TANK Posted June 18, 2021 Share Posted June 18, 2021 Hello guys, novice here. Seem to be going round in circles here, sure I already posted this topic a week or so ago but have since had no replies/unable to find the thread again so I'm posting again. Apologies if it is indeed posted elsewhere in the forum and I'm just going mad... The question I have is a simple one, yet I can't seem to find anything anywhere relating to it. I have dug strip foundations for a medium sized single skin block outbuilding, and half filled this with concrete. I am currently bricking up to get out of the ground to dpc. What do I use to fill the gap upwards of the concrete between the brick and the ground? Many thanks in advance. Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 18, 2021 Share Posted June 18, 2021 Are you talking about inside the footprint of the building ? I.e under the floor slab ? A quick hand sketch would clarify. Link to comment Share on other sites More sharing options...
Gus Potter Posted June 18, 2021 Share Posted June 18, 2021 (edited) Hello Tank. To get the best out of Build Hub you can try doing a quick sketch on a bit of A4 showing the ground level, your foundation etc. Don't worry about the quality.. no one will slag you off for a bad drawing..you need to see some of mine! Take a photo of your page and post it. Sometimes it's easier to make a drawing than to try and explain it in writing. The main thing is to have a bit of fun posting on BH and don't worry about using "technical" speak..just spill it out! I'm guessing but have you a found and you are trying to work out how you lay the masonry so that when you get out the ground the brick / block courses are level? If this is the case.. (most founds are not that flat and level) then for example you can lay concrete blocks "on the flat" which is the wide side down and adjust the mortar bed thickness..aiming to keep the mortar thickness to less than 20mm.. does not always work in practice for DIY but that is the aim. If you have not done it before it takes a bit of thinking out.. but great when you get it right! Edited June 18, 2021 by Gus Potter Link to comment Share on other sites More sharing options...
joe90 Posted June 19, 2021 Share Posted June 19, 2021 When we did our founds, because of a high water table we backfilled outside with 50mm drainage stone, this became a French drain when piped to a ditch to keep water away from the build. Link to comment Share on other sites More sharing options...
Declan52 Posted June 19, 2021 Share Posted June 19, 2021 9 hours ago, TANK said: Hello guys, novice here. Seem to be going round in circles here, sure I already posted this topic a week or so ago but have since had no replies/unable to find the thread again so I'm posting again. Apologies if it is indeed posted elsewhere in the forum and I'm just going mad... The question I have is a simple one, yet I can't seem to find anything anywhere relating to it. I have dug strip foundations for a medium sized single skin block outbuilding, and half filled this with concrete. I am currently bricking up to get out of the ground to dpc. What do I use to fill the gap upwards of the concrete between the brick and the ground? Many thanks in advance. It will depend on how much you have to fill. Well compacted clean hardcore up to a certain depth then you will have any insulation,dpm and then the finished floor. So you need to firstly get your finished height worked out then from that take away the items above and that will be the top of the hardcore. Eg. Finished floor - 100mm Insulation - 150mm??? What exactly is this building going to be used for, another shed for storing crap or fixing cars or a summerhouse and BBQ area?? If it's just a shed then you won't need insulation but in the future it might come in handy for other uses and it's going to be much easier to put in now. Link to comment Share on other sites More sharing options...
saveasteading Posted June 19, 2021 Share Posted June 19, 2021 The other advantage of gravel as an infill, especially rounded beach gravel, is that it compacts naturally and you do not have voids that may settle. This is more important on the inside face as it is supporting the floor. If the quantity is small it can be worth making a lean mix of concrete as that will also compact. Link to comment Share on other sites More sharing options...
dangti6 Posted June 19, 2021 Share Posted June 19, 2021 Internally I filled mine with type 1 as I was doing the sub base. Externally it became the dumping ground for left over cement initially and then type 1 whilst I was laying the sub base for a path around the building Link to comment Share on other sites More sharing options...
Temp Posted June 19, 2021 Share Posted June 19, 2021 18 hours ago, TANK said: I have dug strip foundations for a medium sized single skin block outbuilding, and half filled this with concrete. I am currently bricking up to get out of the ground to dpc. What do I use to fill the gap upwards of the concrete between the brick and the ground? Soil is fine on the outside. In the inside it depends how you are doing the floor. If its going to be a concrete slab then hardcore. If its a suspended floor then soil is OK. Some of us on sloping sites or clay soil have dropped perforated pipe into the space and covered with gravel to make a French drain. Link to comment Share on other sites More sharing options...
Bozza Posted June 19, 2021 Share Posted June 19, 2021 I was away to post a similar question so have kind of jumped into this post. I decided to have fun by building my own workshop (30sq timber frame) having not been allowed near the actual house. Trying to build to a decent quality. Per attached pic my foundation system is strip foundations, deeper at corners. Hardcore then concrete. Then one course of block work onto which I’ll attach the timber frame. Inside the block work I’m planning on: hardcore, then sand, then DPC, then 50mm PIR, then probably 50mm concrete floor or screed. Would be interested on any thoughts or nuggets of ideas in particular the final floor surface - non load bearing - whether to reinforce with chicken wire. Or better ideas / thoughts. Whether to put the dpc between PIR and concrete for example. ** the timber in the pic is just temporary used to get layout heights levels etc ** answers / thought should help both OP & I Link to comment Share on other sites More sharing options...
tonyshouse Posted June 19, 2021 Share Posted June 19, 2021 Remove all organic material from inside. backfill with rubble or stones compacted in 150mm layers Link to comment Share on other sites More sharing options...
