Ticky

The guys coming with the grinder are doing it as a freebie as they were the guys that originally took the tree down. I did consider getting a little digger but decided it was doable with a bit of graft. As much as it's hardwork I quite enjoy it.

I do have someone coming on Friday with a stump grinder to get rid of the rest of the tree stump

Been doing my own Nick. It's a nice little workout when the sun is shining (not so much today though) Filled half an 8 yard skip so far with the wheelbarrow and spade

I've already been digging the garden out this weekend to get to the main roots. I've not quite gone down 600 deep but these are about 450-500 below. Also uncovered what looks like a little pond (which I'm going to have to deal with as it holds water still)

Thanks @Iceverge - again, great tips. For the foundaton. What depth should each of the layers be that sit underneath the EPS? And yes, I'll be documenting with pics as I'm going along

Good safety advice, thanks Did you have a DPC? Would I need to cut holes in it to allow the bolts to pass through?

Thanks @Iceverge @IanR I'm gonna go with that (full circle) design One thing I've been thinking about it the best way to fix the faceplate to the concrete. What I don't want to do is blow the sides out of the slab by drilling/screwing too close to the sides and as 50mm of it will be made up of EPS, is the best way for me to do it, to set some bolts into the concrete facing up, and then fix the faceplate to those. Any tips on that? Also, what would be the depths of the hardcore/type-1/pea shingle layers? And what's the difference between hardcore and type-1? Is hardcore much bigger stone/bricks etc? My day job has delayed my progress this last month, but keen to start pushing forward now. I've already started digging out the space I'll use, first big job is removing the roots of the tree that was in the way, which was taken down last month. Got the guy coming back to grind the stump down to about 500mm below ground level, but I need to clear the way for him. I've got a skip coming this week to fill with the ground I'm removing. I started filling rubble bags but it was taking too long, plus I can use the skip for other crap I need to chuck.

Thanks again. I'm starting to think that the easier options will be my best approach to which I'd have to accept the slab being 15cm off the ground as in @Iceverge's last drawing. A couple more questions about that. 1. How would the concrete board be fixed to the upstand? In an earlier comment you said EPS doesn't need any DPM between it and hardcore as long as there's a perimeter drain. How does the layers below the EPS differ to my drawings of hardcore with a layer of sand. 2. With the wallplate being shorter depth than the studs does that mean that the studs have the corners cut so they sit around/over it? I'm just trying to picture it.

Thank you @Iceverge Looks like you put some time into that so I really appreciate it.

Yep, I had that as an after thought about the perimeter strip. Thanks @JohnMo I guess with this strip foundation design I could interchange the position of the slab and insulation? @Iceverge does this help me overcome the concerns you were pointing out? as my floor level will remain close to ground level.

Something like this @JohnMo ? Am i right in thinking that the blocks would be the same depth as the timber that would be fixed on top of it? In my head this seems like a much simpler approach and less to worry about regarding exposing the insulation to heavy load/moisture

What does raising my current design by that amount achieve? I appreciate I wouldn't need the brick/block work and the timber could be fixed directly to the slab, so that would solve the thermal bridge bit I presume, but what else would it mean? Thanks

@Iceverge Do you mean the slab itself being 150mm above ground or just that the finished floor is? What does raising my current design by that amount achieve. I appreciate I wouldn't need the brick/block work, so that would solve the Thermal bridge bit I presume, but what else would it mean. Again, apologies if all this is obvious. I'm brand new to all this but willing to take advice of those that know a whole lot more

Thanks @IanR, that makes sense. I've literally just got the same answer back from the supplier. It was the load of the building itself that I didn't take into consideration. Thanks for pointing that out Looking at EPS - Would I want something like this? Jablite Jabfloor EPS150 100mm Polystyrene Insulation Board 2400mm x 1200mm - FWDirect (flooringwarehousedirect.co.uk) This data sheet for it PowerPoint Presentation (flooringwarehousedirect.co.uk) says that to meet the u-value I'd need approx 100mm (my P/A ratio is 1.067) as all perimeter walls of my 5m x 3m room will be exposed.

Celotex GA4000 PIR at 75mm has an R-Value of 3.4 (see link) and going through the calculator on the following site it gave me the u-value of 0.25 for a similar floor, and that figure is recommended from a building regs point of view. It looks like 100mm of EPS100 has an lower R-value at 2.78m2K/W. So I appreciate the PIR was more expensive but it's thinner and gives better insulation (as far as I can see). Celotex GA4000 Thermal PIR Insulation Board | Saint-Gobain (insulation-uk.com) I see a number of mentions that PIR can be used under the slab. A couple of examples below. IMA-Best-Practice-Guide-No3-Floors-Final.pdf (insulationmanufacturers.org.uk) Celotex GA 4000 Floor Insulation Guide (insulationshop.co) (this one for the specific model too) Any solutions around the thermal bridge @Iceverge?

