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Shameful lack of progress as usual due to various other things draining my time, but I have been thinking about roof design and have settled on the below. Not to scale!

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On my previous workshop I used individual trusses constructed out of 47x100 timber with 22x100 cross-ties and a central vertical piece also. It did not have a ridge beam at all, and the structure of the roof was supported on 47x47 purlins which ran lengthwise. Rigidity was provided by the OSB deck which was screwed to the top and the roofing material was mounted onto this also. This worked very well however it made insulating it a bit of a pain and while it never gave me a single problem it wasn’t as strong as it could be.

This time I am going with a more simple construction which will also be a lot stronger. The ridge beam will be of 225x47 and if I can source it, in a single (c. 6.6m) length. It will be semi-structural in that I hope to have a bay in the middle of the building where I can omit the cross-tie on two of the rafter pairs. At 600 rafter centres this will give me a c. 1.8m wide access to loft storage either side. As the roof pitch is going to be steeper (c. 35 degrees - lots of rain!) I will have lots of storage above the rafter ties, even with them raised to around 1/3 the depth of the roof. With 2.5 metres to the eaves and then likely another 750mm to the underside of these ties I will not be short of headroom in the building!

With closer spaced and thicker rafters I will be able to fit 100mm thick insulation panels in between, flush with the lower space allowing 50mm above for eaves-to-ridge ventilation. I can then deck the roof with OSB and fit my sheeting on top. The interior of the walls will be boarded out to retain their insulation and if I’m feeling particularly flush I can do the roof too, but I don’t think it will be required. The underside of the rafter ties will be where I mount my lighting as per the previous building. 

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I can't quite tell from the drawing but it looks as though you have the roof gables extended a little away from the gable-end walls. I like this, especially over a doorway. It's surprising how much extra shelter it provides (as long as the rain isn't driving towards the gable). I have this on my house and garage, extending a good 300mm. You do therefore have a soffit to fit and maintain but I think it look better and as I said, weatherwise it works too.

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As we build the ABRI on a slope, we had to put the uprights (??) for the roof into the solid, original, soil and not the loose stuff we put on it to level the thing.

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They went down some 2 mtrs - or about 6 Ft. 5" in your money..

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We did obviously do an overkill - but it makes for a very, very solid building.

In your case, the digger going down should reach good solid soil and that should do.

We're starting late this year on another ABRI (40x6,5x4 mtrs.) with some serious concrete floors and the

uprights go into the ground about a metre.

 

Have Fun Building !

 

 

 

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Yes there will be an eaves overhang of around 200mm and around the same at the gable end. The eaves is key to ventilating the roof structure and the gable provides a bit of rain cover as you say. It means the building can't go right up to the fence as I can't oversail someone else's land, however you need a good 300mm of space around the outside for maintenance anyway.

Building footprint is 6m long and 4m wide on paper - same as the previous one. However I may try and squeze that to 4.2m wide if I can.

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7 minutes ago, Retroanaconda said:

Yes there will be an eaves overhang of around 200mm and around the same at the gable end. The eaves is key to ventilating the roof structure and the gable provides a bit of rain cover as you say. It means the building can't go right up to the fence as I can't oversail someone else's land, however you need a good 300mm of space around the outside for maintenance anyway.

Building footprint is 6m long and 4m wide on paper - same as the previous one. However I may try and squeze that to 4.2m wide if I can.

Is there any scope to bring the front of the roof out a few metres so you've got some covered area? or have you already planned a carport type structure?

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Playing more with rough levels today.

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Assuming I bring the compacted type 1 up to around the existing ground level the deepest part of the slab will be around 400mm thick. I might be able to lose 50-100mm by bringing the type 1 up higher depending on the angle of repose at the back, but that would be all.

On the upslope side I will be able to have it 100 or 150mm thick which should be plenty, with the same thickness of type 1 underneath. Which one will depend on the total quantity once I’ve dug out, and how that compares to a full lorry load.

Does anyone know the maximum gradient that you can reliably compact type 1 at?

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  • 2 weeks later...

Been playing with the digger today, got enough topsoil removed and ready to compact the disturbed ground before adding type 1 to bring the level up where required.

I struggle to knock in a 2x2 peg by hand across most of it so I’m pretty confident it the load-bearing ability of the ground. This is good as it makes the sub-base less important and means it can take more of a regulating role than a load-bearing one.

Pulled one of the several big lumps of slate out which left a nice hole showing the nature of the ground and just how much slate is in it.

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  • 2 weeks later...

Today has been a day of spreading type 1 and compacting it and the underlying sub grade. I have built things up a bit on the bottom side but the slab is still going to be around 350mm thick there, tapering up to 150mm at the top closest to the house.

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Surprising how long it takes to make the timber forms, would be easier if the site was flat and I could just use standard road forms. Each one is made to suit the profile of the base - which isn’t as level as it could be.