Temp Posted June 19, 2021 Share Posted June 19, 2021 (edited) Google found some info from the NHBC written in 2011.. http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/Part5/section1/sitework.htm Main points.. Quote TRENCH BACKFILL 5.1 - S6 Backfill to trenches shall be adequately compacted To avoid settlement at junctions between the substructure wall and the ground bearing floor, trenches should be backfilled with solid material, graded and compacted according to the guidance given in Clause S4. Alternatively, concrete may be used (see Chapter 2.1 'Concrete and its reinforcement' (Sitework)). Fill should be placed in layers of equal thickness to both sides of substructure walls so that compaction on one side is not more than one layer ahead of the other. Where this is not possible, the wall will be acting as a retaining wall and the advice given in Clause S2(b) should be followed. GROUND BELOW FILL 5.1 - S3 Ground shall be adequately prepared to provide consistent support to the fill and the ground bearing slab All vegetable soil and organic matter, including tree roots, should be removed to provide an even bearing surface. Ground bearing floors may be used only where: trenches are backfilled with properly compacted material infill is less than 600mm in depth and properly compacted the ground is suitable to support floor loads and any other loads. Where more than 600mm of infill is required at any point within a self-contained area, or the bearing capacity and nature of the ground varies, the floor over the self-contained area should be of suspended construction. Reference should be made to Chapter 5.2 'Suspended ground floors' (Sitework). Edited June 19, 2021 by Temp Link to comment Share on other sites More sharing options...
TANK Posted June 21, 2021 Author Share Posted June 21, 2021 Thanks for all the replies guys. Mine is a fairly unique situation, and I prob should have elaborated a tad more. Bear with me here... There used to be a prefab outbuilding here for years, built upon a concrete slab. The previous owners pulled it down for some reason just leaving the slab (which was bordered on one side by a path, and the one end by tarmac where it meets the drive). I decided against using the slab on which to build a timber building due to A) close proximity to the border, B) it beginning to crumble in places on the top, and C) I wanted to take the opportunity to place some insulation down, so I did away with it, leaving the dpm and compacted hardcore underneath. So now that I've dug around this, as I build back up from the middle of the foundation strip there will be a gap between the brick and the edge of what used to be the slab, of around 100mm. The other side can just be earth/soil/hardcore I suppose but it is the material on the inner side which I'm confused over. If I put another concrete slab down which stretches to meet the brick work then I suppose the fill will need to be substantial and stable. But I don't even know whether I need to put another Slab down... Are there any other easier alternatives. The shed will mainly be used for general storage, plus a little bit of a workshop, but nothing much heavier than bikes and a lawnmower in there really! Cheers again. Link to comment Share on other sites More sharing options...
Temp Posted June 21, 2021 Share Posted June 21, 2021 (edited) That makes things clearer. Might also help if we knew how much height you have to play with? If you want a solid floor you would either remove the old slab or break it up into hardcore and compact it. They pour a new slab on top. Then sand blind, DPM, Insulation and screed. You could also go for a suspended timber floor but that may need sleeper walls in the middle to reduce the span. What's the shortest dimension of your building? A suspended timber floor also needs ventilating (eg air bricks or periscope vents through the walls). If you go this route I would build and insulate the floor as you go. eg fit a Joist, then Insulation, then a joist. That way the joists are tight up against the insulation and no need to cut insulation to fit between joists. Insulation not shown in this.. You could also go for a concrete beam and block floor with insulation and screed on top. . Edited June 21, 2021 by Temp Link to comment Share on other sites More sharing options...
TANK Posted June 22, 2021 Author Share Posted June 22, 2021 Thanks for the ideas. I don't have a great deal of wriggle room height wise, so I want the floor as low as I can get it. This prob rules out the suspended timber floor. I think I'll prob end up laying some insulation on what already there then casting another slab on top. What's the thinnest I could get away with? And would it be possible to make it thinner if I cast, say, 6 smaller individual slabs instead? Link to comment Share on other sites More sharing options...
Temp Posted June 23, 2021 Share Posted June 23, 2021 I'm thinking fill the trenches with compacted hardcore then 25mm sand blind, DPM, 100mm+ PIR insulation and 60mm screed (perhaps with mesh in it?). The screed needs to be reasonably thick/strong in case you get settling around the edges where trenches have been filled. Link to comment Share on other sites More sharing options...
TANK Posted June 23, 2021 Author Share Posted June 23, 2021 Well that would be fantastic if you think that is viable. I would like to avoid a thick slab of I can, due to cost and height. I suppose with some small rebar it Could be sufficient. BTW I'm new to all this and not really up on thy terminology - what is sand 'blind'? Just a covering/layer of sand? Link to comment Share on other sites More sharing options...
Marvin Posted June 23, 2021 Share Posted June 23, 2021 12 minutes ago, TANK said: is sand 'blind'? Just a covering/layer of sand? Yes. To protect the DPM from sharp edges and fill voids to make a flat surface to lay the DPM ON. Link to comment Share on other sites More sharing options...
TANK Posted June 24, 2021 Author Share Posted June 24, 2021 Thanks again. Link to comment Share on other sites More sharing options...
TANK Posted July 6, 2021 Author Share Posted July 6, 2021 Guys, wondering if you amazing people could help me again, this time going slightly off track from the floor question (but thought best put it in here since it's the fame project) - I'm wondering about wall piers, as the length of the building is 6m I'm researching that I should have a pier midway on this stretch... Now, do the piers rise from the foundation itself, or just from the internal floor? Link to comment Share on other sites More sharing options...
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