iSelfBuild Posted January 10 Share Posted January 10 I'm just embarking on a large extension and as part of that I'm building a 30m2 home gym / garage. Please see my marvellous sketch... At the moment there is a large deep boundary hedge which is about 2.7m high - blocking stunning views over the seafront. I am wanting to be able to overhead press in the gym and need 2.8m ideally. So I wondered if I can sink down the base and build up with blocks (laid on their side up to above the driveway height. Fortunately next door it drops away about 1.5m so I'm thinking if I make a French drain all the way around and fill in the sides with EPS then crushed rock it should be ok... Silly idea or should it be ok? Floor level would be 500mm lower than the drive. Link to comment Share on other sites More sharing options...
joe90 Posted January 10 Share Posted January 10 (edited) As long as you can drain downhill then I can’t see why it won’t work.however the 45’ rule would apply surely. Edited January 10 by joe90 Link to comment Share on other sites More sharing options...
saveasteading Posted January 10 Share Posted January 10 The sketch is perfect. Thd issue is the load of the new building thrusting against the existing retaining wall. Imagine loads spreading at 45 degrees. What is the wall construction? Keeping the gym dry inside will need careful detailing and some cost. Will there be a door at ground level and steps down inside? 1 Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 10 Author Share Posted January 10 27 minutes ago, saveasteading said: The sketch is perfect. Thd issue is the load of the new building thrusting against the existing retaining wall. Imagine loads spreading at 45 degrees. What is the wall construction? Keeping the gym dry inside will need careful detailing and some cost. Will there be a door at ground level and steps down inside? Hadn't really considered that! It's just a stone wall - in good condition no cracks etc - but there is a big root structure of the Leylandii hedge which I imagine "reinforces" it all. I imagine the soil I take out will be more ground pressure than the new structure (as it will be timber frame) however definitely worth considering and looking into! Yes a door on the drive way and steps down. Link to comment Share on other sites More sharing options...
saveasteading Posted January 10 Share Posted January 10 4 hours ago, iSelfBuild said: imagine the soil I take out will be more ground pressure than the new structure (as Unfortunately not. I think you will have to take the foundation down to next door's ground level. Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 11 Author Share Posted January 11 14 hours ago, saveasteading said: Unfortunately not. I think you will have to take the foundation down to next door's ground level. I would be using a raft foundation so the 45* impact would be less than strip footings I imagine? Taking a closer look it looks like once I remove the banked up soil (there is also a dwarf wall my side) the drop to next door will be more like 1m. If I keep it 1m away from the boundary retaining wall by the time the 500mm wall height and 200mm raft epth it's going to be almost level with their side. Just my house to worry about falling into my man cave 😆 Link to comment Share on other sites More sharing options...
Marvin Posted January 11 Share Posted January 11 Hi @iSelfBuild Items you may wish to consider.. Soil mechanics! Load baring capacity of the Soil Slip plane Heave Full design details of existing retaining wall (survey may be required) Existing services. Old and new drainage. Localised flooding Leylandii hedge is known for its shallow but wide root system, depending on the soil and the variety of leylandii. Permitted development rules. https://www.gov.uk/government/publications/permitted-development-rights-for-householders-technical-guidance Who owns the retaining wall Conversation with the neighbours Undermining the stability of the existing retaining wall whilst your gym vibrates as you pump iron🤣 43 minutes ago, iSelfBuild said: I would be using a raft foundation so the 45* impact would be less than strip footings I imagine? Taking a closer look it looks like once I remove the banked up soil (there is also a dwarf wall my side) the drop to next door will be more like 1m. If I keep it 1m away from the boundary retaining wall by the time the 500mm wall height and 200mm raft depth it's going to be almost level with their side. Yes this is the problem. Without a drawing with accurate dimensions (not a scaled drawing)written on it, with both horizontal and vertical distances, ideas given could be excellent or Ballox and pictures of the walls really help. (is the retaining wall vertical or leaning towards your drive at the top?) In my opinion a raft foundation is more likely to cause heave or lateral pressure on the retaining wall. Good luck Marvin 2 Link to comment Share on other sites More sharing options...
saveasteading Posted January 11 Share Posted January 11 Yes @iSelfBuild. We are here to advise but not design. The advice now is that it can be done and that you need professional advice and more money than you first hoped. 2 Link to comment Share on other sites More sharing options...