Hi @Temp Can you add a bit more to what you mean here? In my design I'm going to have both the DPM and the separation layer up the side of my slab. I guess I can cut the separation layer where it surfaces as that will be covered by the engineering bricks. But to terminate the DPM, could i continue it up and seal it to brickwork with liquid rubber? Something like this below. Also thinking..... will I need to be pretty acccurate with the size of the shuttering/slab? My DPM is going to be coming up the outside of it so if I need to fold it over the exposed surface of the slab to terminate it on the brick I guess the more accurate the better. Speaking to a colleague, he thinks that I will need brickwork/footings instead of shuttering as when the shuttering's removed I've only got insulation, protected by my DPM. Is he correct or is the DPM covered insulation going to be OK if it's packed in with the soil/grass of my garden?

@Moonshine @Temp, is this just 2 x regular-sized bricks (on top of each other) - that would give me the 150mm clearance (great) but how would you secure the timber to the brick? Would there be a certain type of brick/block to go for? Also, how do I 'terminate' (maybe not the right terminology) the DPC if I had this brickwork above the slab? Do I fold it under like I have in my image? I guess that would screw with the securing the brickwork to the slab

Hi @JohnMo, I'm not 100% sure if that's an answer to my questions or a description of your own build? I'm thinking it's the latter. I feel the foundations are gonna be the most important part for me to get right the first time round. I'm really struggling to think of a simple way to keep the slab at ground level whilst somehow raising the timbers 15cm. Do most people just pour a 150mm concrete slab (above ground level) and then fix timber from there? For once in my life I wish I was a lot shorter too! ha

Hey everyone, thanks again for all the advice here. It's all a very steep learning curve I'd really like to maximise the head height, so still favouring the insulation below the slab. Plus, if I kept the concrete slab to ground level but then used some form of brickwork or concrete block on the perimeter (> 15cm) then the timber walls are fixed to those, would that be suitable? I guess I'm then shifting load from the slab to the brickwork then? Also, would I be ok just backfilling where the shuttering was with soil/gravel be ok as they'll be in direct contact with the DPM?

Thanks for your feedback and suggestions. I suppose I'll just accept that the slab will be raised 150mm, as pointed out I should still get 2m if I choose the right roof design. Thanks for sharing your design @IanR. I like the use of the lip below the cladding (along with the alu clad/render) to help direct any rain away from the base. However, I notice that your design doesn't have any DPM between the lowest layer of insulation and therefore your 50mm upstand is directly exposed to the ground apart from the aluminium clad. Would my idea of folding over the DPM and separation layer be ok if I raised everything by 150mm? Also, what would be the recommended depth for my concrete? Would rebar allow me to keep the depth to 100mm? I'm thinking of using Celotex GA4000 PIR at 75mm, as aiming for a U value of 0.25 and that seems to offer it (based on their calculator).

Hi all, I'm new to the forum but already found some useful guidance on here, so thanks. I'm also new to this level of DIY but I'm not shy at having a go, like to make sure things are done correctly (hence my questions) and have a brother who's handy at a lot of things to help (who's also a spark :)) So let me set the scene first. The garden room I want to build will be 5m x 3m to stay within the 15m2 limit and needs to be close to the perimeter so I'm limited to 2.5m height - I'm 6ft 2in so need to maximise the headroom. Because of this, I'm leaning towards an insulated concrete slab, with the insulation below the concrete. As it will be used as an office, I'd even consider something like polished concrete as the finish. Ideally, my slab would be something like my attached diagram, with insulation below the slab but also 25mm to the sides as well. That would mean both the DPM and the separation layer would need to be folded over the side insulation and the slab with the idea that the wall timbers would rest on top. The reason I've put 5x2 as an option is that the timbers would need to overhang the slab to cover the 25mm of extra side insulation so just thinking of getting enough coverage to fix to the slab without potentially cracking the concrete. Also, I appreciate that the wall timber will be close to the ground but I thought the OSB and coverings would add protection (happy to be corrected/guided) I'm not planning on pouring the concrete myself but I'm thinking of doing all the prep work myself so it's done as I want it Also, having the slab at almost ground level would mean I can get the most headroom before I hit the roof joists, but I'm conscious this brings more challenges with regards to damp etc I'd be very grateful for your feedback on this. Thanks