Spent all day today on it and got almost three quarters of the way around.

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Very neat.... just a wee note of caution,... shuttering always moves more than you hope or expect, if you have any type 1 left a bit of backfill helps a lot,... or anything with mass, either that or a few extra pegs at least at the deep end. 

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I would second that, concrete is a heavy beast and once it starts moving to area you don't want it to be in, it's a nightmare to do anything with.

What size mesh are you going to use? 1 course or 2 courses? Also, what finish are you going for, brushed or floated?

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At the back where the greatest forces are it's braced against the base of the 4" fence posts which are nice and solid, plus there is a bank of earth there as well. I can easily add more stakes for good measure. And I do have some type 1 left - good idea.

There will be two layers of reinforcing mesh in the slab, more to control cracking than to add strength, but it's cheap enough and can't be added later. There will be one along the bottom and one closer to the top, though the spacing will vary a bit as the depth of the slab does. It’ll likely be A193 mesh (7mm steel).

I'm hoping to achieve a reasonably smooth floated finish so that things like engine cranes roll easily. My last workshop had a rough concrete floor and it was a nightmare trying to move anything heavy.

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20 hours ago, Retroanaconda said:

I'm hoping to achieve a reasonably smooth floated finish so that things like engine cranes roll easily. My last workshop had a rough concrete floor and it was a nightmare trying to move anything heavy.

Heavy-duty self-levelling latex screed is only ~£30 a bag and leaves a beautifully smooth surface - even nicer if you epoxy paint it too. Best thing I ever did in my garage!

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51 minutes ago, daveturnbull said:

Just how heavy duty is it tho? Land Rover on a trolley jack rolled across it heavy duty? With a pry bar under the jack to move it sideways a bit heavy duty?

Yeah I've used jacks & stands (ambulance weighs ~2.8t) & engine cranes on it, hammered on stuff on the floor, dragged stuff across it... the only thing that's dented it in a couple of places is hammering on the end of a bar/tube with the other end on the floor or dropping something really heavy & pointy - but honestly it's stuff that would've damaged concrete too. Plus the ability to sweep up easily, clean up spills rather than have them soak in, and roll things on wheels so easily is just great. Also it's brighter and easier to find that m6 nut you just dropped... :ph34r:

That was HD levelling screed from Jewson, and epoxy floor paint from Ask Coatings. My garage build thread: putting screed down, and painting the floor.

 

Oh and another thing I just spotted in my garage thread is to run a bit of plastic duct in through the base for the electrics etc. before you pour the slab, makes life easier & neater. I got some ~3" corrugated duct (smooth lined, very important!) and ran it from the edge of the house (where the power was going to come from) under the garden and up through the slab at a convenient point for the fusebox etc. - currently got a power feed and a long network cable to a cheap wifi repeater for uninterrupted tunes / surfing for manuals etc. in the garage.

 

A couple more floor paint glory shots :rofl:

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I could hire a power float, but I've not used one before and I would probably be more comfortable doing it the 'old fashioned' way where if it goes a bit wrong it can be touched up by hand and you can stop before you wreck half the slab! People I've spoken to say they're a handful to use for the inexperienced.

A decent smooth concrete floor will hopefully be more than sufficient in terms of a good surface - it will be painted light grey to seal it and stop too much dust being produced, with the benefit of being lighter for finding those M6 nuts. I can see the obvious advantages of the screed when extending or raising existing surfaces but hopefully given that mine is all new it will be good enough. My biggest challenge will be timing the pour with a window of dry weather.

There will be a cable duct coming up in the corner nearest the house, through which I will run my 10mm² SWA for power and some rope for any future requirements. Ethernet shouldn't be required as the router is in the closest part of the house already and being timber-framed there's only one skin of blockwork for the WiFi to break through to get outside, but if it is for whatever reason it will then be easy to draw it through.

 

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  • 2 weeks later...

I got the formwork more or less finished at the weekend, just need to dig the trench for the cable duct before I can close it off.

Speaking to the concrete company today I’ll not get the mix truck down the side of the house and so will need to hire a dumper to transfer it, bit of a pain but doable and a lot cheaper than a pump truck.

They're trying to convince me that using a poly-fibre mix will negate the need for any steel reinforcement. The slab will be C25-C30 (or thereabouts), 150mm at the thinnest point and onto hard ground so I’m not worried too much about outright strength but I would like to try and control cracking, plus it’s cheap to do and can’t be added later!

The primary benefit of just using the poly-fibre mix is that I could more or less drive the dumper into the excavation which would save on the amount of spreading/raking and levelling by hand. I believe a plasticiser additive is available that can help it flow better though which may negate this to some extent.

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Advice from the last concrete guy I used was a wheelie bin is an excellent way to move concrete - wheelbarrows can't take the weight!

Also worth looking for mini-mixer companies that might be able to get their truck up your back passage :blink: save a lot of faff.

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