Marvin Posted January 11 Share Posted January 11 (edited) And my advice is that it can technically be built but it may depend on planning rules, building regulations, ownership of the retaining wall, property deeds, and everything else I'm ignorant of. As my brother used to say 'It's not if, but how much.' Good luck M Edited January 11 by Marvin further thought Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 11 Author Share Posted January 11 Money is no problem, It just might make sense to make a partial basement on my extension instead of the garage where I was first thinking. Extension is 100m2 don't quite need that big of a man cave though! I'll let the structural engineer advise on suitability just floating ideas for now 👍 If I do build something on the drive I will likely keep the garage at under 30m2 and 1m away from the boundary to avoid a load of bollox so it's outside of planning and regulations. 1 Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 11 Author Share Posted January 11 Wondering even if i just take out the hedge to open up the sea views...could that cause any issues to the retaining wall which has been there 100 years or so? Link to comment Share on other sites More sharing options...
Marvin Posted January 11 Share Posted January 11 2 minutes ago, iSelfBuild said: Wondering even if i just take out the hedge to open up the sea views...could that cause any issues to the retaining wall which has been there 100 years or so? could that cause any issues to the retaining wall??? Yes. But it might not. The devil is in the detail. Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 11 Author Share Posted January 11 (edited) 21 minutes ago, Marvin said: could that cause any issues to the retaining wall??? Yes. But it might not. The devil is in the detail. Only one way to find out... 🤣 There is also the neighbours garage on the right side which is part of their retaining structure - probably comes 1/3 of the way. Edited January 11 by iSelfBuild Link to comment Share on other sites More sharing options...
ProDave Posted January 11 Share Posted January 11 I can't see your neighbours best pleased with you taking the hedge down and then having a window from your gym looking straight into that gable end window (presumably a bedroom) Link to comment Share on other sites More sharing options...
iSelfBuild Posted January 11 Author Share Posted January 11 Definitely no windows planned. The hedge from their side is a mess. Cut back and it's all brown and dead. I shall replace it with a nice fence most likely. Link to comment Share on other sites More sharing options...
iSelfBuild Posted Thursday at 15:59 Author Share Posted Thursday at 15:59 Wee update - decided going down the planning and regs route is much more hassle than it's worth. Sticking a log cabin alongside the hedge - 2m away from boundaries on a reinforced raft. Single Wooden Garage TWIN (44 mm), 4x6 m (13'x20'), 24 m² Won't block too much view from the downstairs and makes absolutely no difference to upstairs or the new extension. Just need to convince my wife that adding a basement is a good idea for the big extension... even though I know myself it's a horrible idea that will be nothing but a headache and expense! Would love to build the garage myself but too busy with my business, thanks again everyone for your input and suggestions - always good to get others opinions and insight. Rich Link to comment Share on other sites More sharing options...
Nickfromwales Posted yesterday at 00:28 Share Posted yesterday at 00:28 Ola. How long are you staying there? If sub 10 years, ditch the madness, but if it's forever then get the wife drunk and get her to sign it all off in triplicate. This message will self-destruct in 5 seconds................. 1 Link to comment Share on other sites More sharing options...
iSelfBuild Posted 22 hours ago Author Share Posted 22 hours ago 8 hours ago, Nickfromwales said: Ola. How long are you staying there? If sub 10 years, ditch the madness, but if it's forever then get the wife drunk and get her to sign it all off in triplicate. This message will self-destruct in 5 seconds................. Hmmm tricky one, I love it here - depends how much money I make though ultimately - 5 year plan is buying a farm with plenty of space to develop a small holiday park and run my other business's from. Taking myself back to the Scotland project and the 33m long x 3.6m retaining wall I built... which we had a concrete blow out. Not sure I want the hassle of a basement! 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted 21 hours ago Share Posted 21 hours ago 1 hour ago, iSelfBuild said: Hmmm tricky one, I love it here - depends how much money I make though ultimately - 5 year plan is buying a farm with plenty of space to develop a small holiday park and run my other business's from. Taking myself back to the Scotland project and the 33m long x 3.6m retaining wall I built... which we had a concrete blow out. Not sure I want the hassle of a basement! KISS then. Make it as nice as possible, practically, enjoy your time there, and move on without regret / remorse. 👊👌 Also with a significant chunk of change STILL in the bank. 🤝 Link to comment Share on other sites More sharing options...
Alan Ambrose Posted 18 hours ago Share Posted 18 hours ago Lovely location Link to comment Share on other sites More sharing options...
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