Garden Room - Floor below ground level?

[darkkent8]

Hey all,

I am looking at building a garden room - I have the overall plan and materials sorted however i know there is 2.5m height restriction with these things

I am trying to maximise the headroom and also have a warm roof construction rather than a cold roof

My idea is to dig down and build part of it underground so that you step down into the build and have more headroom

I wanted to use either concrete blocks/thermal blocks below the ground but of course there is going to be water ingress etc. Is there any good way of water proofing the underground bit?

i was thinking tanking slurry on the inside? Any other ideas?

Thanks for all your help

 

[mrrusty]

Why don't you just get PP? it'll cost you ~£250 which is way under the cost of digging down. If you are allowed PD then there is little reason to refuse PP. On your PP application make a comparison to the largest building you could build under PD and show how your PP plans are more reasonable.

 

[darkkent8]

I'de rather not go through the hassle plus, i have most of the materials and machinery needed already. Also just due to the position and neighbours i am sure they will shoot down the idea

 

[mrrusty]

Also just due to the position and neighbours i am sure they will shoot down the idea

The neighbours can only make a valid objection if there is something valid to object to. The fact is you could build a 2.5m high outbuilding right up against the boundary under permitted development. Make even a small concession to what you are allowed under PD in a planning application and it is likely to pass - perhaps a pent roof 2.3 at the boundary but 2.8 at the front aspect. There is little hassle - you download the location and site plans from the internet (£10ish), and a simple hand-drawn 1:100 scale drawing of the different plan and elevation of the building is enough. The fee will be £250ish. If PP fails you still have the PD option. I doubt you will successfully waterproof a below-ground structure unless you spend big £££ on both structure and drainage,- all you risk building is a covered pond.

 

[Loofah]

More certain results by building above ground, however there is this stuff https://www.permagard.co.uk/advice/foundation-wall-waterproofing-guide
Have no idea if a good solution or total garbage

 

[cdbe]

Far better lowering the adjacent ground level and providing perimeter drainage, unless you would end up below the water table.

 

[freddiemercurystwin]

There are a few ways to do this, I would not consider an internal render as one of them though, for a new build. The devil's in the detail and ensuring your dpm or membrane at floor level is linked to your wall membrane is the key. An internal render will not allow that. As mentioned lowering the ground level all around is far simpler if the drainage permits it.

 

[darkkent8]

Thanks for you replies

I am going to use an auger to drill a couple of holes and fill with pea gravel just aid with any drainage

Other than that i am think of usings two layers of DPM one from under the insulation and the other from under the slab itself and wrapping up the outside of the walls.
I also have a bunk of black jack left and additive to make the mortar waterproof so will also use that

Lastly i could use some tanking fluid on the inside but i think that may be overkill

I am open to any more ideas, if not i will let you know how it all goes

Thanks again

 

[mikeey84]

Surely using the tanking slurry on the outside would be better?

 

[John D v2.0]

The pressure of even 10cm of water would be 1kn/m2, which may not sound much but when it's inside even the tiniest movement gap it will let plenty of water through. I have no experience but I would have thought for economy you'd either need a fully supported watertight membrane or a pump in the inside to deal with any moisture.

 

[Cha0s]

Did you end up building below ground?