Garden room on wonky slab

[MDK 24]

Hi all - hoping you can give me some good advice on how to prevent water ingress in my garden room, hope this qualifies as a DIY disaster….. it’s more of a bodge to fix someone’s else’s original bodge job!
Long story shortish my ‘mate’ built me a retaining wall and garden room 4 years back and the retaining wall started collapsing into the building, so I made the decision in January to knock the whole room down so I could rebuild the retaining wall. As the original room was built so close to the wall and I have built the new wall out further for more stability and strength, when I rebuilt the garden room I couldn’t do it on the original slab / plate as there wouldn’t be enough gap to re clad it and to add the original slab was also at an angle pointing back toward the corner of my house which annoyed me every day. Now you will see from the picture I’m left with the original concrete slab coming out further than the cladding which I know is obviously a big no no as you want water to run off the cladding and away from the base. I have silicone round the exterior plate and also stuck cuts of DPM up the side of the walls before cladding and cut the DPM so it laps over the old plate, in the hope that water will run off however I’m still concerned water will find a way through. My only thought of what I can do now for peace of mind is to hire a breaker and take out the top layer of the slab on the outside so that it’s lower than the new plate and in theory water can’t run back into the new room? That’s the short version of my adventure, hoping someone can give me some advice / reassurance that I haven’t just wasted another 2 grand rebuilding it and that there are options to stop water ingress! Note - I plan to deck round the whole perimeter to hide the old slab and DPM. Thanks

 

[Mr diy a lot.]

Yeh it’s a bit suboptimal. And you are right it’s all about making sure water flows away from the room.

1. Breaking it especially with the room build back could be faffy and dusty. But def possible with a neat and deep straight line cut with a Stihl saw into the pad along the edge then break it all up. You might need to remove the cladding from that side of the building tho.

2. alternative is to cast a new concrete angled gradient on that bit so water runs off the side and front and does not lie on the slab.

Option 1. Prob better if you can muster the can do spirit to get it blitzed.

 

[MDK 24]

Thanks appreciate the reply. Disc cutter is a good idea to make sure I don’t break away too much. Another thing I thought just now is if instead of decking I were to use slabs around the perimeter on a slight gradient and bring them flush up to the walls of the building. I’d still need to break some of the concrete out so they fit under the bottom cladding boards. As I said the OSB walls have got DPM tacked all the way round about a foot high so that coupled with nicely pointed slabs might prevent any ingress?

 

[Notch7]

There is a fairly neat way to do it

remove the lower cladding, cut a line with a 9” angle grinder with a diamond blade as close as practical to the building - then either stitch drill or use a kango to break the rest off.

be careful, there is a risk a breaker might just crack the concrete slab under the building.

because you won’t be able to get tight to the building, fit a timber cill to form an overhang, then dress with say lead which runs up the building say 100mm, across the cill and down beyond the front edge.

then refit cladding so it runs down over the leadwork.

 

[chalkywhite]

Perhaps jack the room up slowly and sling beams under?

 

[MDK 24]

Thanks for the replies, Iv already had the roof felted so didn’t think jacking up would be an option? But I did consider it beforehand

notch7 - I have managed to get an angle grinder and breaker and gonna attempt your suggestion this weekend. Only problem is I don’t see how could refit cladding neatly once I take it off, and since it’s been nail gunned in I’m gonna have to break off the existing boards and then try and cut the nails out?

can you give me anymore details on how you would fit the timber cill? And if my end goal is to lay decking round the perimeter what level would that be compared to the cill? Just thinking I don’t really want to have the lead visible, and is lead absolutely necessary if the cill slopes at an angle away from the building?

thanks!