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Mike G's How to Build a Shed

Roll up, roll up. Here you will find everything from new workshop designs, through builds to completed workshop tours. All magnificently overseen by our own Mike G and his tremendously thorough 'Shed' design and generous advice.

Re: Mike G's How to Build a Shed

Postby John Brown » 22 Oct 2020, 13:27

Turns out it didn't really matter - 22mm 25mm, doesn't make that much difference when nailing on waney edged larch boards. Especially not when working at my level of accuracy...
However, I am curious about the gable ends. Do I stop the cladding short of the roof to enable airflow behind the cladding? Or isn't it important? I am just about up to top of the end wall, before the pitch starts, and need to make a decision.
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Re: Mike G's How to Build a Shed

Postby 9fingers » 22 Oct 2020, 13:39

I did not bother to vent my gable ends as there is crossflow ventilation at soffit level behind the gutter/fascia.

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Re: Mike G's How to Build a Shed

Postby John Brown » 22 Oct 2020, 18:36

9fingers wrote:I did not bother to vent my gable ends as there is crossflow ventilation at soffit level behind the gutter/fascia.

Bob

Soffits at the eaves, or at the verges?
Sorry, I'm having trouble visualizing this...
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Re: Mike G's How to Build a Shed

Postby Mike G » 22 Oct 2020, 18:50

So long as it is vented at the bottom, that's enough. There are enough gaps around the boards to provide a little additional air movement. If you render, or use a sheet material, aluminium cladding panels, or a cementitious board or similar, then you'll need to build in ventilation at the top, too, but with timber boards it isn't necessary. If you create dead areas, particularly above windows and doors for instance, where there is no vent at the base, then ideally you'd build in some ventilation somewhere in the panel.
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Re: Mike G's How to Build a Shed

Postby John Brown » 22 Oct 2020, 19:07

OK, Thanks.
I will plod on without worrying.
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Re: Mike G's How to Build a Shed

Postby John Brown » 26 Nov 2020, 17:50

While I'm searching in vain for cheap PIR for my roof, I wondered what the downside might be to using the surplus batts of rockwool I have left over - apart from the obvious problem of keeping it im place and getting fibres in my hair and eyes...
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Re: Mike G's How to Build a Shed

Postby RogerS » 26 Nov 2020, 17:53

John Brown wrote:While I'm searching in vain for cheap PIR for my roof, I wondered what the downside might be to using the surplus batts of rockwool I have left over - apart from the obvious problem of keeping it im place and getting fibres in my hair and eyes...

Are Seconds and Co still going ?
If opportunity doesn't knock, build a door.
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Re: Mike G's How to Build a Shed

Postby Malc2098 » 26 Nov 2020, 18:34

RogerS wrote:
John Brown wrote:While I'm searching in vain for cheap PIR for my roof, I wondered what the downside might be to using the surplus batts of rockwool I have left over - apart from the obvious problem of keeping it im place and getting fibres in my hair and eyes...

Are Seconds and Co still going ?




Yes.

https://www.secondsandco.co.uk/
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Re: Mike G's How to Build a Shed

Postby John Brown » 27 Nov 2020, 16:50

They seem to have a minimum order value of £350, I only need 6 1220 x 2440 boards, so probably not for me.
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Re: Mike G's How to Build a Shed

Postby MY63 » 27 Nov 2020, 19:49

I visited a local supplier I asked if they had any seconds I could buy, the foreman asked what it was for. I told him I was building a workshop. He took me to a stack of pallets outside and told me to take what I wanted.
I was still loading when they knoced off so he left it all outside for me. They were not allowed to sell it and could not take cash or beer, so I cleared a shelf at M&S of biscuits and dropped them off the next day.
There was enough in sheets and rolls to do my whole workshop. There was some high tech foil stuff that I am keeping for my utility conversion.
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Re: Mike G's How to Build a Shed

Postby John Brown » 28 Nov 2020, 11:14

Well that's you sorted then...
Not much help to me. I suppose I could buy a few lottery tickets, see if I can get lucky too.
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Re: Mike G's How to Build a Shed

Postby MY63 » 28 Nov 2020, 17:01

John Brown wrote:Well that's you sorted then...
Not much help to me. I suppose I could buy a few lottery tickets, see if I can get lucky too.

