2 rip along the whole length prior to coverings).

As you may see in the images, the rear wall is about 15 degrees off perpendicular to the both fences.

 

It also has a staggerd build with an old hollow steel stanchion inset tight in the middle left - see sketch, (which in a dreamy way would make a great chimney) but its too tight and can't be insulated)

Anyway,

I will maintenance the angle as every mm counts in this small urban 4 x 10 garden.

A fella told me, if there is not a single brick or block layed in the structure, then you do not need planning permission and just wait around 4 years before you declare the structure existence in situ and all will then accepted.( I might be slightly off here with the dodge)

 

Is this just tosh? 

Thanks all.

 

 

[Temp]

This is the basic idea of what I built...

 

The basic frame was 4x2 and 4x4 in the corners. Clad with 12mm WBP plywood and a vapour permeable membrane (VP400). Then battens and cladding boards. The WBP prevents racking due to wind loads.

 

If I was going to insulate it I'd put a DPM down inside then insulation and boards but it was intended as a workshop.

 

Construction was interrupted a few times by..

 

 

 

[Temp]

PS: I wasn't worried about the height as I needed planning permission anyway. That might be more of an issue for you.

[SteamyTea]

On 11/03/2023 at 22:02, Temp said:

Construction was interrupted a few times by..

 

Great Crested Newts are their favourite supper.