Waterproofing a building below ground level?

[perky416]

What do you mean by step?

The wall will be full height on the outer skin, and only 2 blocks high on the inner skin.

I was going to build both skins straight onto the flat top of the foundation exactly as per my picture. Is this correct or the wrong thing to do?

 

[freddiemercurystwin]

It's correct if you don't mind it being there. If for instance you were going to line the inside with insulation and plasterboard it'd get in the way but as you're not then it doesn't seem to be a problem.

 

[perky416]

Ohhh im with you. Yeah it will be in the way lol. Im going to plaster inside. To bring the outer course level with the inner i was going to use 100mm battens and build a stud wall, effectively on top of the inner course. Screw the plasterboard to the battens and use adhesive at the bottom of the board where the block is.
Im likely going to clad the exterior rather than render it. I can plaster, but have never rendered, i didnt want to risk it looking rubbish and given i was quoted 1k to plaster a 10sqm ceiling recently, im guessing to have the whole build rendered (around 50sqm) will cost a fortune in comparison to cladding.

 

[bolst3r]

how did you get on with your building? I'm needing to excavate for an outhouse for similar reasons too, and i'm weighing up the pros and cons of each solution. My building was going to be a timber structure on a concrete slab, I was thinking of a slightly different method as I have enough surround area to create a trough all around it (50cm = front and sides, 20cm back)

So something like this... any thoughts?

 

[freddiemercurystwin]

The above only works if you've dug a test pit over the winter and seen what the water table does. Even then it's not foolproof.

 

[bolst3r]

back to the drawing board on my build then. As it was going to be a timber construction on a concrete slab it seem more problematic?

 

[Bradp97]

how did you get on with your building? I'm needing to excavate for an outhouse for similar reasons too, and i'm weighing up the pros and cons of each solution. My building was going to be a timber structure on a concrete slab, I was thinking of a slightly different method as I have enough surround area to create a trough all around it (50cm = front and sides, 20cm back)

So something like this... any thoughts?

View attachment 302535

This is similar to what I want to do timber building on concrete slab below ground level. Around 15 to 20cm with a single skin of blue brick to ground level or just above with the dpm wrapped up the sides and bitumen the bricks inner and outer, but looking at the lads drawing here with the two skins and dpm between looks like that's what I might have to do. The blue bricks are going to take me to ground level or over then I'll building timber frame on top seems crazy for 15 to 20cm extra hight on the inside but this will be a gym when done and it will give me around 2.4m ceiling hight fully done so pull up and over head pressing not be a problem

 

[bolst3r]

This is similar to what I want to do timber building on concrete slab below ground level. Around 15 to 20cm with a single skin of blue brick to ground level or just above with the dpm wrapped up the sides and bitumen the bricks inner and outer, but looking at the lads drawing here with the two skins and dpm between looks like that's what I might have to do. The blue bricks are going to take me to ground level or over then I'll building timber frame on top seems crazy for 15 to 20cm extra hight on the inside but this will be a gym when done and it will give me around 2.4m ceiling hight fully done so pull up and over head pressing not be a problem

it is a lot of work for that extra 15-20cm. I also decided if I do it I wont worry about doing a warm deck roof as this will give me a little more clearance, and as i'm not using it all day as an office i'm ok with the compromise

 

[Bradp97]

It is more work with bricking it, and doing a perimeter Foundation but this doesn't need to be as thick with me not loading on it it's only 2 or 3 courses high and finished coping or fascia board.

I would still be digging to slab it... Dig! Mot1! Sand! Concrete! Just digging lower and setting the slab top finish to 15 to 20cm below ground for the hight inside it's more work but worth it as it's risk going over 2.5 or get planning and they want drawings properly draw and this is a diy garden room it's already going to cost over 4k to build so this seems the way to go just mean all I have to do is add another brick course on the outside to sandwich dpm. This would work out cheaper than the proper way it's done for house... Foundation build wall with bricks dig out the area inside hardcore sand dpm then concrete it. Very costly for a garden room gym

 

[Bradp97]

This is what I plan to do 3 bricks now giving 22.5 CM extra height making my 2.5m to 2.7m