Oh I am sorry I was merely trying to suggest you could visit local suppliers of insulation and ask the same question.
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Re: Mike G's How to Build a Shed

Postby John Brown » 28 Nov 2020, 18:03

Well, yes, I suppose I could, except that apart from Travis Perkins, I'd probably have to drive to Bristol on the offchance, in lockdown.
However, please don't take offence, I didn't mean to give any, but I think you were extraordinarily fortunate.
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Re: Mike G's How to Build a Shed

Postby John Brown » 02 Dec 2020, 20:22

While wrestling with the first piece of 100mm PIR insulation, it occurred to me that the air"flow" between the insulation and the OSB roof, will be fairly mimimal, as although the 50mm void is open at the bottom, it is closed at the top. I am assuming this minimal airflow is sufficient.
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Re: Mike G's How to Build a Shed

Postby Mike G » 02 Dec 2020, 20:47

Ideally it would be up and over the ridge and thus continuous. However, partial ventilation is much better than none at all, and you will be fine.
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Re: Mike G's How to Build a Shed

Postby John Brown » 04 Dec 2020, 23:37

Ok. Does anyone have a good plan for getting the PIR in between the rafters, with those pesky joists/ties in the way? I've tried doing in in one piece, but it seems impossible to fit it around the joists. I've tried two pieces, with only marginally better results... I'm shortly going to run out of swear words. Hoping the OSB won't be quite so difficult.
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Re: Mike G's How to Build a Shed

Postby Mike G » 05 Dec 2020, 08:28

Cut it about 20mm undersize (10mm all round), wedge it in place, and spray expanding foam with a foam gun into the gaps. Once it has all set, pull the wedges out and spray foam in the holes they leave.
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Re: Mike G's How to Build a Shed

Postby greeno » 15 May 2021, 11:32

I've built my shed, based on Mike's design.

A friend now wants a home office / garden room.

Two questions:

Why does the slab need to be 50mm proud? For aesthetics, is there anyway to do the design flush?

They're wanting it plastered inside. Would it just be a case of swapping the OSB for a vapour barrier then plasterboard? I remember that when I added the OSB it really stiffened the structure, would there be any advantage to using say 9mm OSB then plasterboard on top?

It's going to be a slow build so photos might follow in the future.

Thanks.
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Re: Mike G's How to Build a Shed

Postby 9fingers » 15 May 2021, 13:33

I think you will need a different slab design/DPC arrangement to take it from the shed design to more of a habitable space that will stay adequately dry with less "open to the air" ventilation. You don't want an exposed edge of the floor slab with the ability wick damp into the inner floor.
Mike might have a different solution but I'd be thinking of a strip foundation maybe with steel rebar, dwarf walls with DPC 150mm above ground. An internal insulated slab floor with DPM under tucked into the DPC all round.

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Re: Mike G's How to Build a Shed

Postby Mike G » 15 May 2021, 17:41

Hey Greeno.....you must have read my mind. Whilst working on my garage today I was thinking that I really should update this "how to" thread with a more orthodox alternative, more suitable for a home office or any outbuilding which must be in compliance with the regulations, for whatever reason. I 'm busy, busy, but if you can stop your friend before they commit to casting a slab, there is a more suitable alternative which won't show any concrete, and which will have a DPM continuous with the DPC. More later. I'm just resting my back after a lot of heavy lifting.
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Re: Mike G's How to Build a Shed

Postby greeno » 16 May 2021, 09:22

Thanks Mike, no rush. The slab will probably be in a couple of months. If there's no simple alternative then we might stick with the original design.

Out of interest, what is the thinking behind the 50mm?

Any thoughts on vapour barrier + plasterboard or osb and plasterboard?
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Re: Mike G's How to Build a Shed

Postby greeno » 16 May 2021, 09:26

9fingers wrote:I think you will need a different slab design/DPC arrangement to take it from the shed design to more of a habitable space that will stay adequately dry with less "open to the air" ventilation. You don't want an exposed edge of the floor slab with the ability wick damp into the inner floor.
Mike might have a different solution but I'd be thinking of a strip foundation maybe with steel rebar, dwarf walls with DPC 150mm above ground. An internal insulated slab floor with DPM under tucked into the DPC all round.

Bob


Thanks for your thoughts Bob, I was watching my neighbours builders do the ground work for their extension trying to get an idea of the sequence for a more domestic building where there obviously isn't the 50mm step.

If it was mine then I might do something a little more complex but this build will be a combination of him, me and contractors to do the heavy work as we're both short of time so Cherry picking the bits we do.
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Re: Mike G's How to Build a Shed

Postby Mike G » 16 May 2021, 14:00

greeno wrote:Thanks Mike, no rush. The slab will probably be in a couple of months. If there's no simple alternative then we might stick with the original design.

Out of interest, what is the thinking behind the 50mm?

Any thoughts on vapour barrier + plasterboard or osb and plasterboard?


There is a simple alternative.

The 50mm gap serves two purposes. We have an unprotected concrete slab exposed to the weather and ground water, so having it exposed to the air helps it to dry out. Secondly, that first mortar bed, between the concrete and the brick, is very vulnerable, and if that is below ground, or if there is a "shelf" of concrete outside the brickwork on which water can sit, then water will seep through it. Actually, more than seep. It can come in at a fair old rate of knots.

Let's show you the design that will work before we mess with the ordinary design to try to adapt it for an office.
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