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gerard b

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Good evening all,

I'm a long time lurker but only now getting around to contributing (hopefully). I'm in the planning stages for a while now and have a few questions I'm hoping some of you fine people can help me with.

I'm a reasonably competent all round diy'er and this will be a 1 man self build but some of the detail has me a bit stumped at the moment.

Structure is going to be 9.6m by 4.8m outside measurements. 2x4 stud framed walls with a flat epdm roof. and larch clad. My first question is around the stud spacing. I'm thinking 400mm on centre, with 18mm OSB on the inside as lining as well as acting as a vapour barrier. The OSB comes in measurements of 2440x1220mm. Does this work for 400mm centres, I mean in regards the sheets lining up half way over each stud? Hope this makes sense to someone lol...
 

Doug71

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Sheets like plywood and OSB are still in imperial sizes 8' x 4' (2440x1220) but other things like plasterboard are metric so 2400x1200 #-o

In the old days studs were set at 16" centres because everything was imperial. These days it's normally 400mm centres to allow for metric size boards, you have to trim the imperial size boards to fit.

Bear in mind your timbers will be metric lengths for example 4.8m which a bit shorter then 16'.

People tend to work in metric and trim the sheets to size, the sheets are often not perfectly square or bang on size anyway.
 

MikeG.

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Hi and welcome.

For a start, this building will require Building Regs approval, which is a game changer. That means orthodox foundations, or a structurally engineered raft. It may or may not need to comply with Part L regimes, depending on whether or how you plan to heat it and so on. The typical structure linked to in my signature will not be in compliance. Your costs will be much higher than most of the workshop builds here, which probably average £125 to £175 per square metre.

If there is any way to build this as two separate buildings with neither over 30 sq internally, then you can avoid Building Regs.

As for your questions.......

Treat the nominal stud spacing as a guide, and alter it to suit your sheathing boards. 18mm OSB is fearsomely heavy, and not necessary for strength in the walls. Most people use 9 or 11mm. 600 centres is perfectly possible for a workshop, but this affects your wall plate or roof design.
 

DBT85

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Good luck!

I made my plans and Fusion mocukup in such a way that I can change it if the sheet gods for some reason turn up in 1220 or 1200. I've seen some people get half of one size and half of the other!

Mike knows everything, but buy all means pop in to my build thread and see what I've been upto. Much of what you want may be in there already. Or in any of the dozens of others!

My only question is why the flat roof over a pitched roof?
 

gerard b

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Hi guys and thanks very much for the prompt replies.

So if my sheets are 2440x1220 I go with 16” centres and if they’re 2400x1200 I go with 400mm on centre? That makes sense I think.

Mike, I was going 16” or 400mm centres as I thought that would be best for structural strength with 9x2’s on the roof. I’ll be going with a warm roof. I think you’re right on the 18mm osb, 11mm will be fine.
 

gerard b

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DBT85, thanks I look forward to checking out your build.

The flat roof I figure is just easier, this is a daunting enough project as it is lol... it also makes more sense for what I’ve planned to use the inside space for. I just find there’s a lot of wasted space in a pent roof too.
 

MikeG.

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gerard b":19r5rmtl said:
......... I just find there’s a lot of wasted space in a pent roof too.
You don't mean pent roof, I reckon. You mean a pitched roof. A pent roof is a misused term at the best of times, as it is built against an abutment wall (or two). You are proposing a flat roof or a mono-pitched roof. The upside of a flat roof is easier construction. The downside is that it is uglier than a pitched roof. The "wasted space" you talk about in a pitched roof is wonderful storage, and also a good place to run ducting if you have an extraction system. Indeed, some people put the whole system up there. Mine is absolutely chocker block with wood.

Whilst on the subject of rooves, you do realise that you are going to end up with a roof which is about 400mm thick, don't you? That's what a warm roof does. I can only assume you have planning permission for this building, because otherwise you are going to struggle to fit under the 2.5m height limit for Permitted Developments because of the warm roof choice.

You haven't answered the point about the size of your building and building regulations. You are going down the route of a 1m+ dig for foundations (or structural engineers fees and a massive raft), cavity walls, and council inspections. Why?
 

DBT85

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gerard b":l6ps2ajg said:
DBT85, thanks I look forward to checking out your build.

The flat roof I figure is just easier, this is a daunting enough project as it is lol... it also makes more sense for what I’ve planned to use the inside space for. I just find there’s a lot of wasted space in a pent roof too.
You sound like you have a similar DIY experience to myself. Have a watch of some videos about cutting rafters, it's not too hard.

The reason I went with a pitched roof was for headroom over anything. One 3m section of my workshop will have nearly 3.5m from floor to the middle of the ceiling, while with raised ties the rest of the ceiling will be around 2.5m.

That's hard to do with a flat roof and the 2.5m eaves height rules as you need thick rafters to span the kind of gap you are talking about.

Another note, 600mm centres works fine.
 

gerard b

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Hi Mike, yes I mean pitched roof and the flat roof is purely for simplicity for me. I've got nowhere near the skills most of you guys on here have and no doubt I'll have to make some compromises along the way.

I live in a very rural part of Ireland, miles from any other dwellings so planning is not an issue.

Thanks again for all your help so far guys, very much appreciated.
 

gerard b

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@DBT85, I read through all of your build so far just lat night, brilliant I really enjoyed it, it's going great.
 

gerard b

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By the way guys, how long is it before you get permissions to send private messages on here?
 

gerard b

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Ignore that, I have access now, you must have had to have a certain amount of posts before you got pm privileges.
 

gerard b

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Well I got the base in, unfortunately I haven't figured out how to add pictures here yet, I think the file size is too big. Anyway base consists of compacted hardcore, sand blinding, dpm, 100mm board insulation followed by 5" of concrete pour.

Thinking ahead to the wall framing and the roof, I'm still trying to figure out how to put the slope on the flat roof. I was thinking of making furring strips as this seems to be the simplest method. Is this practical though over a span of 5mtrs?
 

DBT85

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Do you have your images uploaded anywhere or are they only on your machine? You can either upload to a host like Flickr like I do or upload to the forum itself.

Them you'd post the image by putting in its hyperlink like this. Just remove the * I've added in.

[*img] image url here [/img]
 

MikeG.

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Yes, firring pieces are the standard way of producing a fall.

A 5m span, though, is not a great idea. With overhangs this means you are going to be looking for roof timbers of 5.4m, and around here that is a special order, and pricey. It also means your roof timbers need to be 250 thick. With firring, insulation and two layers of board that means a roof some 450mm thick if you do a warm roof.
 

DBT85

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Davies timber who I got my ridge from carry that kind of size as standard I think. But most won't.

Go pitched. Can't be that hard, I'm doing it tomorrow!
 

DBT85

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Ah, to share flom Flickr your want to click the share button, it's a little sort of up and right arrow in the bottom right corner. You then want to select bbcode as the format to share.
 

gerard b

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MikeG.":26itckai said:
Yes, firring pieces are the standard way of producing a fall.

A 5m span, though, is not a great idea. With overhangs this means you are going to be looking for roof timbers of 5.4m, and around here that is a special order, and pricey. It also means your roof timbers need to be 250 thick. With firring, insulation and two layers of board that means a roof some 450mm thick if you do a warm roof.
Plan was to go with 9x2’s (220mm) and they come in 5.4m lengths where I’m buying my timber, above that size and as you say, they get pricey.

Is it just a matter of doing a taper cut the full length of the 9x2 to make the firring strips?
 
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